PROCESS FOR FUNCTIONALIZING DEXTRAN WITH (METH)ACRYLATES AND USING THE DEXTRAN THUS FUNCTIONALIZED TO PREPARE A HYDROGEL

Abstract

The present invention relates to a process for functionalizing dextran with (meth)acrylate groups, wherein the dextran is reacted with (meth)acrylic anhydride in an aqueous medium at a pH between 9 and 11 and in the presence of a base, the number of mole equivalents of (meth)acrylic anhydride being less than 0.5 compared to the number of moles of hydroxyl groups in the dextran. The present invention also relates to a process for preparing a wet or dry hydrogel using such dextran functionalized with (meth)acrylate groups.

Description

Title of the invention: PROCESS FOR FUNCTIONALIZING DEXTRAN BY (METH)ACRYLATES AND USE OF THE DEXTRAN THUS FUNCTIONALIZED FOR PREPARING A HYDROGEL Technical field

[0001] The present invention belongs to the general technical field of biopolymers and, in particular, to their preparation process.

[0002] The present invention relates to a process for obtaining, efficiently and rapidly, the (meth)acrylation of dextran in an aqueous medium, with a small quantity of (meth)acryling agent and under relatively unrestricted temperature and atmospheric conditions. This process can be carried out with reagents that are of little or no harm, making it possible to use the (meth)acrylated dextran thus obtained to prepare hydrogels useful in biomedical applications.

[0003] Also, the present invention also relates to a process for preparing a hydrogel from a (meth)acrylated dextran directly obtained by such a (meth)acrylation process. State of the prior art

[0004] Biopolymers have received increasing attention in recent decades as an alternative to the use of synthetic polymers. Biopolymers are composed of covalently attached monomer units. The monomer units or the biopolymers themselves are synthesized by living organisms such as plants, algae, animals or bacteria, which are renewable resources. Biopolymers are generally biocompatible and biodegradable, which has opened up a wide range of applications for these materials in the food, cosmetic or medical fields.

[0005] Dextran is an exopolysaccharide produced by various microorganisms, including bacteria, or enzymatically, essentially composed of α-1,6-linked D-glucopyranose residues with α-1,2-, α-1,3-, or α-1,4-linked side chains. As such, it is water-soluble and can be used for various medical applications as an antithrombotic agent, a bulking agent in hypovolemia, or an agent reducing blood viscosity. It can be added to various pharmacological products (protein stabilization in vaccines or ophthalmic formulations, viscosity and consistency ingredient in oral formulations, etc.).

[0006] Dextran can also be chemically modified to introduce chemical groups capable of physically or chemically crosslinking the polymer in order to obtain a hydrogel matrix corresponding to a three-dimensional, hydrophilic and water-insoluble network made up of crosslinked polymers. A chemically modified dextran is characterized by its degree of substitution (DS), defined as the number of functional groups per 100 glucopyranose units of the dextran. Hydrogels swell upon contact with water due to the presence of hydrogen bonds, allowing them to absorb and retain a large quantity of water.

[0007] Polysaccharide-based hydrogels, such as dextran hydrogels, generally exhibit biocompatibility and biodegradability, with highly adjustable characteristic properties such as water swelling or mechanical strength. These parameters can be tuned depending on the nature of the inter-polymer chain bonds (physical, chemical, biologically cleavable or not), the crosslinking density, the molar mass of the polymer chains and their degree of branching. Hydrogels can also be obtained in a dried form by different processes such as drying or lyophilization, which makes them easier to handle for certain applications.

[0008] Due to its ease of use and versatility, chemical photocrosslinking is one of the classic methods used to crosslink polymer chains and form hydrogels. Chemical crosslinking is in this case achieved when the polymer mixture prepared in water, most often with the addition of a water-soluble photoinitiator, is exposed to UV light, generally at 365 nm or 405 nm. The polymer mixture generally comprises one or more photosensitive biopolymers. Photosensitive biopolymers are generally obtained by chemical modification of the polymer to introduce photosensitive chemical groups, such as unsaturated functional groups (acrylate, methacrylate, alkene, alkyne, etc.).Acrylates and methacrylates are well-known photopolymerizable groups for functionalizing polysaccharides because they exhibit high reactivity and high efficiency to polymerize in the presence of a photoinitiator. Acrylated or methacrylated polysaccharides are therefore widely used to form hydrogels via photocrosslinking reactions in biomedical applications.

[0009] Different processes are known in the prior art for preparing acrylated or methacrylated dextran.

[0010] Indeed, the synthesis of acrylated or methacrylated dextran (Dex-MA) to design dextran-based electrophoretic hydrogels was first described in US patent 4,094,832 [1]. The synthesis of Dex-MA was carried out in water, using methacryloyl chloride (2.5 eq), pyridine and hydroxyquinone. However, the reaction showed low efficiency, with low DS being obtained. No purification method was described and the polymer was used as such in combination with acrylamide to obtain mixed hydrogels for electrophoresis.

[0011] Acrylation of dextran was subsequently reported by Edman et al in 1980 [2]. In the method described, dextran acrylate was prepared by reacting dextran with glycidyl acrylate (0.2 eq) in carbonate buffer at pH 11 for 5 days. However, a DS of only 5% was achieved, which corresponds to less than 10% of the initially introduced glycidyl acrylate and demonstrates an inefficient reaction. Furthermore, 5 days were required to complete the reaction, again demonstrating its inefficiency.

[0012] A very efficient synthesis was described by van Dijk-Wolthuis et al in 1995 [3] and 1997 [4]. In the latter, dextran was methacrylated with glycidyl methacrylate in the presence of 4-dimethylaminopyridine (DMAP) as an organic catalyst in dimethyl sulfoxide (DMSO), under nitrogen and at room temperature. More than 90% of the glycidyl methacrylate involved was introduced onto the dextran chain, with good DS control. The main disadvantage of this synthetic route stems from the presence of a toxic and carcinogenic methacrylating agent, a toxic solvent, a toxic catalyst (necessary for the reaction), the long reaction time (48 h) and the use of argon as an inert atmosphere during the reaction. Indeed, van Dijk-Wolthuis et al showed that the reaction between dextran and glycidyl methacrylate requires the presence of DMAP as an organic catalyst to direct it towards the formation of Dex-MA [3, 4].

[0013] Several years later i.e. in 2000, Kim et al described the methacrylation of dextran using methacrylic anhydride in the presence of triethylamine as catalyst in a mixture of lithium chloride and dimethylformamide (LiCl / DMF) under nitrogen [5]. Although higher DS were obtained by increasing the temperature, concentration of the methacrylating agent and catalyst, lower reaction control was observed compared to previous methods. Thus, lower reaction control, higher equivalents of methacrylating agent, longer reaction time (10-30h) and the requirement for nitrogen, are the main disadvantages of the method described in [5]. In addition, traces of impurities are visible on the 'H NMR spectrum, which shows an inefficient purification method.

[0014] Table 1 summarizes the methods known in the prior art on the (meth)acrylation of dextran.

[0015] [Tables 1] Reagents / Solvent Reaction time / T° DS (%) Yield (%) Ref. Dextran Methacryloyl chloride (2.5 eq) Pyridine Hydroxyquinone Distilled water 1h + 4h / 20°C 2.8 Purity: / [1] Dextran Glycidyl acrylate (0.2 eq) Carbonate buffer pH 11 5 days 5 Purity: / [2] Dextran Glycidyl methacrylate (0.017-0.17 eq) DMAP DMSO Argon 48h / Room temperature 4.5-45 70-90 Dialysis [3, 4] Dextran Methacrylic anhydride (0.5 - 2 eq) Triethylamine DMF-LiCl Argon 10-30h / 40-80°C 9-75 49-58 [5]

[0016] Table 1

[0017] In summary, the dextran (meth)acrylation processes currently implemented are characterized by (i) the use of toxic reagents and / or the presence of toxic catalysts and solvents; (ii) a long reaction time (between 10 - 48h); (iii) the restrictive use of an argon or nitrogen atmosphere and (iv) sometimes insufficient purifications.

[0018] With regard to the use of toxic reagents, it should be noted that glycidyl (meth)acrylate is a good (meth)acrylating agent due to the presence of a highly reactive epoxy function. It has been used to (meth)acrylate various polysaccharides. However, the toxicity and carcinogenicity of glycidyl (meth)acrylate glycidyl make it less attractive as a (meth)acrylating agent for polysaccharides compared to (meth)acrylic anhydride, especially when considering biomedical applications.

[0019] For this purpose, the methacrylation of polysaccharides other than dextran has been reported using methacrylic anhydride in the presence of NaOH (to reach a pH of 8) in distilled water, with hyaluronic acid [6, 7], sodium alginate [7], sodium carboxymethylcellulose [8], chondroitin sulfate [9], cellulose [10, 11], methylcellulose

[11] and chitosan

[12] .

[0020] The processes described use a large excess of methacrylic anhydride (0.79 to 20 equivalents) and a reaction time of between 12h and 24h, or even 48h to effectively modify the biopolymers mentioned above.

[0021] Note however that Kelly et al, 2021 propose a process for functionalizing cellulose nanofibrils with polymers comprising a preliminary step during which reactive groups of the methacrylate type are grafted onto the cellulose nanofibrils [H]. This grafting is carried out, in 2 h and at room temperature, using 0.17 to 1.55 equivalents of methacrylic anhydride in distilled water and in the presence of KOH whereby the pH of the reaction mixture is between 9.5 and 10.5. The DS measured by attenuated total reflectance (or ATR in English) is at most 7%.

[0022] The inventors set themselves the goal of proposing a method for functionalizing dextran with acrylate or methacrylate groups that addresses the technical problems of the prior art methods, i.e., a method that is easy to implement, fast, efficient in terms of DS and yield, and does not require restrictive conditions. The inventors also set themselves the goal of proposing a method that can be implemented with low-harm reagents and solvents so that the (meth)acrylated dextran thus prepared can be used to prepare hydrogels for biomedical applications and that the preparation method has a lower impact on the environment. Presentation of the invention

[0023] The present invention makes it possible to achieve the goal set by the inventors.

[0024] Indeed, surprisingly, the inventors have shown that it is possible to quickly obtain a dextran functionalized with (meth)acrylate groups in an aqueous solvent using a small amount of (meth)acrylic anhydride as (meth)acrylation agent in the presence of a base, without any toxic reagent and without any catalyst.

[0025] Under these conditions, the reaction showed high efficiency, making it possible to obtain a dextran derivative with (meth)acrylate groups with a degree of substitution (DS), defined as the number of (meth)acrylate or (meth)acryloyl functional groups per 100 glucopyranose residues of dextran, high and high yield after complete purification.

[0026] Indeed, the modified polysaccharides, i.e. the dextran derivatives with (meth)acrylate groups, were characterized by proton Nuclear Magnetic Resonance (*H NMR) and by Fourier transform infrared spectroscopy (IRTF spectroscopy) and the results obtained showed that the dextran derivatives with (meth)acrylate groups are very pure (less than 0.01% signal of another organic product on the *H NMR spectra) with different DS.

[0027] It was not at all obvious at the date of filing of the invention that such results could be obtained, in a short time, by using (meth)acrylic anhydride whose number of equivalents in moles is less than 0.5 relative to the number of moles of hydroxyl groups in the dextran and in an aqueous medium without toxic compounds such as 4-dimethylaminopyridine (DMAP), dimethyl sulfoxide (DMSO) or a mixture of lithium chloride and dimethylformamide (LiCl / DMF). Indeed, the processes described in the prior art for (meth)acrylating dextran or any other polysaccharide use, for the most part, much larger quantities of (meth)acrylating agent and reaction times and / or restrictive and / or harmful operating conditions.

[0028] In other words, surprisingly high DS and yields were obtained with the process according to the invention, using a very small amount of (meth)acrylic anhydride, in the presence of a base and in an aqueous medium, and without a catalyst. In comparison, the typical (meth)acrylation of dextran is carried out in an organic solvent, using a catalyst in large quantities, and a high number of equivalents of methacrylic anhydride [5]. The typical methacrylation of other polysaccharides carried out in water requires a large excess of methacrylic anhydride to effectively modify the corresponding polysaccharide (about 2-20 eq) and the reaction time is generally in the order of 10 - 48 h.

[0029] Furthermore, even if Kelly et al, 2021

[11] propose a process for functionalizing cellulose nanofibrils with reactive groups of the methacrylate type, in 2 h and at room temperature, using a small amount of methacrylic anhydride in distilled water and in the presence of KOH, the low value obtained for the maximum DS for the modified cellulose nanofibrils would have dissuaded those skilled in the art from implementing such a process to modify dextran.

[0030] Without wishing to be bound by any theory, this unexpected effect (high efficiency in water with a low number of equivalents of (meth)acrylic anhydride) could be due to the greater solubility of dextran in water than in gold solvents. organic, involving better reactivity of the hydroxyl groups, which results in a lower amount of (meth)acrylic anhydride required to modify the dextran to obtain a DS of 13 - 62%. In addition, in the presence of a larger amount of (meth)acrylation reagent, highly substituted polymers are quickly obtained, which makes the polymer insoluble and precipitates it in water, preventing the reaction from completing properly.

[0031] Consequently, the present invention therefore relates to a process for functionalizing dextran with (meth)acrylate groups, in which the dextran is reacted with (meth)acrylic anhydride, in an aqueous medium, at a pH between 9 and 11 and in the presence of a base, the number of mole equivalents of (meth)acrylic anhydride being less than 0.5 relative to the number of moles of hydroxyl groups of the dextran.

[0032] By "functionalizing dextran with (meth)acrylate groups" is meant, in the context of the present invention, the modification of dextran to introduce (meth)acrylate groups therein. This modification consists of replacing at least a portion of the free hydroxyl groups of the dextran present before the process of the invention with (meth)acrylate groups. This modification can also be considered as the replacement of the hydrogen atoms of at least a portion of the free hydroxyl groups of the dextran present before the process of the invention with (meth)acryloyl groups.

[0033] Thus, the dextran derivative obtained at the end of the process according to the invention is a (meth)acrylated dextran, i.e. a chemically modified dextran in which all or part of the free hydroxyl groups have been esterified to form (meth)acrylate ester groups. In other words, the process according to the invention is a process for esterifying at least part of the free hydroxyl groups of the dextran.

[0034] From a reaction point of view, the process according to the invention consists of a nucleophilic attack of the hydroxyl groups of the dextran on one of the carbonyl groups of the (meth)acrylic anhydride, which fragments the (meth)acrylating agent, resulting, on the one hand, in the esterification of the polysaccharide and, on the other hand, in the formation of (meth)acrylic acid as a by-product. The (meth)acrylic acid is neutralized using a base in order to direct the reaction towards esterification.

[0035] The expression "(meth)acrylate group" is the formula conventionally used to describe the two alternatives "acrylate group" or "methacrylate group". This also applies to the following expressions and terms: "(meth)acrylated", "(meth)acrylation", "(meth)acrylic anhydride" and "(meth)acryloyl group".

[0036] In a particular embodiment, the method according to the invention is a method for functionalizing dextran with methacrylate groups.

[0037] The dextran used in the context of the present invention is essentially composed of D-glucopyranose residues linked in α-1,6 with linked side chains in a-1,2, a-1,3 or a-1,4 and advantageously in a-1,3 or a-1,4.

[0038] The dextran used can be a dextran obtained naturally or by synthesis.

[0039] The dextran used in the context of the present invention can also be a modified dextran, i.e. a dextran in which some of the hydroxyl groups have been substituted prior to implementing the method according to the invention. As particular examples of such a modified dextran, mention may be made of a dextran sulfate, a carboxymethyl-dextran or a diethylaminoethyl dextran (or DEAE-dextran).

[0040] Typically, the dextran used has a low or medium molar mass ranging from 1.103 g / mol to 7.104 g / mol. Alternatively, it may have a high molar mass, i.e. greater than 7.104 g / mol, greater than or equal to 1.105 g / mol, in particular greater than or equal to 1.106 g / mol, in particular greater than or equal to 1.107 g / mol and, more particularly greater than or equal to 1.109 g / mol.

[0041] As previously explained, the process according to the invention uses a small amount of (meth)acrylic anhydride as (meth)acryling agent. The semi-developed formulas of acrylic anhydride and methacrylic anhydride are respectively:

[0042] [Chem. 1] H2C=C(H)-C(=O)-OC(=O)-C(H)=CH2 and H2C=C(CH3)-C(=O)-OC(=O)-C(CH3)=CH2.

[0043] The amount of (meth)acrylic anhydride in the process according to the invention is expressed as the number of mole equivalents of (meth)acrylic anhydride relative to the number of moles of hydroxyl groups in the dextran. It is calculated as the ratio between the number of moles of (meth)acrylic anhydride and the number of moles of hydroxyl groups in the dextran.

[0044] Typically, the number of equivalents in moles of (meth)acrylic anhydride used in the process according to the invention is less than 0.5 relative to the number of moles of hydroxyl groups of the dextran. In particular, the number of equivalents in moles of (meth)acrylic anhydride used is between 0.01 and 0.48, in particular between 0.02 and 0.45, and, more particularly, between 0.05 and 0.40 relative to the number of moles of hydroxyl groups of the dextran.

[0045] Any base can be used in the context of the present invention. Thus, the latter can be chosen from organic bases and inorganic bases.

[0046] Advantageously, the base used in the context of the present invention is chosen from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonium hydroxide (NH4 OH), sodium hydrogen carbonate (NaHCO3), potassium hydrogen carbonate (KHCO3), calcium hydrogen carbonate (Ca(HCO3)2), sodium carbonate (Na2 CO3), potassium carbonate (K2CO3), calcium carbonate (CaCO3), lithium hydroxide (LiOH), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), methylamine, ethylamine, isopropylamine, monoisopropylamine, diethylamine, diisopropylamine, di-butylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, choline, monoethanolamine, diethanolamine, 2-aminoethanol, 2-(ethylamino)ethanol, 2-(methylamino)ethanol, N-methyldiethanolamine, di-methylaminoethanol, diethylaminoethanol, nitrilotriethanol, 2-(2-aminoethoxy)ethanol, l-amino-2-propanol, triethanolamine, monopropa-nolamine, dibutanolamine, pyridine and a mixture thereof.

[0047] In a particular embodiment, the base used is chosen from inorganic bases, in particular when the modified dextran prepared by the method according to the invention is used to prepare hydrogels for biomedical applications. Thus, the base used is chosen from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonium hydroxide (NH4OH), sodium hydrogen carbonate (NaHCO3), potassium hydrogen carbonate (KHCO3), calcium hydrogen carbonate (Ca(HCO3)2), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), calcium carbonate (CaCO3), lithium hydroxide (LiOH) and a mixture thereof.

[0048] In an even more particular embodiment, the base used is sodium hydroxide (NaOH).

[0049] A person skilled in the art will be able to determine, without inventive effort, the quantity of base to be used so that the reaction between the dextran and the (meth)acrylic anhydride takes place at a pH of between 9 and 11. In other words, the quantity of base to be provided will be chosen so that the reaction solution has a pH of between 9 and 11 throughout the process.

[0050] The process according to the invention is carried out in an aqueous medium. Thus, the solvent of the reaction solution comprising dextran, (meth)acrylic anhydride and the base is water. By "water" is meant, in the context of the present invention, tap water, deionized water, distilled water or even ultra-pure water (18.2 MΩ). Advantageously, the solvent of the reaction solution used in the process according to the invention is distilled water.

[0051] In the process according to the invention, the reaction between dextran and (meth)acrylic anhydride is carried out for a period of less than 3 h, in particular less than 2 h. Advantageously, the duration of the reaction between dextran and (meth)acrylic anhydride is between 15 min and 90 min, in particular between 20 min and 75 min and, in particular, between 30 min and 60 min.

[0052] Unlike some of the processes describing, in the prior art, the modification of dextran by (meth)acrylate groups, there are no particular constraints as to the temperature and atmosphere under which the process according to the invention must be carried out.

[0053] Typically, the method according to the invention is carried out at a temperature below 35°C, in particular at a temperature between 15°C and 30°C and, in particular, at room temperature (i.e. 23°C ± 5°C).

[0054] Similarly, it is possible to carry out the process according to the invention under an inert atmosphere such as under helium, argon, nitrogen or one of their mixtures. Advantageously, the process according to the invention is carried out under air.

[0055] Advantageously, the method according to the invention comprises the steps consisting of: (a) prepare an aqueous solution of dextran; b) adding, to the aqueous dextran solution prepared in step a), (meth)acrylic anhydride in an amount such that the number of mole equivalents of (meth)acrylic anhydride is less than 0.5 relative to the number of moles of hydroxyl groups of the dextran, whereby an aqueous solution containing dextran and (meth)acrylic anhydride is obtained; c) maintaining the pH of the aqueous solution containing dextran and (meth)acrylic anhydride obtained in step b), at a value between 9 and 11, by adding a base, for a time sufficient to obtain dextran functionalized by (meth)acrylate groups; then d) recovering the dextran functionalized by (meth)acrylate groups obtained during step c).

[0056] Advantageously, step a) consists of dissolving, in water, dextran in solid form. This dissolution is carried out with stirring using a mixer, a stirrer, a magnetic bar, an ultrasonic bath or a homogenizer.

[0057] In a particular embodiment, the (meth)acrylic anhydride is added, during step b), to the aqueous solution containing dextran slowly and, in particular, dropwise. Once the addition is complete, the aqueous solution containing dextran and (meth)acrylic anhydride is typically obtained with stirring using a mixer, a stirrer, a magnetic bar, an ultrasonic bath or a homogenizer.

[0058] The base is added, during step c), to the aqueous solution containing dextran and (meth)acrylic anhydride, throughout the reaction in order to maintain the pH of the latter at a value between 9 and 11. This addition can be made dropwise. At the same time as these successive additions, the aqueous solution containing dextran, (meth)acrylic anhydride and the base is typically maintained under agitation using a mixer, stirrer, magnetic bar, ultrasonic bath or homogenizer.

[0059] In other words, the reactive solution is maintained, with stirring, and at a pH between 9 and 11 by successive additions of base, for a reaction time as previously defined, whereby the dextran and the (meth)acrylic anhydride react together and dextran functionalized by (meth)acrylate groups is obtained (step d)).

[0060] The dextran functionalized by (meth)acrylate groups obtained at the end of step d) is separated from the other elements contained in the solution and in particular from the (meth)acrylic anhydride, the (meth)acrylic acid and the base by any technique for separating two liquids by membrane known to those skilled in the art such as filtration, selective precipitation or dialysis. In other words, the recovery technique used during step d) is filtration, selective precipitation or dialysis.

[0061] As previously explained, the dextran functionalized by (meth)acrylate groups obtained at the end of the process according to the invention is a photo-crosslinkable derivative which is particularly interesting for preparing hydrogels such as hydrogels for biomedical applications, in particular due to its purity at the end of step d).

[0062] The dextran functionalized with (meth)acrylate groups obtained at the end of the process according to the invention can be used to design a hydrogel matrix by photocrosslinking the (meth)acrylate functions and thus construct a 3D network of crosslinked polymer chains. Photocrosslinking is generally obtained by the radical polymerization of the modified polymer in the presence of a photosensitive initiator or photo-initiator which initiates the reaction using ultraviolet-visible (UV-vis) light at a specific wavelength. UV-vis photocrosslinking is a rapid reaction which can be carried out in water under mild and attractive conditions or after drying, with good control of the process and the properties of the material obtained.

[0063] Therefore, the present invention also relates to a method of preparing a hydrogel comprising the steps of: i) preparing a dextran functionalized by (meth)acrylate groups according to the process as previously defined; ii) preparing an aqueous solution containing the dextran functionalized with (meth)acrylate groups prepared in step i) and a photoinitiator; iii) applying the solution prepared in step ii) to a support; iv) optionally drying the solution applied in step iii), whereby a product containing dextran functionalized by (meth)acrylate groups and a photoinitiator is obtained; v) subjecting the solution applied in step iii) or the product obtained in step iv) to irradiation, whereby a wet hydrogel or a dry hydrogel is obtained.

[0064] The dextran functionalized by (meth)acrylate groups prepared according to the process as previously defined can be used during step ii) immediately after its preparation and in particular after the purification step as previously defined. Alternatively, after purification, the dextran functionalized by (meth)acrylate groups can be lyophilized and stored at -20°C before its subsequent use, i.e. before carrying out step ii).

[0065] The solution of step ii) can be prepared (i') by dissolving, in water or an aqueous solution, dextran functionalized by (meth)acrylate groups and a photoinitiator in solid form, (ii') by mixing together dextran functionalized by (meth)acrylate groups in the form of an aqueous solution and at least one photoinitiator in the form of an aqueous solution, (iii') by dissolving dextran functionalized by (meth)acrylate groups in solid form in an aqueous solution of a photoinitiator or (iv') by dissolving a photoinitiator in solid form in an aqueous solution of dextran functionalized by (meth)acrylate groups.

[0066] By "aqueous solution" is meant a solution whose solvent comprises water or consists of water as previously defined. Typically, this aqueous solution is a buffered aqueous solution such as PB buffer (phosphate buffer), PBS buffer (phosphate buffer saline), Tris buffer or HEPES buffer.

[0067] Any photoinitiator known to those skilled in the art can be used in the context of the present invention. Such a photoinitiator is excited by the radiation triggered by irradiation during step v) (most often by UV, visible or UV-visible, but also by γ radiation or by electron beams) allowing the production of radicals by more or less complex mechanisms. As examples of photoinitiators that can be used in the context of the present invention, mention may be made of rose bengal, rhodamine B, eosin Y, roboflavin, 2-hydroxy-1-[4-(2-hydroxyethoxy),phenyl]-2-methyl-1-propanone (also known as "Irgacure 2595"), monoacylphosphine oxide (MAPO) and water-soluble bisacylphosphine oxide (BAPO) derivatives, 1-hydroxy-cyclohexyl-phenylketone (also known as "Irgacure 184"), 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone (also known as "Irgacure 369"), (2-methyl-4'-(methylthio)-2-morpholinopropiophenone (also known as "Irgacure 907"), lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (also known as "Irgacure 2959"), the 2,2'-azobis[2-methyl-N-(2-hydroxyethyl) promionamide (also known as “VA-086”) and erythrosine.

[0068] However, for hydrogels for biomedical applications, cytocompatible and water-soluble photoinitiators such as lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (also known as "Irgacure 2959") are advantageously chosen.

[0069] It is possible that the solution prepared in step ii) comprises, in addition to the dextran functionalized by (meth)acrylate groups and the photoinitiator, at least one other element such as, for example, a pharmaceutically or cosmetically active principle, a tracer or another polymer different from the dextran functionalized by (meth)acrylate groups, possibly crosslinkable.

[0070] The support on which the aqueous solution prepared in step ii) is deposited during step iii) will have a shape and geometry suitable for giving the hydrogel obtained after photocrosslinking or after drying and then photocrosslinking a given shape and possibly a micro- or nano-structured shape. For this purpose, the support used during step iii) may be a mold and in particular a silicone or Teflon mold.

[0071] To prepare dry hydrogels, it is possible to subject the aqueous solution containing the dextran functionalized by (meth)acrylate groups and a photoinitiator deposited on the support to drying. It is obvious that the duration of the drying will depend on the size and thickness of the hydrogel to be dried. For example, this drying is carried out in the open air for a period of between 12 h and 48 h, in particular 18 h and 36 h and, in particular, of the order of 24 h (i.e. 24 h ± 3 h).

[0072] Finally, as previously mentioned, the aqueous solution applied to the support or the product obtained, on the support, after drying of the aqueous solution are subjected to irradiation, most often, by UV-vis, but also by γ radiation or by electron beams. The wavelength for UV-vis irradiation will be chosen according to the characteristics of the photoinitiator present in the solution or the product. As a particular example, when the photoinitiator used is LAP, UV-vis irradiation at 405 nm will be implemented during step v).

[0073] Hydrogels obtained from dextran functionalized with (meth)acrylate groups can be prepared and used in the wet or dry state, as illustrated in the experimental part below.

[0074] The wet hydrogels thus prepared can be used as drug delivery systems implanted, injectable or controlled on the skin. They can also be used in the form of wet micro- or nano-gels.

[0075] The dry hydrogels thus prepared can be used as patches for the absorption of biological fluids such as sweat, saliva, burine, blood... They can also be used as drug delivery systems implanted or controlled on the skin. They can also be used in the form of micro- or nano-gels.

[0076] Other characteristics and advantages of the present invention will become apparent to those skilled in the art upon reading the examples below given for illustrative and non-limiting purposes, with reference to the appended figures. Brief description of the figures

[0077] [Fig-1] presents the 'H NMR spectra at 300 MHz, in deuterium oxide (D2 O)) a) dextran, b) methacrylated dextran (0.0625 eq of methacrylic anhydride), c) methacrylated dextran (0.125 eq of methacrylic anhydride), d) methacrylated dextran (0.25 eq of methacrylic anhydride) and e) methacrylated dextran (0.3 eq of methacrylic anhydride).

[0078] [Fig.2] presents the IRTF spectra of dextran (Dex) and methacrylated dextran (Dex-MA) with DS ranging from 13 to 62%.

[0079] [Fig.3] presents the steric exclusion chromatogram coupled to a detector of Multi-angle light scattering (GPC-MALS) of dextran T70 before modification (Mn number-average molar mass of 63,900 ± 300 g / mol) and after modification with a DS of 52% (Mn number-average molar mass of 78,300 ± 4,400 g / mol).

[0080] [Fig.4] shows the evolution of the degree of methacrylation of dextran and the yield of the reaction as a function of the number of equivalents of methacrylic anhydride added during the reaction.

[0081] [Fig.5] presents the kinetics of the methacrylation of dextran in water with different equivalents of methacrylic anhydride showing the evolution of DS as a function of time.

[0082] [Fig.6] presents the effect of pH on the DS of Dex-MA prepared using methacrylic anhydride in distilled water. Description of the embodiments

[0083] Example 1: Process for the methacrylation of dextran according to the invention.

[0084] Products used:

[0085] Dextran T70 (Dex, Mw = 70,000 g / mol, Pharmacosmos); methacrylic anhydride (94%), lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP, < 95%), phosphate-buffered saline (or PBS for "Phosphate-buffered saline") (IX: 137 mM NaCl, 2.7 mM KC1, 10 mM Na2HPO4, 1.8 mM KH2PO4; pH = 7.4) were purchased from Sigma-Aldrich.

[0086] Dialysis membranes (molecular weight 12,000-14,000 Da) were purchased from Fisher Scientific. Water was deionized using the ELGA-Veolia Purelab purifier (18.2 MOhm.cm). The freeze dryer was purchased from Labconco.

[0087] Protocol:

[0088] Dex (5 g) was dissolved in 100 mL of distilled water in a beaker. After complete dissolution, different numbers of mole equivalents of methacrylic anhydride (from 0.0625 to 0.5 equivalents) relative to the number of moles of hydroxyl groups of dextran were added dropwise into the dextran solution to obtain the desired DS.

[0089] Then, the pH was adjusted using NaOH (3 mol.L-1) to be around 9-11 for the entire duration of the reaction (1 h at room temperature (RT), 20-25°C).

[0090] The reaction scheme corresponding to this protocol is represented in scheme 1 below:

[0091] [Chem.2] pH: 941. NaQH. RT Finally, the Dex-MA polymer was dialyzed against distilled water for 1 week (12,000 Da-14,000 Da membrane) with approximately 14 bath changes to remove impurities, and lyophilized at -46°C, 0.140 mbar for 1 week. The white solid was characterized by 1H Nuclear Magnetic Resonance (1H NMR), Fourier Transform Infrared Spectroscopy (FTIR spectroscopy), and Size Exclusion Chromatography coupled with a Multi-Angle Light Scattering (GPC-MALS) detector, and stored at -20°C before use.

[0092] Results:

[0093] 1H NMR spectra ■.

[0094] The 'H NMR spectra (in deuterium oxide (D2O)) of Dex and Dex-MA, recorded by a Bruker spectrometer at 300 MHz (Bruker Avance-300) are presented [Fig.l]. The typical protons of Dex carried by carbons C2 to C6 (noted from 2 to 6) give a signal of 3.5 to 4.2 ppm. The H1 proton carried by carbon Cl gives a signal at 5.1 ppm and 5.4 ppm, noted 1, corresponding respectively to the α-1,6 bond and the α-1,3 bond. A usual value of 4% of α-1,3 bond relative to the α-1,6 bond was calculated, from the integrals of the signals corresponding to 5.4 ppm and the signals of the other protons of Dex.

[0095] On the spectra of dialyzed and lyophilized Dex-MA polymers, the absence of signals of methacrylic acid at 5.4 and 5.7 ppm and other trace impurities indicate a well-purified polymer (>0.01%). In addition to the Dex protons previously described, the protons of the methacrylate group (vinyl protons denoted 9, and methyl protons denoted 10, with a ratio between vinyl and methyl signals of 2:3) are clearly visible on the spectra of the different Dex-MAs, showing the good incorporation of the methacrylate entities. The degree of substitution, defined as the amount of methacryloyl groups per 100 glucopyranose residues of dextran, is calculated as follows:

[0096] [Chem.3] (U * ho) / 5 DS = .............................................................. (h (5.1 ppm)+ l2 + !3 + l4 + l5 + l6) / 6.96

[0097] with Ib I2,I3,I4,I5,I6,19 and Ii0 representing respectively the integral of the intensity of the peaks of protons 1, 2, 3, 4, 5, 6, 9 and 10 respectively.

[0098] These methacrylated polymers can be used to prepare hydrogels free of toxic compounds, which makes them extremely interesting for biomedical applications.

[0099] IRTF spectra:

[0100] FTIR spectroscopy was performed with a Shimadzu IRAffinity-1 spectrophotometer with a DLATGS (Deuterated Triglycine Sulphate doped with 1-Alanine) detector. All measurements were performed under a dry atmosphere at room temperature with lyophilized samples compressed against a KBr disk. The FTIR spectra of Dex and Dex-MA presented [Fig.2] confirm the methacrylatelation of dextran. The characteristic bands of Dex are present at 3100-3600 cm 1 (-OH) and 2930 cm 1 (-CH2). The successful incorporation of the methacrylate group on Dex was confirmed by the appearance of ester bonds at 1710 cm1 (C=O), 1636 cm 1 (C=C), 1299 and 1147 cm 1 (CO), which increased with increasing DS. A decrease in the intensity of the hydroxyl band between 3100 - 3600 cm1 (-OH) was also notable, indicating good esterification of these functions.

[0101] GPC-MALS:

[0102] GPC-MALS was performed on a Shimadzu HPLC system consisting of a SIL-20A sample changer, an LC-20AD high-pressure pump, a DGU-20A 3R degasser, and a CTO-20A column oven. The eluent used is 0.1 M sodium nitrate + 0.03% sodium azide at a flow rate of 0.5 ml / min. The injected volume for each measurement is 100 pL. The elution time is 70 min. The eluent is filtered at 0.1 pm. The stationary phase has SHODEX OHpak columns consisting of a guard column and 2 SB 806 M HQ columns: Exclusion limit (Pullulan) of 20,000 kDa. The sample is dissolved with the eluent used on the system. The sample is filtered through 0.2 pm. The spectra obtained by GPC-MALS are presented [Fig.3] also confirm the chemical modification of Dex with an increase in molar mass between an unmodified Dex and a Dex-MA with a DS of 52%, going from a number average molar mass of 63,900 ± 300 g / mol to 78,300 ± 4,400 g / mol. In addition, the absence of other signals indicates a preserved integrity of the polymer chains after the reaction and an efficient purification method. A narrow polymer chain dispersity is also preserved between a Dex (Mw / Mn = 1.14) and a Dex-MA with a DS = 52% (Mw / Mn = 1.09), which seems to show a homogeneity of the chemical modification.

[0103] Yields:

[0104] Yields of 85 - 92% are obtained for DS of 13 - 62% when 0.0625 to 0.3 equivalents of methacrylic anhydride are used (Table 2). In comparison, a yield of only 9% is obtained for a DS of 62 to 84% using 0.5 equivalents of methacrylic anhydride due to the precipitation of the majority of the Dex-MA when a high number of equivalents of methacrylic anhydride is used ([Fig.4]). In addition, a linear evolution of the DS of 13 - 62% as a function of the number of equivalents of methacrylic anhydride from 0.0625 to 0.3 eq is obtained, showing a process offering good control over the reaction and the DS obtained (see [Fig.3]).

[0105] [Tables2] Dextran Methacrylic Anhydride DS (%) Yield (%) Solubility in water 5g 0.915 mL - 0.0625 eq 13 + 0.5 92 Yes 5g 1.83 mL - 0.125 eq 26+1 90 Yes 5g 3.66 mL - 0.25 eq 52 + 2 89 Yes 5g 4.39 mL - 0.3 eq 62+1 85 Yes 5g 7.32 mL - 0.5 eq 62-84 9 Partial

[0106] Table 2: Summary of the different formulations used with DS, corresponding yield and solubility of the modified biopolymer obtained after purification.

[0107] The calculation of the number of equivalents in moles of methacrylic anhydride is done, in this example, as follows:

[0108] [Chem.4] Density of methacrylic anhydride (g / mL) Volume of pure methacrylic anhydride (mL) Molar mass of methacrylic anhydride Number of equivalents = V (mL) x 1.04 / 154.165 3 xm {g} / 162 Number of hydroxyl groups per glucopyranose unit Mass of Dextran used Molar mass of a glucopyranose unit of Dextran (g / mol)

[0109] The number of hydroxyl groups per glucopyranose unit is 3.

[0110] Comparative Example 2: Process for methacrylation of dextran in water, without solvent, catalyst or toxic reagent, and with a high number of equivalents of methacrylating agent (1-20 equivalents).

[0111] Dextran (5 g) was dissolved in 100 mL of distilled water in a beaker. After dis complete solution, different numbers of equivalents of methacrylic anhydride (from 1 to 20 equivalents) relative to the hydroxyl groups of dextran were added dropwise into the dextran solution.

[0112] Then, the pH was adjusted using NaOH (3 mol.L-1) to be around 8 - 11 for the whole duration of the reaction (24 h at room temperature, 20-25°C).

[0113] The appearance of a white solid is clearly visible after a few minutes of reaction. Therefore, the precipitated Dex-MA polymers are washed with water, solubilized in ethanol and precipitated in water several times to remove impurities, and dried under vacuum. The white solid was characterized by FTIR spectroscopy, and stored at -20°C before use.

[0114] After the purification step, the modified biopolymers are insoluble in water. The typical bands of Dex-MA are visible by FTIR spectroscopy. However, traces of impurities are noticeable on the FTIR spectra. In addition, lower yields are obtained due to the partial loss of powder during the precipitation / washing steps.

[0115] Example 3: Kinetics of the methacrylation of dextran according to the process of the invention.

[0116] A kinetic study of the reaction carried out as described in Example 1 was carried out in the presence of several equivalents of methacrylic anhydride (relative to the hydroxyl groups of Dex), taking aliquots at regular intervals, which were lyophilized and analyzed by 'H NMR spectroscopy in D2O, as shown [Fig.5].

[0117] DSs were determined from the corresponding protons of the vinyl groups of the modified polysaccharides at 9 ppm and the 2 - 6 protons of Dex at 3.5-4.2 ppm. Unexpectedly high kinetics and efficient methacrylation were achieved with a time of only 60 min using only between 0.0625 and 0.25 equivalents of methacrylic anhydride to obtain a DS of 13% to 62%.

[0118] This is surprising in comparison with the typical methacrylation of Dex which usually requires about 24 to 48 h in an organic solvent. Thus, the reactivity of the secondary hydroxyl groups of Dex seems to be better in an aqueous solvent, which may explain the difference in kinetics and efficiency of this reaction compared to the previously published study carried out in an organic solvent [3, 4],

[0119] Example 4: pH optimization for the methacrylation of dextran in water.

[0120] It is well known that the methacrylation of polysaccharides using methacrylic anhydride thacrylic acid in water results in the production of methacrylic acid. This results in many pH variations during these syntheses.

[0121] The synthesis of Dex-MA was studied using a fixed amount of 0.125 equivalents of methacrylic anhydride at different pH using NaOH as a base and the final DS was determined by 'H NMR. The results are shown [Fig.6].

[0122] The highest DS is obtained for a pH between 9 and 11, which is equal to 26%. A competition between methacrylation and the hydrolysis reaction is observed by 1 H NMR, and a ratio of 69:31 between the two reactions is obtained. Large pH variations are observed for this pH range, indicating the formation of methacrylic acid which is then neutralized by the addition of NaOH.

[0123] No methacrylation takes place without the addition of NaOH due to the total deactivation of the hydroxyl groups, leading to zero DS. It is observed that at pH above 12, only hydrolysis of methacrylic anhydride takes place with only a few percentages of methacrylate introduced onto the dextran (low DS).

[0124] When the pH of the reaction is between 6 and 8, a competition between the methacrylation and the hydrolysis reaction is observed by *H NMR, this time with a ratio of 50:50 between the two reactions and a DS equal to 6% is obtained.

[0125] Thus, pH adjustment is a key parameter for this reaction and the optimal pH for Dex methacrylation has been determined to be between 9 and 11.

[0126] Example 5: Optimization of the basic catalyst for the methacrylation of dextran in water.

[0127] Different basic catalysts were used following the same protocol as in Example 1. The different formulations were analyzed by 'H NMR in D2O. A summary of the results is presented in Table 3.

[0128] [Tables3] DS (%) Methacrylation (%) Hydrolysis (%) Unreacted methacrylic anhydride (%) NaOH 26 69 29 2 KOH 24 64 36 0 Na2CO3 19 51 49 0 k2co3 20 53 46 1 Et3N 25 67 33 0

[0129] Table 3: Summary of the results of the methacrylation of dextran by methacrylate anhydride in distilled water using different basic catalysts.

[0130] Although quite similar results are obtained, it is observed that the highest DS was obtained when NaOH is used reaching a value of 26%. Moreover, the ratio between the competitive reactions of methacrylation and hydrolysis is also higher in favor of methacrylation when NaOH is used.

[0131] Thus, NaOH is one of the most optimal catalysts for the methacrylation of dextran in DW. Other alternatives to be favored for biomedical application are KOH, Na2CO3 or K2CO3 unlike triethylamine (Et3N) which is a corrosive organic base.

[0132] Example 6: Methacrylation of Dex of different molar masses.

[0133] Dextran T20 (Dex T20, Mw = 20,000 g / mol) and Dextran 550 (Mw = 550,000 g / mol) were purchased from Pharmacosmos and Sigma-Aldrich, respectively. The methacrylation reaction was carried out as detailed in Example 1 with 0.125 and 0.072 equivalents of methacrylic anhydride for Dex T20 and Dex 550, respectively. DS was characterized by proton NMR as described in Example 1. The results obtained are described in the following Table 4.

[0134] [Tables4] Dextran Methacrylic anhydride DS (%) Yield (%) Solubility in water at room temperature T20 1.83 mL - 0.125 eq 26 90 Yes 550 1.06 mL - 0.072 eq 14 - Yes

[0135] Table 4

[0136] Example 7: Preparation of wet-photocrosslinked Dex-Met hydrogels.

[0137] Dex-MA of different DS (13% to 52%) prepared as in Example 1 and LAP were mixed in a 10 mL glass vial, and dissolved in PBS (1X) to obtain a polymer concentration of 10%, 20% or 30% w / w, and a final LAP concentration of 0.1% to 1% w / w. The solution was cast into a Teflon mold and exposed to UV-vis light (300 W) at 405 nm for 60 s to obtain a wet hydrogel. The obtained hydrogels are not soluble in water, demonstrating the efficiency of polymer crosslinking.

[0138] Example 8: Swelling rate and mechanical properties of dried and photocrosslinked Dex-Met hydrogels.

[0139] Dex-MA of different DS (13% to 52%) and LAP were mixed in a 10 mL glass vial, and dissolved in PBS (1X) to obtain a polymer concentration of 10%, 20% or 30% w / w, and a final LAP concentration of 0.1% to 1% w / w. The solution was cast into a Teflon or silicone mold and allowed to air dry for 24 h. After the solution was completely dried, the mixture was exposed to UV-vis light (300 W) at 405 nm for 60 s to obtain a solid dried hydrogel.

[0140] Interestingly, no shrinkage of the polymer was observed and the dried material had the same shape as the Teflon or silicone mold. The hydrogels photocrosslinked with 0.1% w / w LAP appeared as transparent materials while those crosslinked with 0.5% and 1% w / w LAP appeared slightly yellow (due to the action of UV-vis light on the LAP photocrosslinker).

[0141] Interestingly, when a Dex-MA material (DS = 52%) crosslinked in the presence of 1% w / w LAP was immersed in a PBS solution, the yellow material became transparent, indicating that the unreacted LAP fragments present inside the Dex-MA hydrogel were removed during washing with PBS.

[0142] The hydrogels were characterized by a swelling test. The dried photocrosslinked Dex-Met materials were weighed (weight W0). The samples were placed in a vial containing PBS (IX) at room temperature (21-24°C). They were removed every hour and their surface was quickly wiped with a paper towel to remove excess water. Then, the samples were immediately weighed (Wt), and placed back in PBS for the next measurement points. This operation was repeated until no more weight changes were detected. The swelling ratio (TG) was calculated according to the formula TG = (Wt - W0) / W0. Three experiments were performed in parallel for each sample, and the average value was calculated (Tables 5 and 6).

[0143] [Tables5] Swelling rate (%) DS = 52% DS = 26% DS = 13% 30% w / w of Dex-MA 48.0+1.9 50.1 + 2.3 84.4 + 2.3 20% w / w of Dex-MA 49.5 + 2 56.8+1.5 96.4 + 3.7 10% w / w of Dex-MA 52.0 + 2.1 66.4 + 3.1 111.8 + 2.9

[0144] Table 5: Evolution of TG (%) at different DS and different concentrations of Dex-Met

[0145] [Tableauxô] Swelling Rate (%) 1% w / w LAP 0.5% w / w LAP 0.1% w / w LAP 30% w / w Dex-MA 84.4 + 2.3 133.6 + 3.6 189.3 + 5.4 20% w / w Dex-MA 96.4 + 3.7 142.9 + 3.9 207.8 + 6 10% w / w Dex-MA 111.8 + 2.9 158.0 + 3.7 238.1 + 5.6

[0146] Table 6: Evolution of TG (%) at different concentrations of Dex-MA whose DS is 13% and different concentrations of LAP

[0147] The maximum swelling ratio (TG) for each formulation is reached in about 1-2 h. The TG decreases with increasing polymer content from 52% at 10% w / w to 48% at 30% w / w due to the lower porosity of the material at high polymer concentration (Tables 5 and 6).

[0148] When the polymer and LAP concentration are set at 10% and 1% w / w respectively, an increase in TG is observed with a decrease in DS, from 52% for a DS of 52% to 111.8% for a DS of 13%. Indeed, by decreasing the DS, the crosslinking density of the material also decreases, implying a network with a lower density.

[0149] The same phenomenon is observed when the LAP concentration decreases. Indeed, by reducing the initiator content, larger meshes are obtained and therefore a network with a lower density.

[0150] Compression tests were also performed on the dry hydrogels using a TAXT.Plus texturometer (Stable Micro Systems). The compression speed was set at 0.5 mm.s 1 with a maximum compression force of 50 N. The values ​​of the compression modulus E were calculated as the slope of the curve of the applied force versus the displacement.

[0151] E values ​​around GigaPascal are obtained (Tables 7 and 8). It is observed that the DS polymer and the LAP concentration do not significantly affect the mechanical properties of the materials, unlike the polymer concentration (Tables 6 and 7).

[0152] [Tables?] Sample 10% w / w 20% w / w 30% w / w DS (Dex-MA) 52% + 1% LAP 32 + 1 MPa 165 + 8 MPa 322 + 9 MPa DS (Dex-MA) 26% + 1% LAP 42 + 2 MPa 129 + 7 MPa 342 + 10 MPa DS (Dex-MA) 13% + 1% LAP 34 + 2 MPa 153 + 6 MPa 333 + 8 MPa Dex 38 + 2 MPa 158 + 3 MPa 338 + 5 MPa

[0153] Table 7: Evolution of the compression modulus E as a function of the DS of Dex-MA and the polymer concentration.

[0154] [Tables8] Sample 10% w / w 20% w / w 30% w / w 1% w / w LAP 34 + 2 MPa 153 + 6 MPa 333 + 8 MPa 0.5% w / w LAP 29 + 2 MPa 143 + 9 MPa 316+ 6 MPa 0.1% w / w LAP 27 + 2 MPa 167 + 5 MPa 328 + 8 MPa

[0155] Table 8: Evolution of the compression modulus E with a DS of Dex-MA at 13% as a function of the polymer and LAP concentration. BIBLIOGRAPHICAL REFERENCES

[0156] [1] US Patent 4,094,832 published June 13, 1978.

[0157] [2] Edman et al, 1980, “Immobilization of proteins in microspheres of biode gradable polyacryldextran”, J. Pharm. Sci., vol. 69, pages 838-842.

[0158] [3] Van Dijk-Wolthuis et al, 1995, “Synthesis, characterization, and polymerization of glycidyl methacrylate derivatized dextran”, Macromolecules, vol. 28, pages 6317-6322.

[0159] [4] Van Dijk-Wolthuis et al, 1995, « Reaction of dextran with glycidyl méthacrylate: an unexpected transestérification », Macromolecules, vol. 30, pages 3411-3413.

[0160] [5] Kim et al, 2000, « Synthesis and characterization of dextran-methacrylate hydrogels and structural study by SEM », Journal of Biomédical Materials Research, vol. 49, pages 517-527.

[0161] [6] Smeds et al, 1999, « Synthesis of a novel polysaccharide hydrogel », J. Macromol. Sci., vol. 36, pages 981-989.

[0162] [7] Kimberly et al, 2001, « Photocrosslinkable polysaccharides for in situ hydrogel formation », Journal of Biomédical Materials Research, vol. 54, pages 115-121.

[0163] [8] Qian et al, 2014, « Delivery of doxorubicin in vitro and in vivo using bio- reductive cellulose nanogels », Biomater. Sci., vol. 2, pages 220-232.

[0164] [9] Wang et al, 2001, « Synthesis and characterization of chondroitin sulfate-methacrylate hydrogels », Carbohydrate Polymers, vol. 52, pages 389-396.

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[10] Chen et al, 2010, « Facile methacrylation of cellulose via alkaline aqueous esté rification for thiol-ene click functionalization », Materials Letters, vol. 245, pages 18-21.

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[11] Kelly et al, 2021, « Aqueous polymer modification of cellulose nanofibrils by grafting-through a reactive méthacrylate group », Macromol. Rapid Commun. Macromol. Rapid Commun, vol. 42, 2000531.

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[12] Kolawole et al, 2018, « Methacrylated chitosan as a polymer with enhanced mu- coadhesive properties for transmucosal drug delivery », International Journal of Phar-maceutics, vol. 550, pages 123-129.

Claims

Claims

1. Process for functionalizing dextran with (meth)acrylate groups, characterized in that the dextran is reacted with (meth)acrylic anhydride, in an aqueous medium, at a pH between 9 and 11 and in the presence of a base, the number of mole equivalents of (meth)acrylic anhydride being less than 0.5 relative to the number of moles of hydroxyl groups of the dextran.

2. Functionalization process according to claim 1, characterized in that said number of equivalents in moles of (meth)acrylic anhydride used is between 0.01 and 0.48, in particular between 0.02 and 0.45, and, more particularly, between 0.05 and 0.40 relative to the number of moles of the hydroxyl groups of the dextran.

3. Functionalization process according to claim 1 or 2, characterized in that said base is chosen from sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonium hydroxide (NH4OH), sodium hydrogen carbonate (NaHCO3), potassium hydrogen carbonate (KHCO3), calcium hydrogen carbonate (Ca(HCO3)2), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), calcium carbonate (CaCO3), lithium hydroxide (LiOH) and a mixture thereof.

4. Functionalization process according to any one of claims 1 to 3, characterized in that said base is sodium hydroxide (NaOH).

5. Functionalization process according to any one of claims 1 to 4, characterized in that the duration of the reaction between the dextran and the (meth)acrylic anhydride is less than 3 h, advantageously less than 2 h, in particular between 15 min and 90 min, in particular between 20 min and 75 min and, very particularly, between 30 min and 60 min.

6. Functionalization process according to any one of claims 1 to 5, characterized in that said process is carried out at a temperature below 35°C, in particular at a temperature between 15°C and 30°C and, in particular, at room temperature (i.e. 23°C ± 5°C).

7. Functionalization process according to any one of claims 1 to 6, characterized in that said process is carried out in air.

8. Functionalization method according to any one of the claims 1 to 7, characterized in that said process comprises the steps of: a) preparing an aqueous solution of dextran; b) adding, to the aqueous solution of dextran prepared in step a), (meth)acrylic anhydride in an amount such that the number of mole equivalents of (meth)acrylic anhydride is less than 0.5 relative to the number of moles of hydroxyl groups of the dextran, whereby an aqueous solution containing dextran and (meth)acrylic anhydride is obtained; c) maintaining the pH of the aqueous solution containing dextran and (meth)acrylic anhydride obtained in step b), at a value between 9 and 11, by adding a base, for a time sufficient to obtain dextran functionalized by (meth)acrylate groups; then d) recovering the dextran functionalized by (meth)acrylate groups obtained in step c).

9. Functionalization process according to claim 8, characterized in that the recovery technique used during said step d) is filtration, dialysis, or selective precipitation.

10. A method for preparing a hydrogel comprising the steps of: i) preparing a dextran functionalized with (meth)acrylate groups according to the method as defined in any one of claims 1 to 9; ii) preparing an aqueous solution containing the dextran functionalized with (meth)acrylate groups prepared in step i) and a photoinitiator; iii) applying the solution prepared in step ii) to a support; iv) optionally drying the solution applied in step iii), whereby a product containing dextran functionalized with (meth)acrylate groups and a photoinitiator is obtained; v) subjecting the solution applied in step iii) or the product obtained in step iv) to irradiation, whereby a wet hydrogel or a dry hydrogel is obtained.

11. Preparation process according to claim 10, characterized in that said photoinitiator is lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

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