EP3774933A1

EP3774933A1 - Method for producing a three-dimensional object by a multiphoton photopolymerisation process, and associated device

Info

Publication number: EP3774933A1
Application number: EP19720696.4A
Authority: EP
Inventors: Laurent GALLAIS-DURING; Jean-Claude Andre
Original assignee: Aix Marseille Universite; Centre National de la Recherche Scientifique CNRS; Ecole Centrale de Marseille
Current assignee: Aix Marseille Universite; Centre National de la Recherche Scientifique CNRS; Ecole Centrale de Marseille
Priority date: 2018-03-28
Filing date: 2019-03-27
Publication date: 2021-02-17
Also published as: US20210087301A1; FR3079517A1; WO2019186070A1; FR3079517B1

Abstract

The invention relates to a method for producing a three-dimensional object (3), comprising the following operations: introducing a composition (11) into a polymerisation vessel (9); and polymerising the composition (11) by multiphoton polymerisation, by means of a light source (5), in predetermined spots, in order to produce the three-dimensional object (3), the composition (11) comprising at least one monomer (12), at least one filler and at least one photoinitiator, said composition (11) having a transmittance per unit of length to the emission wavelengths of the light source (5), which is preferably higher than 75%, and the at least one filler comprises nanoparticles.

Description

Method for producing a three-dimensional object by a multi-photonic photo polymerization process and associated device

The present invention relates to the field of three-dimensional printing. More particularly, the present invention relates to a method for producing a three-dimensional object and a device for implementing this method.

Three-dimensional printing technologies have enjoyed considerable popularity since their first use in the mid-1980s. The three-dimensional printing techniques generally used are based on the principle of additive manufacturing, that is, an object is obtained sequentially by the superposition of layers or by sequential or continuous supply of material.

Document FR 2567668 discloses a device for producing models of industrial parts. This device makes it possible to produce parts by scanning successive planes, for example horizontal planes, the scanning being effected from the bottom to the top of the tank containing a monomeric liquid.

Among the various three-dimensional printing methods, there is more particularly FDM (corresponding to the acronym Fused Deposition Modeling) corresponding to a modeling by deposition of molten material, stereo-lithography also known by the acronym SLA, and selective laser sintering in which a laser agglomerates a layer of powder. These different techniques have been considerably improved in recent years so that they are not only used for prototypes, but more and more often for the realization of functional objects.

A three-dimensional printing technique was developed in 1984. It is the stereo-lithography by photopolymerization of a liquid resin. This technique makes it possible to manufacture a three-dimensional object by a series of layers of photopolymerizable resin. The object is made in a bath of liquid resin. The resin is generally polymerized by radical polymerization from an acrylate monomer composition or by cationic polymerization from an epoxy monomer composition and a photoinitiator or photoinitiator which allows the polymerization under the effect of a luminous radiation. Certain compositions applied to one-photon stereolithography applications are commercially available. These compositions include monomers, typically acrylates or epoxies, and the photochemical initiator. According to this technique, a spatially localized process is exploited with amplification linked to a chain reaction.

According to this technique, a mobile platform is generally immersed in a tank of liquid resin. This platform supports the object during its manufacture. The platform is positioned at a certain depth below the level of the resin. A laser beam is directed on the surface of the liquid resin to perform a scan adapted to photopolymerize the resin and thereby form a wafer of the three-dimensional object to be manufactured. After the treatment of a slice, the platform descends a predefined distance corresponding to the thickness of a slice and the process is renewed for each slice of the object thus obtaining the complete structure in three dimensions of the object. Once the stereolithography process is complete, the three-dimensional object is removed from the tank, washed and any holding elements are mechanically stripped. The unpolymerized liquid resin present in the tank can subsequently be reused. Depending on the resin used, a final post-treatment step of the object can be carried out in order to harden it, such as for example a cooking step. According to this technique, the deposition times of the different layers can be long if not stimulated, especially in the case of using viscous resins which have a low volume shrinkage of the polymerization. In the case of using viscous resins with this technique, the use of scrapers is often recommended in order to obtain a layer having a flat and uniform surface to ensure the good adhesion of the different layers to each other and also to prevent any collapse of the object during its manufacture.

These techniques have the disadvantage of not allowing the realization of very thin layers, typically of the order of a few tens of gm, or, in certain delicate conditions, less than gm. Indeed, such layers have the risk of moving or being torn off during the manufacture of the three-dimensional object. Moreover, these three-dimensional printing techniques by superposition of layers does not allow the manufacture of complex objects or requiring a high degree of finish. This is due in particular to the viscosity of the resin and its surface tension. As a general rule, a resin of low viscosity, generally of the order of a few tens of centi-poises (cP), is preferred because it corresponds to an optimum between the resolution of the object and the time of setting up and stabilizing layers. Added to this is the fact that it is also necessary to manufacture holding elements, such as one or more supports, for example rods, which will be removed once the three-dimensional object is removed from the resin to maintain good place this object during its construction in the tank. These holding elements are necessary because of the low viscosity of the resin and its liquid nature on the one hand, and by the density of the polymerized material which is generally slightly greater than the resin which gave rise to it other go. An object created in a low-viscosity resin and without holding elements or supports would tend to move, if only when adding a layer of resin, which makes the manufacture of the object difficult, or even impossible. Depending on the complexity of the object to be produced, some of these supports can not be removed easily and in some cases the object can not be manufactured by this three-dimensional printing technique. The realization of holding elements or manufacturing appendices, whose sole purpose is to enable the manufacture of the object, further increases the time of design, digitization, manufacturing and finishing.

Moreover, with the three-dimensional printing processes using the melting of a laser-induced powder, the powder medium has a coherence of materials conferring on it a structure close to that of a solid. Under these conditions, it is in principle not necessary to introduce supports in the process, even if it uses layers. However, the strong anisotropy related to the melting process leads some manufacturers to recommend the use of supports that compensate mechanical stresses, particularly in the case of use of metal powders.

On the other hand, for objects requiring a finite surface appearance, it is necessary to use a manufacturing resolution adapted to the desired surface state or to perform a complementary treatment such as machining at the end of the process. impression.

In order to overcome these limitations, it is possible to use multi-photon photopolymerization (SL2P) techniques, in particular two photons. For example, two-photon photopolymerization techniques have been developed by Shoji Maruo, Osamu Nakamura and Satoshi Katawa, "Three-dimensional microfabrication with two-photon-absorbed photopolymerization", Opt. Lett. 22, pp. 132-134 (1997). These techniques consist in directly reaching, by means of a photon flux, advantageously formed by at least one focused laser beam, a designated place in a volume, for example a tank, in order to photopolymerize the resin only at this place. An object can thus be manufactured continuously by directing the focused laser beam in the volume of the vessel containing the composition without it being necessary to manufacture the object in slices or in successive layers. The production of three-dimensional objects by multi-photon photopolymerization thus makes it possible to produce three-dimensional objects of great complexity with a high degree of finish, which may, for example, be of the order of a few tens of nanometers. These SL2P printing techniques require the use of initiators capable of absorbing two photons sequentially or simultaneously to form reactive species for initiating photopolymerization. The two-photon absorption requires, according to the material, a significant light density, of the order of a hundred mj / cm ² at the focal point, the photo-polymerization is limited to the immediate vicinity of the focal point, where the Luminous density is important enough to activate the initiator. One of the main advantages of two-photon stereo-lithography (SL2P) is to allow the fabrication of three-dimensional objects without the need to manufacture the object in superimposed slices or layers. In one- or two-photon photopolymerization processes, in order for the polymerization of the resin to take place, it is necessary to cross a threshold related to the oxygen consumption of the oxygen which is a polymerization inhibitor. This makes it possible to gain spatial resolution relative to the shape of the light beam. This effect is greater with bi-photon absorption than with single-photon absorption.

This fixed resolution is connected to an elementary volume, called voxel, produced by the laser pulse. Voxel is the acronym for "pixel volumetry", ie volumetric pixel in French. If one wishes to have a good resolution without further processing, when the object to be manufactured requires a high resolution, this leads to very long manufacturing times and potentially prohibitive operating costs. That is why this SL2P technique is generally limited to small objects, often in the millimetric or even micro- or nanometric range, and of simple shape with connection of voxels in the manufacturing process. In addition, this technique requires the use of a high light density at the focal point which is generally of micrometric size and which is therefore not optimized for the manufacture of objects of centimeter size, or even decimetric, that is to say ie written in a volume typically between about 1 and 1000 cm ³ .

More recently, SL2P techniques with variable resolution have been developed. From the document "Stereolithography with variable resolutions using high contrast-gratings" Li et al, J. Vac. Sci. Technol. B, Vol. 33, No. 6, Nov / Dec 2015, a three-dimensional printing method by stereo-lithography. The variation of the resolution is obtained by the use of optical filters changing the wavelength of the laser beam, thus allowing to have a variable pixel size of 37 and 417 mih. This method has the disadvantage of using two different wave bunners and thus to allow only two pixel sizes depending on the wavelength of the laser beam and the optical filter. Moreover, this technique remains only adapted to objects of micrometric size.

The document "Using variable beam spot scanning to improve the SL process", Yi et al., Rapid Prototyping Journal, Vol. 19, No. 2, 2013, pp. 100-110, describes a method of stereo-lithography with variable resolution. The variation of the resolution is obtained by an optical device. This method makes it possible to form three-dimensional objects of centimeter size. However, this method has many disadvantages and requires significant optimization of the device according to the objects to be made. Although it is possible with this method to change the size of the voxel in two dimensions, this is not possible in the third dimension, perpendicular to the first two dimensions, such as in depth.

More recently, so-called bio-printing processes have been developed for the manufacture of living tissues, or even organs. These methods are described in particular in the following publications:

• André J.C., Malaquin L., Guedon E. (2017), "Bio-printing; where are we going ? », Engineering Techniques - ref. RE2 68 VI, 23 pp. (2017);

• Chua C.K., Yeong N.Y. (2015), "Bio-printing: principles and applications", e-book World Scientific Ed. - Singapore;

• Morimoto Y, Takeuchi S. (2013), "3D cell culture based on microfluidic technique to mimic living tissues", Biomatter. Sri., 1, 257-264.

These bio-printing processes are additive manufacturing processes from living cells associated with supports made for example in stereo-lithography. One of the disadvantages of these methods is that they generate shearing movements during the establishment of successive layers. These movements can damage living cells and affect their survival.

The object of the present invention is to propose a method for producing a three-dimensional object implementing a multi-photonic photopolymerization, in particular with two photons, making it possible at least partially to overcome the disadvantages of the state of the aforementioned technique and which is effective for producing objects of nanometric size, or centimeter or decimetric.

Another object of the present invention, different from the preceding objective, is to propose a method for producing a complex-shaped object with fluid resins, and in particular to propose a method making it possible to overcome manufacturing artifacts. such as holding elements for example.

Another object of the present invention, different from the preceding objectives, is to propose a method for producing a three-dimensional object in which the movement of the voxels during the production of this object can be prevented and prevented.

Another objective of the present invention, different from the preceding objectives, is to propose a method for producing a three-dimensional object in which the shearing movements of the material constituting the object that may occur during the production of this object are prevented.

In order to at least partially achieve at least one of the aforementioned objects, the present invention relates to a method of producing a three-dimensional object comprising the following operations:

• introduce a composition into a polymerization tank,

Multi-photon polymerization by means of a light source, at predetermined locations, the composition for producing the three-dimensional object, the composition comprising at least one monomer, at least one filler and at least one photoinitiator ,

the composition having a transmittance per unit length preferably greater than 75% at the emission wavelengths of the light source and the at least one filler comprising nanoparticles.

After completion of this three-dimensional object, the latter can be removed from the photopolymerization tank and then washed with a solution for removing the unpolymerized composition from the three-dimensional object. This washing solution may for example be isopropanol or acetone.

With this method, we gain significantly in efficiency to achieve three-dimensional objects of complex shapes, currently inaccessible with fluid resins. Indeed, produced voxels normally need to be supported. By playing on the high viscosity of the composition allowed by the addition of nanoparticles, it is possible to to overcome manufacturing artifacts, such as the production of elements or appendages maintenance or support, which had to be eliminated once the three-dimensional object finished in the known methods of the prior art. By choosing high viscosities, the composition behaves substantially like a solid during the production of the three-dimensional object, which makes it possible to prevent the possible movements of the voxels.

In addition, the use of nanoparticles makes it possible to modify the viscosity of the composition while avoiding the problems related to the dispersion of light.

The production method according to the present invention may further comprise one or more of the following features taken alone or in combination.

The composition has a viscosity greater than or equal to 0.30 Pa.s.

The nanoparticles have an average diameter less than or equal to 100 nm.

In one aspect, the difference in refractive indices of the nanoparticles and the monomer is less than 0.4.

The composition may comprise from 10 to 70% by volume of nanoparticles with respect to the volume of said composition.

In one aspect, the fillers include a monomer-soluble component.

The nanoparticles may be made of a material chosen from: silica, glass, especially borosilicate glass or soda-lime glass, an organic material insoluble in a resin constituting the three-dimensional object.

According to a particular embodiment, the nanoparticles can be functionalized.

In one aspect, the monomer is selected from the following compounds: acrylic resins, L-lactic acid, glycolic acid, caprolactones, these compounds may be used alone or in combination.

According to this aspect, the filler may also comprise an additional constituent chosen from: living cells, a hydrogel chosen from collagen, fibrin, alginate, chitin, chitosan, hyaluronic acid, poly (2) hydroxyethyl) methacrylate, polyvinyl alcohol and polyethylene glycol, alone or in admixture.

In another aspect, the monomer is an acrylic monomer, particularly a multifunctional acrylic monomer. According to this other aspect, the acrylic monomer may be chosen from polyethylene glycol diacrylates, tri (ethylene glycol) dimethacrylates, pentaerythritol tetracrylates, 1,6-hexanediol diacrylate, or a combination of these compounds.

According to this other aspect, the photoinitiator (s) are chosen from: aromatic ketones, aromatic derivatives, eosin Y, or other xanthene dyes

According to one variant, the composition may comprise at least one epoxy monomer.

According to this variant, the photoinitiator is an onium salt.

According to a particular embodiment, the multi-photon polymerization is carried out using a laser beam and the spatial resolution of polymerization is adapted by placing an optical diffuser, in particular between 1 ° and 20 °, in the laser beam, the optical diffuser being configured to change the depth of the laser beam field.

According to another particular embodiment, the three-dimensional object comprises an external surface and an internal volume and localized locations in the internal volume are polymerized with a lower resolution than places forming the outer surface of the three-dimensional object.

According to this particular particular embodiment, different portions of the three-dimensional object are successively polymerized in different tanks each containing a specific composition for obtaining a voxel size, or even predetermined functions.

According to this other embodiment, the internal volume is polymerized in a first tank containing a first composition comprising first charges in the form of nanoparticles making it possible to obtain a first size of voxel and the external part of the three-dimensional object is polymerized in a second vessel containing a second composition comprising second charges in the form of nanoparticles or no charge to obtain a second voxel size, less than the first voxel size.

The present invention also relates to a device for producing a three-dimensional object by multi-photon photo-polymerization, in particular at two photons, comprising:

A light source emitting a laser beam,

A polymerization vessel containing a composition comprising:

⁰ at least one monomer, ⁰ at least one filler comprising nanoparticles as defined above, and

0 at least one photoinitiator,

said composition having a transmittance per unit length preferably greater than 75% at the emission wavelengths of the light source,

A device for focusing the laser beam and adapting its numerical aperture,

A displacement unit for moving the focussing zone of the laser beam inside the vessel at the predetermined locations to produce the three-dimensional object, and

A polymerization resolution adapter comprising at least one optical diffuser mounted on a support to be placed on the optical path or out of the laser beam in order to adapt the polymerization resolution.

Other features and advantages of the present invention will appear more clearly on reading the following description, given by way of illustration and not limitation, and the accompanying drawings in which:

FIG. 1 is a simplified diagram of an assembly of a device for producing a three-dimensional object,

FIG. 2 is a detailed diagram of a composition used for producing a three-dimensional object,

FIG. 3 illustrates in a table a non-exhaustive list of monomers that can be used in the composition,

FIG. 4 illustrates in a table a non-exhaustive list of photoinitiators that can be used in the composition,

FIG. 5 illustrates a conventional ionic polymerization mechanism with priming, propagation and transfer steps,

FIG. 6 is a diagram of multifunctional monomers of crosslinked systems, insoluble in an initial resin,

FIGS. 7A and 7B are photographs respectively representing voxels obtained in the case of a Gaussian beam on the one hand, and voxels obtained by placing a diffuser at the entrance of an objective to control the depth of field of the Gaussian beam. on the other hand, the two figures 7A and 7B being of the same scale, FIG. 8 is a diagram for illustrating the method of producing a three-dimensional object according to a particular embodiment,

FIG. 9 is a graph showing the measurement of the diameter of the beam as a function of the distance to the objective in the case of the objective alone and in the case of a 1 ° and 10 ° diffuser,

FIG. 10 is a schematic representation of a flowchart illustrating a method for producing a three-dimensional object, and

FIG. 11 is a schematic representation in perspective of an object manufactured by the method of FIG. 10.

Fig. 12 is a photograph showing a Dodecahedron obtained by the process of the present invention.

Fig. 13 is a photograph showing a bicycle obtained by the method of the present invention.

Fig. 14 is a photograph showing an object having a double-helical DNA portion form obtained by the method of the present invention.

In the different figures, the identical elements bear the same reference numbers.

The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment or that the features apply only to a single embodiment. Simple features of different embodiments may also be combined and / or interchanged to provide other embodiments.

In the following description, reference is made to first and second photopolymerization vessels, first and second compositions, first and second feeds, first and second voxel sizes. It is a simple indexing to differentiate and name elements close to or of the same nature or structure but not identical. This indexing does not imply a priority of one element with respect to another and it is easy to interchange such denominations without departing from the scope of the present description. This indexing does not imply either an order in time for example to appreciate the operation of the embodiment device or the method of producing the three-dimensional object. With reference to FIG. 1, there is shown a device 1 for producing a three-dimensional object 3 by multi-photon photopolymerization, in particular with two photons.

This embodiment device 1 comprises a light source 5 emitting a laser beam 7 and a polymerization tank 9, forming a polymerization reactor, containing a composition 11.

The light source 5 may for example be a particularly pulsed laser and in particular femto / picosecond emitting for example at a wavelength of 1030 nm and coupled, where appropriate, with nonlinear optical crystals to double or triple, for example. a nonlinear effect, the frequency of the laser beam 7 to obtain a wavelength of 515 nm and / or 343 nm. The light source 5 emits, according to this example, a pulsed light beam. The choice of the light source 5 may depend on the absorption of the composition 11, which may contain colored additives, for example. Thus, other types of light sources 5, including pulses, can be used.

The choice of the multiphotonic photo-polymerization waveguide, in particular at two photons, is determined by the choice of the photoinitiator and its ability to prime the reactive species under the effect of laser irradiation.

Typically, the output diameter of the laser beam 7 may be about 2.5 mm, the divergence 0.6 mrad and the linear polarization.

The pulse energy typically has a duration of 500 fs and is between 40 gj and 2 mj, and the repetition frequency of the pulses can reach 300 kHz, but can be rather located around 1 kHz. Another light source 5 may be used provided that the wavelength of its laser beam 7 is adapted and that the instantaneous power of the laser makes it possible to carry out the photon-multi-photon polymerization, in particular at two photons, of the composition 11. which is in the polymerization tank 9.

The embodiment device 1 furthermore has a focusing device 13 for the laser beam 7 and for adapting its digital aperture disposed on the optical path of the laser beam 7. This focusing device 13 may be formed by one or more optical components, in particular an objective for focusing the laser beam 7 inside the composition 11 and adapting the numerical aperture of the laser beam 7.

Optionally, the embodiment device 1 may have a polymerization resolution adapter comprising at least one optical diffuser 14 placed in the optical path of the laser beam 7 to be able to control the depth of field of the laser beam 7. For this purpose, the embodiment 1 comprises a rotatable support 15 with a through hole 14A for focusing the laser beam 7 without modifying the beam in the composition 11 and housings in which are respectively mounted different diffusers 14 to adapt the depth of field. It is thus possible, as has been introduced, to vary the size of the voxels. The support 15 with its or its diffusers 14 and the through hole 14A makes it possible to adjust the dimensions of the voxels and to obtain a variable resolution in the manufacturing process by adjusting the focusing optics and the instantaneous power of the laser beam 7.

The polymerization tank 9 is for example placed on a displacement unit 16 displaceable along the x, y and z axes (shown in FIG. 1) to enable the focusing zone of the laser beam 7 to be displaced inside the 9 and thus the polymerization of the composition 11 at predetermined locations to achieve the three-dimensional object 3. It is therefore understood that according to this particular embodiment is the polymerization tank 9 which is moved to allow to position the focal point the laser 5 at the locations to be photopolymerized and not the focal point of the laser 5. To do this, the displacement unit 16 is motorized to allow its movement. This displacement unit 16 is connected, like the laser 5, to a control unit 17 which controls both the operation of the laser 5 and the positioning of the displacement unit 16.

According to a variant not shown here, mobile mirrors are placed on the optical path of the laser beam 7 to direct the laser beam 7 at the places to be photo-polymerized and a laser focusing system and adaptation of its numerical aperture, allowing to move the focal point on the axis of propagation. In this case, the moving mirrors are connected to a control unit to direct the laser beam 7.

Referring to Figure 2, there is shown schematically and schematically the composition 11 for producing the three-dimensional object 3 by a multi-photon photo polymerization process. The composition 11 comprises at least one monomer 12, at least one filler 20 comprising nanoparticles, and at least one photoinitiator.

The monomers 12 are transparent at the predetermined wavelength of the pulsed source which serves for the photopolymerization. These monomers 12 have a refractive index nmonomer at the predetermined wavelength of photopolymerization of the laser 5. By a transparent material or medium, it is meant that the laser beam 7 can pass, at least in part (that is, that is, it can be weakly absorbent), through this medium as opposed to a material or an opaque medium. By charge 20 is meant a material or a material in the broad sense which is added to the composition 11, but which does not participate in the polymerization reaction. The filler 20 can be considered inert with respect to the polymerization. The charges 20 are transparent or very weakly absorbing nanoparticles at the predetermined wavelength of the pulsed source used for the photo-polymerization. These fillers 20 have a refractive index n _C har _g are at the predetermined wavelength of photopolymerization.

Since the irradiation is carried out at the predetermined wavelength λ, this wavelength can be partially absorbed during its course in the tank containing the polymerizable resin. If a corresponds to an absorption coefficient (measured in m ¹ ), the relative energy located at a distance d (d ¹ 0) from the beam input is determined by the formula exp (-ad) <1. The loss of photons can be detrimental to the process since it is the square of the instantaneous power that regulates the kinetics of polymerization. However, it is possible to increase the power of the laser to compensate for the effects of the absorption of incident photons. For example, it is limited to a 75% transmittance corresponding to a loss of polymerization yield of 0.56, which is acceptable although slowing down the manufacturing time of a part according to the process.

Thus, the composition 11 has a transmittance per unit length greater than 75% at the emission wavelengths of the laser 5. According to the particular embodiment represented here, the unit of length corresponds to a dimension of the vessel of polymerization 9, and more precisely at a height of the polymerization vessel 9 disposed along the z axis (as shown in Figure 1). However, according to other variants not shown here, the unit of length may for example be a metric unit, such as 1 decimeter or 1 meter.

When a light beam illuminates a dispersion, namely here the composition 11, characterized by its refractive index, the light undergoes a diffusion / absorption process which is a function of the wavelength of the incident light and the optical properties of the light. dispersed and continuous phases. The diffusion / absorption phenomena thus induce an extinction of the incident light in the initial direction of the incident beam. The intensity of the diffuse light depends on the direction of diffusion with respect to the direction of the incident beam, the polarization of the incident light, and the characteristics of the scattering medium.

For a small number of diffusers, most of the incident light passes through the medium without being scattered. For a strong extinction of the incident beam ( multiple scattering), the light scattered by a particle, which corresponds to any type of insolubilized particle present in the medium, constitutes a secondary source for neighboring particles. In the case of a particle, the waves scattered by the different regions of the material interfere with each other. The interaction of an incident wave with a spherical, homogeneous, isotropic and non-magnetic particle of diameter d in a non-absorbing medium is described by the Maxwell equations.

Only the resolution of Maxwell's equations then makes it possible to determine the intensity diffused by the particle in all directions. Mie is the first to solve the problem for homogeneous dielectric spheres and to obtain an analytical solution for a spherical particle of arbitrary size. Mie's theory provides a rigorous solution to Maxwell's equations. At low scattering angles, scattering intensity is particularly important in the case of large particles. In addition, the angular variation of scattered light evolves non-monotonously for non-absorbent particles and decreases with scattering angle due to destructive interference in the backward direction. The light absorption phenomena tend to suppress the diffusion lobes and the fine structure of the radiation pattern. The angular dependence of diffuse light less pronounced for small particles, thus allows to draw information on the size of the particles.

The intensity of the diffuse light also depends on the values of the refractive indices of the particles and the surrounding medium as well as the wave length of the incident light. Depending on the size of the particles with respect to the wavelength of the incident light, however, approximations can satisfactorily account for the phenomena of light scattering.

Rayleigh's theory describes the scattering of light by particles of very small dimensions in front of the wavelength of the incident light (diameter of the particle less than one tenth of the wavelength of the incident beam). In this case, the incident electric field illuminating a particle can be considered uniform in the diffuser and the intensity of the diffuse light is then proportional to the square of the volume of the particle. For non-absorbent particles, the scattered intensity per unit volume is expressed as follows: Where lo designates the intensity of the incident light of wavelength l, Q the angle of diffusion, m = n _P articulate / n _m the index ratio (choice of index) between the particle and the medium host, here the monomer 12, and N the number of non-absorbent particles per unit volume. When the particle size is very large in front of the wavelength of the incident light (particle diameter greater than 10-20 Å), the scattered intensity is essentially concentrated in the forward direction. Geometric optics approximations are then used to describe the scattering of light.

The preceding expression makes it possible to obtain the absorption cross section (s) of a set of particles:

Considering a configuration m = 1.05, d = 10 nm, λ = 1030 nm, and 1 particle in 10 nm ³ , we obtain s of the order of 10 ³ , making it possible to neglect the diffusion effects.

The composition 11 is therefore transparent, at least in first approximation to the wavelength of the light source 5. It is therefore not necessary to modify the load torque 20 / monomer 12 to have a low index difference. . The difference between nmonomères refractive index of the monomer 12 and the refractive index n _C har _g es loads 20 is less than 0.4, and preferably less than 0.05 (| n _m onomères - n _C har _g es1 <0.05), and more particularly less than 0.01 (| n _m onomers - n _C har _g es 1 <0.01), or even the refractive index of the monomers 12 and the refractive index of the fillers 20 are equal (| nmonomers ^- nchar _g es1 - 0). By choosing a difference in refractive indices that is low or even zero, this makes it possible to reduce or even eliminate any phenomenon of dispersion of the laser beam 7 in the composition 11, in particular at the interfaces between the monomers 12 and the charges 20 at the length of the wave emitted by the light source 5 as far as the size of the charges 20 affects the displacement of the light in the case of charges of size much greater than the wavelength.

The refractive index n _CO mposition of the composition 11 is the result of all components Ci (monomers 12 and loads 20) according to their proportions in the composition 11. Thus, if VR is the density of the composition 11 and VR _Î the density of each of the components Ci, and% is a rational number between 0 and 1, we have:

Where _j is the refractive index of the component Ci, and

Where i, j, m being integers, m corresponding to the number of components Ci constituting the composition 11.

In this case, it is understood that by adjusting the proportions of the components Ci, it is also possible to adjust the refractive index n _CO mposition of the composition 11 (and also to adjust the refractive index of the monomer (s) 12 of a side with respect to the refractive index of the load 20 on the other side) if at least one refractive index ny of the component C _j (i¹j) is for example greater than the second refractive index n ₂ .

The viscosity of the composition 11 can be adjusted by the choice of the volumetric percentage of charge 20, and in particular of nanoparticles; at a value greater than 0.30 Pa.s and preferably between 0.30 and 5.00 Pa.s (Pascal-second), in order to obtain a stable or fixed composition, that is to say in which the object being manufactured but also the load 20 does not move. The viscosity of the composition 11 is adjusted in particular as a function of the manufacturing time of the three-dimensional object 3 or again depending on the size, and in particular the radius or the equivalent radius when the three-dimensional object 3 is not spherical, the three-dimensional object 3 to be manufactured so that the displacement of this three-dimensional object 3 during its manufacture by photo-polymerization is negligible. On the other hand, the use of a slightly heated composition 11 makes it possible to reduce its viscosity and to fill the tank while avoiding the possible presence of air bubbles. This principle can be applicable to the separation of the three-dimensional object 3 once made of the composition 11. By modifying the high viscosity of the composition 11, it is possible to dispense with manufacturing artifacts such as, for example, holding elements. or supports. Indeed, in hydrodynamics, the Reynolds number Re reflects the relative importance of viscosity effects and inertia effects according to the following relation: Re = pVD / m

Where p is the density of the fluid, m viscosity, V and D are a speed and a characteristic length of the flow considered. The flows at low Reynolds numbers are characterized by the predominance of the effects due to viscosity compared to those due to inertia. Thus, by choosing high viscosities, the composition behaves almost like a solid, which avoids the movement of voxels.

The filler 20 in the form of nanoparticles, for example formed of insoluble nanoparticles or comprising a component that is soluble in the monomer 12, for example soluble macromolecules such as, for example, linear acrylic polymers solubilized in an acrylic resin, in the composition 11. The average size nanoparticles is much lower than the excitation wavelength of the laser beam 7.

"Solubility" is the ability of a substance, called a solute, to solubilize in another substance, called a solvent, to form a homogeneous mixture called a solution.

According to a particular embodiment, when the filler 20 comprises insoluble nanoparticles, the volumetric percentage of filler 20 in the composition 11 is between 10% and 70% by volume relative to the volume of said composition 11, in particular between 30% and 60% and more particularly between 40% and 50%. More precisely 100% represents the total volume of the composition 11 and this volume is separated into different proportions by volume for each of the constituents of this composition 11.

On the other hand, the nanoparticles have an average diameter less than or equal to 100 nm, in particular between 7 nm and 70 nm and more specifically 10 nm. The maximum size of the nanoparticles is chosen according to the diffraction limit of the incident wavelength resulting from the laser beam 7, ie approximately one-tenth of the incident wavelength coming from the light source 5.

The nanoparticles are, for example, made of a material chosen from: silica, such as, for example, fused silica, glass, in particular borosilicate glass or soda-lime glass, an organic material insoluble in a resin constituting the three-dimensional object 3, as for example acrylic nanoparticles or epoxies. Alternatively or in addition, the nanoparticles can be functionalized in order to modify their chemical affinity with the monomers 12 or to give them particular properties.

According to a particular embodiment, the nanoparticles are mono-dispersed, that is to say that they all have the same diameter. Alternatively, these nanoparticles can be of variable sizes, but they respect the diffraction stress defined above.

The use of mono-dispersed nanoparticles makes it possible to define in certain configurations the size of the voxels. Indeed, when the diameter of the nanoparticles is greater than the focal volume of the laser beam 7, the size of the voxel is no longer determined by the focal volume of the laser beam 7 but by the diameter of the nanoparticles. In particular, the shape of the voxels can thus be perfectly spherical, although the focal volume of the laser beam 7 is not, the laser beams 7 serving only to agglomerate at the focal point the nanoparticles, thanks to the photopolymer created, which then define the size of the voxels.

According to another embodiment, the composition 11 is a frozen composition, for example a composition comprising, as monomers, oligomers of high molecular weight making it possible to obtain a solid or quasi-solid composition at ambient temperature, so that it is possible to perform a photo-polymerization of an object without having to make support or holding appendages. Before and / or after phototransformation, the composition 11 may be heated beyond the melting temperature of the resin in order to introduce the resin into the photopolymerization tank 9 in a liquid (or viscous) form and / or in order to separate the object from the composition 11 that gave it birth. This has the advantage of significantly reducing the time of realization of the three-dimensional object 3 as well as making highly complex parts that would be difficult or impossible to manufacture by other methods requiring the implementation of appendices of support.

In the case of a liquid composition, the monomers 12 present in the composition 11 are monomers 12 commonly used in three-dimensional printing by mono- or multi-photon photopolymerization. These monomers 12 are, for example, acrylic monomers, more specifically acrylates. On the other hand, these acrylic monomers can be multifunctional. A non-exhaustive list of monomers 12 that can be used in composition 11 is provided with reference to FIG. It is noted that the viscosity of the composition 11 (greater than or equal to 0.05 Pa.s = 0.5 teaspoons = 50 cP) has the effect that the filler 20, in particular in the form of nanoparticles, is almost frozen in the composition 11, that is to say their displacement is low or almost zero during a time corresponding to a duration of realization of a three-dimensional object 3. Under these conditions, the effects of the gravitational force on the nanoparticles are negligible . No remarkable sedimentation effects were observed.

Preferably, the acrylic monomer is chosen from poly (ethylene glycol) diacrylates, tri (ethylene glycol) dimethacrylates, pentaerythritol tetracrylates, 1,6-hexanediol diacrylate, or a combination of these compounds.

The radical photoinitiators or photoinitiators contained in the composition 11 must make it possible to initiate the polymerization at the predetermined wavelength of photopolymerization. There are a large number of photoinitiators adapted according to the operating conditions and the choice of which can be easily determined by those skilled in the art. The photoinitiators below are given by way of non-limiting example. These are typically aromatic ketones, such as, for example, 2,2-dimethoxy-l, 2-phenylacetophenone (DMPA), marketed under the name Irgacure 651®, aromatic derivatives, eosin Y for photopolymerizations. in the visible range, or thermal initiators such as benzoyl peroxide for infra-red photopolymerizations, or other xanthene dyes. Photoinitiators particularly suitable for the process according to the present invention are shown with reference to Figure 4 and marketed under the trade names Darocure 1173® and 116®, Quantacure PDO®, Irgacure 184®, 651®, and 907®, and Trigonal 14®.

Preferably, the radical photochemical initiator is DMPA marketed under the name lrgacure 651®.

According to another embodiment, the process of the invention uses an ionic photopolymerization mechanism, for example cationic. In which case, the monomers 12 present in the composition 11 are, for example, epoxidic monomers and the photoinitiator is an onium salt, such as for example Rhodorsil 2074®. The following reference: JP & al Vairon, "Industrial Cationic Polymerization: An OverView in Cationic Polymerizations," Matyjaszewski, K., Ed., Marcel Dekker: New York, NY, USA, 1996, pp. 683-750 indicates a list of different photochemical initiators usable in the process which is the subject of the invention. FIG. 5 illustrates a conventional ionic polymerization mechanism with the following steps: priming (A), propagation (B) and (C), transfer (D).

With multifunctional monomers, crosslinked systems, insoluble in the initial resin, can be formed as shown in the scheme of Figure 6.

Apart from the compounds of the family of epoxies, it is possible to use a large number of monomers described in a synthetic manner in the following reference: Oskar Nuyken & Stephen D. Pask, "Ring-Opening Polymerization - An Introductory Review", Polymers , 2013, 5, pp. 361-403, doi: 10.3390 / polym5020361.

As indicated above, a focusing optics 13 and a diffuser 14 making it possible to control and / or modify the depth of field of the laser beam 7 are arranged on the optical path of the laser beam 7.

FIG. 7A shows several voxel voxels vox-A, vox-B, vox-C, vox-D and vox-E without diffuser 14 with different laser beam powers 7.

FIG. 7B shows several voxel voxels vox-A ', vox-B', vox-C ', vox-D' and vox-E ', with a diffuser 14 on the optical path of the laser beam 7 and at powers 7 different laser beam.

The use of a diffuser 14 adapted 1 ° and 20 ° (a diffuser 1 ° means an opening of the laser beam 7 at the output of the diffuser 14 of 1 °) allows to vary the size of the photopolymerized voxels. However, obviously, the power of the light source 5 must be adapted so that the power density is identical or as close as possible to that defined for voxels of smaller size (substantially varying between the square and the cube of the voxel size).

Due to a high viscosity of the composition 11 (for example greater than 1.00 Pa.s for 40% by volume of nanoparticles in relation to the volume of the composition 11), the method according to the invention makes it possible to design the producing three-dimensional objects 3 at least centimeter in size without resorting to support or holding appendages for complex objects. The method according to the invention also makes it possible to reduce the time required for producing the three-dimensional object 3 by multi-photon photopolymerization, in particular with two photons.

Indeed, it is possible to distinguish the three-dimensional object 3 on an outer surface and an internal volume. The optimization consists in polymerizing localized locations in the internal volume (solid part) with a low resolution, determined according to the object to be printed, and in polymerizing the zones forming the external surface of the three-dimensional object 3 with a high resolution to obtain a good surface quality for the external surface (s) of the three-dimensional object 3.

This is shown schematically in FIG. 8. For simplification of presentation, it is assumed that the voxels are cubes and that, for example, at least one first resolution is available which makes it possible to produce voxels of size Dz and a second resolution, finer, allowing to realize voxels Dzz of smaller size, for example 10 * Dzz = Dz.

It is easy to understand that if the voxels inside the three-dimensional object are made with the resolution Dz and the voxels forming the external surface of the three-dimensional object 3 with the resolution Dzz, the manufacturing time of the three-dimensional object 3 significantly.

According to a particular embodiment, the manufacture of the three-dimensional object 3 can be carried out successively. The internal volume is polymerized from a first composition 11 comprising first charges 20 in the form of nanoparticles making it possible to obtain a first voxel size, which is high compared with the three-dimensional object 3 to be manufactured. The internal part of the object is then removed from the first tank 9 comprising the first composition 11. This internal part is then pbngée in a second tank 9 comprising a second composition 11 comprising finer nanoparticles than the first composition 11, or not containing no charge 20, for the polymerization of the outer surface of the three-dimensional object 3. These first and second successive compositions 11 make it possible to reduce the size of the first and second voxels as a function of the finish of the three-dimensional object 3 to be formed. The method thus makes it possible to polymerize at localized locations in the internal volume with a lower resolution than the places forming the external surface of the three-dimensional object 3.

This method can be generalized and it is possible to provide different portions of the three-dimensional object 3 successively by polymerization in different tanks 9 each containing a specific composition 11 to obtain a predetermined voxel size.

This method thus makes it possible to easily and quickly produce three-dimensional objects whose shape may be more complex than that accessible with conventional stereo-lithography methods. It is thus possible to envisage the manufacture of complex objects having centimeter dimensions, or even about ten centimeters, in a reasonable manufacturing time and without resorting to holding elements present in the structure of the three-dimensional object 3.

This method therefore has a decisive advantage with respect to one-photon stereolithography, since the layer thickness can not, in general, be easily changed during the polymerization of a resin layer. If it is possible to modify the size of the light spot, only two space parameters (voxel) can be modified, whereas according to the method described here, it is possible to adjust the size of the voxels according to three parameters: the diameter of the voxel, the depth and the power of the light source to produce an object according to a setpoint taking into account the surface state of the portion of the three-dimensional object 3 made.

According to a particular embodiment, the method may be a bio printing process. In this case, the composition 11 comprises monomers 12, advantageously biocompatible, at least one filler 20 comprising nanoparticles and at least one biological material corresponding to an additional living component of the filler 20.

By way of nonlimiting example, the monomers 12 may be chosen from the following compounds: acrylics, L-lactic acid, glycolic acid, caprolactones, these compounds may be used alone or in combination. The filler 20 comprises the nanoparticles making it possible to modify the viscosity of the composition 11 and in addition at least one biobigic material corresponding to the additional constituent of the filler 20, for example living cells. According to this particular embodiment, the charges 20 are therefore composed of nanoparticles associated with living cells, these nanoparticles being able to be in a mixture of collagen and living cells, for example.

A hydrogel is necessary in order to preserve the viability of the cells during printing. By way of non-limiting example, the hydrogel may be chosen from collagen, fibrin, alginate, chitin, chitosan, hyaluronic acid, poly (2-hydroxyethyl) methacrylate (PHEMA), polyvinyl alcohol (PVA) and polyethylene glycol (PEG) alone or in combination.

With reference to FIG. 10, there is shown schematically a method of producing the three-dimensional object 3.

This process involves an introduction operation El of the composition 11 in the polymerization tank 9, the composition 11 comprising at least one monomer 12, at least one filler 20 in the form of nanoparticles and at least one photoinitiator. When the composition 11 has a high viscosity, this composition 11 can be slightly heated in order to allow a decrease in its viscosity to facilitate this introduction operation El. Moreover, in such a situation, the appearance of air bubbles in the polymerization tank 9 can be prevented by this slight heating of the composition 11.

The process then performs a polymerization operation E2 by multi-photon polymerization using the light source 5 at predetermined locations. During this polymerization operation E2, the polymerization vessel 9 is displaced along the x, y, z axes (shown in FIG. 1) so as to allow the displacement of the focusing zone of the laser beam 7 allowing the polymerization of the composition 11.

Optionally, the method then implements an E3 removal step of the printed three-dimensional object 3 of the polymerization vessel 9. In the presence of nanoparticle-shaped charges 20, this E3 removal operation can be carried out in a conventional manner. by withdrawal with the forceps, or with a sieve for example.

Then, and also optionally, the method can implement an E4 removal operation of supernumerary nanoparticles. These supernumerary nanoparticles form with the unpolymerized monomer 12 a film on the three-dimensional object 3 obtained. This film can be removed by wiping, using a dipping in a bath or by rinsing with a solvent that solubilizes the non-polymerized monomer 12, which allows the removal of nanoparticles present on the surface. This elimination operation E4 can be performed at the end of the resin prints in the mass. In some cases, the fluidification of the composition 11, and in particular at least one monomer 12, unpolymerized can be done by adding monomer 12 liquid, which allows recycling of non-transformed materials or using a conventional monomer solvent 12.

In particular, even if the nanoparticles of the charge 20 are in mutual contact (maximum charge density), or even in compact stack, the monomer 12 in liquid form is inserted into the free spaces and, by polymerizing, binds the nanoparticles around the points where the laser beam 7 is focused. Nanoparticles at the periphery, not or insufficiently bonded by polymerization, are abraded during the removal operation E4. According to the particular embodiment of FIG. 10, this elimination operation E4 is carried out by rinsing with a solvent, in particular chosen from ketone or alcoholic compounds, in particular acetone or else isopropanol.

Referring to Figure 11, it is shown schematically of the three-dimensional object 3 obtained according to this method. According to this representation, the three-dimensional object 3 is of substantially elliptical shape. However, according to other embodiments, and in particular according to other types of displacement of the polymerization tank 9, other forms, including forms of higher complexity, can be obtained. Thus, some objects having more or less complex geometric shapes can be obtained by this method. By way of example, Fig. 12 shows a photograph of an object having a complex shape of Dodecahedron, Fig. 13 shows a photograph of an object having a bicycle shape and Fig. 14 shows a photograph of an object having a form of double helix DNA. The width scale on these figures corresponds to 1 mm (scale of 2.45 cm = 1 mm real).

According to a particular embodiment not shown here, the polymerization tank 9 may have a support, such as for example a bracket, on which the three-dimensional object 3 is manufactured by multi-photon photopolymerization. The use of such a support makes it possible to guarantee the stability of the three-dimensional object 3 during its manufacture. Indeed, when the manufacturing times of the three-dimensional object 3 are long, for example greater than 15 seconds, the latter may be caused to move towards the bottom of the polymerization vessel 9 according to the Stokes law. Such displacement of the object during its manufacture could adversely affect the manufacturing accuracy of this three-dimensional object 3. This displacement can therefore be prevented by means of the support present in the polymerization vessel 9 on which the three-dimensional object 3 is realized. Specific examples of compositions 11 are developed hereinafter as well as a process for preparing the nanoparticles serving as filler 20.

Preparation of nanoparticles:

The nanoparticles are prepared according to a two-step method consisting of obtaining the nanoparticles in powder form and then dispersing them in the monomer 12. This method is described in particular in the following documents:

• Kulkarni et al, "Application of nano-fluids in heating buildings and reducing pollution", Applied Energy, 2009, 86, pp. 2566-2573;

• Longo and Zilio, "Experimental measurement of thermal-physical properties of oxide-water nano-fluids down to ice-point", Experimental Thermal and Fluid Science, 2011, 35, pp. 1313-1324;

Ho et al, "An experimental investigation of forced convection cooling performance of microchannel heat sink with Al203 / water nano-fluids", Applied Thermal Engineering, 2010, 30, pp. 96-103; and

• Zhang et al, "Effective thermal conductivity and thermal diffusivity of nano-fluids containing spherical and cylindrical nanoparticles", Experimental Thermal and Fluid Science, 2007, 31, pp. 593-599.

In order to ensure the good distribution of the nanoparticles in the composition 11, this composition is stirred for about 1 hour by mechanical stirring and / or by ultrasonic stirring of about 25 kHz over possibly longer periods. These stirring times can become higher when the filler rate increases, which may correspond to a "gelation" in particular localized medium.

As indicated above, the use of nanoparticles allows a suitable increase in the viscosity of the composition 11 without the light scattering effects of the laser beam 7 needing to be taken into consideration.

Choice of monomers 12:

The following monomers are particularly suitable for the process described above:

The refractive indices were measured by an Abbe refractometer (Kern Optics ORT 1RS Refractometer) calibrated using a calibration oil.

On the other hand, Norland monomers 65 and 81 incorporate a photoinitiator and have been used without the addition of photoinitiator or complementary photoinitiator.

Example of Composition 11:

This composition 11 was polymerized by two-photon polymerization using a Frequency doubled 5 Yb: KGW laser at 515 nm with pulse durations of 500 fs to obtain an object to obtain a substantially cylindrical shaped object.

On the other hand, the composition 11 has a satisfactory viscosity to avoid displacements of the object to be printed during its production and has a small variation of the refractive index of its various components. The composition 11 is also transparent to the predetermined wavelength of photopolymerization.

Another example, obtaining variable voxels:

An experiment was carried out to determine the effects of diffusers 14 placed at the entrance of the objective and making it possible to present a wide range of spatial frequencies. Indeed, if the initial laser beam 7 is characterized as a plane wave propagating in a certain direction, the diffuser separates this wave into multiple waves propagating randomly in a characteristic angle of the diffuser 14 (related to the roughness or " spatial frequency ").

The embodiment device 1 comprises a light source 5 such as a He / Ne laser of wavelength 543 nm, a long-distance working lens and a set of different diffusers 14 mounted on a filter wheel.

The measurement of the caustic of the laser beam 7 is shown in FIG. 9. These measurements make it possible to determine the influence of the diffusers 14 on the diameter of the laser beam 7.

In this figure 9 are represented three curves 101, 103 and 105. The curve 101 shows the diameter of the laser beam 7 in gm as a function of the position in z in mm without diffuser, the curve 103 with a diffuser 14 of 1 °, and the curve 105 with a diffuser 14 of 10 °.

It is observed that this method makes it possible to control the depth of field of the Gaussian beam without reducing the diameter of the laser beam 7 at the focal point and thus to control the dimensions of the voxel.

In this case, the diameter of the laser beam 7 may be 100 gm in diameter and a depth of field defined by a increased diameter of 2 ⁰ _^'5, of about 300 gm or a diameter / depth of the order of 0.3 (Figure 3).

Claims

claims

A method of producing a three-dimensional object (3) comprising the following operations:

Introducing (El) a composition (11) into a polymerization vessel (9),

Polymerizing (E2) by multi-photon polymerization using a light source (5), at predetermined locations, the composition (11) for producing the three-dimensional object (3), the composition (11) comprising at least at least one monomer (12), at least one filler (20) and at least one photoinitiator,

characterized in that the filler (20) comprises nanoparticles.

2. Method for producing a three-dimensional object (3) according to the preceding claim, characterized in that the composition (11) has a transmittance per unit length greater than 75% at the emission wavelengths of the light source. .

3. A method of producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the composition (11) has a viscosity greater than or equal to 0.30 Pa.s.

4. A method of producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the nanoparticles have an average diameter less than or equal to 100 nm.

5. A method of producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the difference in refractive indices of the nanoparticles and the monomer (12) is less than 0.4.

6. Method for producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the composition (11) comprises from 10 to 70% by volume of nanoparticles with respect to the volume of said composition (11). ).

7. A method of producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the charges (20) comprise a component soluble in the monomer (12).

8. A method of producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the nanoparticles are made of a material selected from: silica, glass, especially borosilicate glass or soda glass - Calcium, an organic material insoluble in a resin constituting the three-dimensional object (3).

9. Process for producing a three-dimensional object (3) according to any one of the preceding claims, characterized in that the monomer (12) is chosen from the following compounds: acrylic monomers, L-lactic acid, glycolic acid, caprolactones, these compounds can be used alone or in combination.

10. A method of producing a three-dimensional object (3) according to claim 9, characterized in that the charge (20) may further comprise an additional constituent selected from: living cells, a hydrogel selected from collagen, fibrin alginate, chitin, chitosan, hyaluronic acid, poly- (2-hydroxyethyl) methacrylate, polyvinyl alcohol and polyethylene glycol, alone or as a mixture.

11. A method of producing a three-dimensional object (3) according to any one of claims 1 to 8, characterized in that the monomer (12) is an acrylic monomer.

12. Process for producing a three-dimensional object (3) according to claim 11, characterized in that the acrylic monomer is chosen from poly (ethylene glycol) diacrylates, tri (ethylene glycol) dimethacrylates and pentaerythritol. -tetracrylates, 1,6-hexanediol-diacrylate, or a combination of these compounds.

13. A method of producing a three-dimensional object (3) according to any one of claims 11 or 12, characterized in that the one or more photoinitiators are chosen from: aromatic ketones, aromatic derivatives, eosin Y , or other xanthene dyes

14. A method of producing a three-dimensional object (3) according to any one of claims I to 8 and 11 to 13, characterized in that the composition (11) comprises at least one epoxy monomer.

15. A method of producing a three-dimensional object (3) according to claim 14, characterized in that the photoinitiator is an onium salt.

16. A method of producing a three-dimensional object (3) according to any preceding claim wherein the multi-photon polymerization is carried out using a laser beam (7), characterized in that the spatial resolution polymerization is adapted by placing an optical diffuser (14), in particular between 1 ° and 20 °, in the laser beam (7).

17. A method of producing a three-dimensional object (3) according to any one of the preceding claims wherein the three-dimensional object (3) comprises an outer surface and an internal volume, characterized in that localized locations in the internal volume. are polymerized with a lower resolution than places forming the outer surface of the three-dimensional object (3).

18. A method of producing a three-dimensional object (3) according to claim 17, characterized in that different portions of the three-dimensional object (3) are successively polymerized in different tanks (9) each containing a specific composition to obtain a voxel size, or even features, predetermined.

19. A method of producing a three-dimensional object (3) according to any one of claims 17 or 18, characterized in that the internal volume is polymerized in a first tank (9) containing a first composition (11) comprising first fillers (20) in the form of nanoparticles making it possible to obtain a first size of voxel and the external part of the three-dimensional object (3) is polymerized in a second tank (9) containing a second composition (11) comprising second fillers ( 20) under nanoparticle form or no charge to obtain a second size of voxel, less than the first voxel size.

20. Apparatus (1) for producing a three-dimensional object (3) by multi-photon photopolymerization, in particular with two photons, characterized in that it comprises:

A light source (5) emitting a laser beam (7),

A polymerization vessel (9) containing a composition (11) comprising:

⁰ at least one monomer (12),

⁰ at least one filler (20) comprising nanoparticles according to any of claims 3 to 7, and

0 at least one photoinitiator,

A focusing device (13) for the laser beam (7) and for adapting its numerical aperture,

A displacement unit (16) for allowing the focusing zone of the laser beam (7) to move inside the tank (9) at the predetermined locations to produce the three-dimensional object (3), and

A polymerization resolution adapter comprising at least one optical diffuser (14) movably mounted on a support (15) to be placed on the optical path or outside the laser beam (7) in order to adapt the polymerization resolution.

21. Apparatus (1) for producing a three-dimensional object (3) by multi-photon photocure polymerization according to the preceding claim, characterized in that said composition (11) has a transmittance per unit length, preferably greater than 75%. at the emission wavelengths of the light source (5).