THREE-DIMENSIONAL BODY IMPLANTS

Abstract

The present invention relates to three-dimensional body implants comprising a hydrogel of cross-linked alginate and gelatin, and in particular to breast implants. The hydrogel of the implants according to the invention may further comprise fibrinogen. The implants according to the invention are acellular, that is, free of cells at the time of their manufacture.

Description

Description Title of the invention: TRIDIMEN- BODY IMPLANTS ZIONLES FIELD OF INVENTION

[0001] — The present invention relates to the general field of biomaterials and in particular- particular implants, intended to be introduced into the human body / living organism, particularly in replacing and / or augmenting a more or less soft tissue and / or filling a space between the skeleton and the skin, or even sutured onto the skin.

[0002] The present invention relates to three-dimensional body implants comprising a hydrogel comprising cross-linked alginate and gelatin, and in particular temporary or permanent implants. The implants of the invention have a determined and particularly advantageous porosity and mechanical resistance. These implants are also acellular, meaning that no cells, and in particular No living cells are incorporated into the implant during its manufacture. In all the In addition to aspects of this invention, the hydrogel may further comprise fibrinogen. STATE OF THE ART

[0003] — Prior art is known of hydrogel-based structures comprising alginate and gelatin, but they lack satisfactory mechanical strength, because These constituents most often exhibit limited elasticity (low modulus) Young's, in particular), which makes the resulting structures difficult to manipulate. pullables.

[0004] Recent scientific reviews by Armin Vedadghavami et al, 2017, Acta Bioma- terialia 62, 42-63, by Marta Calvo Catoira et al., 2019, Journal of Materials Science: Materials in Medicine, 30:115, and Gils Jose et al, 2020, Current Medicinal Chemistry, 27, 2734-2776, highlight the biocompatible properties of natural hydrogels, particularly those based on alginate and gelatin, but also their limitations in terms of mechanical properties. Indeed, these natural polymers possess mechanical resistances too low for the production of manipulable devices and / or implantable and for the implementation of complex structural products and dimensions beyond 5 cm?, thus limiting the clinical applications of this technology.

[0005] — The mechanical properties of the structures obtained in the prior art therefore remain insufficient to make them suitable for handling. Moreover, in the case of structures intended to be implanted in the human or animal body, and where necessary sutured, There is a need to obtain structures that possess the mechanical properties adequate, and whose degradability upon contact with living cells or tissues is not too fast. Description of the invention One of the aims of the invention is to overcome the disadvantages of prior art implants, and to make it possible to provide biocompatible implants, the main constituents of which are of natural origin. The implants of the invention have particularly advantageous mechanical characteristics and have never been described in the prior art, in particular with regard to (i) the mechanical resistance of the constituents, which is similar to that of native tissues when introduced, (ii) stability over time, (iii) flexibility and (iv) remarkable resistance to tearing and shocks. To this end, it is proposed to provide, according to the present invention, a three-dimensional body implant which: - exhibits an overall porosity of at most 5000 µm and - includes a hydrogel comprising crosslinked alginate and crosslinked gelatin, said hydrogel having a mechanical resistance, also referred to here as elasticity or Young's modulus, of 1 to 1000 kPa. The implants according to the invention may have areas of different porosity within their three-dimensional structure, in particular in the form of a gradient distributed over more than one area of ​​the implant. The implants of the invention may also, where appropriate, contain cross-linked fibrinogen. The implants of particular interest according to the invention are breast implants which preferably have at least two, and in particular three, zones, each with a different porosity. In summary, the present invention relates to a three-dimensional body implant comprising a hydrogel comprising crosslinked gelatin and crosslinked alginate characterized in that said hydrogel has a mechanical resistance of 1 to 1000 kPa and that said implant has an overall porosity of at most 5000 um. Preferably, the gelatin is cross-linked by an enzyme, preferably a transglutaminase. Preferably, the implant exhibits a porosity gradient distributed over more than one area of ​​the implant. Preferably, the implant has a volume in the range of 0.05 mL to 3 L, preferably from 100 mL to 600 mL. Preferably, the implant is a breast implant. Preferably, the implant hydrogel comprises 0.5 to 3% alginate and | to 17.5% gelatin. Preferably, the implant hydrogel further comprises cross-linked fibrinogen, and preferably from 0.0001% to 6% fibrinogen. Preferably, the implant is obtained by a process which includes a crosslinking step of the hydrogel carried out using a solution containing a divalent cation, preferably calcium, and an agent capable of forming covalent bonds between the lysine and glutamine residues such as an enzyme, preferably a transglutaminase. Preferably, said solution further comprises thrombin when the hydrogel comprises fibrinogen. Preferably, the implant is obtained using a 3D printing process. DESCRIPTION OF FIGURES Other features, purposes and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which: [Fig.1] Fig.1 is a schematic representation of a breast implant according to the invention, which has a porosity gradient distributed over three zones. [Fig.2] Fig.2 represents the comparison of the Young's modulus and viscosity of AG and FAG hydrogels which constitute the implants according to the invention. [Fig.3] Fig.3 represents the comparison of Young's moduli E0 (Pa) of an AG hydrogel in which the gelatin is crosslinked with and without transglutaminase and, stored for up to 7 days at 37°C. [Fig.4] Fig.4 represents the comparison of Young's moduli E0 (Pa) of an AG hydrogel and commercial crosslinked or non-crosslinked hydrogels with transglutaminase. [Fig.5] Fig.5 represents the viability and cell growth measured kinetically on FAG and AG hydrogels which constitute the implants according to the invention, and which were colonized in vitro by fibroblasts after their manufacture. [Fig.6] Fig.6 represents the viability and cell growth measured kinetically on FAG and AG hydrogels which constitute the implants according to the invention, and which were colonized in vitro by adipose tissue stem cells after their manufacture. [Fig.7] Fig.7 represents the metabolic activity of AG implants according to the invention at different culture points following their in vitro colonization by a fraction of purified adipose tissue, after their manufacture. [Fig. 8] Figure 8 shows the histological analyses by Hematoxylin, Phloxin, and Saffron (HPS) staining of AG implants according to the invention after 2 days (4 images on the left) or 7 days (2 images on the right) of in vitro incubation with a fraction of purified adipose tissue, following their manufacture (Top: outer edges of the matrices; Bottom: internal pores of the matrices; images taken under white light; magnification 100X; scale 100 µm). [Fig.9] Fig.9 represents the immunostaining of perilipin-1 and the staining of cell nuclei with Dapi, on AG implants according to the invention after 2 days (top image) or 7 days (bottom image) of in vitro incubation with a fraction of purified adipose tissue, after their manufacture (fluorescence imaging; magnification 200X; scale 50 µm). [Fig.10] The [Fig.10] represents the comparison of Young's moduli of AG implants for crosslinking of varying durations at 21 and 37°C. [Fig.11] The [Fig.11] represents the comparison of Young's moduli E0 and viscosities of AG and FAG implants after crosslinking with different concentrations of CaCl2, TAG and thrombin. [Fig.12] The [Fig.12] represents the comparison of Young's moduli E0 and viscosities of AG and FAG implants after sequential or concomitant crosslinking with CaCl2, TAG and thrombin. [Fig.13] The [Fig.13] represents the comparison of Young's moduli E0 and viscosities of AG and FAG implants after crosslinking with a solution containing calcium chloride or barium chloride. [Fig.14A] [Fig.14A] illustrates the study of the variation of the dimensions and pores of AG and FAG implants according to the invention before and after crosslinking (A) and [Fig.14B] [Fig.14B] illustrates the impact of sterilization on the dimensions and Young's modulus of these implants (B). [Fig.15] Fig.15 illustrates the repeatability of the production of AG implants according to the invention in terms of dimensions, volume and porosity. [Fig.16] Fig.16 illustrates the repeatability of the retraction of AG implants according to the invention after consolidation. [Fig.17] Fig.17 illustrates the repeatability of the retraction of AG implants according to the invention as a function of the sterilization method. [Fig.18A] [Fig.18A] illustrates the repeatability of the extrusion diameter (A) and [Fig.18B] [Fig.18B] illustrates the repeatability of the pore length (B) of AG implants according to the invention. [Fig.19] Fig.19 represents images of pores of varying sizes in an AG implant according to the invention. [Fig.20] Fig.20 represents the surgical plan (left) of the in vivo subcutaneous implantation (right) of AG and FAG implants according to the invention. [Fig.21] Fig.21 represents the histological analyses after Masson's trichrome staining on sections of AG implants according to the invention, after subcutaneous implantation in vivo in rat back sites for 3 weeks (images at low, medium and high magnification). DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to provide three-dimensional body implants, which have particularly advantageous mechanical characteristics, especially in terms of the mechanical resistance of the constituents, which is similar to that of native tissues, stability over time and remarkable resistance to tearing and shocks. The implants according to the present invention can be used in place of (replacing all or part of) or as an addition (augmentation) to various organs or tissues of the animal body, and more particularly of the human body, either permanently or temporarily. By definition, the implants according to the invention are suitable for contact with living fluids or tissues of living organisms. They are specifically intended to be implanted under the skin, or even on the skin, particularly for skin regeneration and / or healing. For the purposes of this description, the terms "host" and "recipient" are equivalent and used interchangeably to designate the organism into which the implants according to the invention are likely to be introduced. The implants of the invention are therefore substitutes or additions, replacing and / or augmenting and / or reinforcing soft or flexible, and sometimes elastic, tissues. They preferably allow for the complete or partial replacement, augmentation, or reinforcement of connective tissues, skin, and adipose tissue. The implants of the invention can be large, both in volume since they can in particular reach a volume of 0.05 mL to 3L, and preferably from 100 mL to 600 mL, but also in size, which can range from 0.5x0.5x0.2 to 20x15x15, that is to say a size within the following ranges of length x width x thickness: length from 0.5 cm to 20 emm x width from 0.5 cm to 15 emm x thickness from 0.2 cm to 15 cm. According to a particularly preferred embodiment, the implants of the present invention are breast implants. According to one embodiment, the implants according to the invention are temporary because they are resorbable due to their composition and disappear over time after implantation in the body, leaving in their place cells and neo-tissues naturally vascularized by the living host organism. These temporary implants are therefore more precisely those that can be colonized by the cells of the host organism, notably through the existence of a specific porosity (using a maximum value) and / or the use of an implant material that preserves cell viability and is conducive to cell proliferation. These implants thus define an internal space, a kind of skeleton / framework / scaffold (or "scaffold") allowing colonization by cells, particularly... cells of the recipient organism. The porosity of the implant is a key parameter that must be adjusted according to the tissues or organs involved, which are to be replaced and / or augmented. Indeed, porosity reflects the empty space within the implant, which can be adapted to add or remove material and thus provide a certain level of mechanical resistance that closely matches that of the native tissue in the implantation area. Within the framework of the present invention, the implants are characterized at the level of their structure by their porosity, expressed here in two different but correlated and therefore equivalent or alternative ways: the size of the pores expressed in micrometers and / or the hydrogel filling rate expressed as a percentage (volume of hydrogel / total volume of the implant). For soft tissue, a high overall implant porosity, on the order of 1000 to 5000 µm, and / or an implant fill rate of 50% to 95% is preferred, while a low overall implant porosity, particularly less than 1000 µm, and / or an implant fill rate of 0% to 50% will provide the implant with high mechanical resistance for rigid tissues. Furthermore, the porosity can be adapted according to the different cell types present in the tissue.Again, a dense and low-porosity environment, with an implant pore size, in particular less than 1000 µm and / or an implant filling rate of 0 to 50%, will be preferred for osteoblast-type cells evolving in a very rigid matrix, while a soft and more porous environment, with an implant pore size, in particular between 1000 and 5000 µm and / or an implant filling rate of 50% to 95%, will promote the survival, proliferation and metabolism of fibroblast-type cells and adipocytes evolving in a soft matrix. Finally, the choice of overall porosity allows for adjusting the implant's degradation time within the body. An implant with low overall porosity, particularly less than 1000 µm, and / or a fill rate of 0 to 50%, will be composed of more material, and the total degradation time will then vary depending on the implant's size. Conversely, the more rapid implant degradation is desired, for example, less than 12 months, the more a high overall implant porosity, particularly between 1000 and 5000 µm, and / or a fill rate of 50% to 95%, will be preferred. When the implants according to the invention are prepared using a 3D printing technique, the pore sizes as specified above correspond to the length between the deposited hydrogel filaments, and in particular to the void distance between these filaments. The implants according to the invention are therefore intended for both plastic, reconstructive or regenerative surgery. All the components of the implants of the invention described below must meet the regulatory requirements specific to devices intended to be implanted, particularly with regard to purity grades. Thus, the present invention relates to a three-dimensional body implant comprising a hydrogel comprising cross-linked alginate and cross-linked gelatin, characterized in that said hydrogel has a mechanical resistance of 1 to 1000 kPa and said implant has an overall porosity of at most 5000 µm. In the context of the present invention, the overall porosity corresponds to the average of the porosity values ​​measured over all areas of the implant considered. The implants according to the invention, in view of their constituents, preferably exhibit a mechanical resistance of 10 to 800 kPa, or even more preferably of 50 to 300 kPa. The implants of the invention therefore exhibit mechanical properties that are similar to those of native tissues that one seeks to replace or augment. For example, the average mechanical resistances of different native tissues are mentioned in Table 1 below (as described by Guimaräes C. et al Nature Reviews Materials volume 5, pages 351-370 (2020)): [Table 1] Human Tissue Young's Modulus (kPa) Cartilage 1000 Coma 300 Bladder 200 Skin 100 Glandular Tissue 35 Breast Lung Adipose Tissue 10 Liver 5 The mechanical resistance referred to here can also be called elasticity or Young's modulus. By elasticity or Young's modulus, we mean the longitudinal modulus of elasticity or tensile modulus, which is the constant that relates the tensile (or compressive) stress to the onset of deformation of an isotropic elastic material. Young's modulus is therefore the mechanical stress that causes a material to elongate by 100% of its initial length, that is, to double its length. This Young's modulus is governed by Hooke's law: 0 = E, where: 0 is the mechanical stress (in units of pressure); Æ is Young's modulus (in units of pressure); e is the relative elongation or deformation (dimensionless); (€ = £ — £a / éo; fy being the initial length and £ that after deformation). In addition to the exceptional mechanical strength conferred by their constituents, the implants of the present invention have an overall porosity of no more than 5000 µm. While the implants according to the present invention may have no porosity (overall porosity of 0 µm), they preferably have an overall porosity of at least 10 micrometers, and even more preferably of at least 50 micrometers. Thus, the porosity of the implants according to the invention can range from 0 micrometers to 5000 micrometers, preferably from 0 to 1000 micrometers, even more preferably from 10 to 1000 micrometers, or from 20 to 1000 micrometers, or even from 1000 to 5000 micrometers. On this point, the implants according to the invention may have areas of different porosity within their three-dimensional structure, in particular in the form of a gradient distributed over more than one area of ​​the implant. In a preferred embodiment, the implants according to the present invention comprise at least two, preferably three, zones of different porosity that constitute a porosity gradient, each zone having a constant porosity. This makes it possible to define zones of varying rigidity depending on the type of tissue to be regenerated or in contact with the implant in the host organism. For implants that have them, the porosity gradient preferably ranges from 100 to 3000 micrometers. To produce a porosity gradient, different zones can be defined, each with a sub-range of porosity, as long as the final gradient obtained remains within a range of 100 to 3000 micrometers. The porosity sub-ranges that can be considered within the same zone, and combined to form a gradient from 100 to 3000 micrometers, are preferably sub-ranges with porosity on the order of 100 to 250, 250 to 800, and 1000 to 2500 micrometers when the implant contains three zones of different porosity to form the gradient, or on the order of 100 to 250 and 250 to 3000 micrometers when the implant contains only two zones of different porosity to form the gradient. The architecture of the implants according to the invention is preferably divided into 3 distinct zones: - The base of the implant (5 to 40% of the total implant volume, preferably 20 to 40%) is preferably placed directly in contact with the muscle tissue, and has a Intermediate porosity (250 to 800 micrometers) promotes colonization by endothelial cells and surrounding vascular structures. Endothelial cells readily migrate through this porosity and organize into vascular / microvascular structures, enabling neovascularization of the implant and thus better integration with adjacent tissues. The easy vascularization of the structure also helps limit the risk of necrosis of tissues that have colonized the implant. The implant core (20 to 70% of the total implant volume, preferably 30 to 50%) is not in direct contact with the host tissues of the implantation site. This zone has a fine porosity (100 to 250 micrometers) and serves as a support for tissue regeneration.This area is composed of more matter than other areas, so biodegradation in the body will be slower in order to provide cells with a supporting matrix for proliferation. The implant shell (5 to 40% of the total implant volume, preferably 10 to 40%) is ideally positioned to be the first part to come into contact with the implant in case of shocks and / or compressive stresses. The shell has a large porosity (1000 to 2500 micrometers) allowing for easy migration of cells to the implant core. This shell provides mechanical protection for the implant core. Solid areas forming channels that pass through the implant may also be present in the structure to provide additional mechanical resistance. These channels serve to reinforce the structure mechanically. In breast reconstruction, these channels are largely inspired by Cooper's ligaments, reflecting a biomimetic approach. In a particularly preferred embodiment, the present invention relates to a breast implant, and in particular a breast implant which has a porosity gradient distributed over three zones, as mentioned below in Table 2 and illustrated in [Fig.1]. [Tables 2] Zone Porosity (in micrometers) (69) 1000-2500 2) 100-250 8) 250-800 (4) No porosity - ; Solid zones The implants according to the present invention offer particular advantages in the context of breast reconstruction, since the implants must be sufficiently resistant to withstand high compressive stresses on this This anatomical area is very regularly subjected to this type of stress. Due to their significant mechanical resistance, the implants of the invention make it possible to produce less mechanical stress on the host tissues in direct contact, and thus reduce the phenomena of necrosis. Various methods well known to those skilled in the art can be used to measure porosity. Among them, we can mention optical microscopy, electron microscopy, weighing (using the density of the material), volume displacement (Archimedes' method), etc. Preferably within the framework of the present invention, the ranges specified here correspond to a measurement of porosity by optical microscopy. The porosity characteristic of the implants of the invention can also be expressed by the filling ratio of the hydrogel implant structure, since varying the filling ratio allows for influencing the implant porosity and vice versa. As shown in the examples, the chosen filling parameters allow for obtaining a given range of pore sizes. Conversely, a given range of pore sizes is correlated with specific filling parameters. The implants of the invention can have a hydrogel filling rate ranging from 5% to 100% of the total implant volume. The less the implant is filled (filling rate less than 50%), the more flexible it will be, allowing the flexibility / firmness ratio to be adjusted according to its intended placement in the body. Conversely, the more the implant is filled (filling rate greater than 50%), the more rigid it will be. A 100% fill rate necessarily corresponds to an implant consisting of a single zone (with 0 porosity), which can be achieved, in particular, using a manufacturing technique such as molding. As mentioned above, the implants according to the invention can contain several zones with different fill rates (in the same way that several zones of the implant can have different porosities), including, for example, a zone with a 100% fill rate (a porosity of 0). The porosity, and therefore the fill level, of the implants of the invention promotes colonization by cells. The three-dimensional structure, combined with variable porosity or fill level, thus makes it possible to obtain implants containing multiple cavities, which can be colonized, once the implant is in place, by cells from the host organism that can then proliferate and differentiate in situ. That being said, an implant with a 100% fill level (0 porosity) remains compatible with cell colonization because, once the implant is in place, the host cells will gradually degrade and replace the implant. When the implants of the invention are prepared using a technique In 3D printing, particularly by extrusion of viscoelastic material, the existence of pores in implants can then be associated with a three-dimensional structure in the form of "lattices" (mesh), preferably cubic or planar hexagonal, whose size in the XY plane is given by the porosity and the height by the thickness of the printing filament, and in particular from 200 to 1000 micrometers. The implants according to the invention preferably have a volume of 0.05 ml to 3 liters, and even more preferably from 100 ml to 600 ml. Furthermore, the size of the implants according to the invention is notably within the following length x width x thickness ranges: length from 0.5 cm to 20 cm x width from 0.5 cm to 15 cm x thickness from 0.2 cm to 15 cm. For example, the size of implants for tissue augmentation generally does not exceed 20x15x15 cm. It is preferably in the order of 12x12x3 cm for a breast implant. Implants can be of any shape associated with the volumes mentioned in this description. The three-dimensional structure and the particularly advantageous mechanical properties of the implants according to the invention are maintained after sterilization, in particular by irradiation or by plasma. As mentioned, the main constituents of the implants according to the invention are of natural origin. Alginate is a linear polysaccharide extracted from marine algae, primarily from the brown alga Phaeophyceae. This biocompatible polymer is composed of homopolymeric blocks of 1,4-D-mannuronic acid (M) and its epimer, 5-Al-guluronic acid (G). This biopolymer consists of sequences of M-blocks and G-blocks interspersed with sequences of MG-blocks. Only the G units appear to be involved in intermolecular cross-linking during polymerization. Sodium alginate is widely used as a hydrogel. Regarding alginate, and as mentioned above, an alginate enriched in M ​​units will be more flexible because the chain will have a more linear configuration, while a gel containing more G units will be more rigid because it is more polymerized. In the context of the present invention, the alginate used preferably has an M / G ratio of 1.9. Preferably, the gelatin contained in the hydrogel is type A. Gelatin is a macromolecule derived from collagen that contains bioactive sequences such as the RGD (arginine-glycine-aspartic acid) motif for cell adhesion. It is obtained by denaturing the native triple helix structure of collagen through acid treatment (type A gelatin) or alkaline treatment (type B gelatin). The amino acid composition of gelatin is similar to, but differs from, that of collagen following denaturation (deamination of glutamine to glutamic acid in the manufacturing process of type B gelatin). The structure of gelatin change during gelation. The preparation of hydrogels is well known in the art (EM Ahmed; Journal of Advanced Research, 2015, 6, 105-121), as is the polymerization and crosslinking of alginate and gelatin (Chen Q, Tian X, Fan J, Tong H, Ao Q, Wang X. An Inter- penetrating Alginate / Gelatin Network for Three-Dimensional (3D) Cell Cultures and Organ Bioprinting. Molecules. 2020:25(3):756.)). Preferably, the alginate is crosslinked using a crosslinking agent chosen from among divalent cations, in particular non-toxic, and preferably calcium. Preferably, the gelatin is crosslinked using any enzymatic, physical method such as UV light, or chemical method, and in particular by an enzymatic method carried out using an agent capable of forming covalent bonds between lysine and glutamine residues, and most particularly preferred by a transglutaminase. The enzyme transglutaminase (TAG) is an extracellular aminoacyltransferase. It is a monomeric protein containing a single catalytic cysteine ​​residue (active site). In the context of this invention, the hydrogel gelatin is preferably cross-linked with a type 2 transglutaminase. This TAG is notably produced commercially as a recombinant microbial protein by the fermentation of the microorganism Streptoverticillium moboarense. According to the present invention, the alginate and gelatin which are in the hydrogel which is included in the implant are crosslinked, that is to say transformed from a linear polymer into a three-dimensional polymer by means of the action of a crosslinking agent from among those mentioned above. In a particularly preferred embodiment, the implant according to the invention comprises a hydrogel containing from 0.5 to 3% alginate and from 1 to 17.5% gelatin, and even more preferably from 1 to 2.5% alginate and from 2 to 10% gelatin. Advantageously, the hydrogel comprises 2% alginate and 5% gelatin. Unless otherwise stated, the percentages mentioned in this description are expressed by weight / volume and are relative to the total composition. Preferably, in the hydrogel of the implants of the invention, the cross-linked alginate and gelatin are present in a mass ratio ranging from 1:0.3 to 1:35, and particularly in a mass ratio of 1:2.5, respectively. The hydrogel of the implants of the invention may also include, in addition to alginate and gelatin, fibrinogen also cross-linked. The fibrinogen monomer is composed of two repeats of three chains a, B and y linked by a central domain E and two fibrinopeptides A and B (FpA, FpB) linking the chains to the E domain. It has a large number of cell adhesion motifs and thus allows increased cell development within the hydrogel. In this case, the hydrogel will preferably comprise from 0.0001% to 6% of cross-linked fibrinogen, and in particular 2% of cross-linked fibrinogen. According to a particularly preferred embodiment, the hydrogel of the implants of the invention is composed of cross-linked alginate and gelatin, or of cross-linked alginate, gelatin and fibrinogen, without any other constituent capable of forming a gel. Preferably, the hydrogel of the implants of the present invention contains cross-linked alginate, gelatin and fibrinogen in a mass ratio from 1:0.3:0.00003 to 1:35:12, and particularly in a mass ratio of 1:1:2.5, respectively. The implants of the invention advantageously contain alginate, gelatin, and optionally fibrinogen as natural constituents of the hydrogel. However, other natural components may also be present in the implants of the invention, including but not limited to: chitin, chitosan, cellulose, agarose, chondroitin sulfate, hyaluronic acid, glycogen, starch, pullulan, carrageenan, heparin, collagen, albumin, fibrin, fibroin, dextran, xanthan gum, gellan, and any component extracted from extracellular matrix such as collagens, laminin, Matrigel-type proteoglycans, and GelMa-type methacrylate gelatin. Besides the constituents of natural origin, and in particular those listed above, the implants of the present invention may also contain synthetic components, such as polyolefins (PE, PP, PTFE, PVC), silicone (PDMS), polyacrylates (PMMA, pHEMA), polyester (PET, dacron, PGA, PLLA, PLA, PDLA, PDO, PCL), polyethers (PEEK, PES), polyamides, polyurethanes, PEG, pluronic F127. Textile fibers of natural or synthetic origin may also be present in the composition of the implants. The implants according to the invention are said to be acellular, that is to say, they are free of any cells, and in particular of any living cells, at the time of their manufacture. Nevertheless, the implants of the invention, even if they have no porosity, can be fully colonized by living cells after their manufacture, which makes it possible both to overcome any manufacturing constraints related to preserving cell survival, proliferation and / or differentiation, and to carry out in vitro colonization of the implant once manufactured but before its implantation in the host organism in order to optimize its integration. Examples of specific embodiments of implants according to the invention are therefore implants comprising: - a hydrogel made up solely of alginate and gelatin, without fibrinogen; - a hydrogel made up of alginate, gelatin and fibrinogen; - a hydrogel made up of alginate, gelatin and collagen; - a hydrogel made up of alginate, gelatin, collagen and fibrinogen. The embodiments particularly preferred within the scope of the invention relate to the implants defined in the following table 3: [Tables 3] For [Implants A 2% [5% Jo [Implants B |2% [5% Jo [100 In a particularly advantageous embodiment, the implants of the invention are obtained by a manufacturing process in which the alginate and the gelatin are consolidated by cross-linking with a solution comprising at least one divalent cation, preferably calcium, and transglutaminase. For example, the prepared hydrogel is contacted with a consolidation solution containing at least calcium and transglutaminase. During this consolidation, the hydrogel can be brought into contact with the consolidation solution by immersion, in which the hydrogel is fully submerged in the solution. It can also be achieved by imbibition, spraying, using a drip, trickle, or similar system. When the hydrogel contains fibrinogen in addition to alginate and gelatin, the consolidation solution further includes thrombin. According to a preferred embodiment, the implants of the invention are obtained by a manufacturing process in which the consolidation step, which consists of bringing the hydrogel into contact with the consolidation solution, is carried out at a temperature ranging from 15 to 40°C, and preferably from 20 to 40°C, and even more preferably from 21 to 37°C. According to another preferred embodiment, which can also be combined with the preceding one regarding temperature conditions, the implants of The implants of the invention are obtained by a manufacturing process in which the consolidation step, which consists of bringing the hydrogel into contact with the consolidation solution, is carried out for a period ranging from 30 minutes to 6 hours, and ideally for 1 to 3 hours. Thus, according to an advantageous embodiment, the implants of the invention are obtained by a manufacturing process in which the consolidation step is carried out at 37°C for 1 hour and 30 minutes. The implants of the present invention can be manufactured and shaped simultaneously, in particular by any volumetric structuring process (especially 3D), and particularly by adding or agglomerating material through stacking or successive deposition of layers. Among these processes, one may mention in particular injection molding, extrusion, and especially molding and 3D printing. In particular, those skilled in the art should take care to choose a process that allows the shaping of high-viscosity materials, since a hydrogel consisting solely of alginate and gelatin can exhibit a viscosity ranging from 50 to 6000 Pa·s, measured at a temperature of 5 to 45°C. In the context of the invention, the implants are preferably obtained by a 3D printing process. This technique also makes it possible to give the implant a suitable shape. Indeed, as previously mentioned, the implants according to the invention possess advantageous mechanical properties, particularly well-suited to their intended use. Using this technique, the implant can be "molded" to match the physiology and / or preferences of the host. The implants of the invention thus provide structured, "tailor-made" solutions whose dimensions and / or filling / porosity are defined according to the needs of the host body intended to receive the implant and the role / function it will play in that recipient organism. EXAMPLES Materials & Methods Protocol #1 Preparation of an AG hydrogel: To prepare the AG hydrogel, 2 g of alginate (very low viscosity, Alpha Aesar, France), 5 g of gelatin (Sigma-Aldrich, France) are dissolved at 37°C for 12H in 100 mL of a 0.1M NaCl solution (Labelians, France). Protocol #2 Preparation of a FAG hydrogel: To prepare the FAG hydrogel, 2 g of alginate (very low viscosity, Alpha Aesar, France), 5 g of gelatin (Sigma-Aldrich, France) and 2 g of fibrinogen (Sigma-Aldrich, France) are dissolved at 37°C for 12H in 100mL of a 0.1M NaCl solution (Labelians, France). Protocol #3 Molding of an AG and FAG hydrogel: 1.8 mL of the hydrogel prepared according to protocols #1 and #2 are deposited into the wells of a 6-well culture plate and incubated at 21°C for 30 minutes. Protocol #4 Crosslinking of an AG hydrogel: A crosslinking solution is prepared by dissolving 4 g of Transglutaminase (Ajinomoto, Japan) and 3 g of CaCl₂ (Sigma Aldrich, France) in 100 mL of 0.1 M NaCl solution (Labelians, France). The crosslinking solution is then incubated with the hydrogel for 1.5 hours at 37°C (unless otherwise specified). Protocol #5 Crosslinking of a FAG hydrogel: A crosslinking solution is prepared by dissolving 4 g of Transglutaminase (Ajinomoto, Japan), 3 g of CaCl₂ (Sigma Aldrich, France) and 400 Thrombin Units (Sigma Aldrich, France) in 100 mL of a 0.1 M NaCl solution. The crosslinking solution is then brought into contact with the hydrogel for 1.5 hours at 37°C (unless otherwise indicated). Protocol #6 Dynamic Mechanical Analysis (DMA) in Compression: The mechanical properties of FAG and AG hydrogels were measured in triplicate using a rotational rheometer (DHR2, TA Instrument, France), a Peltier plate (TA Instrument, France), and an 8 mm notched geometry (TA Instrument, France). Three 8 mm diameter discs were cut from the hydrogels molded according to protocol #3. The disc was placed on the lower geometry at 37°C for 60 seconds, followed by an oscillatory 10 µm compression procedure from 0.1 to 10 Hz at 100 Jm / s and 37°C. The Young's modulus E0 (Pa) and viscosity n0 (Pa·s) values ​​of the hydrogel were obtained from a visco-hyperelastic solid model using the E' and E'' values ​​acquired during the test. Protocol #7 3D Printing of Hydrogels: Hydrogels prepared according to protocols #1 and #2 are transferred into a 30 mL cartridge (Nordson EFD) equipped with a 410 µm diameter extrusion nozzle (Nordson EFD). The cartridge-nozzle assembly is then placed in a 3D printer (BioassemblyBot, Advanced Solution Lifescience, USA) that applies constant pressure to the cartridge while it moves in three directions. The printing parameters are a speed of 10 mm / sec, a pressure of 25–35 PSI, and a temperature of 21°C. Different infill levels are achieved using the printer's internal slicer software (Tsim, Advanced Solution Lifescience, USA). Protocol #8 In vivo implantation in rats: In vivo implantation studies in rats were conducted at the BIOVIVO preclinical research platform — Institut Claude Bourgelat (Lyon, France). The experiments were conducted in accordance with European Directive 2010 / 63 / EU. The 16 animals (Sprague Dawley rats, 250-300g) were anesthetized by inhalation (oxygen and 5% isoflurane). The dorsal implantation sites were shaved and disinfected with povidone and sterile gauze, and sterile drapes were placed to delineate the surgical area. General anesthesia was maintained with isoflurane (2%) and inhalation oxygen. Pre-surgical analgesia was administered subcutaneously with meloxicam and morphine at 1 mg / kg each. The rats' body temperature and pulse were monitored during the operation. Two 2- to 3-cm skin incisions were made in the dorsal region. A bioprosthesis was implanted in the subcutaneous dorsal region of each animal. The control group consisted of only the incision and dissection. In one animal per group, four surgical sites were created: three bioprostheses and one control. The surgical site was closed in layers using subcutaneous and cutaneous sutures with absorbable braided sutures (PDS® polidioxanone, 4 / 0 and Nylon 3 / 0, Ethicon J&I). Postoperatively, the animals were monitored for signs of distress, and the surgical wounds were inspected daily to check skin healing and for signs of infection. Explantation took place 21 days after implantation. Protocol #9 Histological Analysis: The implants were fixed for 24 hours in a 4% formalin solution (Alphapat, France) and then dehydrated by successive baths of absolute ethanol (vwr chemicals, France) and methylcyclohexane (vwr chemicals, France) with an STP 120 dehydrator (Myr, Spain), and then embedded in paraffin (Sakura, Japan). Thickness sections were prepared using an HM 340e microtome (Microm, France). Hematoxylin and phloxine staining (HPS), Masson's trichrome staining, and DAPI staining were performed. Example | - Mechanical properties of alginate / gelatin (AG) and fibrinogen / alginate / gelatin (FAG) hydrogels AG and FAG hydrogels were prepared from protocols #1 and #2, molded according to protocol #3, then crosslinked using protocols #4 and #5 to study their DMA mechanical properties using protocol #6. The results are summarized in [Fig. 2]. The measured Young's modulus and viscosity values ​​are similar between the AG hydrogel and the FAG hydrogel following their crosslinking by the process of the invention. The Young's moduli under the specific conditions of this study are around 68,000 Pa. Example 2 - Impact of crosslinking with transglutaminase on the mechanical properties of alginate / gelatin (AG) hydrogel Molded AG samples were prepared according to protocols #1 and #3 and crosslinked using a variant of protocol #4. In this variant, the crosslinking solution consisted of either a 30 mg / mL calcium chloride solution alone or a 30 mg / mL calcium chloride solution and a 40 mg / mL transglutaminase solution. Four gels of each condition were molded and then tested by DMA on the same day and after 1, 4, and 7 days of storage at 37°C, respectively, in order to to mimic physiological conditions. The samples were then studied by DMA using protocol #6. The results are summarized in [Fig. 3]. This study demonstrates the beneficial effect of using transglutaminase during crosslinking on the mechanical properties of hydrogels. This effect is even greater when the gels are stored at 37°C, justifying the particular interest of the crosslinking according to the invention for hydrogels intended for implantation. Example 3 - Impact of crosslinking with transglutaminase on the mechanical properties of commercial gelatin and / or collagen-based hydrogels The molded AG samples were prepared from protocols #1 and #3 and crosslinked from protocol #4. The commercial hydrogel samples listed in Table 4 below were prepared according to the protocols provided by the suppliers and molded according to protocol #3. [Tables 4] [Reference [Supplier] BIS-101 Bioink Solution |BIS- 103 |Bioink Solution BIS-108 Bioink Solution VL5000000010 Cellink [5278-5ML CellSystems [B5X-0000 Biogelx |A10483-01 Sigma The hydrogels were crosslinked with a variant of protocol #4, using either a solution comprising only calcium at 30mg / mL (no TAG), or a solution of calcium at 30mg / mL and transglutaminase at 40mg / mL, in order to observe the impact of TAG. The non-crosslinked and TAG-crosslinked samples were then studied by DMA using protocol #6. The results are summarized in [Fig. 4]. Six of the seven commercial hydrogels studied were crosslinked with transglutaminase. Collagen-based hydrogels (Col4Cell, Rat Collagen) are not rigid enough for analysis by DMA, but gelatin-based hydrogels (Gel4cell, Gel4cell-VEGF, and GelMa) exhibit a significantly higher Young's modulus after crosslinking with transglutaminase. (7.3, 9.9 and 50 kPa respectively). This study shows the effect of crosslinking with transglutaminase on the stiffness of commercial hydrogels. Example 4 — Influence of the amount of alginate and gelatin in a fibrinogen / alginate / gelatin (FAG) hydrogel on mechanical properties FAG hydrogels were prepared from a variant of protocol #2, molded according to protocol #3, then crosslinked using protocol #5, and their mechanical properties were studied by DMA using protocol #6. In this variant, we studied these mechanical properties by preparing the FAG hydrogel with 10 or 3 or 2 g of alginate, and 10 or 7.5 or 5 g of gelatin, respectively, and 2 g of fibrinogen. The results are summarized in Table 5 below. The Young's moduli under the specific conditions of this study range from 200 to 800 kPa. [Tables 5] | Gelatin (%) | Alginate (%) | Fibrino, gene (%) Young’s modulus (kPa) 200 600 800 Example 5 — Evaluation of the colonization of fibrinogen / alginate / gelatin (FAG) and alginate / gelatin (AG) hydrogels by fibroblasts AG and FAG hydrogels were prepared according to protocols #1 and #2. Square implants measuring 1.5 cm on each side and 0.2 cm thick were then printed according to protocol #7 and crosslinked using protocols #4 or #5. The printed implants were produced with a 50% infill and an extrusion nozzle with an internal diameter of 410 µm. A negative control (empty well) was also used. Normal human fibroblasts in passage 6 were thawed and amplified in 175 cm² culture flasks in culture medium containing DMEM supplemented with 10% calf serum and 1% antibiotics. Each implant was seeded on its surface with a cell suspension of normal human fibroblasts at a concentration of 4,000,000 fibroblasts / µL. 250 ml of this suspension were dropwise deposited onto each implant, resulting in 1,000,000 fibroblasts per implant. After 1 hour of adhesion, the implants were immersed in culture medium. The implants were cultured in culture medium composed of DMEM containing 10% calf serum supplemented with vitamin C and EGF (Epidermal Growth Factor) at 37°C, 5% CO₂. The implants were cultured with this same medium for 21 days, renewed every 3 days. The metabolic activity of fibroblasts within the implants was studied by analysis Colorimetric analysis with Alamar Blue was performed on culture days 3, 5, 8, 10, 14, and 21 after inoculation. The solution was prepared by diluting Alamar Blue (DAL 1100, Invitrogen) 1:10 in DMEM. After 19 hours of incubation at 37°C, 100 µL of the sumagants were collected, and their absorbance at 570 nm and 600 nm was measured using a spectrophotometer (NanoQuant® infinite M200PRO, TECAN). Cell viability and growth were thus monitored over 21 days of culture using a 6-point kinetics at days 3, 5, 8, 10, 14 and 21. The results are grouped on [Fig.5]. The results confirmed that all implants allowed fibroblast adhesion and survival from the 3rd day of culture. Cell growth was observable for each porous implant over the 21 days of culture, on both types of hydrogels (FAG and AG), and for each porosity used. Example 6: Evaluation of colonization of fibrinogen / alginate / gelatin (FAG) and alginate / gelatin (AG) hydrogels by adipose tissue stem cells (ASC). AG and FAG hydrogels were prepared according to protocols #1 and #2. Square implants measuring 1.5 cm on each side and 0.2 cm thick were then printed according to protocol #7 and crosslinked using protocols #4 or #5. The printed implants were produced with infill levels of 50% and 75% and an extrusion nozzle with an internal diameter of 410 µm. Sterilization was performed by IONISOS (France) by irradiating the implants with a dose of 30 kGy of gamma radiation. Normal human adipocyte stem cells in passage 2 to 5 were thawed and amplified in 175 cm² culture flasks in culture medium containing DMEM supplemented with 10% serum and 1% antibiotics. Each implant was seeded on its surface with an ASC cell suspension at a concentration of 6, 12, or 24 million ASCs / ml. 250 µl of these suspensions were dropwise deposited onto each implant, resulting in 1.5, 3, or 6 million ASCs / implant. After 1 hour of adhesion, the implants were immersed in culture medium. The implants were cultured in DMEM culture medium supplemented with 10% serum and 1% antibiotics for 7 days, then in DMEM culture medium supplemented with 10% serum, insulin, rosiglitasone, and 1% antibiotics for 14 days. The culture media were changed every 3 days. The metabolic activity of fibroblasts within the implants was studied by Alamar Blue colorimetric analysis on culture days 3, 5, 7, 14, and 21 after inoculation. The solution was prepared by diluting Alamar Blue (DAL 1100, Invitrogen) 1:10 in DMEM. After 5 hours of incubation at 37°C, 100 µL of supernatants were collected, and their absorbance at 570 nm and 600 nm was measured using a spectrophotometer (NanoQuant® infinite M200PRO, TECAN). Cell viability and growth were thus monitored over 21 days of culture using a 6-point kinetics at days 3, 5, 7, 14 and 21. The results are grouped on [Fig.6]. The results confirmed that all implants allowed the adhesion and survival of adipocyte stem cells from the 3rd day of culture. Cell growth is observable for each porous implant over the 21 days of culture, on both types of hydrogels (FAG and AG) as well as for each incense density. Example 7: Evaluation of the colonization of alginate / gelatin (AG) hydrogels in contact with a fraction of purified adipose tissue. AG hydrogels were prepared using protocol #1. Cubic implants with sides of 1.5 cm and thicknesses of 0.8 cm were then printed according to protocol #7 and crosslinked using protocol #4. The printed implants are produced with a 50% infill rate and an extrusion nozzle with an internal diameter of 410 µm. The lipoaspirate was centrifuged at 1500 RPM for 2 minutes and then rinsed with 1X PBS. The lipoaspirate was centrifuged again at 1500 RPM for 30 seconds, and the 1X PBS was removed. The lipoaspirate is considered purified. Each implant was then immersed in 6mL of purified lipoaspirate, and the whole was placed in a culture insert in a 6-well plate with incubation in medium containing DMEM supplemented with 10% serum and 1% antibiotics at 37°C 5% CO2 for 2 or 7 days. Following contact with lipoaspirate, the implants were cultured in 6-well plates in culture medium containing DMEM supplemented with 10% serum, insulin, rosiglitasone and 1% antibiotics, with 3 changes of the medium per week up to 21 days. Cellular metabolic activity within the implants was studied by Alamar Blue colorimetric analysis on culture days 2, 7, and 21 after inoculation. The solution was prepared by diluting Alamar Blue (DAL 1100, Invitrogen) 1:10 in DMEM. After 5 hours of incubation at 37°C, 100 µL of the supernatants were collected, and their absorbance at 570 nm and 600 nm was measured using a spectrophotometer (NanoQuant® infinite M200PRO, TECAN). Cell viability and growth were monitored over 21 days. The results are summarized in [Fig. 7]. Significantly higher metabolic activity than the negative control was observed in implants that had been in contact with purified lipoaspirate. Histological analyses were performed to complement this study according to protocol #9. The results are summarized in [Fig. 8]. The images reveal the presence of aggregated, polygonal, uniform, unilocular, and voluminous adipocytes. These morphological characteristics are those of healthy adipocytes, which one can be found in adipose tissue. Immunostaining for perilipin-1 was also performed. Samples were embedded by OCT (CellPath, KMA-0100-00A) and then stored at -80 °C. Sections 16 µm thick were prepared for each sample using a cryostat (Microm, HM 520). The sections were then fixed in a (v / v) acetone / methanol solution for 20 minutes and rinsed three times in 1X PBS. A one-hour incubation at room temperature in a 4% PBS-BSA solution was performed to saturate nonspecific sites. The sections were then incubated overnight at room temperature with a perilipin-1-specific primary antibody solution. The following day, the sections were rinsed three times with 1X PBS and then incubated for 45 minutes with a secondary antibody solution coupled to Alexa fluor 568 at room temperature. The sections were then rinsed three times with 1X PBS and mounted between a slide and coverslip using Dapi fluoromount-G® mounting medium (SouthernBiotech).The images obtained are grouped [Fig.9]. The images show adipocytes with large spherical or polygonal vacuoles, depending on the cell grouping. The adipocytes appear unilocular and their size is also physiological, ranging between 50 and 200 µm. These results confirm the adhesion, survival, and regeneration of human adipose tissue placed in contact with the implants. The specific structure and composition of the implants thus create an environment conducive to the regeneration of healthy adipose tissue. Example 8 - Influence of temperature and crosslinking time on the mechanical properties of an alginate / gelatin (AG) hydrogel The molded AG samples were prepared from protocols #1 and protocol #3 and crosslinked from a variant of protocol #4. In this variant, the crosslinking times and temperatures were modified, from 10 minutes to 14 hours and from 37°C to 21°C. The samples were then studied by DMA using protocol #6. The results are summarized in [Fig. 10]. Crosslinking times and temperature have very little influence on the final mechanics (Young's modulus) of the hydrogels. However, it appears that an optimum can be found around 1.5 hours, regardless of the temperature. These Young's moduli are also very stable over 7 days after crosslinking at 37°C. The gelatin crosslinking was effective since there was no loss of dissolved gelatin in the medium. Example 9 - Impact of the concentration of crosslinking solution components on the mechanical properties of alginate / gelatin (AG) and fibrinogen hydrogels / alginate / gelatin (FAG) once cross-linked Molded samples of AG and FAG were prepared from protocols #1, #2 and #3, crosslinked from a variant of protocols #4 and #5. In this variant, the concentrations of the components of the crosslinking solution were modified (transglutaminase, calcium chloride and thrombin). The samples were then studied by DMA using protocol #6. The results are grouped in [Fig.11]. Over this range of reagent concentrations, no significant variations were observed (E0 all very similar). Example 10 - Impact of sequential or concomitant crosslinking of alginate / gelatin (AG) and fibrinogen / alginate / gelatin (FAG) hydrogels Molded samples of AG and FAG were prepared according to protocols #1, #2, and #3, and crosslinked using a variant of protocols #4 and #5. In this variant, we investigated sequential crosslinking of FAG and AG, which involves crosslinking the hydrogel in multiple steps. Each step lasted 1 hour, and three rinses with a 0.1 M NaCl solution were performed between each step to remove residual crosslinking agents. The samples were then studied by DMA using protocol #6. The results are grouped in [Fig.12]. The sequential crosslinkings (FAG and AG) generate hydrogels with lower Young's moduli than the single-step crosslinking. It can be observed that very flexible and fragile gels are obtained if calcium is not added first; indeed, TAG and thrombin are calcium-dependent, and their activity is therefore significantly reduced without the addition of CaCl₂. The gels are thus difficult to handle without calcium crosslinking. When thrombin is added first, the gels have very little mechanical strength and holes appear. Example 11 - Impact of the nature of the divalent cation on the crosslinking of alginate / gelatin (AG) and fibrinogen / alginate / gelatin (FAG) hydrogels The molded samples of AG and FAG were prepared from protocols #1, #2 and #3, crosslinked from a variant of protocols #4 and #5. In this variant, we studied crosslinking in the presence of barium chloride 30mg / mL. The samples were then studied by DMA using protocol #6. The results are grouped in [Fig. 13]. Crosslinking in the presence of barium yields gels with Young's moduli very similar to those obtained with CaCl2. However, since barium increases the viscosity of the gels, the formation of additional dangling chains can be assumed. Example 12 - Maintaining the three-dimensional structure and mechanical properties of alginate / gelatin (AG) and fibrinogen / alginate / gelatin (FAG) hydrogel implants after sterilization AG and FAG hydrogels were prepared using protocols #1, #2 and #3, crosslinked using protocols #4 and #5, optically observed and then studied by DMA using protocol #6. The printed shapes are 2 cm diameter hemispheres produced with varying infill rates (30, 50 and 75%). Sterilization was carried out by the company IONISOS (France) by irradiation of the implants with a variable dose (30 kGy and 40 kGy) of Gamma ray. The impact of the crosslinking step on the dimensions of alginate / gelatin and fibrinogen / alginate / gelatin hydrogel implants was studied. These dimensions were measured from macroscopic images. The dimensions of the pores obtained as a function of the filling rate were also studied. These dimensions were measured from images taken with a microscope (Olympus, 4x magnification). The results are grouped in FIG. 14. The implants shrink by an average of 10% following the crosslinking step. However, the pore size does not vary significantly ([Fig. 14A]). Regarding sterilization, it appears that the 40 kGy dose results in greater shrinkage of the constructs than the 30 kGy dose. Concerning E0, sterilization does not cause any change in the material mechanics for either dose ([Fig.14B]). Example 13: Production quality of large implant based on an alginate / gelatin (AG) hydrogel: repeatability of printing dimensions, dimensions after consolidation and sterilization of the implant according to several methods. AG hydrogels were prepared according to protocol #1. Hemispherical implants, 6 cm in diameter and 2 cm thick, were then printed according to protocol #7 and crosslinked using protocol #4, then optically observed and measured. The printed shapes were produced with varying infill percentages (25 to 65%) and extrusion nozzles with an internal diameter of 410 or 840 µm. Sterilization was performed by IONISOS (France) by irradiating the implants with two doses (30 kGy and 40 kGy) of beta radiation or a single dose of 30 kGy of gamma radiation. The impact of the crosslinking and sterilization step on the dimensions of large alginate / gelatin hydrogel implants was studied. These dimensions were measured from macroscopic images. The dimensions of the pores obtained as a function of the filling rate were also studied. These dimensions were measured from images taken with a microscope (Olympus, 4x magnification). The results after printing are grouped [Fig. 15]. These results show high repeatability of the dimensions of the large 3D-printed implants, reflecting high production quality. The results after implant consolidation are grouped [Fig. 16]. This graph shows a high repeatability of retraction of large implants after the consolidation stage. The results after sterilization of the implants using 3 methods (B-rays at doses of 40 and 30 kGy and Y-rays at 30 kGy) are grouped [Fig. 17]. These results show less retraction of the large implants with B-rays at 30 and 40 kGy. Large implants were printed using two extrusion nozzles with internal diameters of 410 and 840 µm and infill levels of 25–65%. The repeatability of the extrusion diameter and the resulting pore length were measured. The results are shown in Figure 18. Figure [Fig. 18A] shows the high repeatability of the extruded cord size. Images of pores of varying sizes were taken and are grouped in [Fig.19] This data shows the wide range of pores that can be obtained for implants and their high repeatability and production quality. Example 14 - In vivo implant resistance studies AG and FAG hydrogels were prepared using protocols #1, #2 and #7, crosslinked using protocols #4 and #5. The printed shapes are 1 cm diameter hemispheres, produced with varying infill rates (30, 50 and 75%). The porous hemispheres were sterilized with a dose of 30kGy and then implanted subcutaneously in rats according to protocol #8. The details of the implantation groups are described in the following table 6, which refers to the surgical implantation plan described in [Fig.20]. [Tables 6] [implant no. implant position Animal group number (hydrogel / filling ratio) |FAG 30% AG 30% |aG 50% |AG 75% Histological analyses were performed using protocol #9, and the results are summarized in [Fig. 21]. Explantation validated the implants' resistance to skin tension. Histological analyses allowed for the evaluation of the colo- Cellular insulation, vascularization, extracellular matrix synthesis: presence of areas of inflammation.

Claims

Demands

1. A three-dimensional body implant comprising a hydrogel comprising of cross-linked gelatin and cross-linked alginate characterized in that said hydrogel has a mechanical resistance of 1] to 1000 kPa and that said implant has an overall porosity of at most 5000 µm.

2. Implant according to claim 1, characterized in that the gelatin is cross-linked by an enzyme, preferably a transglutaminase.

3. Implant according to claim 1 or claim 2, characterized in that that it exhibits a porosity gradient distributed over more than one area of the implant.

4. Implant according to any one of claims 1 to 3, characterized in that it has a volume within a range of 0.05 mL to 3L, preferably from 100mL to 600 mL.

5. Implant according to any one of the preceding claims, ca- characterized in that it is a breast implant.

6. Implant according to any one of the preceding claims, ca- characterized in that the hydrogel comprises 0.5 to 3% alginate and 1 with 17.5% gelatin.

7. Implant according to any one of the preceding claims, ca- characterized in that the hydrogel further comprises fibrinogen cross-linked, and preferably containing 0.0001% to 6% fibrinogen.

8. Implant according to any one of the preceding claims, ca- characterized in that it is obtained by a process which includes a step crosslinking of the hydrogel carried out using a solution containing a divalent cation, preferably calcium, and an agent capable of forming covalent bonds between lysine and glutamine residues such than an enzyme, preferably a transglutaminase.

9. Implant according to claim 8, characterized in that said solution also includes thrombin when the hydrogel contains fi- brinogene.

10. Implant according to any one of the preceding claims, ca- characterized by the fact that it is obtained through a 3D printing process.