Cross-Linkable Polymer, Hydrogel, and Method of Preparation Thereof

Abstract

The invention relates to a cross-linkable polymer including a base polymer including functional groups at least some of which have been reacted with a first organic molecule including a cross-linkable unit and with a second organic molecule capable of bonding to organic and/or inorganic substrates. The invention further relates to a hydrogel including the cross-linkable polymer that includes cross-linkable polymer strands, wherein at least some of the cross-linkable units of different cross-linkable polymer strands have reacted to form a covalent bond thereby forming a covalently linked network. The invention further relates to a method for the preparation of the hydrogel and to the use of the hydrogel.

Claims

1. A cross-linkable polymer comprising a base polymer comprising functional groups at least some of which have been reacted with a first organic molecule comprising a cross-linkable unit and with a second organic molecule capable of bonding to organic and/or inorganic substrates.

2. The cross-linkable polymer according to claim 1, wherein the functional groups of the base polymer comprise at least one of hydroxyl groups, amine groups, carboxylic acid groups, amide groups, and thiol groups.

3. The cross-linkable polymer according to claim 1, wherein the base polymer is selected from the group consisting of hyaluronic acid, alginate, chitosan, pectine, poly(ethylene glycol), carboxymethyl cellulose, poly(vinyl alcohol), poly(2-hydroxyethyl methacrylate), poly(acrylamide), fibrin, silk, collagen, and mixtures thereof.

4. The cross-linkable polymer according to claim 1, wherein the cross-linkable unit of the first organic molecule comprises at last one of a carbon-carbon double bond (—C═C—), a thiol group (—SH), an epoxide group, and an acid anhydride group.

5. The cross-linkable polymer according to claim 1, wherein the first organic molecule comprises an attachment unit that allows the attachment of the first organic molecule to the functional groups of the base polymer, wherein in particular the attachment unit is selected from the group consisting of an aldehyde group, an acid chloride group, an acid anhydride group, a carboxylic acid group, an amine group, a catechol group, and a hydroxyl group.

6. The cross-linkable polymer according to claim 1, wherein the first organic molecule is a molecule of the formula X—Y or X—R—Y, wherein X is an aldehyde group, an ester group, an acid chloride group or an acid anhydride group, R is an optionally substituted hydrocarbon moiety with 2 to 10 carbon atoms, and Y is a carbon-carbon double bond, an epoxide group, or an acid anhydride group, and/or wherein the first organic molecule is selected from the group consisting of acrylic anhydride, acryloyl chloride, pent-4-enal, ethyl 2,3-epoxypropanoate, methacrylic anhydride, methacryloyl chloride, mercaptopropionic acid, and maleic anhydride.

7. The cross-linkable polymer according to claim 1, wherein the second organic molecule comprises a bonding unit that comprises at least one of a catechol group; a quinone group; a group of the formula SiX.sup.1X.sup.2X.sup.3, wherein X.sup.1, X.sup.2, and X.sup.3 are independently selected from the group consisting of a halide, in particular chloride, methoxy, ethoxy, isopropoxy, and acetoxy; a thiol group; a phosphono group or its derivatives; a phosphate group or its derivatives; and a dicarboxyl group.

8. The cross-linkable polymer according to claim 1, wherein the second organic molecule comprises a connecting unit that allows the attachment of the second organic molecule to the functional groups of the base polymer, wherein in particular the connecting unit is selected from the group consisting of an aldehyde group, an acid chloride group, an acid anhydride group, a carboxylic acid group, an amine group, and a hydroxyl group.

9. The cross-linkable polymer according to claim 1, wherein the second organic molecule is a molecule of the formula X′—R′—Y′, wherein X′ is an aldehyde group, an acid chloride group, an acid anhydride group, a carboxylic acid group, an amine group, or a hydroxyl group, R′ is an optionally substituted hydrocarbon moiety with 2 to 10 carbon atoms, and Y′ is a catechol group; a quinone group; a group of the formula —SiX.sup.1X.sup.2X.sup.3, wherein X.sup.1, X.sup.2, and X.sup.3 are independently selected from the group consisting of a halide, in particular chloride, methoxy, ethoxy, isopropoxy, and acetoxy; a thiol group; a phosphono group or its derivatives; a phosphate group or its derivatives; or a dicarboxyl group and/or wherein the second organic molecule is selected from the group consisting of 3,4-dihydroxyphenethylamine and aminopropyltriethoxysilane.

10. The cross-linkable polymer according to claim 1, wherein the cross-linkable polymer has a molecular weight less than 500 kDa, in particular from 750 Da to about 500 kDa or from 10 kDa to 500 kDa, and/or is water-soluble.

11. The cross-linkable polymer according to claim 1, wherein from 0.1% to 99%, in particular from 1% to 50%, more particularly from 10% to 30% of the functional groups of the base polymer have reacted with the first organic molecule.

12. The cross-linkable polymer according to claim 1, wherein from 0.1% to 70%, in particular from 1% to 30%, more particularly from 10% to 30% of the functional groups of the base polymer have reacted with the second organic molecule.

13. A hydrogel comprising a cross-linkable polymer according to claim 1, further comprising cross-linkable polymer strands, wherein at least some of the cross-linkable units of different cross-linkable polymer strands have reacted to form a covalent bond thereby forming a covalently linked network.

14. The hydrogel according to claim 13, wherein the hydrogel comprises at least one additive in particular selected from the group consisting of organic fillers, inorganic fillers, aramid fibers, cellulose fibers, poly((meth)acrylates), collagen fibers, silk fibers, chitin, chitosan, starch, nanoparticles, in particular silica, calcium phosphate, nanodiamond, and mixtures thereof.

15. The hydrogel according to claim 13, wherein the hydrogel comprises water, buffer, phosphate buffered saline (PBS), hepes buffer, or alcohol, in particular water, in particular in the amount from 70 to 99 wt. % or from 75 to 99 wt. % or from 80 to 99 wt. %, in each case based on the total weight of the hydrogel.

16. The hydrogel according to claim 13, wherein the hydrogel has an elastic modulus from about 2 kPa to about 4 MPa.

17. The hydrogel according to claim 13, wherein the hydrogel has a swelling ratio from −20% to 150%.

18. The hydrogel according to claim 13, wherein the hydrogel adheres to different human or animal tissues, in particular adheres to at least one of cartilage tissue, meniscus tissue, eye tissue, in particular corneal tissue, skin, nucleus pulposus tissue, annulus fibrosus tissue, cardiovascular tissue, and bone tissue.

19. A method for the preparation of a hydrogel, comprising the steps of a. providing a cross-linkable polymer according to claim 1, b. dissolving the cross-linkable polymer in a solvent to obtain a solution, c. optionally, adding a cross-linking agent to the solution, cross-linking of the cross-linkable polymer by an external stimulus to obtain a hydrogel.

20. The method according to claim 19, wherein the cross-linking agent is biocompatible.

21. The method according to claim 19, wherein the cross-linking agent is selected from the group consisting of a radical initiator, an oxidating agent, and a diamine.

22. The method according to claim 19, wherein the solvent is selected from water, buffer, phosphate buffered saline (PBS), hepes buffer, and alcohol.

23. The method according to claim 19, wherein the external stimulus is selected from the group consisting of UV irradiation, X-ray irradiation, infrared irradiation, and heating.

24. The method according to claim 19, wherein the solution is degassed in a step prior to step d.

25. The method according to claim 19, wherein an additive is added to the solution prior to step d.

26. (canceled)

27. The method according to claim 19, wherein the concentration of the cross-linkable polymer is from 1 to 30 wt. %, in particular from 1 to 25 wt. % or from 1 to 20 wt. %, based on the total weight of the solution.

28. (canceled)

29. (canceled)

30. The hydrogel according to claim 13 for use in the treatment of cartilage damage, meniscus damage, corneal damage, nucleus pulposus or annulus fibrosus damage, cardiac tissue damage, bone tissue damage, dental tissue damage and/or as implant, in particular in surgery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG. 1 shows an NMR spectrum of hyaluronic acid that was reacted with methacrylic anhydride as described in the examples section.

[0069] FIG. 2 shows an NMR spectrum of hyaluronic acid that was reacted with methacrylic anhydride and with dopamine hydrochloride as described in the examples section.

[0070] FIG. 3 shows the swelling ratio of different hydrogels.

[0071] FIG. 4 shows the elastic modulus of different hydrogels.

[0072] FIG. 5 shows the adhesion strength of different hydrogels.

DESCRIPTION OF THE INVENTION

Examples

Materials

[0073] Sodium hyaluronate (hereinafter HA) of three different molecular weights (15-30 kDa, 50-90 kDa and 300-500 kDa) was purchased from Contipro a.s. (CZ). Methacrylic anhydride, sodium hydroxide, dialysis sacks (molecular weight cut-off 6000-8000 Da) and hydrochloric acid were purchased from Sigma-Aldrich. Dopamine hydrochloride (Dopa or Dopamine), N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC, purum, ≥98.0%) and deuterium oxide (D.sub.2O) were purchased from Sigma-Aldrich. For radical polymerization, Irgacure 2959 (BASF) was used as photoinitiator. Nanofibrillated Cellulose (NFC) was provided by EMPA (Swiss Federal Laboratories for Materials Science and Technology, Dithendorf, Switzerland). Phosphate buffered saline with a concentration of 0.155 mol/L sodium chloride and 0.0041 mol/L phosphate (added in the form of Na.sub.2HPO.sub.4 and KH.sub.2PO.sub.4) with a pH of 7.4 was purchased from Thermo Fisher Scientific as “10010 PBS”.

General Synthetic Procedures

[0074] Functionalization of Hyaluronic Acid with Methacrylic Anhydride and Dopamine (Hereinafter MeCHa) as a Cross-Linkable Polymer

[0075] The synthesis of MeCHa was performed in two steps and is depicted schematically in Scheme 1. First, the methacrylation of HA was carried out in aqueous solution at alkaline pH and to the reaction product, catechol groups were subsequently attached by reaction with dopamine under acidic conditions. The order of the functionalization steps is important due to the synthesis pH conditions and in order to avoid deteriorating the dopamine adhesive performance.

##STR00001##

General Methacrylation Procedure

[0076] 0.5 g of HA was dissolved in 50 ml (100 ml) of deionized water in a glass flask with a magnetic stir bar and stirred vigorously for 30 min at room temperature. The flask was then placed in an ice container and the temperature was kept at around 4° C. under a fume hood. While stirring, the pH of the HA solution was adjusted to 8.5 using 1.0 M NaOH.

[0077] Two different protocols (a and b) were followed in order to obtain two different methacrylation degrees:

[0078] a) Low methacrylation degree. One dose of methacrylic anhydride (1.963 mL) was added dropwise to the solution and the pH was adjusted to 8±0.5 with 5N NaOH. The pH was adjusted every 5 minutes for 3 hours (it should be noted that the pH will not remain steady as it will have a tendency to acidify quite rapidly). Thereafter, a second dose of 1.963 mL methacrylic anhydride was added and the pH was adjusted to 8±0.5. The solution was stirred in the cold room at 4° C. overnight while the flask opening was covered with parafilm. Then, the pH was adjusted to 7.5±0.5 and the reaction solution was transferred to 50 mL conical tubes and spun for 5 min at 1200 g. Unreacted chemicals were removed by dialysis for three days and the dialysis water was changed 3 times daily.

[0079] b) High methacrylation degree. 1.4 ml of methacrylic anhydride (1.035 g/mL) was added dropwise to the solution and the pH was adjusted to 8.5 repeatedly during the MA addition. The reaction was allowed to proceed on ice for 4 hours while maintaining the pH at 8.5-9.5. pH adjustment was performed continuously during the reaction, therefore the pH was not allowed to be less than 8.5. It should be also noted that adequate stirring is essential to generate an emulsion during the functionalization, as insufficient stirring leads to phase separation. Thereafter, the reaction was followed by a second addition of 1.4 ml of methacrylic anhydride for another 4 hours. The solution was then stirred vigorously overnight at room temperature when the pH was stable after the 8 hours of modification. Unreacted chemicals were removed by dialysis (6-8 kDa dialysis membrane tubing) for three days and the dialysis water was changed twice daily.

[0080] After dialysis, the solution was transferred to 50 ml tubes in 25-30 ml aliquots and frozen in a −80° C. freezer overnight. Afterwards, the samples were lyophilized for three days. The tubes were transferred in dry ice and covered with a kimwipe before lyophilization.

General Dopamine Functionalization Procedure

[0081] The reaction of hyaluronic acid with Dopa was conducted using N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) as an activation agent of the carboxyl groups on the hyaluronic acid. The reaction was performed at room temperature under nitrogen atmosphere and pH control in order to avoid the irreversible oxidation of dopamine molecules. Briefly, 0.5 g of methacrylated HA was dissolved in 50 ml of phosphate buffered saline (PBS) solution in a three-neck round-bottom flask with a magnetic stir bar and the pH was adjusted to 5.5 using hydrochloric acid (HCl). The solution was then purged with nitrogen for one hour. Then, 175 mg of EDC and 240 mg of dopamine hydrochloride were added into the reaction mixture and the pH of the reaction solution was maintained at 5.5 for 150 minutes. The functionalization process was performed under nitrogen atmosphere. The reaction mixture was afterwards dialyzed using dialysis tubes (6-8 kDa dialysis membrane tubing) against acidic water with pH of around 5.5 for three days until all unreacted chemicals were removed. The dialysis water was changed twice daily. It should be noted that further purification can also be carried out by another dialysis in deionized water. The samples were finally frozen in a −80° C. freezer overnight, covered with a kimwipe and lyophilized for three days. The modified MeCHa was stored at 4° C. under vacuum and protected from the light.

General Hydrogel Synthesis Procedure

[0082] The MeCHa hydrogel was synthesized by dissolving the lyophilized MeCHa polymer as hydrogel precursor in phosphate buffered saline (PBS, pH 7.4) (at a concentration of 4.8 wt %) followed by dissolving Irgacure 2959 (0.1%, w/v) in the resulting solution. The hydrogel precursor was homogenized using vortex and the degassed mixture was then poured into molds made of Teflon and covered with microscope slides. The mixtures containing the MeCHa molecules in the molds were irradiated with ultraviolet irradiation with the wavelength of 365 nm, a light intensity of 5 mW.Math.cm.sup.−2 for 10 minutes to cross-link the MeCHa polymer strands.

[0083] The hydrogel from methacrylated hyaluronic acid was synthesized (to serve as comparative example) by dissolving 4.8 wt % of the lyophilized methacrylated hyaluronic acid as hydrogel precursor in phosphate buffered saline (PBS, pH 7.4) followed by dissolving Irgacure 2959 (0.1%, w/v) in the resulting solution. The hydrogel precursor was homogenized using vortex and the degassed mixture was then poured into molds made of Teflon and covered with microscope slides. The precursor was irradiated with ultraviolet irradiation as described above.

[0084] Poly(ethylene glycol)dimethacrylate (hereafter “PEGDMA”) and nanofibrillated cellulose (NFC)-reinforced double-network PEGDMA-alginate hydrogels were also prepared using the same procedure (to serve as comparative examples). PEGDMA hydrogels were synthesized as a hydrogel with 95.2 wt % water content and with 4.8 wt % PEGDMA. Composite hydrogels were synthesized with 4.8 wt % PEGDMA, 0.55 wt % sodium alginate and 0.5 vol. % NFC, which gives 94 wt % water content. The composite hydrogel precursor was synthesized by mixing PEGDMA, calcium sulphate, NFC (0.5 vol %), and Irgacure 2959 (0.1%, w/v) in distilled water. The hydrogel precursor was homogenized using an Ultra-Turrax at 12000 rpm for 20 min and sodium alginate was added. The PEGDMA molecules were crosslinked by ultraviolet irradiation with the wavelength of 365 nm, with a light intensity of 5 mW.Math.cm.sup.−2 for 30 minutes.

Characterization

[0085] Nuclear Magnetic Resonance (NMR) Analysis. The degree of functionalization for methacrylated polymers and MeCHa polymers was analyzed using .sup.1H NMR spectroscopy with D.sub.2O as the solvent using a 400 MHz Bruker Avance NEO. Briefly, 10 mg of the modified polymers was dissolved in 600 μl of D.sub.2O at room temperature. The solutions were then transferred to NMR tubes and sealed with a cap. The same procedure was used for methacrylated hyaluronic acid (control samples) as well.

[0086] Swelling ratio and water content study. The swelling ratios of a MeCHa-Gel and of methacrylated HA with high and low methacrylation degree, as well as PEGDMA-based hydrogels including single network and composite double-network hydrogels were evaluated in both PBS and distilled water at room temperature. Circular hydrogel samples were obtained using molds with a diameter of 4.6 mm and a depth of 2.4 mm following the general hydrogel synthesis procedure. After irradiation, the hydrogels were removed from the molds and immersed into distilled water or PBS solution, respectively, for 24 h. The swelling ratio (SR) was calculated with the following equation: SR(%)=(Vs−V0)/V0×100, where V0 is the volume of the samples before swelling and Vs is the volume of the samples after swelling.

[0087] Tissue preparation. For the adhesion test, tissue samples were prepared in cylindrical shape with a diameter of 6.6 mm and a height of 10 mm from bovine articular cartilage on femoro-patellar groove.

[0088] Mechanical characterization—unconfined compression and hydrogel-tissue adhesion measurement. After placing the tissue samples into a two-piece mold, the hydrogel precursors were poured onto the prepared samples in the mold and photopolymerized on the top of the tissue surface. The two-piece mold was removed after polymerization and the attached tissue was quickly gripped for the adhesion test. Adhesion measurement was performed using an Instron E3000 linear mechanical testing machine (Norwood, Mass., United States) with a 50 N load cell and a constant speed of 0.15 mm.Math.s.sup.−1. The adhesion strength was determined by dividing the maximum adhesion force by the surface area of the hydrogel-tissue contact.

[0089] To evaluate the synthesis of the modified polymer, the chemical structure of MeCHa was analyzed by .sup.1H NMR spectroscopy. FIG. 1 shows the spectrum of methacrylated HA with a hyaluronic acid molecular weight of 50-90 kDa as a representative .sup.1H NMR spectrum of methacrylated HA. The hydroxyl group peaks are located at the chemical shift of 4.4-4.6 ppm. The degree of methacrylation was determined by integrating the peak area of the protons in the vinyl groups at the chemical shift of δ=5.8 and δ=6.25 ppm, relative to the carbohydrate methyl protons in the hyaluronic acid backbone at δ=3.2-4.2 ppm. Each vinyl group peak corresponds to one proton and the peaks corresponding to the hyaluronic acid backbone correspond to 10 protons. FIG. 2 shows the .sup.1H NMR spectrum of MeCHa with a hyaluronic acid molecular weight of 50-90 kDa as a representative .sup.1H NMR spectrum of MeCHa. The multiplets at the chemical shifts of δ=6.7-7 ppm in the MeCHa spectrum correspond to the protons in ortho and meta coupling position of the phenyl ring of Dopa and multiplet signals at δ=2.87 ppm and δ=3.22 ppm correspond to the protons of the aliphatic ethylene group. The grafting degree of Dopa per unit of hyaluronic acid was evaluated by comparison of the integrated peak areas of aromatic protons of Dopa at the chemical shift of 6.7-7.5 ppm relative to the carbohydrate methyl protons in the hyaluronic acid backbone at δ=3.2-4.2 ppm. The sharp peak at the chemical shift of 4.79 ppm in the NMR spectra is associated with D.sub.2O.

[0090] From the .sup.1H NMR analysis, the successful methacrylation and Dopa conjugation of the polymer backbone can be observed and a 26% methacrylation degree can be determined. As indicated in Scheme 1, the primary alcohol in hyaluronic acid is functionalized by the methacrylic anhydride. Since only the primary alcohol is considered reactive towards methacrylic anhydride, the degree of functionalization is determined only with respect to the primary alcohol functional groups of hyaluronic acid. The same procedure was performed for MeCHa polymer that was synthesized with a high methacrylation degree (approaching 99%, molecular weight of 50-90 kDa, hereinafter “˜100% MeCHa 50-90 kDa”). The degree of functionalization with Dopa was about 15%. Since only the carboxylic acid group is considered reactive towards Dopa, the degree of functionalization is determined only with respect to the carboxylic acid functional groups of hyaluronic acid.

[0091] Thus, the following hydrogels were synthesized with the hydrogels using PEGDMA, NFC-PEGDMA-alginate, and the only methacrylated hyaluronice acid being comparative examples:

TABLE-US-00001 TABLE 1 Hydrogels prepared Molecular weight of cross-linkable cross- Degree of Hydrogel polymer linkable functional- name (concentration) polymer ization Additives PEGDMA* PEGDMA (4.8 20 kDa NA NA wt. %] NFC-PEGDMA- PEGDMA (4.8 wt 20 kDa NA 0.5 vol. % NFC alginate* fibers; 0.55 wt % alginate 26% Hyaluronic acid 50-90 kDa 26% NA Methacrylated functionalized methacryloyl HA 50-90 kDa* by reaction with methacrylic anhydride 26% MeCHa Hyaluronic acid 50-90 kDa 26% NA 50-90 kDa functionalized methacryloyl; by reaction with 15% Dopa methacrylic anhydride and by reaction with dopamine ~100% Hyaluronic acid 50-90 kDa Approximately NA Methacrylated functionalized 99% HA 50-90 kDa* by reaction with methacryloyl methacrylic anhydride ~100% MeCHa Hyaluronic acid 50-90 kDa Approximately NA 50-90 kDa functionalized 99% by reaction with methacryloyl; methacrylic approximately anhydride and 15% Dopa by reaction with dopamine *= comparative example; NA = not applicable

Swelling Ratio and Water Content

[0092] All hydrogels are synthesized with a PBS buffer content of 95.2% except for the NFC-PEGDMA-alginate hydrogels that had a buffer content of 94%. FIG. 3 demonstrates the swelling behaviour of the hydrogels in both PBS and distilled water. The PEG-dimethacrylate based hydrogels present high swelling ratios. It should be noted that PEGDMA-based hydrogels with higher molecular weights display higher swelling ratios (not shown), presumably because the lower crosslink density and network configuration lead to higher chain mobility.

[0093] The methacrylated HA hydrogels generally show lower swelling ratios than PEGDMA-based hydrogels. However, the swelling is conspicuously higher in distilled water than in PBS for both PEGDMA-based and methacrylated HA hydrogels. The MeCHa-Gels present a much lower swelling ratio than the other hydrogel systems. For MeCHa with high methacrylation degree, the swelling ratio is quite negligible.

[0094] The synthesized hydrogels swell by a wide range and a slight shrinkage is also observed in methacrylated HA hydrogels with higher methacrylation degree. This implies that the swelling ratio of MeCHa-Gel can be tuned by alternating the modification degree, crosslink density and network configuration.

Mechanical Stiffness

[0095] To investigate the potential of the hydrogel design for tunable elastic performance, the mechanical stiffness of the synthesized hydrogels was evaluated and compared. For hydrogels based on functionalized hyaluronic acid, only the samples with a molecular weight of the hyaluronic acid of 50-90 kDa were investigated. The values are reported for the hydrogels in swollen state (in PBS and D-water). Hydrogels were compressed to 20% strain with a constant rate of 0.15 mm.Math.s.sup.−1.

[0096] The MeCHa-Gel has a conspicuously higher compression modulus than the PEGDMA and the composite PEGDMA hydrogels. It was found that the swollen MeCHa shows a much higher stiffness even than dry PEGDMA-based hydrogels. It is believed that the significant increase of the elastic modulus is achieved by the controllable cross-link density and chains configuration. FIG. 4 demonstrates the effect of methacrylation degree and Dopa conjugation on the mechanical stiffness of the synthesized hydrogel. It is observed that there is a dramatic increase in the elastic modulus of the hydrogel with the high methacrylation degree of backbone (˜1 MPa). Moreover, while the modified hydrogels with low methacrylation degree (26%) are stiffer than PEGDMA-based hydrogels, they present significantly lower elastic moduli than hydrogels with high degree of methacrylation. Although the hydrogel sample 100% MeCHa 50-90 kDa with a high methacrylation degree has comparatively a very high stiffness, it shows a lower value than that of the methacrylated HA hydrogel without Dopa modification. On the other hand, there is a slight difference between the elastic moduli of the low methacrylated HA hydrogels (26%) with/without Dopa modification (samples 26% Methacrylated HA 50-90 kDa and 26% MeCHa 50-90 kDa). Moreover, it is observed that all swollen hydrogels demonstrate a higher stiffness in distilled water than in PBS (PH=7.4), while they present even higher swelling in distilled water.

Cartilage-MeCHa-Gel Adhesion

[0097] To evaluate the adhesion performance of the synthesized hydrogel, a tissue-hydrogel adhesion test for various hydrogels with high water content of 95.2 wt. % was performed. For hydrogels based on functionalized hyaluronic acid, only the samples with a molecular weight of the hyaluronic acid of 50-90 kDa were investigated. FIG. 5 shows the adhesion strength of the synthesized PEGDMA-based hydrogels, methacrylated HA and MeCHa-Gel on bovine articular cartilage. The stiff and adhesive MeCHa-Gel (sample 100% MeCHa 50-90 kDa) has a significant increase in adhesion strength. It is believed that this is due to the attachment of a polymeric network containing both covalent crosslinks and adhesive components on the polymer backbone chains, which enable the hydrogel to be covalently attached to the tissue surface, without any surface modification, and also form a stiff network with covalent crosslinking. As a single network hydrogel, MeCHa-Gel presents a much higher adhesion than other single network hydrogels with the same water content, for example the sample PEGDMA or the sample 26% Methacrylated HA 50-90 kDa. In addition, the MeCHa-Gel is considerably more adhesive to the tissue than the composite double-network hydrogels (sample NFC-PEGDMA-alginate).

[0098] It appears that both the interfacial bonds and the bulk properties of the hydrogel are the significant contributing factors in order to achieve a high adhesive contact. The critical role of the adhesive component (Dopa) can be seen by comparing the adhesion between the samples 26% Methacrylated HA 50-90 kDa and 26% MeCHa 50-90 kDa. It shows the potential of the adhesive component for creating strong interfacial interactions. On the other hand, these interactions cannot present a high adhesion strength for a hydrogel with low mechanical stiffness (compare samples 26% MeCHa 50-90 kDa and 100% MeCHa 50-90 kDa). Indeed, both interfacial interactions and bulk mechanical properties appear to be required to be acting in concert for an adhesive hydrogel system.

[0099] The hydrogels according to the invention have several advantages: very low and tunable swelling, very high stiffness and unprecedented adhesion performance, all with high water content (95.2 wt %). Moreover, the hydrogels according to the invention show high adhesion while they may have a single network structure. The high adhesion is obtained without the need for a surface modification.

[0100] With the invention, a hydrogel with good adhesive properties and tunable bulk properties through can be prepared. The hydrogels according to the invention allow to combine a high stiffness and good adhesion with unique bulk and adhesive properties including adhesion in high water content, high stiffness and tunable swelling behavior.