WO2022084499A1

WO2022084499A1 - Additive manufacturing inks or resins and additive manufactured structures

Info

Publication number: WO2022084499A1
Application number: PCT/EP2021/079328
Authority: WO
Inventors: Esther Amstad; Alvaro CHARLET; Matteo HIRSCH
Original assignee: Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date: 2020-10-22
Filing date: 2021-10-22
Publication date: 2022-04-28

Abstract

The invention relates to additive manufacturing inks and resins; methods of using said inks and resins in additive manufacturing; and additive manufactured articles made using said inks and resins.

Description

Additive manufacturing inks or resins and additive manufactured structures

Field of the Invention

The invention lies in the field of material science. More particularly, the invention relates to additive manufacturing inks or resins and additive manufactured structures.

Background of the Invention

Hydrogels are often used for moisturizing purposes, for example in wound healing, drug delivery, or food owing to their ability to retain large amounts of water, intrinsic biocompatibility, and the possibility to be functionalized with various moieties. In addition, hydrogels possess the ability to retain a three-dimensional structure and to support cell growth rendering them well-suited replacements for soft biological tissues, and for soft robotics.

Most hydrogels that must retain their 3D structure and bear some load are covalently crosslinked and hence, if swollen, they are inherently brittle. Their toughness can be strongly increased, if reversible crosslinks that rely on non-covalent interactions, slidering structures, host-guest interactions, nanoparticle fillers, or a combination of them are introduced. However, these tough hydrogels are typically rather soft such that they cannot bear significant loads under tension.

Strong and tough complex additive manufactured structures, additive manufacturing inks or resins used to manufacture them, and methods for manufacturing these additive manufactured structures and additive manufacturing inks or resins remain to be established. The present invention addresses this need.

Summary of the Invention

In a first aspect of the present invention, there is provided an additive manufacturing ink or resin comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material; and a crosslinking material precursor within said porous primary material configured to be connectable to form a secondary crosslinked network.

The additive manufacturing inks or resins of the present invention allow additive manufactured structures to be formed with high strength and toughness, yet having desirable mechanical properties which allow the inks or resins to be easily formed into such structures by additive manufacturing.

In an embodiment, the porous primary material comprises a polymeric or an elastomeric material.

In a further embodiment, the porous primary material comprises polyelectrolyte.

In a yet further embodiment, the polyelectrolyte comprises poly(2-acrylamido-2-methyl- 1 -propanesulfonic acid) or polyacrylic acid.

In an embodiment, the additive manufacturing ink or resin comprises about 10 wt% or more, about 20 wt% or more, about 30 wt% or more, about 40 wt% or more, about 50 wt% or more, about 60 wt% or more, about 70 wt% or more, about 80 wt% or more, or about 90 wt% or more, of the porous primary material, based on a dry wt% of the additive manufacturing ink or resin.

In an embodiment, the additive manufacturing ink or resin comprises about 90 wt% or less, about 80 wt% or less, about 70 wt% or less, about 60 wt% or less, about 50 wt% or less, about 40 wt% or less, about 30 wt% or less, about 20 wt% or less, or about 10 wt% or less, of the crosslinking material precursor, based on a dry wt% of the additive manufacturing ink or resin.

In an embodiment, the porous primary material comprises a gel, preferably a hydrogel.

In an embodiment, the crosslinking material precursor comprises a monomeric material.

In a further embodiment, the monomeric material comprises acrylamide. In an embodiment, the porous primary material and/or the crosslinking material precursor comprises a covalent bond forming group and/or a metal-coordination group.

In a further embodiment, the porous primary material and/or the crosslinking material precursor comprises a covalent bond forming group.

In a yet further embodiment, the covalent bond forming group comprises a radical initiator, a radical propagator, a nucleophilic group, an electrophilic group or an oxidisable group.

In a yet further embodiment, the covalent bond forming group comprises a terminal alkene moiety.

In a further embodiment, the porous primary material and/or the crosslinking material precursor comprises a metal-coordination group.

In a yet further embodiment, the metal-coordination group comprises any one of: groups comprising a carboxy moiety; benzenediol or derivatives thereof, preferably catechol or derivatives thereof; benzenetriol or derivatives thereof, preferably gallol or derivatives thereof; histidines and derivatives thereof; ethylenediaminetetraacetic acid and derivatives thereof; sugars and derivatives thereof such as cellulose including carboxymethyl cellulose, alginate and the like; and wherein the metal-coordinating group may optionally be further substituted.

In a yet further embodiment, the metal-coordination group comprises a group comprising a carboxy moiety.

In a yet further embodiment, the metal-coordination group comprises a benzenediol or derivatives thereof.

In a yet further embodiment, the metal-coordination group comprises a catechol or derivatives thereof. In a yet further embodiment, hydroxyl groups are present in the ortho-meta position or meta-para position relative to a point of attachment of the porous primary material to the catechol or derivatives; preferably the meta-para position.

In an embodiment, the jammed particles have a width of about 1 pm to about 1000 pm, preferably about 1 pm to about 500 pm, more preferably about 1 pm to about 200 pm.

In an embodiment, the porous primary material is connected to form a primary crosslinked network. That is to say, the porous primary material comprises a crosslinked network.

In an embodiment, the porous primary material is connectable to form a primary crosslinked network. That is to say, the porous primary material comprises materials which can, but are not yet, formed into a crosslinked network.

In an embodiment, the porous primary material does not form a crosslinked network.

In a further embodiment, the porous primary material is connected to form the primary crosslinked network by physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions.

In a yet further embodiment, the covalent bonds are selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxide, disulfide or polysulfide linkages.

In a yet further embodiment, the covalent bonds are alkylene linkages.

In a yet further embodiment, the metal-coordination bonds comprise a metal cation selected from the group consisting of: metal ions selected from Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³⁺ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, and/or Bi⁵⁺ bismuth (V) ion; preferably iron, aluminium or calcium; and most preferably iron; metal oxides, metal carbides, metal nitrides, metals, and/or metal nanoparticles including iron oxide, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel metal particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles.

In an embodiment, at least part of the plurality of jammed particles is labelled with a marker or a dye, such as a fluorescent dye, crystal label or electronic marker.

In an embodiment, the material is an ink, for example for use in 3D printing.

In an embodiment, the material is a resin, for example for use in stereolithography, digital-light processing or volumetric additive manufacturing.

In a further aspect of the present invention, there is provided a use of the ink or resin as described herein in 3D printing, stereolithography, digital-light processing or volumetric additive manufacturing, preferably 3D printing.

In a further aspect of the present invention, there is provided an additive manufacturing resin comprising a plurality of particles, wherein said particles comprise: a porous primary material; and a crosslinking material precursor within said porous primary material configured to be connectable to form a secondary crosslinked network; wherein said particles are as defined herein. The particles in this embodiment may not be jammed, may be partially jammed or may be jammed. In a further aspect of the present invention, there is provided an additive manufactured structure comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material; and a crosslinking material within said porous primary material configured to be connectable or connected to form a secondary crosslinked network; wherein the secondary crosslinked network is formed both within the plurality of jammed particles and between the plurality of jammed particles.

In an embodiment, the porous primary material is connectable to form a porous primary crosslinked network.

In an embodiment, the porous primary material comprises a porous primary crosslinked network.

In an embodiment, the porous primary material is connected to form the primary crosslinked network by physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions.

In an embodiment, the crosslinking material is connected to form the secondary crosslinked network by physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions.

In a further embodiment, the covalent bonds are selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkage; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxide, disulfide or polysulfide linkages.

In a yet further embodiment, the covalent bonds are alkylene linkages.

In an embodiment, the jammed particles have a width of about 1 pm to about 1000 pm, preferably about 1 pm to about 500 pm, more preferably 1 pm to about 200 pm.

In an embodiment, the additive manufactured structure is a biological part, a tissue replacement part, a robot part, an actuator, a membrane or a coating.

In a further aspect of the present invention, there is provided a use of the additive manufactured structure as described above as a biological part, a tissue replacement part, a robot part, an actuator, a membrane or a coating.

In a further aspect of the present invention, there is provided a computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control an additive manufacturing apparatus to manufacture the additive manufactured structure as defined herein.

In a further aspect of the present invention, there is provided a method of producing an additive manufacturing ink or resin, comprising the steps of: providing particles of a porous primary material; treating the particles of the porous primary material with a crosslinking material precursor in a second medium, the crosslinking material precursor connectable to form a secondary crosslinked network; allowing the crosslinking material precursor to permeate within the porous primary material; and separating the crosslinking material precursor permeated particles of the porous primary material from the second medium.

In an embodiment, the particles of a porous primary material are connectable to form a primary crosslinked network.

In an embodiment, the particles of a porous primary material are connected to form a primary crosslinked network.

In an embodiment, the particles of the porous primary material are separated from the second medium by jamming to provide a plurality of jammed particles.

In an embodiment, the step of providing the particles of the porous primary material comprises the steps of: dispersing a porous primary material precursor in a first medium to form precursor droplets of the porous primary material precursor; allowing a solidification reaction in the precursor droplets to occur, thereby forming particles of the porous primary material; and separating the particles of the porous primary material from the first medium.

In an embodiment, the porous primary material precursor comprises a monomeric material at a concentration of about 10 wt% or more, about 15 wt% or more, about 20 wt% or more, about 25 wt% or more, or about 30 wt% or more, in the first medium.

In an embodiment, the crosslinking material precursor comprises a monomeric material at a concentration of about 10 wt% or more, about 15 wt% or more, about 20 wt% or more, about 25 wt% or more, or about 30 wt% or more, in the second medium.

In an embodiment, the step of dispersing a porous primary material precursor in a first medium involves formation of an emulsion; wherein the emulsion may be a water-in-oil emulsion; an oil-in-water emulsion; a water-in-oil-in-water emulsion; an oil-in-water-in- oil emulsion; a triple emulsion; a multiple emulsion; or a double emulsion with multiple cores.

In an embodiment, the step of allowing the solidification reaction involves a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a thermal trigger or a light trigger.

In an embodiment, the method of producing an additive manufacturing ink or resin further comprises a step of forming the primary crosslinked network by providing a primary crosslinking trigger.

In a further embodiment, the step of forming the primary crosslinked network is conducted during the step of allowing the solidification reaction as described above, or wherein the step of forming the primary crosslinked network is conducted after the step of providing the particles of the porous primary material as described above.

In a yet further embodiment, the step of forming the primary crosslinked network involves formation of physical bonds, covalent bonds, ionic bonds, metal-coordination bonds, hydrogen bonds and/or host-guest interactions. In a yet further embodiment, the step of forming the primary crosslinked network involves formation of covalent bonds selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfides, sulfoxide, disulfides or polysulfide linkages.

In a yet further embodiment, the step of forming the primary crosslinked network involves formation of alkylene linkages and/or metal-coordination bonds.

In a further embodiment, the primary crosslinking trigger is a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a light trigger or a chemical trigger.

In a yet further embodiment, the primary crosslinking trigger is UV light or a complexation agent.

In a yet further embodiment, the complexation agent comprises a metal cation selected from the group consisting of:

Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³⁺ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, Bi⁵⁺ bismuth (V) ion, and/or; preferably iron, aluminium or calcium; and most preferably iron; metal oxides, metal carbides, metal nitrides, metals, and/or metal nanoparticles including iron oxide, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel metal particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles.

In an embodiment, the method of producing an additive manufacturing ink or resin further comprises a step of labelling at least part of the plurality of particles, jammed particles or precursor droplets with a marker or a dye, such as a fluorescent dye, crystal label or electronic marker.

In a further aspect of the present invention, there is provided a method of producing an additive manufactured structure, comprising the steps of: providing an additive manufacturing ink or resin as described herein; and forming the additive manufacturing ink or resin into the additive manufactured structure.

In an embodiment, the method further comprises forming the secondary crosslinked network by providing a secondary crosslinking trigger, thereby forming secondary crosslinks both within the plurality of jammed particles and between the plurality of jammed particles.

In an embodiment, the step of forming the secondary crosslinked network involves formation of physical bonds, covalent bonds, ionic bonds, metal-coordination bonds, hydrogen bonds and/or host-guest interactions.

In a further embodiment, the step of forming the secondary crosslinked network involves formation of covalent bonds selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxide, disulfide or polysulfide linkages.

In a yet further embodiment, the step of forming the secondary crosslinked network involves formation of alkylene linkages and/or metal-coordination bonds. In an embodiment, the secondary crosslinking trigger is a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a light trigger or a chemical trigger.

In a further embodiment, the secondary crosslinking trigger is UV light or a complexation agent.

In an embodiment, the method of producing an additive manufactured structure further comprises a step of forming the primary crosslinked network by providing a primary crosslinking trigger after forming the additive manufacturing ink or resin into the additive manufactured structure, if the primary crosslinked network has not yet been formed.

In a further embodiment, the step of forming the primary crosslinked network is conducted before or after the step of forming the secondary crosslinked network.

In a further embodiment, the secondary crosslinked network and/or primary crosslinked network is formed immediately after formation of the 3D structure. Purely by way of example, with 3D printing, a UV curing lamp may be located immediately proceeding the nozzle such that the material is cured immediately after printing.

In a further embodiment, the secondary crosslinked network and/or primary crosslinked network is formed on a layer by layer basis. Purely by way of example, the 3D structure may be formed layer by layer and the necessary crosslinking takes place once each layer is formed.

In a further embodiment, the secondary crosslinked network and/or primary crosslinked network is formed once the complete 3D structure is formed. Purely by way of example, the 3D structure may be formed and a crosslinking trigger is applied upon completion of the full structure.

In an embodiment, the step of forming the additive manufacturing ink or resin into the additive manufactured structure is conducted using additive manufacturing, further comprising the steps of: obtaining an electronic file representing a geometry of the additive manufactured structure; and controlling an additive manufacturing apparatus to manufacture, over one or more additive manufacturing steps, the additive manufactured structure according to the geometry specified in the electronic file.

In a further embodiment, the step of forming the additive manufacturing ink or resin into the additive manufactured structure is conducted using 3D printing, stereolithography, digital-light processing or volumetric additive manufacturing, preferably 3D printing. In an embodiment, the additive manufacturing ink or resin is formed into a biological part, a tissue replacement part, a robot, an actuator, a membrane or a coating.

Description of the Drawings

Figure 1 shows additive manufacturing of PAM PS-based DNGHs. Schematic representation of microgel fabrication. A monomer-containing aqueous solution is processed into a water-in-oil emulsion (i). AMPS-loaded drops are converted to PAM PS microgels through an UV-induced polymerization (ii). Microgels are soaked in an AM monomer-containing solution (iii). Monomer-loaded microgels are jammed to yield a printable ink (iv). Jammed microgels are extruded as a continuous filament that displays fast shear recovery, enabling the printing of granular hydrogels possessing high aspect ratios with a high shape fidelity (v). The 3D printed objects are post-cured through an exposure to UV light that initiates the polymerization of the AM monomers to form a percolating network, as exemplified by the 3D printed cylinder (vi).

Figure 2 shows rheology of PAMPS-based jammed microgels, a-b, Frequency dependent viscosity (a) and amplitude sweep (b) of jammed microgels containing different crosslinker concentrations. All three samples display a characteristic shearthinning behavior and a low yield strain, c, Self-healing behavior of jammed microgels containing 3.5 mol% crosslinker. The material transitions from a solid-like to a liquidlike state when subjected to high shear (y = 30%). The jammed solution recovers rapidly to its initial condition at low shear (y = 1%). The process can be repeated cyclically without deterioration of the ink performance, d, Step strain relaxation of a DNGH and jammed microgel ink. The difference in relaxation time is due to the presence of the secondary percolating network in DNGH.

Figure 3 shows mechanical characterization of PAMPS-based DNGHs. a, Tensile tests of DNGH are compared to those of bulk PAMPS-PAM DN, and single PAM and PAM PS hydrogels. The granular material displays a toughening behavior typical of DN hydrogels, that is three-fold higher than the bulk DN counterpart, b, Photograph of a hydrogel stripe with a cross section of 10 x 2 mm2 that has been loaded with a 1 kg weight, c, Tensile measurements of DNGHs prepared with 30 wt% AMPS microgels and a PAM secondary network made from varying AM concentrations. The toughness of the samples increases with increasing AM concentration until it peaks at 25 wt% AM. d, Tensile measurements of DNGHs made of PAMPS microgels synthesized with varying AMPS concentrations that are embedded in a percolating network made from 30 wt% AM. The elasticity of the DNGHs increases with increasing AMPS concentration. e,f Color maps of the (e) Young’s moduli and (f) toughness calculated as the area under the stress-strain curve of DNGHs as a function of the concentration of AMPS contained in the microgels and that of AM that forms the secondary percolating network. Reported values represent the mean of five repeated measurements.

Figure 4 shows printing of PAMPS-based jammed microgels, a, Photograph of the jammed microgel filament while it is extruded from a 410 pm conical nozzle. The material can be printed continuously without rupture yielding a filament with high shape fidelity, b, Fluorescent micrograph of the extruded granular filament. Microgels are labelled with sulforhodamine B sodium salt. The resulting granular filament has an average diameter of 500 pm. c, Optical micrograph of a printed grid demonstrating the high shape retaining properties of the extruded layers. The curvature between crossing filaments suggests partial merging of subsequent layers, d, Photograph of a freestanding DNGH grid. Upon UV curing, the printed object can be removed from the substrate while retaining its shape, demonstrating the good interconnectivity between layers that is caused by the percolation secondary PAM network.

Figure 5 shows the effect of printing direction on mechanical properties of PAMPS- based microgels, a, Photograph of DNGH stripes printed with perpendicular (top) or parallel (bottom) filament orientation. Microgels are labeled with sulforhodamine B sodium salt for visualization, b, Tensile measurements of DNGH stripes printed parallel and perpendicular to the long axis of the stripe. No influence of the printing direction on the mechanical properties was observed. The toughness of additive manufactured DNGHs is significantly higher than that of molded samples.

Figure 6 shows an Ashby plot for PAMPS-based microgels. Young’s moduli of various hydrogel inks plotted as a function of the total polymer content. DNGHs of the present invention are stiffer than any other previously reported 3D printed hydrogel.

Figure 7 shows 3D printing of PAMPS-based DNGHs. a, Photograph of a hollow cylinder with an aspect ratio of 2 that can be printed with a high shape fidelity. Microgels are labelled with sulforhodamine B for better visualization, b, Photographs of the hollow DNGH cylinder under compression. While compressed, the cylinder experiences strong deformation and buckling. The good elasticity of DNGH allows the cylinder to return to its initial shape when the stress is released, c, Fluorescent micrograph of two filaments labelled with different dyes, demonstrating the ability to control the composition locally, d, Photographs of an object that has been 3D printed with a structural and sacrificial ink. The sacrificial ink can be removed after the secondary network of the structural ink has been formed by immersing the material into an aqueous solution, e, Photographs of dual-ink printing of a shape-morphing flower. The object is fabricated from two layers with different swelling behaviors. The primary layer is composed of microgels containing 3.5 mol% crosslinker, the microgels contained in the second layer contain 14 mol% crosslinker. As a result of the different swelling behaviors of the microgels and the secondary network, that ensures a good integrity of the overall structure, the DNGH flower can repetitively fold in opposite directions upon drying and immersion in water.

Figure 8 shows rheological characterization of metal-coordinated microgels (MCMGs).

Figure 9 shows mechanical characterization as a function of microgel concentration of various metal-coordinated microgels (MCMGs).

Figure 10 shows further mechanical characterization of Fe-crosslinked MCMGs.

Figure 11 shows homogeneity investigations for various microgel concentrations of MCMGs upon exposure to Fe solution.

Detailed Description of the Invention

The following embodiments apply to all aspects of the present invention.

In the present application, a number of general terms and phrases are used, which should be interpreted as follows.

The present disclosure may be more readily understood by reference to the following detailed description presented in connection with the accompanying figures, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed disclosure.

As used herein and in the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Also, the use of "or" means "and/or" unless stated otherwise. Similarly, "comprise", "comprises", "comprising", "include", "includes" and "including" are interchangeable and not intended to be limiting. It is to be further understood that where descriptions of various embodiments use the term "comprising", those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language "consisting essentially of" or "consisting of."

As used herein, the term “additive manufacturing ink or resin” refers to a semi-solid or liquid (at room temperature conditions, unless otherwise specified) material which is able to flow in response to an applied stress. Therefore, for example, the material may be extruded through nozzles by an additive manufacturing apparatus into various shapes under action of, for example, a pressure piston (e.g. using 3D printing). The materials of the present invention may be used as additive manufacturing inks. Said inks according to the present invention have shear thinning properties that make them suitable for extrusion through a nozzle but with fast shear recovery to enable the printed shape to retain its structure.

The materials of the present invention may be used as additive manufacturing resins. Said resins according to the present invention have suitable wettability and fluidity to allow techniques such as, e.g. stereolithography, digital-light processing or volumetric additive manufacturing. Resins according to the present invention can be selectively solidified (for example through laser or UV illumination) and the unsolidified resin can flow into the thin gap formed due to the wettability and shear thinning properties of the resin. The shear recovery speed may be less crucial with an additive manufacturing resin as opposed to an ink.

The properties of an additive manufacturing inks and resins can be tailored to suit their manufacturing process. By way of example, the shear recovery speed can be tailored to suit a 3D printing ink (fast) or an additive manufacturing resin (less need to be fast). By way of further example, the amount of particles (primary material) in the ink or resin may also be tailored. A resin may not require as high particle (primary material) content as an ink. An additive manufacturing resin may advantageously be able to flow away from an additive manufactured structure back into a container of the additive manufacturing resin, as the structure is being formed and pulled from the container. The “additive manufacturing ink or resin” according to the present invention may be a 3D printing ink, a stereolithographic resin, a digital-light processing resin or a volumetric additive manufacturing resin, preferably a 3D printing ink. The material of the present invention is therefore suitable for use either as an ink in 3D printing or as a resin for other additive manufacturing techniques.

Accordingly, an aspect of the invention relates to an additive manufacturing ink or resin comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material configured to be connectable to form a primary crosslinked network; and a crosslinking material precursor configured to be connectable to form a secondary crosslinked network.

The degree of jamming may depend on the intended use of the material. An additive manufacturing ink may have jammed particles such that the ink has shear thinning properties and fast shear recovery allowing its extrusion and retention of the intended printed shape. An additive manufacturing resin may not require the same level of jamming. The resin does not require the same degree of shear thinning properties or fast shear recovery. An additive manufacturing resin may have a lower level of jamming such that there is a lower particle content within the resin versus an ink.

In an embodiment, in relation to an additive manufacturing resin, the particles are concentrated but are not considered a “jammed” material. The additive manufacturing resin contains particles according to the present invention in sufficient concentration to perform as an additive manufacturing resin.

As used herein, the term “additive manufactured structure” refers to any object which can be manufactured from an additive manufacturing ink or resin described herein. As the additive manufacturing inks or resins described herein provide superior mechanical properties (e.g. strength and toughness), the inks or resins can be formed into a variety of 2D structures, as well as 3D structures. In particular, the “additive manufactured structure” is a 3D printed structure, a stereolithographic structure, a digital-light processed structure or a volumetric additive manufactured structure, preferably a 3D printed structure.

Accordingly, another aspect of the invention relates to an additive manufactured structure comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material connected to form a primary crosslinked network; and a crosslinking material connected to form a secondary crosslinked network; wherein the secondary crosslinked network is formed both within the plurality of jammed particles and between the plurality of jammed particles. In preferred additive manufactured structures, the primary crosslinked network is substantially all within the jammed particles. Preferably, relatively little, or no, crosslinking of the primary network occurs between jammed particles. This is a different structure to that formed by double network hydrogels which have two interpenetrating networks.

The additive manufactured structure can be in many advantageous embodiments a soft additive manufactured structure. In the frame of the present disclosure, a “soft” material or structure is any material or structure that is either compressible, flexible, elastic, has memory shape properties or any combination thereof. If intended to be used in living subjects, moreover, the material may be a biocompatible and/or sterilisable material suitable for medical uses. Advantageously, a soft additive manufactured structure according to some embodiments of the invention can be produced as a gel structure, such as a hydrogel.

In particular, the provided mechanical properties may resemble those of biological materials, and may therefore be suitable for use in biomedical or biomechanical applications. The structure may be a biological part, such as a nose, ear, eye, mouth, digit (e.g. finger or toe), hand, foot, tail, or even limbs (e.g. arm or leg). The structure may be a tissue replacement part, such as a portion of skin, muscle, cartilage, tendon, ligament, part of an organ, or an entire organ.

The structures may be used as bioscaffolds to allow infiltration of cells for use in medical applications. In addition, the provided mechanical properties may be useful in robotics applications, in particular in soft robotics. The structure may be an actuator, in particular materials that change their shape or size in response to stimuli such as electricity, magnetic fields, temperature, light, pressure, chemicals or pH. The structure may be a robot part, such as an artificial muscle or tendon, a contact pad (e.g. on “digits”, “joints”, “hands” or “feet” of the robot) or springs.

Furthermore, the provided mechanical properties may be useful in water treatment applications due to its resistance to mechanical wear and tear. The structure may be a membrane, through which wastewater may be pumped through in order to remove unwanted particulate matter or other impurities.

Moreover, the provided mechanical properties may be useful as coatings to be additive manufactured onto pre-existing surfaces or objects.

As used herein, the term “jammed particles” refers to solid-like particle systems that have an initial immediate response to applied strains by deforming, but without flowing. Thus, jammed systems have non-zero compressional and shear moduli. By contrast, unjammed particle systems have an initial immediate response to applied strains by flowing.

By applying a large enough shear stress, it is possible to cause jammed particles to flow. For a given packing fraction <j> for a jammed particle system, a stress T initially causes the jammed particles to deform and not flow, as described above. However, as the stress T reaches a critical point T_Y, there is a transition from a deformation-type response to a flow-type response. Therefore, for stresses above the critical point T_Y, the system behaves more like an unjammed particle system. Once the stress T is lowered back below the critical point T_Y, the system behaves again as a jammed particle system.

As used herein, the term “particle” refers to a discrete element of solid or semi-solid matter (at room temperature conditions, unless otherwise specified) that is macroscopic or microscopic in size. In some embodiments, the term “particle” may also include capsules with liquid cores and solid shells (liquid/solid at room temperature conditions, unless otherwise specified). In embodiments, the particles are jammed. In embodiments, the particles are deformed (from a spherical shape).

A particle as used herein may have a width of about 1 pm to about 1000 pm. An upper limit of the range of widths may be about 900 pm, about 800 pm, about 700 pm, about 600 pm, about 500 pm, about 400 pm, about 300 pm, about 200 pm, about 100 pm, about 50 pm, about 20 pm or about 10 pm. A lower limit of the range of widths may be about 2 pm, about 5 pm, about 10 pm, about 20 pm, about 50 pm, about 100 pm, about 200 pm, about 300 pm, about 400 pm, about 500 pm, about 600 pm, about 700 pm, about 800 pm, or about 900 pm. Preferably, the width is about 1 pm to about 500 pm. More preferably, the width is about 1 pm to about 200 pm.

A particle as used herein may have a variety of shapes. For example, the particle may be spherical, oblate spheroid, prolate spheroid, non-spherical, polyhedral (such as prismatic, pyramidal, cuboidal, cubical, octahedral, dodecahedral, icosahedral), cylindrical, conical, or a frustum. A particle may be a deformed particle. By way of example, the process of jamming forms deformed particles.

The shape of the particle may be described by its Wadell roundness and/or its Wadell sphericity (see e.g. “Petrology of Sedimentary Rocks” (1980), Robert L. Folk, Hemphill Publishing Company). The Wadell roundness refers to the average radius of curvature of all the corners divided by the radius of the largest inscribed circle. For example, the particle may have a Wadell roundness of about 0.1 to about 1. An upper limit of the range of Wadell roundness may be about 0.9, about 0.8, about 0.7, about 0.6, about 0.5, about 0.4, about 0.3 or about 0.2. A lower limit of the Wadell range of roundness may be about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8 or about 0.9. The Wadell sphericity refers to the cubic root of the volume of the particle divided by the volume of the circumscribing sphere. For example, the particle may have a Wadell sphericity of about 0.1 to about 1. An upper limit of the range of Wadell sphericity may be about 0.9, about 0.8, about 0.7, about 0.6, about 0.5, about 0.4, about 0.3 or about 0.2. A lower limit of the range of Wadell sphericity may be about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8 or about 0.9.

Preferably, the Wadell roundness is about 0.6 to about 1 , about 0.7 to about 1 , about 0.8 to about 1, or about 0.9 to about 1. Preferably, the Wadell sphericity is about 0.6 to about 1 , about 0.7 to about 1 , about 0.8 to about 1 , or about 0.9 to about 1.

As used herein, the term “porous primary material precursor” refers to a substance which is formable into a porous primary material, as described herein.

The “porous primary material precursor” can comprise monomeric materials, oligomeric materials polymeric materials or even colloidal objects that are subsequently polymerised during a manufacturing process. The monomeric materials may be selected from a non-exhaustive list comprising: olefins (e.g. a-olefins, such as linear alkenes including ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1- octene; branched alkenes including isobutylene; a,p-unsaturated carbonyl compounds, including acrylonitrile, acrylamide, acrylates; olefinic electrolytes including 2- acrylamido-2-methyl-1-propanesulfonic acid, acrylic acids), dienes (e.g. butadiene, chloroprene), epoxides, styrenes, fluoroethylenes (e.g. tetrafluoroethylene), chloroethylenes (e.g. vinyl chloride), amines (e.g. diamines, such as hexamethylenediamine), carboxylic acids (e.g. diacids, such as adipic acid), alcohols (e.g. diols, such as ethylene glycol), formaldehyde, alkylsilyl halides (e.g. dimethyldichlorosilane), phenols and thiophenols, or mixtures thereof. The oligomeric materials may be formed from one or more of the above-described monomeric materials, so that a total number of monomer units within the oligomeric material is from 2 to 20, or from 5 to 15, or from 8 to 12. The polymeric material may be formed from one or more of the above-described monomeric materials, so that a number average molecular weight (M_n) of the polymer is from about 500 to about 100,000, or from about 1000 to about 50,000, or from about 10,000 to about 20,000. The colloidal objects may include fragments of silk, fragments of polyaramid fibers, nanocellulose or the like. Preferably, the porous primary material precursor comprises a,p-unsaturated carbonyl compounds or olefinic electrolytes. More preferably, the porous primary material precursor comprises 2-acrylamido-2-methyl-1 -propanesulfonic acid or acrylic acid.

The porous primary material precursor may further comprise a crosslinking agent. The crosslinking agent may be co-polymerised with the monomers, oligomers or polymers described above. Once co-polymerised with the monomers, the crosslinking agent still retains a “metal-coordination group” and/or a “covalent bond forming group” as described herein which is able to form a crosslink between other monomers, oligomers or polymers within the porous primary material precursor, or other crosslinking agents within the porous primary material precursor. Suitable crosslinking agents can comprise for instance N,N'-methylene bisacrylamide, carboxymethyl cellulose methacrylate, 1,4-cyclohexanedimethanol divinyl ether, di(ethylene glycol) diacrylate, di(ethylene glycol) dimethacrylate, N,N'-(1,2-dihydroxyethylene)bisacrylamide, divinylbenzene, p-divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 4,4'-methylenebis(cyclohexylisocyanate), 1 ,4-phenylenediacryloyl chloride, trimethylolpropane ethoxylate triacrylate, poly(ethylene glycol) diacrylate, poly(ethylene glycol) dimethacrylate, tetra(ethylene glycol) diacrylate or tetraethylene glycol dimethyl ether. Preferably, the crosslinking agent is N,N'-methylene bisacrylamide or carboxymethyl cellulose methacrylate.

The porous primary material precursor may further comprise a “radical initiator” as defined herein, for example a radical photoinitiator. A “radical photoinitiator” is a molecule that creates free radicals when exposed to an electromagnetic radiation such as UV or visible light. Non-limiting examples of suitable visible or ultraviolet light- activated photoinitiator include ITX 4-lsopropyl-9-thioxanthenone, Lucirin TPO 2,4,6- Trimethylbenzoyl-diphenyl-phosphineoxide, Irgacure 184 1-Hydroxy-cyclohexyl-phenyl- ketone, Irgacure 2959 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane- 1-one, Irgacure 819 Phosphine oxide, phenyl bis (2,4,6-trimethyl benzoyl), LAP lithium phenyl-2,4,6-trimethylbenzoylphosphinate, Riboflavin 7,8-dimethyl-10-((2R,3R,4S)- 2, 3, 4, 5- tetrahydroxypentyl) benzo[g]pteridine- 2,4 (3H,10H)- dione, Rose Bengal 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein, PL-BDK Benzil dimethyl ketal, PL- CPK 1-hydroxy-cyclohexylphenyl-ketone, Irgacure 11732-hydroxy-2- methylpropiophenone, Camphorquinone, 3-(4-Quantucure BPQ benzoylphenoxy)-2- hydroxy-N , N , N-trimethyl-1 -propanaminium-chloride, APi-180 hydroxyalkylpropanone, bisacylphosphineoxide- or monoacylphosphineoxide-based initiators, peroxides (e.g. benzoyl peroxides, t-butyl hydroperoxide, di-tert-butyl peroxide), persulfates, benzophenones, or AIBN. Preferably, the radical initiator is Irgacure 11732-hydroxy-2- methylpropiophenone.

The monomeric material, oligomeric material or polymeric material may be present at a weight of about 50 wt% or more, about 60 wt% or more, about 70 wt% or more, about 75 wt% or more, about 80 wt% or more, about 85 wt% or more, about 90 wt% or more, about 95 wt% or more, or about 98 wt% or more, based on a total dry wt% of the porous primary material precursor.

The crosslinking agent may be present at a weight of about 20 wt% or less, about 15 wt% or less, about 10 wt% or less, about 7.5 wt% or less, about 5 wt% or less, about 4 wt% or less, about 3 wt% or less, about 2 wt% or less, about 1 wt% or less, about 0.75 wt% or less, about 0.5 wt% or less, or about 0.25 wt% or less, based on a total dry wt% of the porous primary material precursor. Preferably, the crosslinking agent may be present at a weight of about 0.1 wt% to about 20 wt%, about 0.25 wt% to about 20 wt%, about 0.5 wt% to about 20 wt%, about 0.75 wt% to about 20 wt%, about 1 wt% to about 20 wt%, about 2 wt% to about 20 wt%, about 3 wt% to about 20 wt%, about 4 wt% to about 20 wt%, about 5 wt% to about 20 wt%, about 7.5 wt% to about 20 wt%, or about 10 wt% to about 20 wt%, based on a total dry wt% of the porous primary material precursor. More preferably, the crosslinking agent may be present at a weight of about 0.1 wt% to about 10 wt%, about 0.2 wt% to about 10 wt%, about 0.5 wt% to about 10 wt%, about 0.75 wt% to about 10 wt%, about 1 wt% to about 10 wt%, about 2 wt% to about 10 wt%, about 3 wt% to about 10 wt%, about 4 wt% to about 10 wt%, about 5 wt% to about 10 wt%, or about 7.5 wt% to about 10 wt%, based on a total dry wt% of the porous primary material precursor. Changing the concentration of crosslinking agent in the porous primary material precursor can advantageously help tune the amount of crosslinking material precursor that is able to permeate into the porous primary material.

The radical initiator may be present at a weight of about 20 wt% or less, about 15 wt% or less, about 10 wt% or less, about 7.5 wt% or less, about 5 wt% or less, about 4 wt% or less, about 3 wt% or less, about 2 wt% or less, or about 1 wt% or less, based on a total dry wt% of the porous primary material precursor. Preferably, the radical initiator may be present at a weight of about 1 wt% to about 20 wt%, about 2 wt% to about 20 wt%, about 3 wt% to about 20 wt%, about 4 wt% to about 20 wt%, about 5 wt% to about 20 wt%, about 7.5 wt% to about 20 wt%, or about 10 wt% to about 20 wt%, based on a total dry wt% of the porous primary material precursor. More preferably, the radical initiator may be present at a weight of about 1 wt% to about 10 wt%, about 2 wt% to about 10 wt%, about 3 wt% to about 10 wt%, about 4 wt% to about 10 wt%, about 5 wt% to about 10 wt%, or about 7.5 wt% to about 10 wt%, based on a total dry wt% of the porous primary material precursor. As used herein, the term “porous primary material” refers to a solid (at room temperature conditions, unless otherwise specified) material having interstices into which a “crosslinking material precursor” (as described herein) is able to permeate.

For example, the “porous primary material” may be present at a weight of about 10 wt% or more, about 20 wt% or more, about 30 wt% or more, about 40 wt% or more, about 50 wt% or more, about 60 wt% or more, about 70 wt% or more, about 80 wt% or more, or about 90 wt% or more, based on a dry wt% of the additive manufacturing ink or resin.

The porous primary material may allow up to about 90 wt% or less, about 80 wt% or less, about 70 wt% or less, about 60 wt% or less, about 50 wt% or less, about 40 wt% or less, about 30 wt% or less, about 20 wt% or less, or about 10 wt% or less of the crosslinking material precursor to permeate into the porous primary material, based on a dry wt% of the additive manufacturing ink or resin.

In particular, a wt ratio of porous primary material : crosslinking material precursor may be 90:10 to 10:90, 80:20 to 20:80, 70:30 to 30:70, 60:40 to 40:60, 60:40 to 50:50, or 50:50 to 40:60. Preferably, the wt ratio of porous primary material : crosslinking material precursor may be 70:30 to 30:70, 60:40 to 40:60, 60:40 to 50:50, or 50:50 to 40:60. More preferably, the wt ratio of porous primary material : crosslinking material precursor may be 60:40 to 40:60, 60:40 to 50:50, or 50:50 to 40:60.

The porous primary material may have a porosity (the fraction of volume of voids within the porous primary material over the total volume of the porous primary material) of about 0.1 to about 0.9. An upper limit of the range of porosities may be about 0.8, about 0.7, about 0.6, about 0.5, about 0.4, about 0.3, or about 0.2. A lower limit of the range of porosities may be about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, or about 0.8. Preferably, the porosity may be about 0.2 to about 0.8. More preferably, the porosity may be about 0.3 to about 0.7. Even more preferably, the porosity may be about 0.4 to about 0.6. The porous primary material is formed from a porous primary material precursor as described herein. The porous primary material may comprise a material selected from a non-exhaustive list comprising: natural polymeric materials (i.e., non-synthetic polymers, polymers that can be found in nature) and/or polymers derived from Extra Cellular Matrix (ECM) as gelatin, elastin, collagen, agar/agarose, chitosan, fibrin, proteoglycans, a polyamino-acid or its derivatives, preferably polylysin or gelatin methyl cellulose, carbomethyl cellulose, polysaccharides and their derivatives, preferably glycosaminoglycanes such as hyaluronic acid, chondroitinsulfate, dermatansulfate, heparansulfate, heparine, keratansulfate or alginate, silk, polyaramid, nanocellulose, as well as any derivative thereof, fragment thereof and any combination thereof; other polymeric materials such as poly(lactic-co-glycolic acid), lactide and glycolide polymers, caprolactone polymers, polyhydroxybutyrate, polyanhydrides, polyesters, polystyrenes, polyamides (e.g. nylons, such as nylon 6 or nylon 66), polycarbonates, polyphosphazenes, polyphosphoesters and poly(glycerol sebacate acrylate), poly-a-olefins (e.g. polypropylene or its derivatives, polyethylene or its derivatives), polyethylene glycol (PEG), polypropylenoxide or their derivatives, polymethylenoxide or its derivatives, polyethylenoxide or their derivatives, polyacrylate or its derivatives, polyvinylchloride (PVC), polyfluoroethylenes (e.g. polytetrafluoroethylene (PTFE)), poly(vinyl alcohol) (PVA) and copolymers, poly(vinylpyrrolidone) (PVP), and any combination thereof; thermoset materials such as alkyds, epoxies, phenolics (e.g., Bakelite), polyimides, formaldehyde resins (e.g., urea formaldehyde or melamine formaldehyde), polyester thermosets, unsaturated polyesters, polyurethane, bis-maleimides (BMI), silicone materials such as polydimethylsiloxane (PDMS), and any combination thereof; and elastomeric materials such as polyisoprenes (natural or synthetic polyisoprenes), polyacrylates (e.g. poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate)), polybutadienes, polychloroprene, butyl rubber, styrene- butadiene copolymers, nitrile rubber, silicone rubbers (e.g. PDMS), and any combination thereof; as well as any combination of the foregoing.

Preferably, the porous primary material comprises a polymeric or an elastomeric material. More preferably, the porous primary material comprises a polyelectrolyte. Even more preferably, the polyelectrolyte is poly(2-acrylamido-2-methyl-1- propanesulfonic acid) or polyacrylic acid.

As used herein, the term “crosslinking material precursor” refers to a substance which is formable into a crosslinking material, as described herein.

The “crosslinking material precursor” can comprise monomeric materials, oligomeric materials or even polymeric materials that are subsequently polymerised during a manufacturing process. The monomeric materials may be selected from a non- exhaustive list comprising: olefins (e.g. a-olefins, such as linear alkenes including ethylene, propylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -octene; branched alkenes including isobutylene; a,p-unsaturated carbonyl compounds, including acrylonitrile, acrylamide, acrylates; olefinic electrolytes including 2-acrylamido-2- methyl-1 -propanesulfonic acid, acrylic acids), dienes (e.g. butadiene, chloroprene), epoxides, styrenes, fluoroethylenes (e.g. tetrafluoroethylene), chloroethylenes (e.g. vinyl chloride), amines (e.g. diamines, such as hexamethylenediamine), carboxylic acids (e.g. diacids, such as adipic acid), alcohols (e.g. diols, such as ethylene glycol), formaldehyde, alkylsilyl halides (e.g. dimethyldichlorosilane), phenols and thiophenols, or mixtures thereof. The oligomeric materials may be formed from one or more of the above-described monomeric materials, so that a total number of monomer units within the oligomeric material is from 2 to 20, or from 5 to 15, or from 8 to 12. The polymeric material may be formed from one or more of the above-described monomeric materials, so that a number average molecular weight (M_n) of the polymer is from about 500 to about 100,000, or from about 1000 to about 50,000, or from about 10,000 to about 20,000. Preferably, the porous primary material precursor comprises a,p- unsaturated carbonyl compounds. More preferably, the porous primary material precursor comprises acrylamide. The crosslinking material precursor may further comprise a crosslinking agent. The crosslinking agent may be co-polymerised with the monomers, oligomers or polymers described above. Once co-polymerised with the monomers, the crosslinking agent still retains a “metal-coordination group” and/or a “covalent bond forming group” as described herein which is able to form a crosslink between other monomers, oligomers or polymers within the porous primary material precursor, or other crosslinking agents within the porous primary material precursor. Suitable crosslinking agents can comprise for instance N,N'-methylene bisacrylamide, carboxymethyl cellulose methacrylate, 1,4-cyclohexanedimethanol divinyl ether, di(ethylene glycol) diacrylate, di(ethylene glycol) dimethacrylate, N,N'-(1,2-dihydroxyethylene)bisacrylamide, divinylbenzene, p-divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 4,4'-methylenebis(cyclohexylisocyanate), 1 ,4-phenylenediacryloyl chloride, trimethylolpropane ethoxylate triacrylate, poly(ethylene glycol) diacrylate, poly(ethylene glycol) dimethacrylate, tetra(ethylene glycol) diacrylate or tetraethylene glycol dimethyl ether. Preferably, the crosslinking agent is N,N'-methylene bisacrylamide or carboxymethyl cellulose methacrylate.

The crosslinking material precursor may further comprise a “radical initiator” as defined herein, for example a radical photoinitiator. A “radical photoinitiator” is a molecule that creates free radicals when exposed to an electromagnetic radiation such as UV or visible light. Non-limiting examples of suitable visible or ultraviolet light-activated photoinitiator include ITX 4-lsopropyl-9-thioxanthenone, Lucirin TPO 2,4,6- Trimethylbenzoyl-diphenyl-phosphineoxide, Irgacure 184 1-Hydroxy-cyclohexyl-phenyl- ketone, Irgacure 2959 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane- 1-one, Irgacure 819 Phosphine oxide, phenyl bis (2,4,6-trimethyl benzoyl), LAP lithium phenyl-2,4,6-trimethylbenzoylphosphinate, Riboflavin 7,8-dimethyl-10-((2R,3R,4S)- 2, 3, 4, 5- tetrahydroxypentyl) benzo[g]pteridine- 2,4 (3H,10H)- dione, Rose Bengal 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein, PL-BDK Benzil dimethyl ketal, PL- CPK 1-hydroxy-cyclohexylphenyl-ketone, Irgacure 11732-hydroxy-2- methylpropiophenone, Camphorquinone, 3-(4-Quantucure BPQ benzoylphenoxy)-2- hydroxy-N , N , N-trimethyl-1 -propanaminium-chloride, APi-180 hydroxyalkylpropanone, bisacylphosphineoxide- or monoacylphosphineoxide-based initiators, peroxides (e.g. benzoyl peroxides, t-butyl hydroperoxide, di-tert-butyl peroxide), persulfates, benzophenones, or AIBN. Preferably, the radical initiator is Irgacure 11732-hydroxy-2- methylpropiophenone. The monomeric material, oligomeric material or polymeric material may be present at a weight of 50 wt% or more, 60 wt% or more, 70 wt% or more, 75 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, 95 wt% or more, or 98 wt% or more, based on a total dry wt% of the crosslinking material precursor.

The crosslinking agent may be present at a weight of about 20 wt% or less, about 15 wt% or less, about 10 wt% or less, about 7.5 wt% or less, about 5 wt% or less, about 4 wt% or less, about 3 wt% or less, about 2 wt% or less, about 1 wt% or less, about 0.75 wt% or less, about 0.5 wt% or less, or about 0.25 wt% or less based on a total dry wt% of the crosslinking material precursor. Preferably, the crosslinking agent may be present at a weight of about 0.1 wt% to about 5 wt%, about 0.15 wt% to about 5 wt%, about 0.2 wt% to about 5 wt%, about 0.25 wt% to about 5 wt%, about 0.3 wt% to about 5 wt%, about 0.5 wt% to about 5 wt%, or about 1 wt% to about 5 wt%, based on a total dry wt% of the crosslinking material precursor. More preferably, the crosslinking agent may be present at a weight of about 0.1 wt% to about 2 wt%, about 0.15 wt% to about 2 wt%, about 0.2 wt% to about 2 wt%, about 0.25 wt% to about 2 wt%, about 0.3 wt% to about 2 wt%, about 0.5 wt% to about 2 wt%, or about 1 wt% to about 2 wt%, based on a total dry wt% of the crosslinking material precursor. Changing the concentration of crosslinking agent in the crosslinking material precursor can advantageously help tune the mechanical properties of the connections formed between particles via the secondary crosslinked network. For example, higher crosslinking agent concentrations may provide stronger connectivity between particles; lower crosslinking agent concentrations may promote recyclability of the overall material.

The radical initiator may be present at a weight of about 20 wt% or less, about 15 wt% or less, about 10 wt% or less, about 7.5 wt% or less, about 5 wt% or less, about 4 wt% or less, about 3 wt% or less, about 2 wt% or less, or about 1 wt% or less, based on a total dry wt% of the crosslinking material precursor. Preferably, the radical initiator may be present at a weight of about 1 wt% to about 20 wt%, about 2 wt% to about 20 wt%, about 3 wt% to about 20 wt%, about 4 wt% to about 20 wt%, about 5 wt% to about 20 wt%, about 7.5 wt% to about 20 wt%, or about 10 wt% to about 20 wt%, based on a total dry wt% of the crosslinking material precursor. More preferably, the radical initiator may be present at a weight of about 1 wt% to about 10 wt%, about 2 wt% to about 10 wt%, about 3 wt% to about 10 wt%, about 4 wt% to about 10 wt%, about 5 wt% to about 10 wt%, or about 7.5 wt% to about 10 wt%, based on a total dry wt% of the crosslinking material precursor.

As used herein, a “crosslinking material” refers to a solid (at room temperature conditions, unless otherwise specified) material which interweaves within pores of the “porous primary material” described herein. For example, the “crosslinking material” may be contained within the porous primary material at a wt% of about 90 wt% or less, about 80 wt% or less, about 70 wt% or less, about 60 wt% or less, about 50 wt% or less, about 40 wt% or less, about 30 wt% or less, about 20 wt% or less, or about 10 wt% or less, based on a combined wt% of the porous primary material and the crosslinking material.

The crosslinking material is formed from a crosslinking material precursor as described herein. The crosslinking material comprises a material selected from a non-exhaustive list comprising: natural polymeric materials (i.e., non-synthetic polymers, polymers that can be found in nature) and/or polymers derived from Extra Cellular Matrix (ECM) as gelatin, elastin, collagen, agar/agarose, chitosan, fibrin, proteoglycans, a polyamino-acid or its derivatives, preferably polylysin or gelatin methyl cellulose, carbomethyl cellulose, polysaccharides and their derivatives, preferably glycosaminoglycanes such as hyaluronic acid, chondroitinsulfate, dermatansulfate, heparansulfate, heparine, keratansulfate or alginate, silk, polyaramid, nanocellulose, as well as any derivative thereof, fragment thereof and any combination thereof; other polymeric materials such as poly(lactic-co-glycolic acid), lactide and glycolide polymers, caprolactone polymers, polyhydroxybutyrate, polyanhydrides, polyesters, polystyrenes, polyamides (e.g. nylons, such as nylon 6 or nylon 66), polycarbonates, polyphosphazenes, polyphosphoesters and poly(glycerol sebacate acrylate), poly-a-olefins (e.g. polypropylene or its derivatives, polyethylene or its derivatives), polyethylene glycol (PEG), polypropylenoxide or their derivatives, polymethylenoxide or its derivatives, polyethylenoxide or their derivatives, polyacrylate or its derivatives, polyvinylchloride (PVC), polyfluoroethylenes (e.g. polytetrafluoroethylene (PTFE)), poly(vinyl alcohol) (PVA) and copolymers, poly(vinylpyrrolidone) (PVP), and any combination thereof; thermoset materials such as alkyds, epoxies, phenolics (e.g., Bakelite), polyimides, formaldehyde resins (e.g., urea formaldehyde or melamine formaldehyde), polyester thermosets, unsaturated polyesters, polyurethane, bis-maleimides (BMI), silicone materials such as polydimethylsiloxane (PDMS), and any combination thereof; and elastomeric materials such as polyisoprenes (natural or synthetic polyisoprenes), polyacrylates (e.g. poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate)), polybutadienes, polychloroprene, butyl rubber, styrenebutadiene copolymers, nitrile rubber, silicone rubbers (e.g. PDMS), and any combination thereof; as well as any combination of the foregoing.

Preferably, the crosslinking material comprises a polymeric or an elastomeric material. More preferably, the crosslinking material comprises polyacrylamide.

In some embodiments, the crosslinking material may be different to the porous primary material. In other embodiments, the crosslinking material may be the same as the porous primary material.

As used herein, the term “primary crosslinked network” refers to the mesh-like connectivity provided when chains within the primary crosslinked network are connected to other chains within the primary crosslinked network by crosslinks. The crosslinks may include “physical bonds”, “covalent bonds”, “ionic bonds”, “metalcoordination bonds”, “hydrogen bonds” and/or “host-guest interactions”, as described herein. In some embodiments, the primary crosslinked network is generally localised within particles such that the primary crosslinked network forms intraparticle connections with substantially few interparticle connections.

In other embodiments, the primary crosslinked network may also form interparticle connections. In these embodiments, the interparticle connections of the primary crosslinked network are formed after an “ink or resin” as described herein has been formed into a “structure” as described herein, for example, by casting or additive manufacturing.

As used herein, the term “secondary crosslinked network” refers to the mesh-like connectivity when chains within the secondary crosslinked network are connected to other chains within the secondary crosslinked network by crosslinks. The crosslinks may include “physical bonds”, “covalent bonds”, “ionic bonds”, “metal-coordination bonds”, “hydrogen bonds” and/or “host-guest interactions”, as described herein. The secondary crosslinked network is formed both within particles (forming intraparticle connections) and between particles (forming interparticle connections). The secondary crosslinked network percolates both within and between particles. The secondary crosslinked network crosslinks adjacent primary materials and crosslinks within primary material particles.

In some embodiments, the secondary crosslinked network forms irreversible crosslinks. In other embodiments, the formation of the secondary crosslinked network can be reversible, for example under application of heat, light or other (bio)chemical methods (e.g. by exposure to a degradation agent, such as an enzyme or a catalyst). In particular, such a secondary crosslinked network may be applicable in the context of producing green, biodegradable additive manufacturing inks or resins and additive manufactured structures.

The mesh-like connectivity of the secondary crosslinked network interpenetrates between the mesh-like connectivity of the primary crosslinked network. Together, the primary crosslinked network and secondary crosslinked network form a so-called “double network”. One of the networks within the double network may be a highly crosslinked network, imparting high stiffness to structures formed from the double network. The other of the networks within the double network may be a loosely crosslinked network, imparting high toughness to structures formed from the double network. The two networks respond to applied forces substantially independently from each other, such that the overall double network material has advantageous characteristics of both high strength and high toughness. In some preferred embodiments, the mesh-like connectivity of the secondary crosslinked network interpenetrates between the mesh-like connectivity of the primary crosslinked network, and the connectivity of the primary crosslinked network is generally localised within the jammed particles. In such embodiments the primary crosslinked network is generally only present within particles, and the secondary crosslinked network spans the whole material and holds it together.

For the avoidance of doubt, the primary crosslinked network within one particle may have a different material composition compared to a different particle within the plurality of jammed particles. For example, multiple different inks could be used to print different types of jammed particles into a single additive manufactured structure. The secondary crosslinked network can then be formed between these different types of jammed particles to provide a finished product.

As used herein, the term “physical bond” refers to a group which is mechanically linked to one or more other groups. For example, a “physical bond” may include catenanes, having two or more interlocked macrocycles.

As used herein, the term “covalent bond” refers to a chemical bond between two or more atoms that involves the sharing of pairs of electrons between the atoms. Preferably, the “covalent bond” is selected from the group consisting of: an alkylene linkage; an alkenylene linkage; an alkynylene linkage; an ester linkage; an amide linkage; an imine linkage; a hydrazone linkage; a carbocyclic or heterocyclic linkage; a sulfur-based linkage, preferably a sulfide, sulfoxide, a disulfide or a polysulfide linkage. More preferably, the covalent bond is an alkylene linkage.

As used herein, the term “ionic bond” refers to a chemical bond between two or more ions that involves an electrostatic attraction between a cation and an anion. For example, the cation may be selected from “metal cations”, as described herein, or “non-metal cations”. Non-metal cations may include ammonium salts (e.g. alkylammonium salts) or phosphonium salts (e.g. alkylphosphonium salts). The anion may be selected from phosphates, thiophosphates, phosphonates, thiophosphonates, phosphinates, thiophosphinates, sulfates, sulfonates, sulfites, sulfinates, carbonates, carboxylates, alkoxides, phenolates and thiophenolates. As used herein, the term “metal-coordination bond” refers to a reversible ionic bond and/or a reversible dative covalent bond formed between a metal cation and a ligand (e.g. a “metal-coordination group”, as described herein).

As used herein, the term “hydrogen bond” refers to a bonding interaction between a lone pair on an electron-rich atom (e.g. nitrogen, oxygen or fluorine) and a hydrogen atom attached to an electronegative atom (e.g. nitrogen or oxygen).

As used herein, the term “host-guest interaction” refers to two or more groups which are able to form bound complexes via one or more types of non-covalent interactions by molecular recognition, such as ionic bonding, hydrogen bonding, hydrophobic interactions, van der Waals interactions and TT-TT interactions. For example, the hostguest interaction may include interactions formed between cucubiturils with adamantanes (e.g. 1-adamantylamine), ammonium ions (e.g. amino acids), ferrocenes; cyclodextrins with adamantanes (e.g. 1-adamantylamine), ammonium ions (e.g. amino acids), ferrocenes, calixarenes with adamantanes (e.g. 1-adamantylamine), ammonium ions (e.g. amino acids), ferrocenes; crown ethers (e.g. 18-crown-6, 15-crown-5, 12- crown-4) or cryptands (e.g. [2.2.2]cryptand) with cations (e.g. metal cations, ammonium ions); and avidins (e.g. streptavidin) and biotin.

As used herein, the term “covalent bond forming group” refers to a group which is able to chemically react to form a covalent bond with another group. The reaction to form the covalent bond may involve a metal-catalysed reaction (e.g. alkene metathesis, alkyne metathesis, metal-catalysed cross-coupling), radical reaction, nucleophilic attack on an electrophilic group, cycloaddition reaction, or an oxidative reaction. For example, the covalent bond forming group may include aryl/vinyl halides, aryl/vi nyl boronates, aryl/vinyl stannanes, radical initiators, radical propagators, nucleophilic groups (e.g. alcohols, amines), electrophilic groups (e.g. epoxides, carbonyls, sulfonyl halides such as sulfonyl fluorides), oxidisable groups (e.g. thiols and selenols), dienophiles and dipolarophiles (e.g. cyclooctynes, trans-cyclooctene, norbornenes), dienes (e.g. tetrazines), dipoles (e.g. nitrile oxides, nitrones, azides), terminal alkenes and terminal alkynes.

As used herein, the term “radical initiator” refers to a group which is able to fragment to generate two radicals by homolytic fission, for example under irradiation (e.g. with UV light), under heating, or by electrochemical means. A radical initiator may have a low bond dissociation energy, for example 250 kJ/mol or less, 200 kJ/mol or less, or 150 kJ/mol or less. For example, a radical initiator may comprise an 0-0 bond (e.g. peroxides such as benzoyl peroxide, persulfates), an N-0 bond, an N-N bond, a C=O TT bond (e.g. benzophenones), or a C-N bond (e.g. AIBN).

As used herein, the term “radical propagator” refers to a group which is able to react with a radical to form a covalent bond, and generate a new radical during the process of the covalent bond. For example, a radical propagator may include alkene moieties (e.g. terminal alkenes, a,p-unsaturated carbonyls) or alkyne moieties (e.g. terminal alkynes). Preferably, the radical propagator is an alkene moiety.

As used herein, the term “metal-coordination group” refers to a group which is able to coordinate with a metal cation by forming a reversible ionic bond and/or a reversible dative covalent bond between the coordinating group and the metal cation.

The ratio of metal-coordination group(s) to metal ions can be tuned. There may be one, two or three coordinating groups per metal ion.

Preferred metal-coordination groups are groups comprising a carboxyl group. Further preferred metal-coordination groups are benzenetriol or derivatives thereof. Further metal-coordination groups might be histidines or derivatives thereof; and ethylenediaminetetraacetic acid and derivatives thereof.

Preferred metal-coordination groups are carboxyl groups attached to a cellulose moiety. Particularly preferred metal-coordination groups are carboxyl groups attached to a carboxymethyl cellulose moiety.

Preferred metal-coordination groups are benzenediol or benzenetriol. Particularly preferred metal-coordination groups are benzenediol or derivatives thereof.

“Benzenediol” means a benzene ring substituted with two hydroxyl groups and “benzenetriol” means a benzene ring substituted with three hydroxyl groups. The benzene ring may optionally be further substituted. To provide sufficient complexation, the hydroxyl groups may be adjacent to each other, e.g. in a benzenediol, the ortho (catechol) isomer. Thus, in a preferred embodiment, the metal-coordination group is catechol (also known as 1,2-benzenediol) or a derivate thereof. For a benzenetriol, a preferred molecule is gallol.

In a preferred embodiment, two hydroxyl groups are in the ortho-meta positions. In an alternative embodiment, two catechol hydroxyl groups are in the meta-para positions. The meta-para position is especially preferred.

In particular, derivatives of benzenediols (e.g. catechols) and benzenetriols (e.g. gallols) may include one or more electron-withdrawing substituents attached to the benzene ring. Electron-withdrawing substituents may include substituents with a positive Hammett o value (either meta or para o values). Non-limiting examples of electron-withdrawing substituents include halogens (e.g. fluoro, chloro, bromo, iodo), haloalkyls (e.g. fluoroalkyls such as trifluoromethyl), cyano, nitro and carbonyl substituents attached via the carbon atom of the C=O moiety (e.g. ketones, aldehydes, esters, carboxylic acids, amides). Preferably, the electron-withdrawing substituent is a nitro group.

Further metal-coordination groups include specific catechols (such as dopamine, hydrocaffeic acid, and tiron (disodium 4,5-dihydroxy-1 ,3-benzenedisulfonate).

Yet further metal-coordination groups include amino acids. Suitable amino acids include histidine, serine, threonine, asparagine, glutamine, lysine, or cysteine.

As used herein, a “metal cation” can be any metal cation suitable to form ionic bonds, or to coordinate with a metal-coordinating group. For the metal-coordinating group, the metal cation forms reversible ionic bonds and/or reversible dative covalent bonds with metal-coordination group(s). Suitable metal cations include metal ions, metal oxides, metal hydroxides, metal carbides, metal nitrides and/or metal nanoparticles.

Particular metal ions include lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, chromium, manganese, iron, cobalt, nickel, copper, silver, gold, zinc, cadmium, mercury, aluminium, gallium, indium, tin, lead and bismuth. Particularly preferred metal cations include iron, aluminium or calcium, with iron especially preferred. More particularly, suitable cations include Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³+ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, and/or Bi⁵⁺ bismuth (V) ion; preferably iron, aluminium or calcium; and most preferably iron. Particularly preferred metal cations include Fe³⁺ iron (III).

The metal may be added in the form of a metal salt. Suitable metal salts include but are not limited to halides, nitriles, hydroxides and the like.

The metal cation may be in the form of an oxide or nanoparticle. For example, iron oxide nanoparticles may be used. Other suitable oxides or nanoparticles include iron oxides, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles.

Using nanoparticles allows for larger numbers of metal-coordination groups to ionically bond with a single nanoparticle, which may impact the properties of the material.

As used herein, the term “host-guest receptor group” refers to “host” groups or “guest” groups. A “host” group has a pocket which is able to receive another group (i.e. the “guest”), and is able to form one or more types of non-covalent interactions with such a guest by molecular recognition. A “guest” group is any group which is able to be received in a “host” group with high binding affinity by forming one or more types of non-covalent interactions with the pocket of the host. The non-covalent interactions may include interactions such as ionic bonding, hydrogen bonding, hydrophobic interactions, van der Waals interactions and TT-TT interactions. Non-limiting examples of “host” groups include cucubiturils, cyclodextrins, calixarenes, crown ethers (e.g. (e.g. 18-crown-6, 15-crown-5, 12-crown-4), cryptands (e.g. [2.2.2]cryptand) and avidins (e.g. streptavidin). Non-limiting examples of “guest” groups include adamantanes (e.g. 1- adamantylamine), cations (e.g. metal cations, ammonium ions) aromatics (e.g. ferrocene), and biotin and its derivatives thereof. A high binding affinity may include guests which bind to hosts with an equilibrium constant (K_eq) of about 10³ to about 10⁴⁰, about 10⁵ to about 10⁴⁰, about 10⁷ to about 10⁴⁰, about 10¹° to about 10⁴⁰, about 10¹⁵ to about 10⁴⁰, about 10²° to about 10⁴⁰, about 10²⁵ to about 10⁴⁰, about 10³° to about 10⁴⁰, or about 10³⁵ to about 10⁴°.

As used herein, the term “alkylene” refers to divalent straight and branched chain groups having from 1 to 12 carbon atoms. Preferably, the alkylene groups are straight or branched alkylene groups having from 1 to 6 carbon atoms, more preferably straight or branched alkylene groups having from 1 to 4 carbon atoms. An alkylene group may optionally comprise one or more “substituents”, as described herein.

As used herein, the term “alkenylene” refers to divalent straight and branched chain groups having from 1 to 12 carbon atoms, and which comprise at least one carboncarbon double bond. Preferably, the alkenylene groups are straight or branched alkenylene groups having from 1 to 6 carbon atoms, more preferably straight or branched alkenylene groups having from 1 to 4 carbon atoms. An alkenylene group may optionally comprise one or more “substituents”, as described herein.

As used herein, the term “alkynylene” refers to divalent straight and branched chain groups having from 1 to 12 carbon atoms, and which comprise at least one carboncarbon triple bond. Preferably, the alkynylene groups are straight or branched alkynylene groups having from 1 to 6 carbon atoms, more preferably straight or branched alkynylene groups having from 1 to 4 carbon atoms. An alkynylene group may optionally comprise one or more “substituents”, as described herein.

As used herein, the term “ester linkage” refers to a -O-C(=O)- group.

As used herein, the term “amide linkage” refers to a -NR-C(=O)- group, where R is hydrogen or a “substituent” as described herein.

As used herein, the term “imine linkage” refers to a -C(R)=N- group, where R is hydrogen or a “substituent” as described herein. As used herein, the term “hydrazone linkage” refers to a -C(R)=N-NR- group, where R is independently hydrogen or a “substituent” as described herein.

As used herein, the term “carbocyclic linkage” refers to a divalent “cycloalkylene” group, a divalent “cycloalkenylene” group, or a divalent “arylene” group.

A “cycloalkylene” group refers to a divalent alkylene group comprising a closed ring comprising from 3 to 8 carbon atoms, for example, 3 to 6 carbon atoms.

A “cycloalkenylene” group refers to a divalent alkylene group comprising a closed nonaromatic ring comprising from 3 to 8 carbon atoms, for example, 3 to 6 carbon atoms, and which contains at least one carbon-carbon double bond.

An “arylene” group refers to divalent monocyclic, bicyclic or tricyclic aromatic groups containing from 6 to 14 carbon atoms in the ring. Common aryl groups include Ce-Cu arylene, for example, Ce-Cio arylene.

As used herein, the term “heterocyclic linkage” refers to a divalent “heterocycloalkylene” group, or a divalent “heteroarylene” group.

A “heterocycloalkylene” group refers to a divalent saturated or partially saturated 3 to 7 membered monocyclic, or 7 to 10 membered bicyclic ring system, which consists of carbon atoms and from one to four heteroatoms independently selected from the group consisting of O, N, and S, wherein the nitrogen and sulfur heteroatoms may be optionally oxidised, the nitrogen may be optionally quaternised, and includes any bicyclic group in which any of the above-defined rings is fused to a benzene ring, and wherein the ring may be substituted on carbon or on a nitrogen atom if the resulting compound is stable. Non-limiting examples of “heterocycloalkylene” groups include pyrrolidinylene, tetrahydrofuranylene, dihydrofuranylene, tetrahydrothienylene, tetrahydrothiopyranylene, isoxazolinylene, piperidylene, morpholinylene, thiomorpholinylene, thioxanylene, piperazinylene, azetidinylene, oxetanylene, thietanylene, homopiperidylene, oxepanylene, thiepanylene, oxazepinylene, diazepinylene, thiazepinylene, 1 ,2,3,6-tetrahydropyridylene, 2-pyrrolinylene, 3- pyrrolinylene, indolinylene, 2H-pyranylene, 4H-pyranylene, dioxanylene, 1,3- dioxolanylene, pyrazolinylene, dithianylene, dithiolanylene, dihydropyranylene, dihydrothienylene, dihydrofuranylene, dihydropyridazinylene (e.g. 1,4- dihydropyridazinylene), pyrazolidinylene, imidazolinylene, imidazolidinylene, 3- azabicyclo[3.1.0]hexylene, 3-azabicyclo[4.1.0]heptylene, 3H-indolylene, and quinolizinylene. Preferably, the “heterocycloalkylene” group is isoxazolinylene or dihydropyridazinylene (e.g. 1,4-dihydropyridazinylene).

A “heteroarylene” group refers to divalent aromatic groups having 5 to 14 ring atoms (for example, 5 to 10 ring atoms) and containing carbon atoms and 1 , 2 or 3 oxygen, nitrogen or sulfur heteroatoms. Non-limiting examples of “heteroarylene” groups include quinolylene including 8-quinolylene, isoquinolylene, coumarinylene including 8- coumarinylene, pyridylene, pyrazinylene, pyrazolylene, pyrimidinylene, pyridazinylene, furylene, pyrrolylene, thienylene, thiazolylene, isothiazolylene, triazolylene (e.g. 1,2,3- triazolylene), tetrazolylene, isoxazolylene, oxazolylene, imidazolylene, indolylene, isoindolylene, indazolylene, indolizinylene, phthalazinylene, pteridinylene, purinylene, oxadiazolylene, thiadiazolylene, furazanylene, pyridazinylene, triazinylene, cinnolinylene, benzimidazolylene, benzofuranylene, benzofurazanylene, benzothiophenylene, benzothiazolylene, benzoxazolylene, quinazolinylene, quinoxalinylene, naphthyridinylene and furopyridylene. Preferably, the “heteroarylene” group is triazolylene (e.g. 1,2,3-triazolylene), isoxazolylene, pyrazolylene and pyridazinylene. Where the heteroarylene group contains a nitrogen atom in a ring, such nitrogen atom may be in the form of an N-oxide, e.g., a pyridylene N-oxide, pyrazinylene N-oxide, pyrimidinylene N-oxide and pyridazinylene N-oxide.

As used herein, the term “sulfur-based linkage” refers to a -(S)_n- group, wherein n is 1 to 10, or 1 to 6. Preferably, n can be 1 , forming a “sulfide” linkage (e.g. linkages formed by thiolene reactions); or n is 2, forming a “disulfide” linkage; or n is 3 to 6, forming a “polysulfide” linkage. In some embodiments, the sulfur atom may be optionally oxidised. In particular, a sulfide linkage may be a sulfone -S(=O)- linkage, or a sulfoxide -S(=O)2- linkage.

As used herein, the term “substituent” refers to groups such as OR’, =0, SR’, SOR’, SO₂R’, NO₂, NHR’, NR’R’, =N-R’, NHCOR’, N(COR’)₂, NHSO₂R’, NR’C(=NR’)NR’R’, CN, halogen, COR’, COOR’, OCOR’, OCONHR’, OCONR’R’, CONHR’, CONR’R’, protected OH, protected amino, protected SH, substituted or unsubstituted Ci-Ci₂ alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group, where each of the R’ groups is independently selected from the group consisting of hydrogen, OH, NO2, NH2, SH, CN, halogen, COH, COalkyl, CO2H, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group. Where such groups are themselves substituted, the substituents may be chosen from the foregoing list. In addition, where there are more than one R’ groups on a substituent, each R’ may be the same or different.

As used herein, the term “gel” refers to a non-fluid colloidal network or polymer network that is expanded throughout its whole volume by a fluid (liquid or gas). A gel is a solid three-dimensional network that spans the volume of a liquid or gaseous medium and ensnares it through surface tension effects. The internal network structure may result from physical bonds (physical gels) or chemical bonds (chemical gels). For example, a gel may include a hydrogel (wherein the liquid medium is water) or an organogel (wherein the liquid medium is an oil).

A “gel” may comprise about 1 wt% to about 50 wt% of solid material based on a total wt% of the gel. An upper limit to the range of wt% values for the solid material may be about 45 wt%, about 40 wt%, about 35 wt%, about 30 wt%, about 25 wt%, about 20 wt%, about 15 wt%, about 10 wt%, or about 5 wt%. A lower limit to the range of wt% values for the solid material may be about 5 wt%, about 10 wt%, about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 35 wt%, about 40 wt% or about 45 wt%. Preferably, the gel comprises about 10 wt% to about 45 wt%, about 20 wt% to about 45 wt%, or about 30 wt% to about 45 wt%.

As used herein, the term “hydrogel” refers to a gel in which the swelling agent is water. A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. It is synthesized from hydrophilic monomers, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are highly absorbent (they can contain over 90% water) natural or synthetic polymeric networks. As a result of their characteristics, hydrogels develop typical firm yet elastic mechanical properties. Several physical properties of the (hydro)gels are dependent upon concentration. Increase in (hydro)gel concentration may change its pore radius, morphology, or its permeability to different molecular weight proteins. One skilled in the art will appreciate that the volume or dimensions (length, width, and thickness) of a (hydro)gel can be selected based on instant needs, such as for instance the region or environment into which the (hydro)gel is to be implanted if used in a biomedical setting.

In addition or alternative embodiments of the invention, the inks or resins or structures described herein may comprise a marker or a dye to label the jammed particles, such as a fluorescent marker or dye, for example fluorescein or derivatives thereof, such as fluorescein isothiocyanate (FITC) or fluorescein disodium; or rhodamines or derivatives thereof, such as sulforhodamine B.

The additive manufacturing inks or resins and additive manufactured structures according to the invention have been developed by exploiting a new manufacturing method taking advantage from a tailored and elegant mixture of double network systems and jammed particles, and in certain preferred embodiments, materials choice and particle fabrication methods.

Accordingly, an aspect of the invention relates to a method of producing an additive manufacturing ink or resin, comprising the steps of:

(a) providing particles of a porous primary material;

(b) treating the particles of the porous primary material with a crosslinking material precursor in a second medium, the crosslinking material precursor connectable to form a secondary crosslinked network, and suitable to percolate within the porous primary material;

(c) allowing the crosslinking material precursor to permeate within the porous primary material; and

(d) separating the crosslinking material precursor permeated particles of the porous primary material from the second medium. The separation step may be jamming to provide a plurality of jammed particles.

In some preferred methods of the invention, the second medium is partially removed. Generally, sufficient second medium should be separated from the particles to ensure jamming occurs. For example, at least 85 %wt, more preferably at least 90 wt% and more preferably at least 95 wt% of the second medium (e.g. at least 99 wt%) should be removed, based on the total wt% of second medium originally used. In other preferred methods, the second medium is completely removed. In some preferred methods of the invention, the separation step provides a plurality of jammed particles comprising 0 to 5 wt% second medium, and more preferably 0 to 1 wt% second medium, based on the total weight of the jammed particles and second medium

In the first step of the method of producing the additive manufacturing ink or resin, the step of providing particles of the porous primary material may be conducted by mechanical grinding or fragmentation of a bulk porous primary material, or by a dispersion method wherein particles of the porous primary material are generated by solidifying dispersed porous primary material precursors.

In a preferred embodiment, the step of providing particles of the porous primary material is conducted by a dispersion method comprising the steps of:

(a) dispersing a porous primary material precursor in a first medium to form precursor droplets of the porous primary material precursor;

(b) allowing a solidification reaction in the precursor droplets to occur, thereby forming particles of the porous primary material; and

(c) separating the particles of the porous primary material from the first medium.

In the step of dispersing the porous primary material precursor, the “first medium” may be a gaseous phase (at room temperature conditions, unless otherwise specified) or a liquid phase (at room temperature conditions, unless otherwise specified). In some embodiments, the precursor droplets may be dispersed as an aerosol in air or inert atmospheres such as nitrogen or argon. The precursor droplets may be dispersed by means of a spraying device or nebuliser.

In other embodiments, the precursor droplets may be dispersed as an emulsion in an aqueous or organic liquid phase. The precursor droplets may be dispersed by chemical methods such as micelle formation, by means of mechanical agitation, or use of microfluidic devices.

In a particular embodiment of the invention, the formation of an emulsion by micelle formation may involve the use of non-ionic surfactants such as Triton X-100 (polyoxyethylene glycol octylphenol ethers), nonoxynol-9 (polyoxyethylene glycol alkylphenol ethers), polysorbates, Span (sorbitan alkyl esters, e.g. Span80), Poloxamers, Tergitol, Antarox; anionic surfactants such as PENTEX 99 (dioctyl sodium sulfosuccinate), perfluorooctanesulfonate, Calsoft (alkylbenzene sulfonates), Texapon (sodium lauryl ether sulfate), Darvan (lignosulfonate), sodium stearate; or cationic surfactants such as benzalkonium chloride, cetylpyridinium chloride, benzethonium chloride, alkyltrimethylammonium salts (e.g. cetyl trimethylammonium bromide and cetyl trimethylammonium chloride).

In another particular embodiment of the invention, the formation of an emulsion may be performed using a microfluidic device. A “microfluidic device”, “microfluidic chip” or “microfluidic platform” is generally speaking any apparatus which is conceived to work with fluids at a micro/nanometer scale. Microfluidics is generally the science that deals with the flow of liquids inside channels of micrometer size. At least one dimension of the channel is of the order of a micrometer or tens of micrometers in order to consider it microfluidics. Microfluidics can be considered both as a science (study of the behaviour of fluids in micro-channels) and a technology (manufacturing of microfluidics devices for applications such as lab-on-a-chip). These technologies are based on the manipulation of liquid flow through microfabricated channels. Actuation of liquid flow is implemented either by external pressure sources, external mechanical pumps, integrated mechanical micropumps, hydrostatic pressures or by combinations of capillary forces and electrokinetic mechanisms. The microfluidic technology has found many applications such as in medicine with the laboratories on a chip because they allow the integration of many medical tests on a single chip, in cell biology research because the micro-channels have the same characteristic size as the cells and allow such manipulation of single cells and rapid change of drugs, in protein crystallization because microfluidic devices allow the generation on a single chip of a large number of crystallization conditions (temperature, pH, humidity...) and also many other areas such as drug screening, sugar testers, chemical microreactor or micro fuel cells.

In the frame of the present invention, a microfluidic device can be easily adapted to work with fluid volumes spanning from millilitres down to femtoliters, and the dimensions can be adapted accordingly to have channels within the millimetre scale, without substantially departing from the teaching of the invention.

Generally speaking, a microfluidic device or system is intended for production of particles or droplets comprising or substantially composed of a fluid material or combinations of more fluid materials. In a typical scenario, a microfluidic device comprises one or more reservoirs, or is fluidically connected to one or more reservoirs, containing fluid material(s) composing the first phase (also called “dispersed phase”), and one or more reservoirs containing a substantially immiscible second phase, also called “continuous phase”. In this context, “substantially immiscible” means that vast majority of the first phase fluid, i.e. at least 90% thereof, is not solubilized by the continuous phase fluid. The wording “at least partially miscible” can be used interchangeably. This is basically linked to the method of production of the droplets, exploiting the effect of the continuous phase fluid on the dispersed phase.

The four most common strategies for obtaining droplets in a microfluidics setting are the use of step-junction, T-junction, Y-junction or flow focusing geometries. The stepemulsification exploit the transition from confined to unconfined flow for micro-droplet generation. A narrow rectangular inlet channel leads to a wide and deep reservoir. The dispersed phase (non-wetting the channel walls) expands to form a tongue which grows until it reaches the step-like formation at the entrance to the reservoir. At the step the tongue expands into unconfined spherical droplet that pinches-off from the tongue. In a typical T-junction configuration, the two immiscible phases meet face to face and then flow through orthogonal channels, forming droplets by squeeze where they meet depending on the volumetric rates of flow of the two immiscible fluids. A Y-junction configuration is a modification of the T-junction setting wherein the two feeding microchannels (one for the continue phase and one for the dispersed phase) meet with a relative inclination angle different from 0°.

In the flow focusing technique, the continuous phase fluid flanks or surrounds the dispersed phase, exerting pressure and tangential viscous stress over this latter so as to give rise to droplet or bubble break-off through capillary instability in the vicinity of an orifice through which both fluids are extruded. As it will be evident, the principle may be extended to two or more coaxial fluids, and gases and liquids may be combined, depending on the needs. All the above described microfluidic chip configurations for obtaining micro/nanodroplets are well known techniques readily available to a skilled person, and a complete review thereof can be found in Gu et al. (Int. J. Mol. Sci. 2011 , 12, 2572-2597).

In a preferred embodiment, the precursor droplets are dispersed as an emulsion. The starting emulsion comprises a first phase and a second phase; as per the emulsion definition, the two phases are not or minimally miscible between them. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both phases, dispersed and continuous, are liquids. However, in the frame of the present disclosure, the terms “colloid” or “colloidal solution” could be used to indicate an emulsion, and can even be used in its proper sense of a mixture in which one substance of microscopically dispersed insoluble particles (the dispersed phase or first phase) is suspended throughout another substance (the continuous phase or second phase).

As said, the two phases are not or minimally miscible. In this context, the first phase can be an aqueous phase or aqueous solution, and the second phase an organic or non-polar solution, or vice-versa. An “aqueous solution” is a solution in which the solvent is substantially made of water. In the frame of the present disclosure, the term “aqueous” means pertaining to, related to, similar to, or dissolved in water. The expression aqueous solution in the frame of the present disclosure also includes highly concentrated and/or viscous solutions such as for instance syrups (i.e., saturated water/sugars solutions) and the like, in which the water content is e.g. less than 5% weight of the total solution weight. A “non-polar solution” is a solution in which the solvent is a non-polar compound. Non-polar solvents are intended to be compounds having low dielectric constants and that are not miscible with water. A non-exhaustive list of non-polar solutions can comprise for example solutions comprising oils, benzene, carbon tetrachloride, dichloromethane, chloroform, diethyl ether, methyl tert-butyl ether, dimethyl sulfoxide, tetrahydrofuran, xylene, toluene, ethanol, hexanol, heptanol, decanol, dodecanol, hydrocarbon-based solutions (e.g. hexane, cyclohexane, n- octane, isooctane, decane, hexadecane and the like), fluorophilic solvents, ethyl acetate, silicon oils, mineral oils, oils used for food and so forth. An “oil” is any nonpolar chemical substance that is a liquid at ambient temperatures and is both hydrophobic and lipophilic. A fluid material is also intended to comprise any fluid material comprising a gas dispersed within, such as e.g. liquid-gas solutions.

Two liquids can form different types of emulsions. As an example, oil and water can form, first, an oil-in-water emulsion, wherein the oil is the dispersed phase, and water is the dispersion medium. Second, they can form a water-in-oil emulsion, wherein water is the dispersed phase and oil is the external phase. Multiple emulsions are also possible, including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion.

As used herein, the term “drops” may be particles of between 10 nm and 10 mm in size. In the frame of the present disclosure, and for the sake of clarity and conciseness, the term is used indifferently to intend several kinds of particles such as microparticles, (micro)capsules, beads, vesicles, grains and the like. A “microcapsule”, also referred to herein as “core-shell capsule” is a micrometer-scale particle such as for instance gas bubbles or liquid drops surrounded by a solid, liquid, or otherwise fluid shell. Drops according to the invention can have a width typically in the range of about 1 to about 1000 pm. An upper limit of the range of widths may be about 900 pm, about 800 pm, about 700 pm, about 600 pm, about 500 pm, about 400 pm, about 300 pm, about 200 pm, about 100 pm, about 50 pm, about 20 pm or about 10 pm. A lower limit of the range of widths may be about 2 pm, about 5 pm, about 10 pm, about 20 pm, about 50 pm, about 100 pm, about 200 pm, about 300 pm, about 400 pm, about 500 pm, about 600 m, about 700 pm, about 800 pm, or about 900 pm. Preferably, the width is about 1 pm to about 500 pm. More preferably, the width is about 1 pm to about 200 pm.

The porous primary material precursor may include a monomeric material at a concentration of about 5 wt% or more, about 7.5 wt% or more, about 10 wt% or more, about 12.5 wt% or more, about 15 wt% or more, about 17.5 wt% or more, about 20 wt% or more, about 22.5 wt% or more, about 25 wt% or more, about 27.5 wt% or more, about 30 wt% or more, about 32.5 wt% or more, about 35 wt% or more, about 37.5 wt% or more, about or 40 wt% or more, in the first medium. Preferably, the monomeric material is included in a concentration of about 20 wt% to about 40 wt%, about 22.5 wt% to about 40 wt%, about 25 wt% to about 40 wt%, about 27.5 wt% to about 40 wt%, or about 30 wt% to about 40 wt%, in the first medium. More preferably, the monomeric material is included in a concentration of about 20 wt% to about 35 wt%, about 22.5 wt% to about 35 wt%, about 25 wt% to about 35 wt%, about 27.5 wt% to about 35 wt%, or about 30 wt% to about 35 wt%, in the first medium.

The porous primary material precursor may include a crosslinking agent at a concentration of about 50 mol% or less, about 40 mol% or less, about 30 mol% or less, about 20 mol% or less, about 15 mol% or less, about 10 mol% or less, or about 5 mol% or less. Preferably, the crosslinking agent is included in a concentration of about 1 mol% to about 20 mol%, about 1 mol% to about 15 mol%, about 1 mol% to about 10 mol%, or about 1 mol% to about 5 mol%. More preferably, the crosslinking agent is included in a concentration of about 2 mol% to about 20 mol%, about 2 mol% to about 15 mol%, about 2 mol% to about 10 mol%, or about 2 mol% to about 5 mol%.

The porous primary material precursor may include a radical photoinitiator at a concentration of about 50 mol% or less, about 40 mol% or less, about 30 mol% or less, about 20 mol% or less, about 15 mol% or less, about 10 mol% or less, or about 5 mol% or less. Preferably, the radical photoinitiator is included in a concentration of about 1 mol% to about 20 mol%, about 1 mol% to about 15 mol%, about 1 mol% to about 10 mol%, or about 1 mol% to about 5 mol%. More preferably, the radical photoinitiator is included in a concentration of about 2 mol% to about 20 mol%, about 2 mol% to about 15 mol%, about 2 mol% to about 10 mol%, or about 2 mol% to about 5 mol%. In the step of allowing the solidification reaction, the precursor droplets present in the liquid or semi-solid state (liquid or semi-solid at room temperature conditions) are transformed into the solid state (solid at room temperature conditions). The transformation may be initiated by a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst. Preferably, the solidification reaction is initiated using a thermal trigger or a light trigger. More preferably, the solidification reaction is initiated using UV light.

The porous primary material may, in other embodiments, be formed from a suspension of suitable particles. Examples include but are not limited to silk, polyaramid and nanocellulose particles. The particles may be a colloid.

In the step of separating the particles of the porous primary material, a variety of methods may be used. For example, the separation may involve filtration (e.g. gravity or vacuum filtration), centrifugation or decantation. The separation process may further include steps of washing the particles for removing excess porous primary material precursor.

In the second step of the method of producing the additive manufacturing ink or resin, the step of treating the particles of the porous primary material involves a “second medium”. The second medium carries the crosslinking material precursor into pores of the porous primary material so that the crosslinking material precursor permeates within the porous primary material. The second medium may be an aqueous phase or an organic phase. Where an organic phase is used, the second medium may comprise non-limiting examples such as oils, benzene, carbon tetrachloride, dichloromethane, chloroform, diethyl ether, methyl tert-butyl ether, dimethyl sulfoxide, tetrahydrofuran, xylene, toluene, ethanol, hexanol, heptanol, decanol, dodecanol, hydrocarbon-based solutions (e.g. hexane, cyclohexane, n-octane, isooctane, decane, hexadecane and the like), fluorophilic solvents, ethyl acetate, silicon oils, mineral oils, oils used for food and so forth.

The crosslinking material precursor may include a monomeric material at a concentration of about 5 wt% or more, about 7.5 wt% or more, about 10 wt% or more, about 12.5 wt% or more, about 15 wt% or more, about 17.5 wt% or more, about 20 wt% or more, about 22.5 wt% or more, about 25 wt% or more, about 27.5 wt% or more, about 30 wt% or more, about 32.5 wt% or more, about 35 wt% or more, about 37.5 wt% or more, about or 40 wt% or more, in the first medium. Preferably, the monomeric material is included in a concentration of about 20 wt% to about 40 wt%, about 22.5 wt% to about 40 wt%, about 25 wt% to about 40 wt%, about 27.5 wt% to about 40 wt%, or about 30 wt% to about 40 wt%, in the first medium. More preferably, the monomeric material is included in a concentration of about 20 wt% to about 35 wt%, about 22.5 wt% to about 35 wt%, about 25 wt% to about 35 wt%, about 27.5 wt% to about 35 wt%, or about 30 wt% to about 35 wt%, in the first medium.

The crosslinking material precursor may include a crosslinking agent at a concentration of about 50 mol% or less, about 40 mol% or less, about 30 mol% or less, about 20 mol% or less, about 15 mol% or less, about 10 mol% or less, about 5 mol% or less, about 2.5 mol% or less, about 2 mol% or less, about 1 mol% or less, or about 0.5 mol% or less. Preferably, the crosslinking agent is included in a concentration of about 0.1 mol% to about 20 mol%, about 0.1 mol% to about 15 mol%, about 0.1 mol% to about 10 mol%, about 0.1 mol% to about 5 mol%, about 0.1 mol% to about 2 mol%, or about 0.1 mol% to about 1 mol%. More preferably, the crosslinking agent is included in a concentration of about 0.2 mol% to about 20 mol%, about 0.2 mol% to about 15 mol%, about 0.2 mol% to about 10 mol%, or about 0.2 mol% to about 5 mol%, about 0.2 mol% to about 2 mol%, or about 0.1 mol% to about 1 mol%.

The crosslinking material precursor may include a radical photoinitiator at a concentration of about 50 mol% or less, about 40 mol% or less, about 30 mol% or less, about 20 mol% or less, about 15 mol% or less, about 10 mol% or less, or about 5 mol% or less. Preferably, the radical photoinitiator is included in a concentration of about 1 mol% to about 20 mol%, about 1 mol% to about 15 mol%, about 1 mol% to about 10 mol%, or about 1 mol% to about 5 mol%. More preferably, the radical photoinitiator is included in a concentration of about 2 mol% to about 20 mol%, about 2 mol% to about 15 mol%, about 2 mol% to about 10 mol%, or about 2 mol% to about 5 mol%.

In the third step of the method of producing the additive manufacturing ink, the step of allowing the crosslinking material precursor to permeate within the porous primary material can be conducted for over a time period of about 1 hour or more, about 2 hours or more, about 3 hours or more, or about 4 hours or more. For example, the time period may be from about 1 hour to about 72 hours, about 2 hours to about 48 hours, about 3 hours to about 24 hours, or about 4 hours to about 16 hours.

In the fourth step of the method of producing the additive manufacturing ink or resin, the step of separating the permeated porous primary material particles from the second medium is conducted. This may be by using jamming. This process may include separation processes such as vacuum filtration, solvent evaporation, centrifugation (e.g. ultracentrifugation), powder drying and wetting.

As noted above, the concentration of permeated porous primary material particles may depend on the intended use. For a resin, in embodiments, the particles are concentrated but are not considered “jammed”. In other embodiments, the particles are “jammed” but are done so to a lower level of jamming. In other embodiments, for an ink, the particles may be jammed. As such, whether the particles are jammed and the degree of jamming may depend on the intended use of the material. An additive manufacturing ink may have jammed particles such that the ink has shear thinning properties and fast shear recovery allowing its extrusion and retention of the intended printed shape. An additive manufacturing resin may not require the same level of jamming. The resin does not require the same degree of shear thinning properties or fast shear recovery. An additive manufacturing resin may have a lower particle content versus an ink.

The method of producing the additive manufacturing ink or resin may further comprise a step of forming the primary crosslinked network. Preferably, the step of forming the primary crosslinked network, if conducted on the additive manufacturing ink or resin, is conducted such that the primary crosslinked network is generally localised within particles such that the primary crosslinked network forms intraparticle connections with substantially few interparticle connections.

The step of forming the primary crosslinked network may involve the formation of various bonds, such as physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions. Various preferred connections have already been described above and are not repeated here for the sake of brevity. The step of forming the primary crosslinked network may involve the use of a first crosslinking trigger to initiate the crosslinking process. The crosslinking process may be initiated by a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst. Preferably, the formation of the first crosslinking network is initiated using a light trigger or a chemical trigger. More preferably, the formation of the first crosslinking network is initiated using UV light or a complexation agent.

The choice of the crosslinking trigger depends on several factors such as the polymeric matrix, the elected crosslinker or the intended kinetics of the polymerization reaction, just to cite a few. A person skilled in the art would easily derive the crosslinking trigger to be used on a case-by-case basis, depending on the needs and/or circumstances.

In embodiments where UV light is used, the irradiation time can span from few seconds, such as between 3 and 15, up to one minute, depending on the light intensity of the UV light source and the irradiance. Accordingly, the distance of irradiation can vary from e.g. 0.5 to 10 cm, such as between 1 and 3 cm.

In embodiments where a complexation agent is used, the complexation agent may comprise a metal cation as described herein. The complexation agent may be a metal salt. Non-limiting examples of salts include inorganic counter ions such as chlorides, bromides, phosphates, sulfates, and perchlorates, or with organic counter ions such as oxalates, malates, tartrates, citrates, succinates or malonates. Other salts include adipate, alginate, ascorbate, aspartate, benzenesulfonate, benzoate, bisulfate, borate, butyrate, camphorate, camphorsulfonate, cyanide, cyclopentanepropionate, digluconate, dodecylsulfate, ethanesulfonate, formate, fumarate, glucoheptonate, glycerophosphate, gluconate, hemisulfate, heptanoate, hexanoate, hydroiodide, 2- hydroxy-ethanesulfonate, lactobionate, lactate, laurate, lauryl sulfate, maleate, malonate, methanesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate, oleate, palmitate, pamoate, pectinate, persulfate, 3-phenylpropionate, pivalate, propionate, stearate, thiocyanate, p-toluenesulfonate, undecanoate, valerate, and the like.

The step of forming the primary crosslinked network in the additive manufacturing ink or resin may be conducted at various suitable time points. In some embodiments, the primary crosslinked network may be conducted during solidification of the porous primary material precursor. In other embodiments, the primary crosslinked network may be conducted after the step of providing the particles of the porous primary material, for example by adding a crosslinking agent.

According to another aspect of the invention, a method of producing an additive manufactured structure is provided, comprising the steps of:

(a) providing an additive manufacturing ink or resin as described above; and

(b) forming the additive manufacturing ink or resin into the additive manufactured structure.

The method may further comprise:

(c) forming a secondary crosslinked network by providing a secondary crosslinking trigger, thereby forming secondary crosslinks both within the plurality of jammed particles and between the plurality of jammed particles.

The step of forming the additive manufacturing ink or resin into the additive manufactured structure may be conducted using additive manufacturing. Accordingly, the step of forming the additive manufacturing ink or resin into the additive manufactured structure may further comprise the steps of:

(a) obtaining an electronic file representing a geometry of the additive manufactured structure; and

(b) controlling an additive manufacturing apparatus to manufacture, over one or more additive manufacturing steps, the additive manufactured structure according to the geometry specified in the electronic file.

An additive manufacturing apparatus used for the additive manufacturing process may comprise a nozzle through which the additive manufacturing ink or resin can be extruded to form the desired additive manufactured structure under action of a pressure piston. Typical pressures for the pressure piston may be about 5 kPa to about 800 kPa, in particular about 10 kPa to about 500 kPa, about 20 kPa to about 250 kPa, about 30 kPa to about 100 kPa. Details on additive manufacturing methods and apparatuses are described in further detail below.

The step of forming the secondary crosslinked network may involve the use of a secondary crosslinking trigger to initiate the crosslinking process. The crosslinking process may be initiated by a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst. Preferably, the formation of the secondary crosslinking network is initiated using a light trigger or a chemical trigger. More preferably, the formation of the secondary crosslinking network is initiated using UV light or a complexation agent. Even more preferably, the formation of the secondary crosslinking network is initiated using UV light.

In some embodiments, the primary crosslinked network may not yet be formed at the time of forming the additive manufacturing ink or resin into the additive manufactured structure. In these embodiments, the method of producing a additive manufactured structure may further comprise a step of forming the primary crosslinked network by providing a first crosslinking trigger (as described herein), after the step of forming the additive manufacturing ink or resin into the additive manufactured structure. In some embodiments, the step of forming the primary crosslinked network is conducted before the step of forming the secondary crosslinked network. In other embodiments, the step of forming the primary crosslinked network is conducted after the step of forming the secondary crosslinked network.

Additionally, the method can further comprise a step of labelling at least part of the plurality of drops with a marker or a dye, for example fluorescein or derivatives thereof, such as fluorescein isothiocyanate (FITC) or fluorescein disodium; or rhodamines or derivatives thereof, such as sulforhodamine B. This optional step is preferably performed before the polymerisation process starts, and even more preferably a marker or a dye is included as of the beginning into the first phase and within the drops, in embodiments where those drops are present. Metallic, ferromagnetic or superparamagnetic micro/nanoparticles could also be envisaged as a marker, particularly for separation and/or purification purposes, and/or for arranging the jammed particles within the additive manufacturing ink or resin by exploiting for instance a magnetic field. Further possible uses include sensing or actuation purposes. An example micro/nanoparticle is gold. Another example is the iron oxide nanoparticle.

As used herein, “additive manufacturing” refers generally to manufacturing processes wherein successive layers of material(s) are provided on each other to “build-up” layer- by-layer or “additively fabricate”, a three-dimensional component; 3D printing, stereolithography, digital-light processing and volumetric additive manufacturing are types of “additive manufacturing” techniques. This is compared to some subtractive manufacturing methods (such as milling or drilling), wherein material is successively removed to fabricate the part. The successive layers generally fuse together to form a monolithic component which may have a variety of integral sub-components. In particular, the manufacturing process may allow products (e.g. additive manufactured structures) to be integrally formed and include a variety of features not possible when using prior manufacturing methods.

According to the present invention, after (or during) formation of the additive manufactured shape, the materials undergo a crosslinking reaction to form the final material with the desired properties. This can be, for example, a crosslinking trigger to cause secondary crosslinking, primary crosslinking or both primary and secondary crosslinking.

By way of example, with 3D printing, the crosslinking trigger (for example a UV curing lamp) may be configured such that crosslinking takes place immediately after extrusion of the material. On the other hand, the crosslinking trigger may happen on a layer by layer basis. Alternatively, the crosslinking trigger may not occur until the full structure is formed. It is possible to configure the present invention such that a first crosslinking event (if used) takes place during manufacture of the ink whereas the secondary crosslinking takes place after extrusion of the material from the ink head. It is also possible to configure the present invention such that the secondary crosslinking takes place first and the primary crosslinking event takes place afterwards.

By way of further example, when using a resin and a suitable additive manufacturing technique (such as stereolithography or the like), the primary particle material may already be formed (and crosslinked if required) in the resin. The secondary crosslinking (which forms both within and between particles through the secondary network) may be formed as the structure is formed. For example, a photo initiated secondary crosslinking may take place by the laser forming the structure, thereby forming the finished structure. Alternatively, the resin may comprise primary particle material which has not been crosslinked but which contains primary crosslinking precursors and is also infiltrated with secondary crosslinking precursors (which once crosslinked form both within and between particles through the secondary network). In this example, the process which forms the structure may initiate formation of both the primary and secondary crosslinked networks.

The methods described herein enable manufacture of products to any suitable size and shape with various features which may not have been possible using prior manufacturing methods. In general, additive manufacturing can create complex geometries without the use of any sort of tools, molds or fixtures, and with little or no waste material. Instead of machining components from solid billets of plastic or metal, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the part.

As noted above, the process disclosed herein allows a single component to be formed from the additive manufacturing ink or resin. However, the final product may include additional layers, segments, or parts that are formed using different materials, processes, and/or on different additive manufacturing machines. In this manner, components may be constructed which have different materials and material properties for meeting the demands of any particular application. In addition, although the products described herein are constructed entirely by additive manufacturing processes, it should be appreciated that in alternate embodiments, all or a portion of these products may be formed via casting, machining, and/or any other suitable manufacturing process. Indeed, any suitable combination of materials and manufacturing methods may be used to form these components.

3D printing and additive manufacturing processes typically fabricate components based on three-dimensional (3D) information, for example a three-dimensional computer model (or design file), of the component.

Accordingly, examples described herein not only include additive manufactured structures and methods of manufacturing additive manufactured structures as described herein, but also computer software, firmware or hardware for controlling the manufacture of such products via additive manufacturing.

As such, another aspect of the invention relates to a computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control a additive manufacturing apparatus to manufacture the additive manufactured structure as described herein.

The structure of one or more parts of the product may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the product. That is, a design file represents the geometrical arrangement or shape of the product.

Design files can take any now known or later developed file format. For example, design files may be in the Stereolithography or “Standard Tessellation Language” (.stl) format which was created for stereolithography CAD programs of 3D Systems, or the Additive Manufacturing File (.amf) format, which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any additive manufacturing printer.

Further examples of design file formats include AutoCAD (.dwg) files, Blender (.blend) files, Parasolid (,x_t) files, 3D Manufacturing Format (,3mf) files, Autodesk (3ds) files, Collada (.dae) files and Wavefront (.obj) files, although many other file formats exist.

Design files can be produced using modelling (e.g. CAD modelling) software and/or through scanning the surface of a product to measure the surface configuration of the product.

Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processor, cause the processor to control an additive manufacturing apparatus to produce a product according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (an example of which is geometric code or “G-code”) may be calibrated to the specific additive manufacturing apparatus and may specify the precise location and amount of material that is to be formed at each stage in the manufacturing process. As discussed above, the formation may be through deposition, through sintering, or through any other form of additive manufacturing method.

The code or instructions may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. The instructions may be an input to the additive manufacturing system and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of the additive manufacturing system, or from other sources. An additive manufacturing system may execute the instructions to fabricate the product using any of the technologies or methods disclosed herein.

Design files or computer executable instructions may be stored in a (transitory or non- transitory) computer readable storage medium (e.g., memory, storage system, etc.) storing code, or computer readable instructions, representative of the product to be produced. As noted, the code or computer readable instructions defining the product that can be used to physically generate the object, upon execution of the code or instructions by an additive manufacturing system. For example, the instructions may include a precisely defined 3D model of the product and can be generated from any of a large variety of well-known computer aided design (CAD) software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. Alternatively, a model or prototype of the component may be scanned to determine the three-dimensional information of the component.

Accordingly, by controlling an additive manufacturing apparatus according to the computer executable instructions, the additive manufacturing apparatus can be instructed to print out one or more parts of the product. These can be printed either in assembled or unassembled form. For instance, different sections of the product may be printed separately (as a kit of unassembled parts) and then subsequently assembled. Alternatively, the different parts may be printed in assembled form.

In light of the above, embodiments include methods of manufacture via additive manufacturing. This includes the steps of obtaining a design file representing the product and instructing an additive manufacturing apparatus to manufacture the product in assembled or unassembled form according to the design file. The additive manufacturing apparatus may include a processor that is configured to automatically convert the design file into computer executable instructions for controlling the manufacture of the product. In these embodiments, the design file itself can automatically cause the production of the product once input into the additive manufacturing device. Accordingly, in this embodiment, the design file itself may be considered computer executable instructions that cause the additive manufacturing apparatus to manufacture the product. Alternatively, the design file may be converted into instructions by an external computing system, with the resulting computer executable instructions being provided to the additive manufacturing device.

Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification can be realized using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e. , one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

Although additive manufacturing technology is described herein as enabling fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and within the scope of the present subject matter. For example, although the discussion herein refers to the addition of material to form successive layers, one skilled in the art will appreciate that the methods and structures disclosed herein may be practiced with any additive manufacturing technique or other manufacturing technology.

The present invention will now be described by way of the following non-limiting examples. Examples

Materials: Acrylamido-2-methylpropane sulfonic acid (AMPS) (Sigma-Aldrich, 282731), acrylamide (AM) (Sigma-Aldrich, A4058), N,N'-methylene bisacrylamide (MBA) (Carl Roth, 7867.1), 2-hydroxy-2-methylpropiophenone (PI) (Sigma-Aldrich, 405655), mineral oil light (Sigma-Aldrich, 330779), Span80 (TCI Chemicals, S0060), sulforhodamine B sodium salt (Sigma-Aldrich, S1402), fluorescein disodium salt (Carl Roth, 5283.1), ethanol (Sigma-Aldrich, 459844), acrylic acid (AA) (Sigma-Aldrich, 147230), carboxymethyl cellulose sodium salt (CMC, average M.W. 90’000 Da, DS = 0.7) (Acros Organics, ACR33260-1000), glycidyl methacrylate (GMA) (Sigma-Aldrich, 151238), phosphate buffered saline (PBS 1X, pH 7.4, no calcium, no magnesium)(Gibco, 10010056), iron(lll) chloride hexahydrate (Sigma-Aldrich, 236489) are all used as received.

Preparation of PAMPS microgels, preparation of jammed PAMPS ink or resin and structures formed from PAMPS ink or resin

To maximize the contact area between adjacent microgels and minimize interstitial spaces, microgels possessing a high swelling capacity were synthesised. Polyelectrolyte-based microgels have been shown to fulfil these requirements. Hence, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was selected as a model system and AMPS microgels were fabricated from reagent-loaded water in oil emulsion drops, as sketched in Figure 1(i). To test if the size of the produced microgels scales with that of the emulsion drops, this parameter was quantified from optical microscopy images. Drops and crosslinked microgels are nearly identical in size. After having been crosslinked, microgels were washed several times in ethanol and deionized water to remove any unreacted molecules, as sketched in Figure 1 (ii). To ensure good interparticle adhesion, which is key for obtaining good mechanical properties, the microgels were swelled in a solution containing reagents that can be converted into a percolating network after the microgels have been 3D printed. Here, the microgels were swelled in an aqueous solution containing acrylamide (AM) monomers, as sketched in Figure

To avoid any dilution effects from the water exchange, microgels were soaked in the monomer solution for 24h in large excess of the secondary network precursor solution. The degree of swelling of the microgels depends on the crosslinker concentration of the microgels: microgels containing 14 mol% crosslinker have an average diameter of 40 pm whereas those containing 3.5 mol% crosslinker have a diameter of 120 pm.

An important feature of the technique is the processing of individually dispersed microgels into macroscopic materials with structures that are well-defined over the millimeter up to the centimeter-length scales. To enable 3D printing of the dispersed microgels, jamming is conducted using vacuum filtration, as shown in Figure 1 (iv). The resulting ink is additive manufactured into complex structures, as schematically presented in Figure 1(v). The printed construct is then post-cured by exposing it to UV light to allow the formation of a percolating secondary network, as exemplified in Figure 1 (vi).

Example 1

Preparation ofPAMPS microgels'. An aqueous solution containing 20 wt% AMPS, 3.5 mol% MBA, and 3.5 mol% PI is prepared. The aqueous phase is emulsified with a mineral oil solution containing 2 wt% Span80. The water-in-oil emulsion is stirred while being illuminated with UV light (OmniCure S1000, Lumen Dynamics, 320-390 nm, 60 mW/cm²) for 5 min to convert drops into microgels. The resulting PAMPS microgels are transferred into ethanol and centrifuged at 4700 rpm for 15 minutes (Mega Star 1.6R, VWR) to remove the oil. The supernatant is discarded, and the process is repeated three times with ethanol and three times with water. Clean PAMPS microgels are resuspended in water for storage. To render microgels fluorescent, 0.05 mg of sulforhodamine B sodium salt or fluorescein disodium salt per mL of microgel solution is added.

Preparation of jammed PAMPS ink. The solution containing dispersed PAMPS microgels is centrifuged and the supernatant is exchanged with excess aqueous solution containing 30 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI. Microgels are soaked overnight. The solution containing PAMPS microgels is vacuum filtrated (Steriflip 50 mL tube, 0.22 pm, Millipore) to yield a jammed microgel ink.

Example 2 A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 20 wt% AMPS, 7 mol% MBA, and

3.5 mol% PI for the preparation of PAMPS microgels, and with 30 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI for the preparation of jammed PAMPS ink.

Example 3

A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 20 wt% AMPS, 14 mol% MBA, and

Example 4

A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 15 wt% AMPS, 3.5 mol% MBA, and

Example 5

A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 25 wt% AMPS, 3.5 mol% MBA, and

Example 6

A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 30 wt% AMPS, 3.5 mol% MBA, and

Example 7 A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 15 wt% AMPS, 3.5 mol% MBA, and

3.5 mol% PI for the preparation of PAMPS microgels, and with 25 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI for the preparation of jammed PAMPS ink.

Example 8

A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 20 wt% AMPS, 3.5 mol% MBA, and

Example 9

Example 10

Example 11

3.5 mol% PI for the preparation of PAMPS microgels, and with 20 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI for the preparation of jammed PAMPS ink.

Example 12 A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 20 wt% AMPS, 3.5 mol% MBA, and

Example 13

Example 14

Example 15

3.5 mol% PI for the preparation of PAMPS microgels, and with 15 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI for the preparation of jammed PAMPS ink.

Example 16

Example 17 A similar procedure to Example 1 for the preparation of PAMPS microgels and preparation of jammed PAMPS ink was used, with 25 wt% AMPS, 3.5 mol% MBA, and

Example 18

Comparative Example 1

Preparation of bulk DN hydrogel'. An aqueous solution containing 30 wt% AMPS, 3.5 mol% MBA, and 3.5 mol% PI is prepared. The AMPS solution is casted into Teflon molds for tensile measurements. The samples are crosslinked for 5 min under UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²). PAMPS hydrogels are immersed overnight in an aqueous solution containing 20 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI. Soaked samples are then exposed to UV illumination for 5 minutes to trigger the PAM secondary network percolation.

Comparative Example 2

Preparation of bulk AMPS hydrogel'. An aqueous solution containing 30 wt% AMPS,

3.5 mol% MBA, and 3.5 mol% PI is prepared. The solution is transferred into a PTFE mold and is illuminated with UV light (OmniCure S1000, Lumen Dynamics, 320-390 nm, 60 mW/cm²) for 5 min to convert the solution into an AMPS hydrogel.

Comparative Example 3

Preparation of bulk AM hydrogel'. An aqueous solution containing 20 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI is prepared. The solution is transferred into a PTFE mold and is illuminated with UV light (OmniCure S1000, Lumen Dynamics, 320-390 nm, 60 mW/cm²) for 5 min to convert the solution into an AM hydrogel. Preparation of molded DNGHs

The jammed microgel inks of Examples 1-18 and hydrogels of Comparative Examples 1-3 are casted into Teflon molds of cylindrical (d = 8 mm, h = 2 mm) or rectangular (15 x 5 x 2 mm³) shape, for compression and tensile measurements respectively. The samples are crosslinked for 5 min under UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²).

Rheology of jammed PAMPS microgels

Rheology is performed on a DHR-3 TA Instrument with an 8 mm diameter parallel plate steel geometry. All measurements are performed at 25 °C, with an 800 pm gap. Freguency dependent viscosity measurements are made at 0.5% strain. Amplitude sweep is performed at 1.0 rad/s oscillation. Self-healing measurements are performed at 1.0 rad/s, alternating 200 s at 1% strain, with 200 s at 30% strain. Samples are allowed to relax for 200 s at the set temperature before a measurement starts. Stress relaxation measurements are made for crosslinked and uncrosslinked microgels with an initial step strain of 10% and measured for 10 s. The gelation measurement is done at 1% strain and 10 rad/s freguency for 250 s. The liguid sample is loaded on the rheometer, and the UV lamp is switched on at t = 25 s to initiate the polymerization reaction.

A prereguisite for inks to be 3D printed into macroscopic complex structures is their shear thinning behavior, which is a common property of bioinks and jammed microgels. To ensure a reproducible jamming of the microgels, the solid polymer content of samples swollen in deionized water was measured. The results suggest a good reproducibility of the jamming process, where the AMPS polymer content account for 4.83 wt% of the resulting ink. The standard deviation of the solid fraction is as low as 0.22 wt%.

The jammed microgels are shear thinning, as demonstrated by oscillatory rheology in Figure 2a. The viscosity of the jammed PAMPS microgels can be tailored with the crosslinker concentration; it increases from 100 to 1000 Pa s at a shear rate of 10 s’¹, if the crosslinker concentration is increased from 3.5 to 14 mol%. To enable precise dosing, the solid granular ink possesses a low flow point, as shown in Figure 2b. Indeed, the flow point is in the range of 10% for all the different formulations. Furthermore, no influence of the monomer loading was observed on the flow point of the granular ink.

To obtain a good printing resolution, the ink should rapidly solidify after it has been extruded, which is the case if it displays fast stress healing properties. Indeed, the jammed PAMPS solution recovers almost immediately and repetitively from a liquid-like state at high strains, to a viscoelastic state at low strains, as shown in Figure 2c. To test if this behavior is temperature-dependent, step strain relaxation measurements were performed at temperatures varying between 5°C and 45°C. The relaxation time of the jammed microgels remains the same between 5 °C and 45 °C, such that these microgels can be easily processed within this temperature range. Hence, the results indicate that the jammed microgels possess rheological properties that are well-suited for additive manufacturing.

Jammed microgels can form macroscopic, porous primary materials that retain their structure. However, the lack of covalent adhesion between particles makes them mechanically weak such that they cannot bear significant loads. The inventors have advantageously found that the jammed microgels can be transformed into a mechanically robust material by forming a secondary percolating network within the jammed microgels. This was achieved by exposing the granular construct to UV light to initiate the polymerization of the AM monomers. To follow the gelation kinetics of the percolating secondary network, time-dependent oscillatory rheology measurements were performed. Results suggest that gelation plateaus around 150 s. As a result of the formed percolating PAM network, the DNGH retains its integrity, in stark contrast to jammed microgels that relax stress over time, as shown in Figure 2d.

Mechanical characterization of DNGHs

Tensile measurements are performed with a commercial machine (zwickiLine 5 kN, 100 N load cell, Zwick Roell). Rectangular DNGH are mounted and stretched at a constant velocity of 100 mm/min. The Young’s modulus is calculated as the slope of the initial linear region (from 5% to 15% strain). The toughness is calculated as the area below the stress-strain curve of an un-notched sample until fracture. The quantity is expressed as the energy absorbed until fracture per unit volume (J/m³). Compression measurements are performed on a rheometer equipped with a parallel plate geometry (DHR-3, 50 N load cell, TA Instrument). Cylindrical DNGH are compressed at a constant velocity of 1.2 mm/min until 60% strain is reached.

The dry polymer content of AMPS microgels and DNGHs is calculated as the ratio of dry sample weight over as-prepared weight (Wd/W_ap- 100). The equilibrium water content (EWC) is calculated as the ratio of dry sample weight over fully swollen sample weight (Wd/W_s 100).

The mechanical properties of hydrogels are influenced by the weight fraction of the polymers. To characterize the polymer fraction of the DNGHs, the weight of DNGHs as prepared and that of dried DNGHs as a function of their composition were compared. Depending on the composition of the DNGHs, their dry polymer content ranges from 13.6 wt% to 45.7 wt%. To predict their swelling behavior, the dry polymer content with the equilibrium water content (EWC) of the DNGHs were compared. EWCs range from 81.5 wt% to 98.0 wt% depending on DNGH composition.

Granular hydrogels possess locally varying compositions. In the present case, grains are composed of PAMPS that are reinforced by PAM and hence, they constitute DN hydrogels. By contrast, the grain boundaries are composed of PAM only. To test the influence of the composition of the hydrogels on their mechanical properties under tension, tensile tests were performed on as-prepared DNGHs composed of AMPS microgels fabricated from a 30 wt% monomer solution and a secondary network made from a solution containing 20 wt% AM. The granular hydrogel is significantly stiffer and tougher than bulk hydrogels composed of either PAMPS or PAM. The Young’s modulus of the DNGH is 5-fold higher than that of PAMPS and 3-fold higher than that of PAM. Without wishing to be bound by theory, the high stiffness of DNGH may be attributed to the chain entanglements that are topologically constrained between PAM chains and the microgel network, such that they cannot be easily displaced. However, the DNGHs are two-fold softer than unstructured DN counterparts, as summarized in Figure 3a. Again, without wishing to be bound by theory, this difference may be assigned to the PAMPS network that is not percolating the entire DNGHs but is only present within the microgels, in stark contrast to DNs. A key feature for the use of hydrogels for load bearing applications is that they are tough such that they do not fail catastrophically if deformed within a well-defined range. To assess the toughness of the DNGHs, their fracture strengths were quantified. The fracture strength of the DNGH is more than 10-fold higher than that of bulk PAMPS and PAM. Remarkably, the fracture strength of DNGHs is even three-fold higher than that of the unstructured DN counterparts, despite of its lower Young’s modulus, as shown in Figure 3a. Without wishing to be bound by theory, the corresponding increase in toughness may be attributed to a stress concentration at the poles of the microgels due to a substantial mismatch in elasticity of the two interpenetrating networks. These results demonstrate the potential of granular hydrogels possessing locally varying compositions for load-bearing applications and as dampers.

Most soft natural materials are subjected to complex loading profiles. To test if the DNGH is sufficiently robust to sustain more demanding loading profiles, compression measurements on DNGH, PAMPS, and PAM samples were performed. The compressive modulus of the DNGH is 2-fold higher than that of PAM. The compressive stress increases even more: it reaches 0.8 MPa at 60% strain which is 3 times higher than that of the PAM network. Furthermore, its ability to lift a 1 kg weight through a folded rectangular stripe with a cross section of 10 mm x 2 mm was tested, as shown in Figure 3b. Remarkably, the stripe is able to support the applied load for at least 5 loading cycles with no appreciable weakening. These results demonstrate the potential of the DNGHs to be used for load bearing applications.

The elasticity of DN hydrogels depends on the initial polymer content and crosslinker concentration of the first network. To test if this is also the case for the DNGH where the first network is not percolating, microgels containing different polymer contents were fabricated tensile tests were performed on them. Indeed, the Young’s modulus of the DNGH increases from 0.10 MPa to 0.48 MPa with increasing polymer content until it reaches a plateau at 25 wt% AMPS, as shown in Figure 3c.

To determine the best combination of the polymer contents of the microgels and the percolating network, systematic and independent variations were conducted on the polymer content of the microgels and the secondary percolating network, and the Young’s modulus and toughness of the resulting materials were quantified from tensile tests. The Young’s modulus of the DNGHs increases with increasing AMPS concentration, independent of the AM concentration used to form the secondary percolating network, as summarized in Figure 3e. This finding is in agreement with unstructured DN where the elasticity is mainly determined by the first network. The Young’s modulus of the DNGHs can reach values up to 0.57 MPa if they are composed of 30 wt% AMPS and 20 wt% AM.

The toughness of unstructured DNs is mainly determined by the loosely crosslinked secondary network. To test if this is also the case for the DNGHs, the toughness, calculated as the area under the stress-strain curve, was quantified for all the tested samples. Indeed, the toughness of the DNGHs increases with increasing AM concentration, as summarized in Figure 3d. The one clear exception to this trend is the stiffest example DNGH that was formed; the same example also displays a high toughness of 0.53 MJ/m³. The maximum toughness of 0.66 MJ/m³ is achieved for DNGHs prepared with 25% AMPS and 30% AM, as summarized in the color map in Figure 3f. The color maps of the Young’s modulus and toughness of the DNGHs nicely show that their mechanical properties can be tuned over a wide range by adjusting the concentrations of monomers used to form the microgels and the secondary network respectively.

An additional parameter that influences the mechanical properties of unstructured DNs is the crosslinker density of the secondary network. To test if this is also the case for the DNGHs of the present invention, DNGHs with two different AM crosslinker densities were fabricated and tested under tension. At 0.02 mol% crosslinker concentration, due to the low crosslink density, the bonds between microgels can be tuned so that the material is able to rupture along the grain boundaries. These results suggest a weak interparticle adhesion that can be advantageously tuned, for example for promoting recyclability. The toughness strongly increases, the AM crosslink density is increased: by increasing it ten-fold, the fracture strength increases from 50 kPa to 600 kPa. Importantly, the increase in toughness does not compromise the stiffness of the DNGH: the Young’s modulus remains unchanged at 0.28 MPa. As a consequence, the fracture toughness of the DNGH increases more than 10-fold if the AM concentration is increased to 0.2 mol%. These results demonstrate that the mechanical properties of DNGH can be tuned with the crosslink density of the percolating network. However, in contrast to bulk DN materials, the DNGHs of the present invention can be additive manufactured into complex shapes. 3D Printing of DNGHs

The jammed microgel ink is loaded in a 3 mL Luer lock syringe. To remove trapped air, the syringe is sealed and centrifuged at 4700 rpm for 1 min. Additive manufacturing of jammed microgels is performed with a commercial 3D bioprinter (I nkredible+, Cellink). The granular ink is extruded from a conical nozzle (410 pm) through a pressure driven piston (30 kPa). Printing is controlled through G-code commands that are generated by a built-in machine software (Cellink HeartWare). Printing is performed on a glass substrate with a starting gap of 0.1 mm. Printed structures are crosslinked by exposing them to UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²) for 5 min.

An important asset of the DNGH is their fabrication from jammed microgels that shear thin and rapidly recover when stress is relieved. This rheological behavior may render the jammed microgels well-suited inks for 3D printing. When the ink is extruded through a 410 pm diameter nozzle, it is subjected to significant shear stresses that lower the viscosity of the ink locally. The fast recovery of the elastic properties upon relaxation of the stress allows extruding a stable filament whose diameter is similar to that of the nozzle, as shown in the photograph in Figure 4a. Importantly, the extruded filament maintains the characteristic granularity of the ink, as evidenced form the fluorescent micrograph in Figure 4b.

Macroscopic 3D structures are typically printed by depositing multiple layers on top of each other. To ensure good integrity of the 3D printed structures, subsequent layers should partially merge. The ink is fundamentally different in that it is composed of jammed microgels that can re-arrange before a secondary percolating network is formed such that it enables printing junctions with good interconnections. To test the ink, two perpendicular filaments in a grid-like geometry were printed. Indeed, the junctions display good interconnectivity between adjacent layers already before the secondary percolating network is formed, as shown in Figure 4c. After the secondary percolating network is formed, the grid retains its shape and integrity even if removed from the substrate, as shown in Figure 4d.

The mechanical properties of additive manufactured materials are typically inferior to those of the corresponding bulk materials. This discrepancy is often related to a weak adhesion between sequentially deposited layers. The ink of the present invention offers an elegant possibility to overcome this limitation as the second, percolating network is formed after the ink is 3D printed. Therefore, the interfaces between sequentially deposited layers may be equally as strong as the grain boundaries within the printing plane. To test this hypothesis, a solid DNGH rectangular stripe was printed where the printing direction is along its length and one where the printing direction is perpendicular to it, as schematically shown in Figure 5a. Remarkably, no significant influence of the printing direction on the mechanical properties of these stripes was observed, as shown in Figure 5b. This is in stark contrast to polymers that are additive manufactured using conventional, homogeneous inks. Indeed, the Young’s modulus is the same as the one measured for molded samples, 0.28 MPa. Interestingly, the additive manufactured samples possess a higher toughness than the corresponding molded ones: DNGH printed stripes reach a fracture strength of more than 0.8 MPa, and a maximum elongation of around 290%, compared to the molded samples whose fracture strength is 0.6 MPa and the maximum elongation is 150%. Without wishing to be bound by theory, the superior mechanical properties are likely related to the more homogeneous distribution of microgels in printed samples and the lower density of defects such as air inclusions.

To put the mechanical performance of the 3D printed DNGHs in perspective with previously reported 3D printed hydrogels, the Young’s moduli of these systems were compared. The DNGHs are stiffer than any of the previously reported formulations, as summarized in Figure 6. Without wishing to be bound by theory, this difference may be attributed to the novel processing methods: the DNGHs are fabricated from jammed microgels such that the rheological properties of the ink and the composition of the microgels can be independently optimized. This is in stark contrast to most 3D printed hydrogels where these two parameters are closely coupled. Taking advantage of this important aspect, extraordinary mechanical properties of DN hydrogels can be combined with an additive manufacturing process, without compromising the printability and resolution of the ink.

The results suggest that jammed microgels soaked in a monomer solution are well- suited inks to additive manufacture strong and tough 3D hydrogels. This is an asset that has been difficult to achieve with previously reported 3D printed hydrogels. To exploit this new feature, the jammed microgels were 3D printed into high aspect ratio hollow cylinders, as shown in Figure 7a. Indeed, the additive manufactured DNGH structure can be repetitively compressed up to 80%, where it buckles, and retains its initial shape when the stress is released. Importantly, no signs of damage were observed, even after samples have been unloaded, as shown in Figure 7b. The exceptional shape fidelity and mechanical stability of the construct hints at the potential of the jammed microgel-based ink to design mechanically robust granular materials possessing complex geometries.

A key feature of the ink introduced here is its ability to vary the composition of 3D printed objects locally without risking the introduction of weak interfaces that would sacrifice their mechanical properties. This feature can be achieved if materials are 3D printed from multiple inks, each one composed of jammed microgels possessing a well- defined composition that varies between the different inks and all microgels are soaked in the same type of monomer solution. This ink formulation allows covalent crosslinking of adjacent microgels even if these microgels originate from different types of inks and hence possess different compositions after they have been processed into complex 3D structures. To demonstrate feasibility, an ink containing red microgels and one containing green microgels were printed into a grid (red is vertical, green is horizontal) where the two types of hydrogels remain spatially separated, as illustrated in Figure 7c. To demonstrate the importance of the secondary percolating network for the mechanical stability of the DNGHs, the EPFL logo was printed from a structural ink composed of microgels that are soaked in a monomer-containing solution and fill the interstices with a sacrificial ink, namely one composed of jammed microgels that do not contain any monomers. After the secondary percolating network is formed through exposure to UV-light, the sacrificial ink was selectively removed by immersing the 3D printed structure into an aqueous solution. Thereby, an integral material possessing well-defined cm-sized structures was obtained, as illustrated in Figure 7d.

To demonstrate the advantage of co-printing inks composed of microgels possessing different properties, shape-morphing DNGHs were 3D printed. Shape-morphing properties can be imparted to complex structures if they display anisotropic swelling behaviors. To obtain this property, microgels with different crosslink densities were employed such that their swelling behavior varies. Indeed, if a flower whose first layer is composed of microgels possessing a lower crosslink density than those contained in the secondary layer was printed, the flower folds into opposite directions upon drying and soaking, as exemplified in Figure 7e. This example demonstrates the power and versatility of the presented method to fabricate responsive, smart soft materials that are sufficiently strong and stiff to bear significant loads.

Preparation of metal-coordinating microgels (MCMG), preparation of jammed MCMG ink and structures formed from MCMG ink

Example 19

Preparation of CellMA’. Methacrylate groups are grafted on CMC through an epoxy-ring opening reaction. 2 g of CMC are dissolved in deionized water at 40 °C under vigorous stirring. Then, 3.2 mL of GMA are added dropwise and the solution is left to react for 8 hrs to yield CellMA. Unreacted GMA is extracted twice in hexane. The CellMA solution is then purified from hexane through rotary evaporation and freeze-dried. The dried powder is stored at -20 °C for future use.

Preparation of MCMG microgels'. An aqueous solution containing 20 wt% AA, 5 wt% CellMA, and 1.5 mol% PI is prepared. The aqueous phase is emulsified with a mineral oil solution containing 2 wt% Span80. The water-in-oil emulsion is stirred while being illuminated with UV light (OmniCure S1000, Lumen Dynamics, 320-390 nm, 60 mW/cm²) for 30 min to convert drops into microgels. The resulting MCMGs are transferred into PBS and centrifuged at 4700 rpm for 15 minutes (Mega Star 1.6R, VWR) to remove the oil. The supernatant is discarded, and the process is repeated three times with PBS. Clean MCMGs are resuspended in PBS for storage.

Preparation of jammed MCMG ink. The solution containing dispersed MCMGs is centrifuged and the supernatant is exchanged with excess aqueous solution containing 30 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI. Microgels are soaked overnight. The solution containing MCMGs is vacuum filtrated (Steriflip 50 mL tube, 0.22 pm, Millipore) to yield a jammed microgel ink.

Preparation of molded DNGHs. The granular ink is casted into Teflon molds of cylindrical (d = 8 mm, h = 2 mm) or rectangular (15 x 5 x 2 mm³) shape, for compression and tensile measurements respectively. The samples are crosslinked for 5 min under UV light (U P CL-1000, Analytik Jena, 365 nm, 2 mW/cm²). 3D Printing ofDNGHs. The jammed microgel ink is loaded in a 3 mL Luer lock syringe. To remove trapped air, the syringe is sealed and centrifuged at 4700 rpm for 1 min. Additive manufacturing of jammed microgels is performed with a commercial 3D bioprinter (BioX, Cellink). The granular ink is extruded from a conical nozzle (410 pm) through a pressure driven piston (30 kPa). Printing is controlled through G-code commands that are generated by a built-in machine software (Cellink). Printing is performed on a glass substrate with a starting gap of 0.1 mm. Printed structures are crosslinked by exposing them to UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²) for 5 min.

Metal-coordination ofDNGHs. After UV crosslink, 3D printed DNGHs are transferred into an aqueous solution containing 1M FeC . The samples are left to soak overnight to trigger the secondary crosslink in the MCMGs and yield a strong MCGH.

Rheology of jammed MCMGs. Rheology is performed on a DHR-3 TA Instrument with an 8 mm diameter parallel plate steel geometry. All measurements are performed at 25 °C, with an 800 pm gap. Frequency dependent viscosity measurements are made at 0.5% strain. Amplitude sweep is performed at 1.0 rad/s oscillation. Self-healing measurements are performed at 1.0 rad/s, alternating 200 s at 1% strain, with 200 s at 30% strain. Samples are allowed to relax for 200 s at the set temperature before a measurement starts.

Mechanical characterization ofDNGHs and MCGHs. Tensile measurements are performed with a commercial machine (zwickiLine 5 kN, 100 N load cell, Zwick Roell). Dog-bone shaped DNGHs and MCGHs are mounted and stretched at a constant velocity of 100 mm/min. The Young’s modulus is calculated as the slope of the initial linear region (from 5% to 15% strain). The toughness is calculated as the area below the stress-strain curve of an un-notched sample until fracture. The quantity is expressed as the energy absorbed until fracture per unit volume (J/m³). Compression measurements are performed on a rheometer equipped with a parallel plate geometry (DHR-3, 50 N load cell, TA Instrument). Cylindrical DNGHs and MCGHs are compressed at a constant velocity of 1.2 mm/min until 60% strain is reached.

Comparative Example 4 The same procedure as Example 19 was used, but without the step of soaking in the 1M FeCh solution.

Comparative Examples 5 to 14

Preparation of bulk PAM hydrogel’. An aqueous solution containing 30 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI is made. The sample is transferred into a Teflon mold and crosslinked for 5 min under UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²) to yield MCMG-reinforced PAM hydrogels.

Preparation of MCMG-reinforced PAM hydrogels’. The solution containing dispersed MCMGs is centrifuged and the supernatant is discarded. The jammed MCMG solution obtained is mixed at a volume ratios (v/v%) of 10 v/v%, 20 v/v%, 30 v/v%, 40 v/v%, 50 v/v%, 60 v/v%, 70 v/v%, 80 v/v% and 90 v/v%, with an aqueous solution containing 30 wt% AM, 0.2 mol% MBA, and 1.5 mol% PI. The samples are transferred into Teflon molds and crosslinked for 5 min under UV light (UVP CL-1000, Analytik Jena, 365 nm, 2 mW/cm²) to yield MCMG-reinforced PAM hydrogels.

The bulk PAM hydrogel or MCMG-reinforced PAM hydrogels are then transferred into an aqueous solution containing 1M FeCh. The samples are left to soak overnight to trigger the secondary crosslink in the MCMGs.

Comparative Examples 15 to 24

The same procedure as Comparative Examples 5 to 14 was used, but without the step of soaking in the 1M FeC solution.

In order to obtain microgels able to coordinate metal ions, a water-in-oil emulsion as template was first produced. A solution of acrylic acid (AA), Carboxymethyl cellulose methacrylate (CellMA), and 2-hydroxy-2-methylpropiophenone (PI) is injected in a surfactant-containing mineral oil. Emulsions of polydisperse size are obtained through vortex agitation, that are then converted into solid particles through UV illumination. To remove any unreacted species, the obtained microgels are repeatedly washed with PBS prior to storage. Subsequently, the resulting metal-coordinating microgels (MCMGs) are mixed with a monomer-containing solution of acrylamide (AM), N,N’- methylene bisacrylamide (MBA), and PI at various volume fractions to obtain the final double-network granular hydrogel (DNGH) precursor solution. Depending on the relative viscosity of the final mixture, DNGH samples are prepared either through casting or 3D printing. To finally achieve strong and tough metal-coordinating granular hydrogels (MCGHs), the obtained DNGHs are immersed in various ion containing solutions (i.e. Ca²⁺, Fe³⁺, and Al³⁺) to allow for a secondary crosslink through metalligand interaction. The resulting MCGH shows good shape retaining capability together with improved mechanics.

The overall mechanics of DNGHs, and consequently of MCGHs, can depend on the microgel formulation. To evaluate the influence of such parameter on the overall material mechanics, various CellMA concentration were tested, and the rheological behavior of MCMGs in the jammed state was measured. Figure 8a shows amplitude sweep curves for MCMGs with varying CellMA concentrations. The storage modulus (G’) increases with increasing CellMA concentration. Above the yield stress, the MCMG solution flows as confirmed by the crossover between storage and loss moduli (G” > G’). Moreover, jammed solutions should transition from a solid to a liquid-like state when the stress is above the yield point, and quickly recover to a solid-like state upon stress removal. Therefore, to evaluate the potential of MCMGs for additive manufacturing, oscillation cycles at strains above and below the yield point were performed, as shown in Figure 8b. The material shows fast recovery with no appreciable mechanical losses, thus making it a good candidate for 3D printing.

Hydrogel reinforcement through microgel has shown to be dependent on relative concentration of such soft inclusions. To verify if it is also the case in the present system, DNGH samples with varying microgel concentrations were fabricated. Prior to the secondary gelation, viscosity measurements were performed to assess the sedimentation of the microgels in the precursor solution, thus affecting the homogeneity of the prepared samples. Results evidence a strong increase in viscosity for solutions prepared with more than 50 v/v% of MCMGs, as shown in Figure 9a. Indeed, samples with concentrations of 20-30 v/v% present a clear heterogenous appearance, as seen in Figure 9b. References:

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Claims

84

CLAIMS:

1. An additive manufacturing ink or resin comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material; and a crosslinking material precursor within said porous primary material configured to be connectable to form a secondary crosslinked network.

2. An additive manufacturing ink or resin according to claim 1 , wherein the porous primary material comprises a porous primary crosslinked network.

3. An additive manufacturing ink or resin according to claim 1 or claim 2, wherein the porous primary material comprises a polymeric or an elastomeric material.

4. An additive manufacturing ink or resin according to any one of claims 1 to 3, wherein the porous primary material comprises polyelectrolyte.

5. An additive manufacturing ink or resin according to claim 4, wherein the polyelectrolyte comprises poly(2-acrylamido-2-methyl-1 -propanesulfonic acid) or polyacrylic acid.

6. An additive manufacturing ink or resin according to any one of claims 1 to 5, wherein the additive manufacturing ink or resin comprises about 10 wt% or more, about 20 wt% or more, about 30 wt% or more, about 40 wt% or more, about 50 wt% or more, about 60 wt% or more, about 70 wt% or more, about 80 wt% or more, or about 90 wt% or more, of the porous primary material, based on a dry wt% of the additive manufacturing ink.

7. An additive manufacturing ink or resin according to any one of claims 1 to 6, wherein the additive manufacturing ink or resin comprises about 90 wt% or less, about 80 wt% or less, about 70 wt% or less, about 60 wt% or less, about 50 wt% or less, about 40 wt% or less, about 30 wt% or less, about 20 wt% or less, or about 10 wt% or less, of the crosslinking material precursor, based on a dry wt% of the additive manufacturing ink. 85

8. An additive manufacturing ink or resin according to any one of claims 1 to 7, wherein the porous primary material comprises a gel, preferably a hydrogel.

9. An additive manufacturing ink or resin according to any one of claims 1 to 8, wherein the crosslinking material precursor comprises a monomeric material.

10. An additive manufacturing ink or resin according to claim 9, wherein the monomeric material comprises acrylamide.

11. An additive manufacturing ink or resin according to any one of claims 1 to 10, wherein the porous primary material and/or the crosslinking material precursor comprises a covalent bond forming group and/or a metal-coordination group.

12. An additive manufacturing ink or resin according to claim 11 , wherein the porous primary material and/or the crosslinking material precursor comprises a covalent bond forming group.

13. An additive manufacturing ink or resin according to claim 11 or claim 12, wherein the covalent bond forming group comprises a radical initiator, a radical propagator, a nucleophilic group, an electrophilic group or an oxidisable group.

14. An additive manufacturing ink or resin according to any one of claims 11 to 13, wherein the covalent bond forming group comprises a terminal alkene moiety.

15. An additive manufacturing ink or resin according to claim 11 , wherein the porous primary material and/or the crosslinking material precursor comprises a metal-coordination group.

16. An additive manufacturing ink or resin according to any one of claims 11 or 13 to 15, wherein the metal-coordination group comprises any one of: groups comprising a carboxy moiety; benzenediol or derivatives thereof, preferably catechol or derivatives thereof; benzenetriol or derivatives thereof, preferably gallol or derivatives thereof; histidines and derivatives thereof; 86 ethylenediaminetetraacetic acid and derivatives thereof; and wherein the metalcoordinating group may optionally be further substituted. An additive manufacturing ink or resin according to any one of claims 11 or 13 to 16, wherein the metal-coordination group comprises a group comprising a carboxy moiety. An additive manufacturing ink or resin according to any one of claims 11 or 13 to 17, wherein the metal-coordination group comprises a benzenediol or derivatives thereof. An additive manufacturing ink or resin according to any one of claims 11 or 13 to 18, wherein the metal-coordination group comprises a catechol or derivatives thereof. An additive manufacturing ink or resin according to claim 19, wherein hydroxyl groups are present in the ortho-meta position or meta-para position relative to a point of attachment of the porous primary material to the catechol or derivatives; preferably the meta-para position. An additive manufacturing ink or resin according to any one of claims 1 to 20, wherein the jammed particles have a width of about 1 pm to about 1000 pm, preferably about 1 pm to about 500 pm, more preferably about 1 pm to about 200 pm. An additive manufacturing ink or resin according to any one of claims 1 to 21 , wherein the porous primary material is connected to form the primary crosslinked network. An additive manufacturing ink or resin according to any one of claims 1 to 21 , wherein the porous primary material is connectable to form the primary crosslinked network. An additive manufacturing ink or resin according to claim 22, wherein the porous primary material is connected to form the primary crosslinked network 87 by physical bonds, covalent bonds, ionic bonds, metal-coordination bonds, hydrogen bonds and/or host-guest interactions. An additive manufacturing ink or resin according to claim 24, wherein the covalent bonds are selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxide, disulfide or polysulfide linkages. An additive manufacturing ink or resin according to claim 25, wherein the covalent bonds are alkylene linkages. An additive manufacturing ink or resin according to any one of claims 22 or 24 to 26, wherein the metal-coordination bonds comprise a metal cation selected from the group consisting of: metal ions selected from Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³⁺ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, and/or Bi⁵⁺ bismuth (V) ion; preferably iron, aluminium or calcium; and most preferably iron; metal oxides, metal carbides, metal nitrides, metals, and/or 88 metal nanoparticles including iron oxide, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel metal particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles.

28. An additive manufacturing ink or resin according to any one of claims 1 to 27, wherein at least part of the plurality of jammed particles is labelled with a marker or a dye, such as a fluorescent dye, crystal label or electronic marker.

29. An additive manufacturing ink or resin according to any one of claims 1 to 28, wherein the additive manufacturing ink or resin is an ink.

30. An additive manufacturing ink or resin according to any one of claims 1 to 28, wherein the additive manufacturing ink or resin is a resin.

31. An additive manufacturing resin comprising a plurality of particles, wherein said particles comprise: a porous primary material; and a crosslinking material precursor within said porous primary material configured to be connectable to form a secondary crosslinked network; wherein said particles are as defined in any one of claims 1 to 28.

32. Use of the additive manufacturing ink or resin according to any one of claims 1 to 31 in 3D printing, stereolithography, digital-light processing or volumetric additive manufacturing, preferably 3D printing.

33. An additive manufactured structure comprising a plurality of jammed particles, wherein said particles comprise: a porous primary material; and 89 a crosslinking material within said porous primary material configured to be connectable or connected to form a secondary crosslinked network; wherein the secondary crosslinked network is formed both within the plurality of jammed particles and between the plurality of jammed particles. An additive manufactured structure according to claim 33, wherein the porous primary material is connectable to form a porous primary crosslinked network. An additive manufactured structure according to claim 33, wherein the porous primary material comprises a porous primary crosslinked network. An additive manufactured structure according to claim 35, wherein the porous primary material is connected to form the primary crosslinked network by physical bonds, covalent bonds, ionic bonds, metal-coordination bonds, hydrogen bonds and/or host-guest interactions. An additive manufactured structure according to any one of claims 33 to 36, wherein the crosslinking material is connected to form the secondary crosslinked network by physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions. An additive manufactured structure according to claim 37, wherein the covalent bonds are selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkage; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxide, disulfide or polysulfide linkages. An additive manufactured structure according to claim 38, wherein the covalent bonds are alkylene linkages. An additive manufactured structure according to any one of claims 37 to 39, wherein the metal-coordination bonds comprise a metal cation selected from the group consisting of: 90 metal ions selected from Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³⁺ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, and/or Bi⁵⁺ bismuth (V) ion; preferably iron, aluminium or calcium; and most preferably iron; metal oxides, metal carbides, metal nitrides, metals, and/or metal nanoparticles including iron oxide, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel metal particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles.

41 . An additive manufactured structure according to any one of claims 33 to 40, wherein the jammed particles have a width of about 1 pm to about 1000 pm, preferably about 1 pm to about 500 pm, more preferably 1 pm to about 200 pm.

42. An additive manufactured structure according to any one of claims 33 to 41 , wherein the additive manufactured structure is a biological part, a tissue replacement part, a robot part, an actuator, a membrane or a coating.

43. Use of the additive manufactured structure according to any one of claims 33 to 42 as a biological part, a tissue replacement part, a robot part, an actuator a membrane or a coating. 91

44. A computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control an additive manufacturing apparatus to manufacture the additive manufactured structure of any one of claims 33 to 42.

45. A method of producing an additive manufacturing ink or resin, comprising the steps of: providing particles of a porous primary material; treating the particles of the porous primary material with a crosslinking material precursor in a second medium, the crosslinking material precursor connectable to form a secondary crosslinked network; allowing the crosslinking material precursor to permeate within the porous primary material; and separating the crosslinking material precursor permeated particles of the porous primary material from the second medium.

46. A method of producing an additive manufacturing ink or resin according to claim 45, wherein the particles of a porous primary material are connectable to form a primary crosslinked network.

47. A method of producing an additive manufacturing ink or resin according to claim 45, wherein the particles of a porous primary material are connected to form a primary crosslinked network.

48. A method of producing an additive manufacturing ink or resin according to any one of claims 45 to 47, wherein the particles of the porous primary material are separated from the second medium by jamming to provide a plurality of jammed particles.

49. A method of producing an additive manufacturing ink or resin according to any one of claims 45 to 48, wherein the step of providing the particles of the porous primary material comprises the steps of: dispersing a porous primary material precursor in a first medium to form precursor droplets of the porous primary material precursor; allowing a solidification reaction in the precursor droplets to occur, thereby forming particles of the porous primary material; and separating the particles of the porous primary material from the first medium.

50. A method of producing an additive manufacturing ink or resin according to claim 49, wherein the porous primary material precursor comprises a monomeric material at a concentration of about 10 wt% or more, about 15 wt% or more, about 20 wt% or more, about 25 wt% or more, or about 30 wt% or more, in the first medium.

51. A method of producing an additive manufacturing ink or resin according to claim 49 or claim 50, wherein the crosslinking material precursor comprises a monomeric material at a concentration of about 10 wt% or more, about 15 wt% or more, about 20 wt% or more, about 25 wt% or more, or about 30 wt% or more, in the second medium.

52. A method of producing an additive manufacturing ink or resin according to any one of claims 49 to 51 , wherein the step of dispersing a porous primary material precursor in a first medium involves formation of an emulsion; wherein the emulsion may be a water-in-oil emulsion; an oil-in-water emulsion; a water-in- oil-in-water emulsion; an oil-in-water-in-oil emulsion; a triple emulsion; a multiple emulsion; or a double emulsion with multiple cores.

53. A method of producing an additive manufacturing ink or resin according to any one of claims 49 to 52, wherein the step of allowing the solidification reaction involves a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a thermal trigger or a light trigger.

54. A method of producing an additive manufacturing ink or resin according to any one of claims 45, 46 or 48 to 53, further comprising a step of forming the primary crosslinked network by providing a primary crosslinking trigger.

55. A method of producing an additive manufacturing ink or resin according to claim 54, wherein the step of forming the primary crosslinked network is conducted during the step of allowing the solidification reaction according to any one of claims 49 to 53, or wherein the step of forming the primary crosslinked network is conducted after the step of providing the particles of the porous primary material according to any one of claims 45 to 53.

56. A method of producing an additive manufacturing ink or resin according to claim 54 or claim 55, wherein the step of forming the primary crosslinked network involves formation of physical bonds, covalent bonds, ionic bonds, metalcoordination bonds, hydrogen bonds and/or host-guest interactions.

57. A method of producing an additive manufacturing ink or resin according to any one of claims 54 to 56, wherein the step of forming the primary crosslinked network involves formation of covalent bonds selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfides, sulfoxides, disulfides or polysulfide linkages.

58. A method of producing an additive manufacturing ink or resin according to claim 56 or claim 57, wherein the step of forming the primary crosslinked network involves formation of alkylene linkages and/or metal-coordination bonds.

59. A method of producing an additive manufacturing ink or resin according to any one of claims 54 to 58, wherein the primary crosslinking trigger is a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a light trigger or a chemical trigger. 94

60. A method of producing an additive manufacturing ink or resin according to claim

59, wherein the primary crosslinking trigger is UV light or a complexation agent.

61. A method of producing an additive manufacturing ink or resin according to claim

60, wherein the complexation agent comprises a metal cation selected from the group consisting of:

62. A method of producing an additive manufacturing ink or resin according to any one of claims 45 to 61 , further comprising a step of labelling at least part of the plurality of particles, jammed particles or precursor droplets with a marker or a dye, such as a fluorescent dye, crystal label or electronic marker. 95

63. A method of producing an additive manufactured structure, comprising the steps of: providing an additive manufacturing ink or resin according to any one of claims 1 to 31 ; forming the additive manufacturing ink or resin into the additive manufactured structure.

64. A method of producing an additive manufactured structure according to claim 63; further comprising forming a secondary crosslinked network by providing a secondary crosslinking trigger, thereby forming secondary crosslinks both within the plurality of jammed particles and between the plurality of jammed particles.

65. A method of producing an additive manufactured structure according to claim

64, wherein the step of forming the secondary crosslinked network involves formation of physical bonds, covalent bonds, ionic bonds, metal-coordination bonds, hydrogen bonds and/or host-guest interactions.

66. A method of producing an additive manufactured structure according to claim

65, wherein the step of forming the secondary crosslinked network involves formation of covalent bonds selected from the group consisting of: alkylene linkages; alkenylene linkages; alkynylene linkages; ester linkages; amide linkages; imine linkages; hydrazone linkages; carbocyclic or heterocyclic linkages; sulfur-based linkages, preferably sulfide, sulfoxides, disulfide or polysulfide linkages.

67. A method of producing an additive manufactured structure according to claim 65 or claim 66, wherein the step of forming the secondary crosslinked network involves formation of alkylene linkages and/or metal-coordination bonds.

68. A method of producing an additive manufactured structure according to any one of claims 64 to 67, wherein the secondary crosslinking trigger is a thermal trigger, a light trigger, a chemical trigger such as a complexation agent, or a catalyst; preferably a light trigger or a chemical trigger. 96 A method of producing an additive manufactured structure according to claim

68, wherein the secondary crosslinking trigger is UV light or a complexation agent. A method of producing an additive manufactured structure according to claim

69, wherein the complexation agent comprises a metal cation selected from the group consisting of:

Li⁺ lithium ion, Na⁺ sodium ion, K⁺ potassium ion, Rb⁺ rubidium ion, Cs⁺ caesium ion, Be²⁺ beryllium ion, Mg²⁺ magnesium ion, Ca²⁺ calcium ion, Sr²⁺ strontium ion, Ba²⁺ barium ion, Ti²⁺ titanium (II) ion, Ti⁴⁺ titanium (IV) ion, V²⁺ vanadium (II) ion, V³⁺ vanadium (III) ion, V⁴⁺ vanadium (IV) ion, V⁵⁺ vanadium (V) ion, Cr²⁺ chromium (II) ion, Cr®⁺ chromium (III) ion, Cr®⁺ chromium (VI) ion, Mn²⁺ manganese (II) ion, Mn³⁺ manganese (III) ion, Mn⁴⁺ manganese (IV) ion, Fe²⁺ iron (II) ion, Fe³⁺ iron (III) ion, Co²⁺ cobalt (II) ion, Co³⁺ cobalt (III) ion, Ni²⁺ nickel (II) ion, Ni³⁺ nickel (III) ion, Cu⁺ copper (I) ion, Cu²⁺ copper (II) ion, Ag⁺ silver ion, Au⁺ gold (I) ion, Au³⁺ gold (III) ion, Zn²⁺ zinc ion, Cd²⁺ cadmium ion, Hg⁺ mercury (I) ion, Hg²⁺ mercury (II) ion, Al³⁺ aluminium ion, Ga³⁺ gallium ion, ln⁺ indium (I) ion, ln³⁺ indium (III) ion, Sn²⁺ tin (II) ion, Sn⁴⁺ tin (IV) ion, Pb²⁺ lead (II) ion, Pb⁴⁺ lead (IV) ion, Bi³⁺ bismuth (III) ion, Bi⁵⁺ bismuth (V) ion, and/or; preferably iron, aluminium or calcium; and most preferably iron; metal oxides, metal carbides, metal nitrides, metals, and/or metal nanoparticles including iron oxide, iron nitrides, iron carbides, iron metal particles, nickel oxides, nickel carbides, nickel metal particles, titanium oxides, titanium metal particles, titanium nitrides, titanium carbides, silver metal particles and gold metal particles. A method of producing an additive manufactured structure according to any one of claims 63 to 70, further comprising a step of forming the primary crosslinked network by providing a primary crosslinking trigger after forming the additive 97 manufacturing ink or resin into the additive manufactured structure, if the primary crosslinked network has not yet been formed.

72. A method of producing an additive manufactured structure according to claim 71, wherein the step of forming the primary crosslinked network is conducted before or after the step of forming the secondary crosslinked network.

73. A method of producing an additive manufactured structure according to any one of claims 64 to 72, wherein the secondary crosslinked network is formed immediately after formation of the 3D structure.

74. A method of producing an additive manufactured structure according to claim 71 or claim 72, wherein the primary crosslinked network is formed immediately after formation of the 3D structure.

75. A method of producing an additive manufactured structure according to any one of claims 64 to 73, wherein the secondary crosslinked network is formed on a layer by layer basis.

76. A method of producing an additive manufactured structure according to any one of claims 71 to 75, wherein the primary crosslinked network is formed on a layer by layer basis.

77. A method of producing an additive manufactured structure according to any one of claims 64 to 76, wherein the secondary crosslinked network is formed once the 3D structure has been completed.

78. A method of producing an additive manufactured structure according to any one of claims 71 to 77, wherein the primary crosslinked network is formed once the 3D structure has been completed.

79. A method of producing a an additive manufactured structure according to any one of claims 63 to 78, wherein the step of forming the additive manufacturing ink or resin into the additive manufactured structure is conducted using additive manufacturing, further comprising the steps of: 98 obtaining an electronic file representing a geometry of the additive manufactured structure; and controlling an additive manufacturing apparatus to manufacture, over one or more additive manufacturing steps, the additive manufactured structure according to the geometry specified in the electronic file.

80. A method of producing an additive manufactured structure according to claim 79, wherein the step of forming the additive manufacturing ink or resin into the additive manufactured structure is conducted using 3D printing, stereolithography, digital-light processing or volumetric additive manufacturing, preferably 3D printing.

81. A method of producing an additive manufactured structure according to any one of claims 63 to 80, wherein the additive manufacturing ink or resin is formed into a biological part, a tissue replacement part, a robot, an actuator, a membrane or a coating.

82. A method of producing an additive manufactured structure according to any one of claims 63 to 81, wherein the additive manufacturing ink or resin is an ink.

83. A method of producing an additive manufactured structure according to any one of claims 63 to 81, wherein the additive manufacturing ink or resin is a resin.