WO2020233791A1

WO2020233791A1 - Stretchable electrohydrodynamic pump

Info

Publication number: WO2020233791A1
Application number: PCT/EP2019/063086
Authority: WO
Inventors: Jun SHINTAKE; Shingo Maeda; Dario Floreano; Vito CACUCCIOLO; Herbert Shea
Original assignee: Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date: 2019-05-21
Filing date: 2019-05-21
Publication date: 2020-11-26

Abstract

A stretchable pump for providing electrohydrodynamic pumping of a ionisable fluid, said soft pump comprising a stretchable polymeric structure comprising at least one elongated channel, therein; and a first set of at least two electrodes operatively disposed within, or on a surface of, at least a portion of an interior wall of said polymeric structure elongated channel so as to generate an electric field causing a movement of said ionisable fluid.

Description

Stretchable electrohydrodynamic pump

Technical Field

[0001] The present invention belongs to the field of micro-engineering and material science. In particular, the invention concerns an all-polymer soft electrohydrodynamic pump and method for producing and using thereof.

Background of the invention

[0002] Nearly all biological systems include intrinsically highly compliant, and in many cases, stretchable elements, for instance muscle and skin. This mechanical compliance is in marked contrast to most human-made machines, consisting typically of rigid elements and linkages. In the past decade, there has been a great deal of research activity aimed at using elastomers and other very soft materials to develop muscle-like actuators for soft robots and wearables.

[0003] Flexible or stretchable counterparts of most key mechatronic components have been developed, as reviewed by Hines. Remarkable performance has been achieved, mostly widely using fluidically-driven systems, though a large range of actuation principles have been reported (8), including electrostatic, electrically responsive gels, and thermally responsive materials such as liquid metals, and shape memory polymers. Unlike conventional robots where structural elements, actuators and sensors are well defined separate elements, in compliant systems the three functionalities are often combined in one part, adding yet one more challenge to the design.

[0004] Despite the widespread use of fluidic actuation, there exists to date no soft or stretchable counterpart of a pump or a compressor. Conventional pumps and compressors are bulky and rigid systems including impellers, bearings, and electrical motors. They often require lubrication and produce noise. Even miniaturized pumps (e.g., based on piezo-actuators or electrophoresis) share most of these limitations.

[0005] The lack of flexible pumps greatly hinders many applications of fluid-driven soft-systems, ranging from robotics and mechatronics (actuation and sensing) to biology (e.g., microfluidics for cell cultures) to wearable devices (heat distribution).

[0006] Flexible pumps have been proposed such described in Jahahshahi, et al. “Fabrication of an implantable stretchable electro-osmosis pump”, however the device described in this publication uses an osmosis force, which does not provide satisfactory results and is not stretchable. Moreover, in this regard, a primary object of the invention is to solve the above-mentioned problems and more particularly to provide a pump which is flexible and stretchable and which permits elevated flow rate. Another object of the invention is to provide a pump which has a simple structure without moving parts, silent and causing no vibration.

Summary of invention

[0007] The subject-matter of the present disclosure, as described hereinafter and in the appended claims, addresses and overcomes the shortcomings of the actual solutions by providing a class of all-soft-matter pumps, characterized by a stretchable structure with embedded or patterned electrodes, exploiting the EHD (ElectroHydroDynamic) pumping mechanism, in which a dielectric fluid is accelerated within a channel by means of a high DC electric field, producing a pressure proportional to (some power of) the electric field and allowing pumping in both directions. The stretchable pumps of the present invention have no moving parts, are silent, produce no vibration, operate well when highly bent, twisted and even stretched, making them ideal candidates for miniaturization and portability in soft systems and in applications such as e.g., soft robotics.

[0008] Accordingly, one object of the present invention relates to a stretchable pump for providing electrohydrodynamic pumping of a ionisable fluid, said soft pump comprising:

[0009] a) a stretchable polymeric structure comprising at least one elongated channel therein; and

[0010] b) a first set of at least two electrodes operatively disposed within, or on a surface of, at least a portion of an interior wall of said polymeric structure elongated channel so as to generate an electric field causing a movement of said ionisable fluid.

[0011] The stretchable polymeric structure is generally substantially composed of materials having a low elastic modulus (between about 1 kPa and about 100 MPa, preferably between 0.1 MPa and 10 MPa, more preferably between 0.5 MPa and 5 MPa), and in some embodiments comprises elongated compliant electrodes disposed as arrays of interdigitated elements.

[0012] Optionally, the channel is defined by at least a first wall or side of stretchable polymeric material and a second wall or side of stretchable polymeric material opposed to the first side, and a spacer disposed between said first and second wall or side.

[0013] Preferably, the channel is defined by at least a first wall or side of stretchable polymeric material and a second wall or side of stretchable polymeric material opposed to the first side, and the at least two electrodes are adjacently disposed on said a first wall or side.

[0014] In one embodiment, the pump of the invention further comprises a second set of at least two adjacent electrodes operatively disposed within, or on a surface of, at least a portion of an interior wall of said polymeric structure elongated channel in such a way that the electrodes of said first and the second set of electrodes are opposed and overlapped along an axis. [0015] According to a preferred embodiment, the channel is defined by at least one recess provided on the surface of at least one of a first wall or side of stretchable polymeric material and a second wall or side of stretchable polymeric material opposed to the first side.

[0016] Advantageously, the elongated channel is defined by a bore provided within said stretchable polymeric material.

[0017] Preferably, the elongated channel is shaped as a tube having a round or elliptic cross-section, and the electrodes are arranged on some portion of the channel or all-around the channel.

[0018] Another object of the present invention pertains to the use of the stretchable pump of the invention for the electrohydrodynamic pumping of a fluid.

[0019] A further object of the present invention relates to an article of manufacture comprising a stretchable pump of the invention.

[0020] Still a further object of the present invention relates to a method of manufacturing a stretchable pump according to the present disclosure, said method comprising the steps of:

[0021] a) patterning a first set of at least two adjacent electrodes on or within a first stretchable polymeric substrate; and

[0022] b) bonding said first polymeric substrate with a second stretchable polymeric substrate, wherein said bonding is performed via a spacer so to allow the creation of an elongated channel. Alternatively, the bonding step can be replaced by the formation of an elongated channel on said first polymeric substrate.

[0023] The above and other objects, features and advantages of the herein presented subject-matter will become more apparent from a study of the following description with reference to the attached figures showing some preferred aspects of said subject-matter. However, the present invention is not limited to the embodiments as described in the following and/or depicted in the drawings; to the contrary, the scope of the present invention is defined by the appended claims.

Brief description of drawings

[0024] In the drawings:

[0025] In Figure 1 there are depicted two embodiments of stretchable polymeric structures according to present invention, having two electrodes (1A) or a plurality of electrodes (1 B);

[0026] In Figure 2 there are depicted two embodiments of the stretchable electrohydrodynamic pump according to the present invention, having two electrodes (2A) or a plurality of interdigitated electrodes (2B);

[0027] In Figure 3A and 3B there is depicted two embodiments of the stretchable electrohydrodynamic pump according to the present invention comprising a monolithic stretchable polymeric structure having a top side and an opposed second side and an elongated channel in between, without any spacers;

[0028] In Figure 4 there are depicted two embodiments of the stretchable electrohydrodynamic pump according to the present invention having a plurality of interdigitated electrodes on two opposed surface of a channel, said channel being formed from two opposed stretchable polymeric structures separated by spacers (4A) or by a channel obtained in a monolithic polymeric structure (4B);

[0029] In Figure 5 it is shown a schematics of one implemented fabrication process of the pump of the invention;

[0030] In Figure 6 it is shown a comparison by generated pressure at the same applied voltage of three generations of stretchable pumps developed. Both generations inclined 1 and inclined 2 have inclined capacitors as electrodes configuration. Inclined 2 is a scaled version of inclined 1 , with half size of the channel, half gap between opposite electrodes and 8.6 times more electrode pairs. The interdigitated generation has the same channel size and gap between opposite electrodes as inclined 2 but uses interdigitated electrodes rather than inclined capacitors;

[0031] In Figure 7 are shown the two different electrodes geometry and correspondent ElectroHydroDynamic (EHD) mechanisms used in the pump of the invention: 7A) Inclined capacitors. Heterocharge layers form in the proximity of the electrodes. These layers are characterized by a higher concentration of ions of opposite polarity respect to the corresponding electrode. As a consequence, these ions get attracted to the electrode, where they discharge. The inclined capacitors geometry allows net flow thanks to the in -flow component of the electric field in proximity of the electrodes surface; 7B) Interdigitated electrodes. When the electric field is high enough to win the energy barrier, field emission takes place, consisting of jumping of electrons from the cathode surface into the dielectric liquid. The generated ions get accelerated by the electric field until they discharge at the anode, transferring momentum to neutral liquid molecules during their path;

[0032] In Figure 8 is shown the performance of the stretchable EHD pump of the invention: 8A) Pumps connected to rigid holders to apply strain; 8B) Pressure vs. flow rate for the pump at 0% and 10% of strain. For the 10% of strain experiment the voltage was increased by 10% to have the same electric field in both cases, compensating the increased gap between the electrodes; 8C) Pressure and electrical current vs. applied voltage, for zero flow-rate (the output valve is closed). The flow direction can be set by the initial choice of the polarity of the drive voltage; 8D) Response of the pump to a 4.5 kV voltage step, showing a pressure rise time of 0.4 s and a fall time of 0.14 s, both at 10% to 90%; 8E) Pressure generated by the pump in response to a 1 Hz square drive wave; [0033] In Figure 9 is shown a stretchable pump of the invention embedded in a textile glove for thermal regulation on the human body (left). The closed loop fluidic circuit consists of the pump and one serpentine made from flexible tubes sewn into the textile glove (the“cold” side), and of one serpentine made from flexible tubes bonded to a flexible heater (the“hot” side). The wearer can easily flex his wrist with the pump operating. The pump circulates the fluid from the heater to the glove and then back on the opposite side. An infrared camera was used to monitor the change in temperature in the system. The leftmost infrared image shows the set-up when both the heater and the pump are off. For the second infrared image, the heater is on and the pump is off: the temperature at the heater is significantly higher than at the arm. The third infrared picture is taken a few seconds after the pump is activated. One can see as a change in color how the cold liquid enters the circuit from the top tube and how the heat is transported away from the bottom tube. The rightmost infrared image shows that the temperature of the heater is significantly decreased after 40 s of fluid circulation;

[0034] In Figure 10 is shown a “fluidic muscle” obtained by integrating the stretchable pump of the invention in the bottom layer of a bending fluidic actuator: 10A) Schematics of a longitudinal cross section of the fluidic muscle, showing its functional components. The inlet of the pump is connected to a small reservoir in the back of the actuator, while the outlet is connected to the bellows-shaped bending chamber; 10B) The entire actuator is stretchable and can be easily deformed; 10C) Once pre-filled with liquid, the actuator does not require any external tubing and bends when a voltage is applied. The pump moves the liquid from the reservoir to the bending chamber, producing its deformation; 10D) The measured bending angle (relative to the initial pre-bent position of 40°) as a function of the applied voltage. Detailed description of the invention

[0035] The subject-matter herein described will be clarified in the following by means of the following description of those aspects which are depicted in the drawings. It is however to be understood that the subject matter described in this specification is not limited to the aspects described in the following and depicted in the drawings; to the contrary, the scope of the subject-matter herein described is defined by the claims. Moreover, it is to be understood that the specific conditions or parameters described and/or shown in the following are not limiting of the subject-matter herein described, and that the terminology used herein is for the purpose of describing particular aspects by way of example only and is not intended to be limiting.

[0036] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, unless otherwise required by the context, singular terms shall include pluralities and plural terms shall include the singular. The methods and techniques of the present disclosure are generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification unless otherwise indicated. Further, for the sake of clarity, the use of the term“ about” is herein intended to encompass a variation of +/- 10% of a given value.

[0037] The following description will be better understood by means of the following definitions.

[0038] As used in the following 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 for the description of various embodiments use is made of the term "comprising", those skilled in the art will understand that in some specific instances, an embodiment can be alternatively described using language "consisting essentially of or "consisting of."

[0039] In the frame of the present disclosure, the expression “operatively connected” and similar reflects a functional relationship between the several components of the device or a system among them, that is, the term means that the components are correlated in a way to perform a designated function. The“designated function” can change depending on the different components involved in the connection; for instance, the designated function of electrodes operatively connected and disposed into/onto a polymeric support is to deliver electric current so to create a voltage suitable for providing an EHD pumping effect of a fluid medium. A person skilled in the art would easily understand and figure out what are the designated functions of each and every component of the device or the system of the invention, as well as their correlations, on the basis of the present disclosure.

[0040] "Electrohydrodynamics” (“EHD”), also known as "electro-fluid-dynamics

("EFD”),“electro-aero-dynamics” (“EAD”) or“electrokinetics”, is the study of the dynamics of electrically charged fluids. It is the study of the motions of ionized particles or molecules and their interactions with electric fields and the surrounding fluid. In general, the phenomenon relates to the direct conversion of electrical energy into kinetic energy in the form of moving dielectric fluids, and vice versa. Accordingly,“EHD pumping” refers to the acceleration of a fluid such as air, oil, gases or dielectric solids suspended in a fluid by means of an electric field. The term“EHD pump” therefore refers to a device conceived, constructed and employed to pump suitable dielectric or ionized fluids.

[0041] In the first instance, shaped electrostatic fields (ESF's) create hydrostatic pressure (HSR, or motion) in fluid media, so that a flow is produced. Such flow can be directed against the electrodes, generally to move the electrodes: in such case, the moving structure acts as an electric motor. In the second instance, the converse takes place. A powered flow of medium within a shaped electrostatic field adds energy to the system which is picked up as a potential difference by electrodes. In such case, the structure acts as an electrical generator.

[0042] The electrohydrodynamic (EHD) phenomena involve the interaction of electric fields and flow fields in a dielectric fluid medium. This interaction between electric fields and flow fields can induce the flow motion by electric body force. In general, there are three kind of EHD pumping mechanisms based on the Coulomb force: injection pumping, induction pumping and conduction pumping.

[0043] The EHD pump according to some embodiments of the present invention exploits either a conduction pumping or an injection pumping mechanism. Conduction pumping relies on the formation of heterocharge layers in the proximity of the electrodes. Heterocharge layers are non-equilibrium charged layers that form when the electric field exceeds a certain threshold (typically 5 - 6 V/pm) due to ion generation not balanced by recombination. The charges in these layers are of opposite sign to that of the adjacent electrode, thus they move towards the electrode and discharge there. The movement of ions, which drag the liquid molecules and generate the pumping, is identical at the anode and the cathode. As a consequence, the generation of one-way flow requires the electrodes surface to have a component oriented along the flow direction and the flow direction does not change by inverting the field polarity. [0044] Injection pumping is based on field emission. When the electric field is high enough, such as between about 1 and about 10 V/pm, electrons can directly jump from the surface of one electrode into the dielectric liquid molecules. The so formed ions are accelerated by the electrophoretic force until they discharge at the opposite electrode. This mechanism can create net flow with a planar electrodes configuration and the flow direction depends on the polarity of the electric field. Fig. S1 B shows the design of the stretchable pump based on injection pumping, consisting in two overlapped sets of interdigitated electrodes.

[0045] In both injection pumping and conduction pumping mechanisms, over the threshold of electric field needed to start the phenomenon, the pumping pressure Ap generally grows with the square of the electric field and linearly with the dielectric constant of the liquid Ap - k_psE², where k_p is a constant depending on the pump geometry and design, electrodes’ shape and surface properties, as well as chemical properties of the fluid. The generated flow-rate Q has a more complicated relation; it generally depends on the electric field squared and on the fourth power of the channel size D\ Q = k_Q£E²D⁴, with D being the hydraulic diameter.

[0046] As uses herein, “overlapping electrodes" refers to a pair of electrodes placed on opposite sides or walls of a stretchable polymeric structure, facing each other with an optimal or predetermined distance, which can be set based on several constraints such as channel size, electrodes geometry, breakdown voltage of the liquid, fabrication technology and the like, between them along the thickness of the stretchable polymeric structure, and for which the contact area is maximized upon projection of one electrode on the other. For instance, with reference to Figure 4a, overlapping electrodes are electrodes 104a-1Q5a.

[0047] The materials used in accordance with the present invention for the supporting structure are soft polymers. In the frame of the present disclosure, a “soft” polymer or material is any material that is either compressible, reversibly compressible, elastic, stretchable or any combination thereof. The term“stretchable” is herein used to mean an intrinsic or engineered property of a material or structure that allows such material or structure to perform a large elongation upon a strain stress, typically of >5% of the elongation of a soft structure at rest, such as for instance more than about 10%, more than about 20%, more than about 50%, more than about 100% or even more than about 200% of a soft structure at rest. Preferably, the elongation is an elastic elongation, and the term "stretchable” in most of the embodiments according to the present disclosure should be intended as "elastically stretchable”. In preferred embodiments of the invention, the materials used for the supporting structure are elastically stretchable polymers.

[0048] Suitable polymers according to the present disclosure may include, for example, thermosets or thermoplastics such as styrene butadiene, styrene

(SBS) or styrene ethylene butylene styrene (SEBS); soft foams such as polyurethanes including reticulated polyurethanes; polyvinyl chloride (PVC), neoprene, uncrosslinked neoprene, cross-linked polyethylene, polyether, ethylene-vinyl acetate (EVA), polyethylene-vinyl acetate (PEVA), polypropylene glycol (PPG), latex; elastomeric materials such as silicone rubber (e.g. polydimethylsiloxane PDMS) or fluorosilicone rubber; thermoplastic elastomers such as styrenic block copolymer (SBC), ethylene propylene diene monomer (EPDM) rubber, butyl rubber, thermoplastic polyurethanes (TPU), nitrile rubber; natural polymeric materials (i.e., non- synthetic polymers, polymers that can be found in nature) and/or polymers derived from the 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, gels such as for instance PDMS gels, or suitable combinations of any of the foregoing.

[0049] Materials used may be selected based on one or more properties such as a high electrical breakdown strength, a low modulus of elasticity or the dielectric constant. In some embodiments, the polymer is selected such that it has an elastic modulus comprised between about 1 kPa and about 100 MPa, preferably between 0.1 MPa and 10 MPa, more preferably between 0.5 MPa and 5 MPa.

[0050] A“compliant electrode” is any structure or element able to deliver an electric current, and adapted to change its shape according to the shape change of the support it adheres to without substantially compromising mechanical or electrical performance.

[0051] With reference to Figures 1a and 1 b, two embodiments of stretchable polymeric structures according to present disclosure are shown. Soft polymeric structures are the main building blocks of the EHD soft pump according to an embodiment of the invention and comprise a soft polymeric support 100 having an upper surface 101 and a bottom surface 102, and comprising at least a first set 104 of at least two adjacent electrodes 104a and 104b operatively disposed within and/or on a surface 101/102 of said support 100. As shown in the embodiment of Figure 1 a, only two electrodes

104a and 104b are present, but several configurations are possible, in which for instance a plurality of electrodes composes a first set 104 operatively located in/on the support 100. For instance, in the embodiment shown in

Figure 1 b, the electrodes’ sets 104 comprises several parallel, evenly spaced electrodes arranged in an interdigitated fashion. For the sake of clarity and ease of understanding, as in all the other figures, relative dimensions and positioning of the components depicted in Figure 1 are expressly exaggerated and do not necessarily reflect their real arrangements and dispositions. A circuitry 106 is operatively connected to the electrodes of said first set 104 in order to provide a suitable voltage upon connection with a power supply, as will be detailed later on.

[0052] Turning now to the soft pump of the invention, two embodiments thereof being shown in Figures 2a and b, these comprise

[0053] a) a soft polymeric structure 1000 comprising an elongated channel 103, said channel 103 being defined by at least a first side 100 and a second side 100’ opposed to the first side 100; and

[0054] b) a first set 104 of at least two adjacent electrodes 104a/104b operatively disposed within, or on a surface of, said first side 100 of said soft polymeric structure channel 103. In the frame of the pump as described herein, a soft polymeric support 100 as previously described is placed on the top or the bottom of the polymeric structure 1000 so to define a first side comprising a first set 104 of electrodes. Said first side 100 in turn forms part of the internal wall of a channel 103 adapted to let a fluid flow therein; in particular, depending on the disposition of said first side 100, this can form for instance the "roof or the“floor” of the channel 103. In the embodiments depicted in Figure 2, said first side 100 comprising a first set 104 of two electrodes 104a/104b (Figure 2a) or of a plurality of interdigitated electrodes (Figure

2b) is located on the top wall or side of the structure 1000 so to define the roof of the channel 103. Opposite to said first side 100, a second side 100’ substantially composed of a soft polymer, forms a second side of the structure 1000, as well as the floor of the channel 103.

[0055] Polymeric supports 100/100’ of the present invention may cover a wide range of thicknesses, depending on the needs and circumstances. In one embodiment, polymer thickness may range between about 1 pm and about 10 cm, such as for instance between about 1 pm and about 1 cm, between about 10 mΐti and 1 mm, and for instance between about 50 pm and about 250 pm in the case of e.g. silicone elastomers.

[0056] In the embodiment depicted in Figures 2, the top and bottom sides 100 and 100’ of the structure 1000 are separated by soft polymeric spacers 107, defining at least in part the thickness of the soft structure 1000 and consequently the lateral cross-section of the channel 103. This kind of structure is tightly linked to one embodiment of the manufacturing method, as will be described later on. However, the soft polymeric structure 1000 can be a monolithic structure in which the channel 103 can be obtained by e.g., molding or etching, in such a way that is the channel 103 itself that defines the top (first) and bottom (second) sides or walls of the polymeric structure 1000. As a way of example, as depicted in Figure 3A, a monolithic soft polymeric structure 1000 comprising a top wall or side 100 with a first set 104 of interdigitated electrodes and an opposed second wall or side 100’ comprises an elongated channel 103 without any soft polymeric spacers 107. Preferably, the lines of the electric field lines are such that they can reach the central area of the channel 103 rather than being confined on the boundaries. In this context, the ratio of the pitch between the electrodes in the first set 104 to the channel’s 103 cross-section is optimized to be at least 0.1 , and preferably comprised between 0.4 and 2.

[0057] As a way of another example, as depicted in Figure 3B, a monolithic soft polymeric structure 1000 comprising a top wall or side 100 and an opposed second wall or side 100’ comprises an elongated channel 103 wherein the electrodes comprise at least one pair of electrodes disposed adjacently and extending along the channel length in a spiral configuration. Preferably, as for Figure 3A the lines of the electric field lines are such that they can reach the central area of the channel 103 rather than being confined on the boundaries. [0058] In one embodiment according to the invention, the soft pump further comprises a second set 105 of at least two adjacent electrodes 105a/105b operatively disposed within, or on a surface of, the second wall or side 100’ of said soft polymeric structure channel 103, wherein the electrodes of said first and the second set of electrodes, respectively 104 and 105, are overlapped along an axis. Two configurations according to this embodiment are depicted in Figure 4. For the sake of ease of understanding and conciseness, only embodiments in which electrodes sets having a plurality of interdigitated electrodes are shown in the following. However, as will be evident to a person skilled in the art, all previously described configurations, such as the ones having only two adjacent electrodes 104a/104b, are envisaged hereinafter.

[0059] Generally speaking, in this embodiment according to the invention, at least two sets of electrodes 104 and 105 comprising at least two adjacent electrodes are attached to the soft polymeric structure 1000 on its top (100) and bottom (100’) walls or sides, respectively, to provide either a voltage difference across the channel 103 thickness (in the case of a conduction pumping mechanism) or for doubling the pumping effect (in the case of an injection pumping mechanism). In some embodiments, the sets of electrodes 104 and 105 can be partly or completely embedded within the polymeric supports 100 and 100’ they adhere to.

[0060] An important aspect of these embodiments of the soft pump of the invention relates to the spatial configuration of the electrodes’ sets 104 and 105 among them. These are positioned on top side 100 and bottom side 100’ so to have their electrodes overlapped in pairs along an axis. This configuration advantageous for the pumping properties that can be provided by the soft pump, as will be described later on in more details.

[0061] In general, electrodes suitable for use with the present invention may be of any shape and material, provided they are able to supply a suitable voltage, either constant or varying over time, and comply with the above-mentioned (overlapped) configuration constraint. For instance, electrodes can have a round, squared, triangular, rectangular or parallelepiped shape, and they are attached on polymeric supports 100 and 100’ so that for instance the long axes thereof, or at least a symmetry axis (e.g., diameter of a round electrode), are substantially parallel and overlapping. In some embodiments, the axes can be substantially parallel and the surfaces of the overlapping electrodes are completely or partially overlapped, preferably with an overlap comprised between about 50 and 100%, more preferably between about 80 and 100%, even more preferably of 100%. Electrodes in each set 104 and 105 are in some embodiments parallel among them, and can be in some embodiments evenly disposed on polymeric supports 100 and 100', respectively, in order to homogeneously distribute electrical charges, provided by a suitable voltage, to a ionisable fluid along the polymeric structure 1000 and the channel 103 in particular. In preferred embodiments, overlapping electrodes are also substantially identical among them. In some embodiments, electrodes can be different in shape, volume, area or combinations thereof.

[0062] In preferred embodiments of the invention, the electrodes in the sets 104 and 105 are compliant and change shape according to polymeric supports

100/100’, or a polymeric structure 1000, deflection. Generally speaking, the term "deflection” refers to any displacement, expansion, contraction, bending, torsion, twist, linear or area strain, or any other kind of deformation, of at least a portion of the polymeric supports 100/100’ or polymeric structure 1000. Examples of compliant electrodes known in the art include metal thin-films (including patterned electrodes, of out-of-plane buckled electrodes, and corrugated membranes), metal-polymer nano-composites, carbon powder, carbon grease, conductive rubbers or paints, a review of which is provided by Rosset and Shea (Applied Physics A, February 2013, Volume 1 10, Issue 2, pp 281-307), incorporated herein in its entirety by reference. In one embodiment, stretchable electrodes as the one described in International Patent Application WO 2004/095536, incorporated herein in its entirety by reference, can be used. Alternatively or additionally, tubular or plain elements filled with a ionic liquid, a hydrogel or with liquid metals such as mercury or gallium, or even alloys, oxides or combinations thereof, can be used.

[0063] The soft pump of the invention further comprises a circuitry 106 configured to provide a voltage between adjacent electrodes of anyone of the first set 104 and the second set 105 of electrodes independently and/or between overlapped electrodes of different sets of electrodes upon connection with a power supply (see Figures 1 to 4). A suitable actuation voltage can be applied to the soft pump via operative connection with a power supply (not shown) through said circuitry 106 configured to provide a voltage between overlapped electrodes (i.e. 104a-105a, 104b-105b see Figure 4a) in different electrodes’ sets 104 and 105. In one embodiment, the electrohydrodynamic pumping of a ionisable fluid is provided by applying a voltage to any set of electrodes so to create opposed charges in each pair of overlapping electrodes (i.e. 104a-105a) of different electrodes’ sets 104 and 105, and equal charges in adjacent electrodes (i.e. 104a-104b, 105a- 105b) of each electrodes' set. This configuration is used for conduction pumping. Alternatively, the electrohydrodynamic pumping of a fluid, in particular the injection pumping mechanism, is provided by applying a voltage to any set of electrodes comprises so to create alternating unlike charges in adjacent electrodes (i.e. 104a-104b, 105a-105b) of each electrodes’ set 104 and 105 and equal charges in each overlapped electrode (i.e. 104a-105a, 104b-105b) of different sets of electrodes.

[0064] In one embodiment, the power supply connected with the circuitry 106 comprises a controller such as a (micro)processor configured to perform for instance voltage step-up or conversion between AC and DC power, and can receive power from an external or embedded battery.

[0065] In one embodiment, particularly for providing a soft EHD pump working in accordance to the conduction pumping mechanism, the channel 103 has a lateral cross section which diminishes along its longitudinal axis. For instance, the first wall or side 100 and the second wall or side 100’ of the polymeric structure 1000 can be inclined inwardly towards the longitudinal axis of the elongated channel 103, as schematically depicted in Figure 7. In scenarios where sets of interdigitated electrodes are present, some embodiments of a soft pump of the invention exploiting a conduction pumping mechanism foresee two sets 104/105 of inclined electrodes acting as capacitors obtained by overlapping two series of symmetric electrodes on an inclined channel 103, the channel 103 having an inlet section and an outlet section continuous along the long axis, and the channel 103 section being defined by e.g. a conical inner surface whose diameter progressively reduces towards the outlet. In another embodiment, two sets 104/105 of inclined electrodes located on flat channel walls 100 and 100’, respectively, can be implemented. Many different configurations can be envisaged in this context, which would be readily evident to a person skilled in the art.

[0066] In one particular embodiment, the elongated channel 103 is shaped as a tube having a round lateral cross-section, and the electrodes 104a-104b are arranged on some portion of the channel 103 or all-around the channel 103.

[0067] As it will be evident, another object of the present invention relates to the use of the soft pump according to the present disclosure for the electrohydrodynamic pumping of a fluid, particularly a ionisable fluid. Suitable fluids in the frame of the present invention are without limitations dielectric liquids, conductive liquids, oils, liquid polymers, fluorinated solvents, solutions of liquids and solid particles, including nanoparticles, nanotubes and/or magnetic particles, as well as combinations of different liquids that can transfer energy by normal pressure or shear forces.

[0068] A further object of the present invention relates to an article of manufacture comprising a soft pump according to the present disclosure. Articles of manufacturing according to this aspect of the invention comprise without limitations wearable devices, sensors, medical devices, biomedical implants, soft robotics components or soft actuators, to mention a few.

[0069] Still a further object of the present invention relates to a method for providing electrohydrodynamic pumping of a fluid, particularly a ionisable fluid, said method comprising the steps of:

[0070] a) providing a soft pump or an article of manufacture according to the present disclosure comprising a fluid, such as a ionisable liquid, to be pumped; and

[0071] b) applying a voltage to any set of electrodes.

[0072] Depending on the needs and circumstances, such as for instance the design of the pump/electrodes geometry of the invention, the voltage applied to any set of electrodes comprises, whenever applicable, 1 ) creating opposed charges in each overlapped electrode of different sets of electrodes and equal charges in adjacent electrodes of each set of electrodes and/or 2) creating alternating unlike charges in adjacent electrodes of each electrodes’ set and equal charges in each overlapped electrode of different sets of electrodes. The first scenario relates to situations in which a conduction pumping is sought: heterocharge layers form in the proximity of the electrodes, those layers being characterized by a higher concentration of ions of opposite polarity with respect to the corresponding electrode. As a consequence, these ions get attracted to the electrode, where they discharge. In preferred embodiments of this example, an inclined capacitors geometry facilitates the net flow thanks to the in -flow component of the electric field in proximity of the electrodes surface. [0073] In the second scenario, typically an interdigitated geometry of the electrodes arrays allows an injection pumping; when the electric field is high enough to win the energy barrier, field emission takes place, consisting of emission of electrons from the surface of one electrode into the dielectric liquid. The generated ions get accelerated by the electric field until they discharge at the opposite electrode, transferring momentum to neutral liquid molecules during their path. The pump of the present invention is adapted to work on both pumping mechanisms, while maintaining its soft and stretchable nature.

[0074] In one embodiment, the fluid to be pumped is a suspension comprising a dielectric liquid and dielectric particles. For instance, the liquid can be a dielectric oil such as the commercially available FR3 Envirotemp oil, and the particles can be polyvinylidene difluoride (PVDF) particles. In general, a suspension comprising high breakdown strength liquids, which have low dielectric constant, with high dielectric constant solid particles is considered to be a good embodiment in terms of pumping performances.

[0075] Still another object of the present invention relates to a method of manufacturing a soft pump as described herein, said method comprising the steps of:

[0076] a) patterning a first set of at least two adjacent electrodes on or within a first soft polymeric substrate; and

[0077] b) bonding said first polymeric substrate with a second soft polymeric substrate, wherein said bonding is performed via a spacer so to allow the creation of an elongated channel.

[0078] In one embodiment, step b) is replaced by step b’) of forming an elongated channel on said first polymeric substrate. In another embodiment, step b) is replaced by step b”) of forming an elongated channel on said second polymeric substrate and performing said bonding without a spacer. [0079] In one embodiment, the method further comprises a step of patterning a second set of at least two adjacent electrodes on or within said second soft polymeric substrate.

[0080] In one embodiment, the method further comprises a step of patterning a second set of at least two adjacent electrodes on or within a second soft polymeric substrate, and a step of bonding said first and second soft polymeric substrates.

[0081 ] In some aspects, the fabrication of the electrode layers comprises applying, with any suitable means known in the art such as casting, spray drying, lamination, chemical or physical vapor deposition, evaporation, sputtering and the like, a thin film or layer of a conductive material such as carbon, a metal (e.g. Au, Pd, Ft, Ir and/or alloys or oxides thereof) thin film, a conductive paint or the like on a first soft polymeric support or substrate. Said layer can be later on patterned to obtain a first set of electrodes by e.g., laser engraving or (photo)lithographic means. A second soft polymeric support or substrate can be bonded on the bottom electrode layer via spacers using e.g. an adhesive film, said second soft polymeric support having or not a patterned second set of electrodes.

[0082] EXAMPLE

[0083] The inventors have developed, according to the inventive concept of the invention, some exemplary soft micropumps. In the implemented embodiments, the modular pump elements are compact (75 mm long * 19 mm wide ^c 1 .3 mm thick with a fluidic channel of dimensions 55 mm long ^c 2 mm wide ^c 0.5 mm thick), light-weight (1.0 g) and are controlled simply by means of an applied voltage. Established elastomer processing technologies which are highly reproducible were used, which can readily be scaled up for industrial production.

[0084] In the implemented embodiments of the soft pump of the invention, this is composed of two electrode layers that sandwich a channel layer. The electrode layers are symmetric and consist of a stretchable circuit with a PDMS (Polydimethylsiloxane) backing. The PDMS used for the whole pump is Dow Corning Sylgard 184. The electrode is composed of carbon particles dispersed in a soft PDMS matrix (Silbione LSR 4305). The channel layer consists of a laser-cut PDMS membrane, whose thickness determines the height of the channel (1 mm or 0.5 mm in our soft pumps). The layers are connected together and sealed using a silicone adhesive film.

[0085] Figure 5 shows a schematics of one implemented fabrication process of the pump of the invention. The fabrication of the electrode layers starts in (A) by casting an electrode membrane with a thickness of 30 pm on a PET support, which is then cured at 80°C. (B) A 400 pm PDMS membrane is casted on the top of the electrode and cured at 80°C. (C) The sample is flipped in order to expose the electrode membrane, (D) which is then processed by laser engraving to obtain the circuit pattern. This process allows the manufacturing of many samples in parallel (e.g. up to 24 samples). (E) The channel layer, consisting of a 500 pm thick laser-cut PDMS membrane, is bonded on the bottom electrode layer using an adhesive film. (F) The top electrode layer, having two laser-cut holes for fluidic connection, is finally bonded on the top of the channel layer. (G) The PET supports are removed and the soft pump is ready to use.

[0086] Figure 6 shows the different generations of soft pumps developed. In particular, four generations of soft pumps have been designed and developed. The circuit of the first generation (inclined 1 ) consists of a set of

5 inclined capacitors (corresponding to 10 electrode units) separated by a 1 mm gap and working according to EHD conduction pumping. The second generation (inclined 2) is a scaled version of the first one. It has the same circuit design of the first one, but features 43 inclined capacitors (86 electrode units). The third and fourth generations rely instead of the injection pumping mechanism (Figure 7B) and thus presents a different circuit: two series of 17 interdigitated electrodes facing each other (64 electrode units). The third generation uses electrodes based on PDMS with dispersed conductive carbon particles, while the fourth generation uses electrodes with TPU rubber with dispersed conductive silver particles. Additionally, the results in Figure 6 are based on different dielectric liquids for the third and fourth generation: Novec 7100 and Fluorinert FC-40, both by 3M, respectively.

[0087] The inclined design presents lower pumping performance for the same applied voltage compared to the interdigitated design, as shown in Figure 6. Additionally, the interdigitated design allows pumping in either direction, based on the polarity of the applied voltage, while the inclined design always generate flow according to the gradient in the electric field (from larger gap side to smaller gap one).

[0088] A comparison between the inclined 1 and inclined 2 designs shows the scalability of the soft pump both in terms of channel size and electrodes spacing. It can also be observed a direct proportionality between the number of electrode pairs and the generated pressure.

[0089] The inventors measured for the third generation a generated pressure of over 7 kPa for an applied electric field of 11.2 V/pm (i.e., 5.6 kV) and a maximum flow-rate of over 100 mI/s for an electric field of 10 V/pm. The response time is less than 1 second from zero to maximum pressure. Figure 8 shows the results of both steady-state and transient characterization experiments. The very low current (20 pA) and low power (100 mW) allow powering by means of small batteries and miniaturized DC converters. Flow-rate and pressure values are high enough to power macro-scale applications. The intrinsic stretchability, low-mass, and low power consumption make the soft pump an enabling tool for portable soft robotics and wearable applications based on fluid flow. [0090] The broad applicability of the soft pump was demonstrated by implementing articles of manufacture in both a wearable and a soft robotics scenario. For a wearable cooling circuit, a micropump is integrated in a textile glove and circulates a fluid to transport heat from a hot area of the body towards a cold one (Figure 9). Given the large interest for fluidic actuators in soft robotics, the inventors demonstrated a self-contained fluidic actuator with the soft pump embedded in the bending structure (Figure 10). The liquid is moved between two chambers, obtaining large actuation without any external fluidic connections.

[0091] The performance of the pump at 0% and 10% applied strain was also assessed (Figure 8A). The simultaneous measurement of generated flow rate and pressure provides the characteristic curve of the soft pump (Figure 8B), showing a sub-linear decrease of the pressure as the flow-rate is increased. Performance is nearly unchanged at 10% strain, showing the pump is mechanically well suited to most wearable applications. The planar and symmetric electrode design allow the generation of flow in both directions, based on the direction of the applied electric field, as shown in Figure 8C.

[0092] Figure 8D-E shows the transient response of the pump to a single step and a square wave with 1 Hz frequency. Since it has no moving parts, the pump can operate in pulsed mode without the need of valves, unlike traditional pumps and compressors. The response is stable and shows good repeatability.

[0093] Figure 9 presents a stretchable pump as part of a wearable cooling circuit.

The pump, integrated in a textile glove, forces the circulation of the dielectric fluid from a hot zone, consisting of a membrane heater, to a cooling tubing embedded in the glove. The temperature of the system was monitored using an IR camera, which showed how the temperature of the heater was significantly decreased by the circulation of the fluid and how the soft pump did not contribute in heating the system, thanks to its low working power.

[0094] The heater in this experiment can represent for example overheating as a consequence of intense physical activity. To a first approximation, the heat that can be transported from one area to another using a fluidic circuit is proportional to the flow-rate H = Qpc_pAT, where c_p = 1183 J/kg/K is the specific heat of our working fluid (Novec 7100 by 3M) and p 1510 kg/m³ its density. With a temperature difference DG = 10 K and a flow rate Q = 100 mI/s (low pressure gradient), we can estimate a heat transport ability of 1.8 W, over one order of magnitude higher than the power consumption of the soft pump (-0.1 W), showing its effectiveness as a wearable thermal regulation device. The experiment in Figure 9 confirms this estimation, showing that the soft pump transports the heat away from an overheated area to the periphery of the body. Thanks to its small size, compliance and low-weight, the pump does not interfere with the physical movements, paving the way for wearable fluidic circuits for thermal regulation constituted by multiple pumps that can be integrated in everyday clothing, sportwear or wearable protections for severe environments.

[0095] Figure 10 shows a fluidic muscle composed of a bending fluidic actuator with the stretchable pump embedded in its bottom layer. The pump pushes the liquid from a small reservoir in the back of the actuator to a bellows- shaped chamber, whose inflation causes the bending of the actuator. When the voltage is applied, the actuator bends over 40° relative to its rest position

(Figure 10C-D). Figure 10D shows the response curve of the fluidic muscle, whose shape results from a combination of the nonlinear response of bending fluidic actuators and the one of the soft pump (Figure 8C). When the voltage is removed, the fluidic muscle returns to its initial position thanks to the restoring elastic forces of the chamber. Such an actuator is a promising building block for the next generation of soft robots, combining the robustness, large deformation and versatility of fluidic actuators with the portability of an integrated system that does not require external compressors and can be modulated by controlling the applied voltage.

[0096] The stretchable pump can be readily integrated in a wide range of wearable or soft objects, allowing a broad range of applications from haptics to organ- on-a-chip to robotics to benefit from the advantages of fluidic actuation but without any external pumps.

Claims

Claim 1. A stretchable pump for providing electrohydrodynamic pumping of a ionisable fluid, said soft pump comprising: a) a stretchable polymeric structure (1000) comprising at least one elongated channel (103), therein; and b) a first set (104) of at least two electrodes (104a/104b) operatively disposed within, or on a surface of, at least a portion of an interior wall of said polymeric structure elongated channel (103) so as to generate an electric field causing a movement of said ionisable fluid.

Claim 2. The stretchable pump of claim 1 , wherein said channel is defined by at least a first wall or side (100) of stretchable polymeric material and a second wall or side (100’) of stretchable polymeric material opposed to the first side (100), and the at least two electrodes are adjacently disposed on said first wall or side (100).

Claim 3. The stretchable pump of claim 1 , wherein said channel is defined by at least a first wall or side (100) of stretchable polymeric material and a second wall or side (100’) of stretchable polymeric material opposed to the first wall (100), and a spacer disposed between said first and second wall.

Claim 4. The stretchable pump of claim 1 , wherein said channel is defined by at least one recess provided on the surface of at least one of a first wall (100) of stretchable polymeric material and a second wall (100’) of stretchable polymeric material opposed to the first wall (100).

Claim 5. The stretchable pump of claim 1 , wherein the elongated channel (103) is defined by a bore provided within said stretchable polymeric material (1000).

Claim 6. The stretchable pump of claim 1 , wherein the elongated channel (103) is shaped as a tube having a round or elliptic cross-section, and the electrodes are arranged on some portion of the channel (103) or all-around the channel (103).

Claim 7. The stretchable pump of claim 1 , further comprising c) a second set (105) of at least two adjacent electrodes (105a/105b) operatively disposed within, or on a surface of, the second wall or side (100') of said soft polymeric structure channel (103), wherein the electrodes of said first and the second set of electrodes, respectively (104) and (105), are overlapped along an axis.

Claim 8. The stretchable pump of anyone of claims 1 , wherein each set of electrodes comprises two arrays of interdigitated electrodes.

Claim 9. The stretchable pump of anyone of the previous claims, wherein the electrodes in each set are parallel among them.

Claim 10. The stretchable pump of anyone of the previous claims, wherein the electrodes in each set are evenly disposed.

Claim 1 1. The stretchable pump of anyone of the previous claims, wherein the electrodes are compliant.

Claim 12. The stretchable pump of claim 11 , wherein the compliant electrodes comprise a soft composite material including conductive particles; a ionic solution; a deformable metal thin film; a hydrogel; a conductive liquid metal, or oxides, alloys or combinations thereof; or any combination of any of the foregoing.

Claim 13. The stretchable pump of anyone of the previous claims, wherein the electrodes comprise at least one pair of electrodes disposed adjacently and extending along the channel length in a spiral configuration.

Claim 14. The stretchable pump of anyone of the previous claims, further comprising a circuitry (106) configured to provide a voltage between adjacent electrodes of anyone of the first set and the second set of electrodes (104 and 105) independently and/or between overlapped electrodes of different sets of electrodes upon connection with a power supply.

Claim 15. The stretchable pump of anyone of the previous claims, wherein said channel (103) has a lateral cross section which diminishes along its longitudinal axis.

Claim 16. The stretchable pump of anyone of the previous claims, wherein the soft polymeric structure comprises thermosets or thermoplastics such as styrene butadiene, styrene (SBS) or styrene ethylene butylene styrene (SEBS); soft foams such as polyurethanes including reticulated polyurethanes; polyvinyl chloride (PVC), neoprene, uncrosslinked neoprene, cross-linked polyethylene, polyether, ethylene- vinyl acetate (EVA), polyethylene-vinyl acetate (PEVA), polypropylene glycol (PPG), latex; elastomeric materials such as silicone rubber (e.g. polydimethylsiloxane PDMS) or fluorosilicone rubber; thermoplastic elastomers such as styrenic block copolymer (SBC), ethylene propylene diene monomer (EDPM) rubber, thermoplastic polyurethanes (TPU), butyl rubber, nitrile rubber; natural polymeric materials (i.e., non-synthetic polymers, polymers that can be found in nature) and/or polymers derived from the 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, or suitable combinations of any of the foregoing.

Claim 17. The stretchable pump of anyone of the previous claims, wherein the soft polymeric structure (1000) has an elastic modulus comprised between about 1 kPa and about 100 MPa, preferably between 0.1 MPa and 10 MPa, more preferably between 0.5 MPa and 5 MPa.

Claim 18. The use of the stretchable pump of anyone of claims 1 to 17 for the electrohydrodynamic pumping of a fluid.

Claim 19. An article of manufacture comprising a soft pump according to anyone of claims 1 to 17.

Claim 20. The article of manufacture of claim 19, said article being a wearable device, a sensor, a medical device, a biomedical implant, a soft robotics component or a soft actuator.

Claim 21. A method of manufacturing a soft pump according to anyone of claims 1 to 17, said method comprising the steps of: a) patterning a first set (104) of at least two adjacent electrodes (104a/104b) on or within a first soft polymeric substrate (100); and b) bonding said first polymeric substrate (100) with a second soft polymeric substrate (100’), wherein said bonding is performed via a spacer (107) so to allow the creation of an elongated channel (103).

Claim 22. The method of claim 21 , further comprising a step of patterning a second set (105) of at least two adjacent electrodes (105a/105b) on or within said second soft polymeric substrate (100’).

Claim 23. The method of claim 21 , wherein step b) is replaced by step b’) of forming an elongated channel (103) on said first polymeric substrate (100).

Claim 24. The method of claim 21 , wherein step b) is replaced by step b”) of forming an elongated channel (103) on said second polymeric substrate (100’) and performing said bonding without a spacer (107).

Claim 25. The method of anyone of claims 23 or 24, further comprising a step of patterning a second set (105) of at least two adjacent electrodes (105a/105b) on or within a second soft polymeric substrate (100’), and a step of bonding said first and second soft polymeric substrates (100 and 100’).

Claim 26. A method for providing electrohydrodynamic pumping of a fluid, comprising: a) providing a soft pump according to anyone of claims 1 to 17 or an article of manufacture according to anyone of claims 19 or 20 comprising a fluid to be pumped; and b) applying a voltage to any set of electrodes.

Claim 27. The method of claim 26, wherein applying a voltage to any set of electrodes comprises, whenever applicable, creating opposed charges in each overlapped electrode of different sets of electrodes and equal charges in adjacent electrodes of each set of electrodes.

Claim 28. The method of claim 26, wherein applying a voltage to any set of electrodes comprises, whenever applicable, creating alternating unlike charges in adjacent electrodes of each electrodes’ set and equal charges in each overlapped electrode of different sets of electrodes.

Claim 29. The method of anyone of claims 26 to 28, wherein the fluid is a suspension comprising a dielectric liquid and dielectric or conductive particles.