AU2015207764A1 - Method of making a hydrogel, hydrogel and formulation for carriers and/or substitute of connective tissues obtained using such method - Google Patents

Description

METHOD OF MAKING A HYDROGEL, HYDROGEL AND FORMULATION FOR CARRIERS AND/OR SUBSTITUTE OF CONNECTIVE TISSUES OBTAINED USING SUCH METHOD

Field of the Invention

[0001 ] The present invention generally finds application in the field of biomaterials for implantation in the human body and namely relates to a method of making a hydrogel.

[0002] The invention also relates to a hydrogel and a formulation comprising such hydrogel, which are designed for use as carriers and/or substitute of connective tissues of autologous, homologous, heterologous, synthetic origin.

Background art

[0003] Biomaterials are known to be transplanted in the human body for regeneration/substitute of of certain tissue types after traumas or certain pathological conditions.

[0004] As a rule, such biomaterials may be of synthetic origin or derive from biological materials and may be transplanted in the body by means of surgery or injection in the region concerned by the disease or the trauma.

[0005] Namely, the main purpose of these biomaterials is to replace the extracellular matrix of connective tissues, and promote regeneration of the damaged tissue by supporting and inducing cell proliferation, possibly in response to certain mechanical stimuli from within or outside the body.

[0006] These biomaterials include, amongst others, hydrogels based on polymers that can be solubilized and/or hydrated in aqueous solutions, and are polymerized and sterilized by γ or β radiation. Water- soluble polymers may have different molecular weights according to their degree of polymerization, i.e. the number of basic units that compose their chemical structure.

[0007] Particularly, the final viscosity of the aqueous solution, and hence that of the desired gel, is given by the molecular weight of water- soluble polymers in direct proportion, according to the Mark-Houwink equation, which is as follows:

[η]=ΚΜ³

[0008] where [η] is the viscosity of the solution, K is the direct proportionality constant, M is the molecular weight of tehe polymer, a is a parameter associated with the polymer-solvent interaction.

[0009] Nevertheless, the main drawback of these materials is the degree of polymerization obtained upon irradiation is not easily controllable.

[0010] The difficulty in controlling polymerization causes difficulty in regulating the viscosity of the biomaterial, and hence reduces the ability to predict its physico/chemical behavior versus the tissue in which it is implanted.

[0011 ] Generally, these hydrogels have lower mechanical properties than the extracellular matrix, which limits proliferation of implanted cells and thus causes only partial tissue regeneration.

[0012] In an attempt to obviate these drawbacks, hydrogels have been developed which comprise, in addition to the above mentioned water- soluble polymers, additional components designed to limit the polymerization process after irradiation.

[0013] US5540033 discloses a PEO (polyethylene oxide)-based hydrogel comprising a polymerization inhibitor agent selected from the group comprising ascorbic acid and its derivatives.

[0014] Particularly, ascorbic acid allows sequestration of free radicals formed upon irradiation, thereby delaying polymerization reactions of polyethylene oxide (PEO) molecules.

[0015] Nevertheless, a first drawback of these materials is that the use of ascorbic acid and/or its derivatives in combination with PEO only delays polymerization, and hence viscosity is not constantly regulated.

[0016] As a result, this hydrogel tends to change its mechanical properties with time upon the action of biological tissues or the adhesion and proliferation of cells and other biological material on its surface.

[0017] A further drawback is that the use of these particular types of components provides a hydrogel having some consistency, but unsuitable for injection using syringes or similar instruments.

[0018] Finally, a serious drawback is that the viscosity of the material before and after irradiation may change considerably, and this will require repeated actions on the hydrogel composition before implantation.

Disclosure of the invention

[0019] The object of the present invention is to overcome the above drawbacks, by providing a method of making a hydrogel, as well as a hydrogel and a formulation for carriers and/or substitute of connective tissues that are highly efficient and relatively cost-effective.

[0020] A further object of the present invention is to provide a hydrogel and a formulation for carriers and/or substitute of connective tissues that allow viscosity to remain substantially constant over time.

[0021 ] Another object of the present invention is to provide a hydrogel and a formulation for carriers and/or substitute of connective tissues whose mechanical and chemical properties are suitable to enhance cell proliferation.

[0022] Also, a further object of the present invention is to provide a hydrogel and a formulation for carriers and/or substitute of connective tissues whose mechanical and chemical properties are substantially similar to those of the extracellular matrix of the tissues to be reintegrated.

[0023] Another object of the present invention is to provide a method of making a hydrogel, a hydrogel and a formulation for carriers and/or substitute of connective tissues that can provide implantable products having differentiated consistencies.

[0024] These and other objects, as more clearly explained hereafter, are fulfilled by a method of making a hydrogel as defined in claim 1 .

[0025] In a further aspect, the invention relates to a hydrogel and a formulation for carriers and/or substitute of connective tissues as defined in claims 1 0 and 1 2 respectively.

[0026] With these characteristics, a controllable-viscosity hydrogel may be obtained, which may act as a support for the growth of substitute of cells for damaged biological tissues, while mimicking the mechanical properties of the extracellular matrix.

[0027] Advantageous embodiments of the invention are as defined in the dependent claims.

Brief description of the drawings

[0028] Further features and advantages of the invention will be more readily apparent upon reading of the detailed description of a non- limiting embodiment of a method of making hydrogels, a hydrogel and a formulation for carriers and/or substitute of connective tissues, which are shown as a non limiting example with the help of the annexed figures, in which:

FIGURES 1 to 4 show diagrams of the consistency and/or viscoelasticity curves of a first hydrogel sample with a water-soluble polymer having a first molecular weight;

FIGURES 5 and 6 show diagrams of the consistency and/or viscoelasticity curves of a second hydrogel sample with the same water- soluble polymer as that of Figures 1 to 4, with a second molecular weight, different from the first;

FIGURES 7 to 1 0 show diagrams of the consistency and/or viscoelasticity curves of a third hydrogel sample with a second water-soluble polymer having a molecular weight different from the first two.

Detailed description of a few preferred embodiments

[0029] The present invention addresses a method of making a hydrogel designed for use as a carrier and/or substitute of connective tissue.

[0030] A hydrogel obtained using the method of the invention may be advantageously directly implanted in situ in the human body, due to its high biocompatibility and its virtual non-toxicity to the biological tissues to be regenerated.

[0031 ] Particularly, the method may provide a hydrogel that can mimic the structure of the extracellular matrix for connective tissue regeneration.

[0032] In its basic form, the method comprises a step of providing a predetermined amount of an aqueous solution, a step of adding a predetermined amount of a polymerization regulator agent in the aqueous solution, for regulating the polymerization of a first electromagnetic radiation- polymerizable water-soluble polymer and a step of adding, hydrating and/or solubilizing a predetermined amount of the first water-soluble polymer in the aqueous solution.

[0033] Preferably, the aqueous solution may be selected from the group comprising PBS or other buffered salines.

[0034] The use of PBS will allow the operating pH to be maintained at a value substantially close to the physiological value of 7.4, such that the hydrogel also has a pH compatible with that of the body.

[0035] Conveniently, the amount of the first water-soluble polymer is selected according to the volume of the aqueous solution and the final amount of

hydrogel to be obtained, to prevent saturation of the solution, and formation of precipitates that might alter the final physico/chemical properties of the hydrogel.

[0036] Furthermore, the step of adding, hydrating and/or solubilizing the first water-soluble polymer in the aqueous solution may be speeded up using well-known processes, such as magnetic stirring, mechanical stirring or heating of the aqueous solution.

[0037] The steps of adding the regulator agent and the first water- soluble polymer provide a homogeneous aqueous solution mixture.

[0038] This solution may have a predetermined concentration of the first water-soluble polymer, designed to provide homogenous solubilization and prevent the occurrence of precipitates or floes.

[0039] Furthermore, the hydration and/or solubilization step may be carried out through repeated additions of partial amounts of the first water- soluble polymer, in view of speeding up the process and providing a homogeneous mixture.

[0040] The step of adding the first water-soluble polymer is followed by a step of applying an electromagnetic radiation of predetermined frequency to the mixture, for achieving polymerization of the first polymer with a predetermined viscosity, and for obtaining a sterile hydrogel.

[0041 ] Advantageously, the electromagnetic radiation allows a radical rearrangement reaction to be activated on the molecules of the first water-soluble polymer, to promote reaction among the molecules and hence their polymerization.

[0042] Preferably, the electromagnetic radiation applied to the mixture may have a frequency that falls in the range of ionizing radiations, preferably close to the frequency spectrum of β rays.

[0043] The electromagnetic radiation of type β may be applied to the mixture for the latter to have an average radiation-absorbed dose of 25 KGy.

[0044] Furthermore, the electromagnetic radiation of type β will also promote sterilization of the mixture, to eliminate any risk of bacterial or viral infection upon implantation of the hydrogel.

[0045] Advantageously, the step of applying the electromagnetic radiation may be preceded by a step of combining the mixture with biological material of the substitute of connective tissue type, such that the latter may be sterilized upon irradiation.

[0046] According to a peculiar aspect of the invention, a second radiation-polymerizable water-soluble polymer, which is different from the first and non-reactive to the regulator, is added to the aqueous solution before application of the electromagnetic radiation to obtain a sterile hydrogel.

[0047] Particularly, the amount of the regulator agent relative to the first water-soluble polymer and the amount of the second polymer are selected to allow control the final consistency and viscosity of the sterile hydrogel.

[0048] Conveniently, long-lasting control of the viscosity of the hydrogel is essential to obtain a biomaterial whose chemical, physical and mechanical properties are substantially identical to those of the extracellular matrix to be replaced.

[0049] In the case of water-soluble polymers, the consistency and viscolaesticity values of the hydrogel obtained at the end of the process are related to the degree of polymerization of the polymer, i.e. the number of monomers that compose the polymer chain, and to the molecular weight of the polymer.

[0050] Particularly, as the number of monomers that form the chains increases, the degree of polymerization also increases, and provides high consistency and viscoelasticity values of the final product.

[0051] Advantageously, the regulator agent is adapted to regulate the degree of polymerization of the first water-soluble polymer and hence, indirectly, the final consistency and viscoelasticity of the hydrogel.

[0052] Furthermore, the second water-soluble polymer will be selected in view of being fully polymerized upon application of the electromagnetic radiation.

[0053] This method, particularly due to the combined effect of the regulator agent and the second water-soluble polymer, will provide a hydrogel having constant controlled consistency and viscoelasticity with time.

[0054] A hydrogel obtained using the method of the present invention may be an ideal medium for proliferation of substitute of connective tissue cells that can mimic the mechanical properties of the extracellular matrix.

[0055] Conveniently, the regulator agent may be selected from the group comprising ascorbic acid and its derivatives and may be adapted to reduce the degree of polymerization of the first water-soluble polymer as its concentration in the mixture increases, as shown by the diagrams of the figures.

[0056] As is known in the art, ascorbic acid, or vitamin C, generally acts as an antioxidant, by sequestering the free radicals formed as a result of certain electrochemical reactions.

[0057] Advantageously, in the method of the present invention, ascorbic acid and/or its derivatives sequester the radical species of the first water-soluble polymer formed upon application of the electromagnetic radiation, thereby fostering limitation of the polymerization process and the final degree of polymerization of the hydrogel. [0058] Thus, if such radical species of the water-soluble polymer were not sequestered by ascorbic acid, they might keep on reacting with one another and continue their polymerization process.

[0059] Of course, the regulator agent may also be different from ascorbic acid and its derivatives and may be particularly selected from the group comprising carotenoids, lipoic acid, vitamins E, D, B and glutathione, which also have similar antioxidative effects to the radical species.

[0060] Advantageously, the concentration of the regulator agent in the mixture may be maintained at a value of 100 imM or less.

[0061] Particularly, such ascorbic acid concentration will promote post-irradiation protection to the biological material combined with the mixture.

[0062] Nevertheless, a regulator concentration of 2 imM was also experimentally found to be sufficient to modulate and control the degree of polymerization of the first water-soluble polymer, and hence the final viscosity of the hydrogel.

[0063] Advantageously, the first water-soluble polymer may be selected from a first group comprising polyethylene glycol (PEG) to obtain an injectable hydrogel.

[0064] The polyethylene glycol (PEG) suitable for preparation of the hydrogel may have a molecular weight ranging from 10 K g/mol to 100 Kg/mol, preferably from 10 Kg/mol to 40 Kg/mol.

[0065] Particularly suitable polyethylene glycol (PEG) types may have molecular weights of 10 Kg/mol, 20 Kg/mol and 35 Kg/mol respectively.

[0066] The use of these types of polyethylene glycol (PEG), in combination with the regulator agent and the second water-soluble polymer, will provide a hydrogel that may have suitable consistency and viscoelasticity values for an injectable preparation.

[0067] Alternatively, the first water-soluble polymer may be selected from a second group comprising polyethylene oxide (PEO) to obtain a substantially semisolid hydrogel.

[0068] The polyethylene oxide (PEO) suitable for preparation of the hydrogel may have a molecular weight ranging from 1 00 Kg/mol to 1 000 Kg/mol, preferably from 1 00 Kg/mol to 600 Kg/mol.

[0069] Advantageously, suitable polyethylene oxide (PEO) types may have molecular weights of 100 Kg/mol, 200 Kg/mol, 400 Kg/mol and 600 Kg/mol respectively.

[0070] The use of these types of polyethylene oxide (PEO), in combination with the regulator agent and the second water-soluble polymer, will provide a hydrogel with higher consistency and viscoelasticity values than the first hydrogel.

[0071 ] Conveniently, the weight percent of the first water-soluble polymer may range from 1 % to 20% based on the total weight of the hydrogel.

[0072] Particularly, the weight percent of polyethylene glycol (PEG) polymer in an injectable preparation may range from 5% to 1 5% based on the total weight of the hydrogel.

[0073] Alternatively, the weight percent of polyethylene oxide (PEO) polymer may range from 2% to 1 0% based on the total weight of the hydrogel.

[0074] Advantageously, the second water-soluble polymer may be selected from the group comprising cellulose derivatives such as hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), ethyl cellulose (EC), methyl cellulose (MC) or the like.

[0075] The use of cellulose derivatives promotes constant control of hydrogel viscosity, and prevents their solubilization from interfering with the solubilization of the first water-soluble polymer.

[0076] Furthermore, polymerization of cellulose monomers, particularly for low-concentration solutions, mainly occurs by an esterification reaction which is not affected by ascorbic acid or its derivatives and other anti-oxidant agents as regulator agents.

[0077] For this reason, cellulose polymers are inert to the regulator agent, and their polymerization continues independent of the polymerization of the first water-soluble polymer. [0078] Nevertheless, polymerization of cellulose polymers may be affected and/or limited by intermolecular steric hindrance by the chains of the first water-soluble polymer, whose degree of polymerization is modulated by ascorbic acid and/or its derivatives.

[0079] Preferably, the weight percent of the second water-soluble polymer may range from 0.1 % to 1 0%, preferably from 0.5% to 5% based on the total weight of the hydrogel.

[0080] Of course, the use of cellulose as the second water-soluble polymer shall be intended by way of example and without limitation, as cellulose may be replaced by other water-soluble polymers having equivalent viscoelastic properties.

[0081 ] In a further aspect, the invention relates to a hydrogel designed for use as a carrier and/or a substitute of connective tissue, which comprises an aqueous solution, a first polymer polymerized in an aqueous solution and a predetermined amount of the regulator agent for regulating the degree of polymerization of the first polymer in the aqueous solution.

[0082] A peculiar aspect of this hydrogel is that it comprises a predetermined amount of a second water-soluble polymer which is different from the first and is inert to the regulator agent.

[0083] Furthermore, the amounts of the regulator agent and the second water-soluble polymer are selected to allow control of the final consistency and viscosity of the sterile hydrogel.

[0084] Advantageously, the first water-soluble polymer may be selected from the group comprising polyethylene glycol (PEG) or polyethylene oxide (PEO), whereas the regulator agent may be selected from the grout comprising ascorbic acid and its derivatives.

[0085] Furthermore, the second water-soluble polymer may be selected from the group comprising cellulose derivatives such as hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC) or the like.

[0086] This hydrogel may have different consistency and viscoelasticity values according to the type of first water-soluble polymer in use and to the amount of regulator agent that has been added during its preparation.

[0087] Particularly, a hydrogel comprising polyethylene glycol (PEG) may have low consistency and viscoelasticity, and may be used as a carrier and/or an injectable substitute of connective tissue, whereas a hydrogel comprising polyethylene glycol (PEO) may have relatively high consistency and viscoelasticity and may be adapted for use as a carrier and/or a semisolid pre-formed substitute of connective tissue.

[0088] Also, in a further aspect, the invention relates to a formulation designed for use as a carrier for cells and/or connective tissues of autologous, heterologous or synthetic origin and/or bioactive molecules.

[0089] Particularly, the cells may be bone and/or cartilage tissue cells of equine origin.

[0090] The bioactive molecules may be selected from the group comprising growth factors, drugs or bacteriocins.

[0091 ] It shall be understood that the formulation may comprise cells different from those mentioned above, derived from non-bone tissues of autologous, homologous or synthetic origin.

[0092] Two examples of two different hydrogel compositions of the invention are provided below.

EXAMPLE 1

Preparation of a polyethylene glycol (PEG)-based hydrogel and analysis of the consistency and viscoelasticity of the hydrogel

[0093] The hydrogel was prepared by first providing a predetermined volume of an aqueous solution, which depends on the final desired amount and weight of the hydrogel.

[0094] The aqueous solution preferably consisted of a Phosphate Buffered Saline (PBS) at 1 X concentration.

[0095] Predetermined amounts of ascorbic acid and/or its derivatives were later solubilized in PBS by magnetic stirring using an ARGOLAB M2-A stirrer in a beaker at 300 rpm for 1 0 min or to full solubilization of ascorbic acid and/or its derivatives. [0096] Then, the solid components, particularly the water-soluble polymers to be later dissolved in the aqueous solution, were weighed.

[0097] Particularly, two different samples were prepared, referred to as LMW 35K and LMW 20K, which comprise two types of polyethylene glycol (PEG) whose molecular weights are 35K g/mol and 20K g/mol respectively. Then, a constant amount of hydroxypropyl methylcellulose (HPMC) was added to both samples.

[0098] The weight ratio of polyethylene glycol (PEG) to hydroxypropyl methylcellulose (HPMC) was substantially maintained at a value of 15:1 or less.

[0099] Then the two polymers (PEG and HPMC) were added slowly using a spatula.

[00100] While polymers were being added, the solution was maintained under stirring in a beaker using a fixed-blade column stirrer (ARGOLAB AM20-D) at 300 rpm. The mixture was stirred for 24 h or to full hydration of the polymers.

[00101 ] Different ascorbic acid concentrations were used for each of the two samples, such that their effect on the final consistency and viscoelasticity of the hydrogel could be assessed.

[00102] After solubilization of the polymers, the mixture so obtained was distributed in appropriate plastic or glass containers, or combined with substitute of connective tissues.

[00103] Later, the mixture was irradiated with electromagnetic radiation of type β to promote ascorbic acid-mediated polymerization of the polyethylene glycol (PEG) and hydroxypropyl methylcellulose (HPMC).

[00104] The samples so obtained underwent a test for measuring consistency and viscoelasticity using the Stable Micro Systems TA.XT Plus texture analyzer.

[00105] Particularly, the samples were placed in cylindrical plastic glasses and a compression and relaxation test was carried out using an appropriate cylindrical probe P25.

[00106] The test consists in causing a probe to slide in the hydrogel to a fixed distance of 1 0 mm at a constant speed of 0.5 mm/s, and, after 1 20 seconds waiting time, monitoring relaxation of the sample.

[00107] The measure of the compression resistance force when 10 mm have been covered provides quantification of the viscoleasticity of each sample.

[00108] The viscosity values of both samples LMW 35K and LMW 20K and their different compositions are set forth in Table and Table II below.

The values of Table I are represented in the charts of FIGS. 1 -4, whereas the values of the samples 10NS and 1 0S of Table II are represented in the charts of FIGS. 5, 6.

Table I

[00109] The words "NON STERILE" and "STERILE" designate the samples before and after application of the electromagnetic radiation respectively. [00110] The tables and charts show that the addition of increasing concentrations of ascorbic acid limits the consistency and viscoelasticity of the hydrogel upon application of the electromagnetic radiation.

[00111 ] Without ascorbic acid, viscosity tends to reach very high values, due to the higher degree of polymerization of polyethylene glycol (PEG), and injectability of the hydrogel is not ensured.

[00112] Furthermore, it will be appreciated that, for both preparations comprising polyethylene glycol (PEG), viscosity is substantially unchanged before and after application of the electromagnetic radiation due to the effect of ascorbic acid at 1 imM concentration.

EXAMPLE 2

Preparation of a polyethylene oxide (PEO)-based hydrogel and analysis of the consistency and viscoelasticity of the hydrogel

[00113] The hydrogel was prepared by first providing a predetermined volume of an aqueous solution, which depends on the final desired amount and weight of the hydrogel.

[00114] The aqueous solution preferably consisted of a Phosphate Buffered Saline (PBS) at 1 X concentration.

[00115] Predetermined amounts of ascorbic acid and/or its derivatives were later solubilized in PBS by magnetic stirring using an ARGOLAB M2-A stirrer in a beaker at 300 rpm for 1 0 min or to full solubilization of ascorbic acid and/or its derivatives.

[00116] Then, the solid components, particularly the water-soluble polymers to be later dissolved in the aqueous solution, were weighed.

[00117] Particularly, a sample comprising polyethylene oxide (PEO) was prepared, whose molecular weight was 400 Kg/mol. Then, a constant amount of hydroxypropyl methylcellulose (HPMC) was added to the sample.

[00118] The weight ratio of polyethylene oxide (PEO) to hydroxypropyl methylcellulose (HPMC) was substantially maintained at a value of 15:1 or less.

[00119] Then the two polymers were added slowly using a spatula.

[00120] While polymers were being added, the solution was maintained under stirring in a beaker using a fixed-blade column stirrer (ARGOLAB AM20-D) at 1 00 rpm.

[00121 ] The mixture was stirred for 24 h or to full hydration of the polymers.

[00122] Different ascorbic acid concentrations were used such that their effect on the final consistency and viscoelasticity of the hydrogel could be assessed.

[00123] After solubilization of the polymers, the mixture so obtained was distributed in appropriate plastic or glass containers, or combined with substitute of connective tissues.

[00124] Later, the mixture was irradiated with electromagnetic radiation of type β to promote ascorbic acid-mediated polymerization of the polyethylene oxide (PEO) and hydroxypropyl methylcellulose (HPMC).

[00125] The samples so obtained underwent a test for measuring consistency and viscoelasticity using the Stable Micro Systems TA.XT Plus texture analyzer.

[00126] Particularly, the samples were placed in cylindrical plastic glasses and a compression and relaxation test was carried out using an appropriate cylindrical probe P25.

[00127] The test consists in causing a probe to slide in the hydrogel to a fixed distance of 1 0 mm at a constant speed of 0.5 mm/s, and, after 1 20 seconds waiting time, monitoring relaxation of the sample.

[00128] The measure of the compression resistance force when 10 mm have been covered provides quantification of the viscoleasticity of each sample.

[00129] The viscosity values of the samples and their different compositions are set forth in Table III below.

[00130] The values of Table III are represented in the charts of FIGS.

7-1 0. Table III

[00131] The tables and charts show that the addition of increasing concentrations of ascorbic acid limits and progressively reduces the consistency and viscoelasticity of the hydrogel upon application of the electromagnetic radiation.

[00132] Without ascorbic acid, viscosity tends to reach very high values, due to the higher degree of polymerization of polyethylene oxide (PEO).

[00133] The method, hydrogel and formulation of the invention are susceptible of many changes and variants within the inventive principle disclosed in the annexed claims.

Industrial Applicability

The present invention finds industrial application in the field of medical devices and biomaterials for therapeutic and medical/cosmetic use, and particularly in the field of biomaterials for implantation in the human body as substitute of connective tissues.

Claims (12)

1 . A method of making a hydrogel for use as a carrier and/or a substitute of connective tissue, comprising the steps of:

- providing a predetermined amount of an aqueous solution;

- adding a predetermined amount of a polymerization regulator agent to said aqueous solution, for regulating the polymerization of a first electromagnetic radiation-polymerizable water-soluble polymer;

- adding, hydrating and/or solubilizing a predetermined amount of said first water-soluble polymer in said aqueous solution, to obtain a mixture;

- adding, hydrating and/or solubilizing a second electromagnetic radiation-polymerizable water-soluble polymer, different from the first, in said mixture;

- applying an electromagnetic radiation of predetermined frequency to said mixture, for achieving polymerization of said first polymer and said second polymer with a predetermined viscosity, and for obtaining a sterile hydrogel;

characterized in that said second water-soluble polymer is non- reactive to said regulator agent and in that said second polymer has a degree of polymerization that varies according to the intermolecular steric hindrance of the chains of said first polymer, the amount of said regulator agent relative to said first polymer and the amount of said second polymer being selected to allow control of the final consistency and viscoelasticity of said sterile hydrogel.

2. A method as claimed in claim 1 , characterized in that said first water-soluble polymer is selected from a first group comprising polyethylene glycol (PEG) and has a molecular weight ranging from 10 Kg/mol to 1 00 Kg/mol, preferably from 1 0 Kg/mol to 40 Kg/mol, for said hydrogel to be of injectable type.

3. A method as claimed in claim 1 , characterized in that said first water-soluble polymer is selected from a second group comprising polyethylene oxide (PEO) and has a molecular weight ranging from 1 00 Kg/mol to 1 000 Kg/mol, preferably from 1 00 Kg/mol to 600 Kg/mol, for said hydrogel to be substantially semisolid and pre-formable.

4. A method as claimed in claim 2 or 3, characterized in that the weight percent of said first water-soluble polymer ranges from 1 % to 20% based on the total weight of the hydrogel.

5. A method as claimed in claim 1 , characterized in that said regulator agent is selected from the group comprising ascorbic acid and its derivatives, said regulator agent being adapted to reduce the degree of polymerization of said first water-soluble polymer as its concentration in the mixture increases.

6. A method as claimed in claim 1 , characterized in that the concentration of said regulator agent is 1 00 imM or less.

7. A method as claimed in claim 1 , characterized in that said second water-soluble polymer is selected from the group comprising cellulose derivatives such as hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), ethyl cellulose (EC), methyl cellulose (MC) or the like.

8. A method as claimed in claim 1 , characterized in that the weight percent of said second water-soluble polymer ranges from 0.1 % to 1 0%, preferably from 0.5% to 5% based on the total weight of the hydrogel.

9. A method as claimed in claim 1 , characterized in that said electromagnetic radiation has a frequency that falls in the range of ionizing radiations, and is preferably close to the frequency spectrum of β rays.

1 0. A hydrogel for use as a carrier and/or a substitute of connective tissue, comprising an aqueous solution, a first water-soluble polymer polymerized in said aqueous solution, a second water-soluble polymer, different from the first, and a predetermined amount of the regulator agent for regulating the degree of polymerization of said first polymer in said aqueous solution, characterized in that said second water-soluble polymer is non- reactive to the regulator agent and has a degree of polymerization that varies according to the intermolecular steric hindrance of the chains of said first water-soluble polymer, the amounts of said regulator agent and said second polymer being selected to allow control of the consistency and viscoelasticity of said hydrogel.

1 1 . A hydrogel as claimed in claim 10, characterized in that said first water-soluble polymer is selected from the group comprising polyethylene glycol (PEG) or polyethylene oxide (PEO), said regulator agent is selected from the group comprising ascorbic acid and its derivatives, and said second water-soluble polymer is selected from the group comprising cellulose derivatives such as hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC) or the like.

12. A formulation designed for use as a carrier for cells and/or connective tissues of autologous, heterologous or synthetic origin, and/or bioactive molecules, comprising a hydrogel as claimed in one of claims 10 and 1 1 or both.