Self-healing electroconductive hydrogels, their composition, uses, and methods of production

Abstract

The present disclosure relates to a pre-hydrogel composition for forming an electroconductive hydrogel of poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and gelatine, cross-linked with riboflavin, with the ability to self-heal, and recover its mechanical and electroconductive properties. The method for producing the hydrogel, as well as compositions for use in medicine comprising the pre-hydrogel, or hydrogel, described, are also disclosed. In particular, compositions for use in tissue engineering, controlled drug delivery, and / or for biosensors are disclosed.

Description

D E S C R I P T I O NSELF-HEALING ELECTROCONDUCTIVE HYDROGELS, THEIRCOMPOSITION, USES, AND METHODS OF PRODUCTIONTECHNICAL FIELD

[0001] The present invention relates to the synthesis of an electroconductive hydrogel made of poly (3,4- ethylenedioxythiophene) and poly (styrene sulphonate) (PEDOT:PSS) and gelatine, cross-linked with riboflavin and exposed to ultraviolet (UV) or blue light, which is capable of self-regeneration when exposed to a certain temperature range.BACKGROUND

[0002] Hydrogels are three-dimensional cross-linked networks of polymeric chains that have the ability to swell and absorb water and are insoluble in water. The degree of cross-linking of hydrogels dictates their mechanical properties, elasticity and physical integrity [Y. Sun et al. Sun et al., Polym. Test., 2020, 81, 106283; Y. Sekine et al., ACS Appl. Polym. Mater., 2020, 2, 5482-5491]. The swelling capacity of a hydrogel can be related to its degree of cross-linking, but also to the functional groups present in the polymer chains, such as hydroxyl and carboxylic acid groups [I. Corkovic et al., Foods, 2021, 10, 1252; S. Grijalvo et al., Gels, 2019, 5, 5020024].

[0003] Different hydrogels can be obtained by different synthesis methods, resulting in responsiveness to different stimuli according to the application in question [P. Kesharwani et al, J. Drug Deliv. Sci. Technol., 2021, 66,102914; C. Alvarez-Lorenzo et al, Int. J. Pharm., 2020, 579, 119157]. Hydrogels can be responsive to mechanical stress [Y. Peng et al., Macromol. Mater. Eng., 2021, 306, 2100309], pH [L. Xu et al, J. Mater. Chem. B, 2018, 6, 510-517; Y. Shin et al, Polymers, 2021, 13, 3197], temperature [J. Zhang, N.A. Peppas, Macromolecules, 1999, 33, 102-107; Y. Zhang et al., Biomacromolecules, 2019, 20, 1478-1492], and ionic concentration [S.A. Tayel et al., Int. J. Phar., 2013, 443, 293-305; S.R. Salunke, S.B. Patil, Int. J. Biol. Macromol., 2016, 87, 41-47]. Hydrogels can be highly biocompatible and have properties similar to human tissues that make them suitable for use in various biomedical applications, including drug delivery [L. Xu et al, J. Mater. Chem. B, 2018, 6, 510-517; Y. Shin et al, Polymers, 2021, 13, 3197; L. Wang et al, ACS Appl. Mater. Interfaces, 2021, 13, 58329- 58339], tissue engineering [Y. Zhang et al., Biomacromolecules, 2019, 20, 1478-1492], and wound healing [L. Wang et al, ACS Appl. Mater. Interfaces, 2021, 13, 58329- 58339; M.P. Ribeiro et al., Mater. Sci. Eng. C, 2013, 33, 2958-2966] . This last use is one of the most important biomedical applications of hydrogels today, as innovative solutions for wound treatment continue to be needed on the market. This is due to the high incidence of chronic wounds among patients as the geriatric population increases, associated with conditions that can favour their appearance, such as diabetes, obesity, and cancer [A. Gupta et al. Gupta et al, Eur. Polym. J., 2019, 111, 134-151; S. Meaume et al., J. Tissue Viabil., 2013, 22, 122-130; F. Quattrone et al., J. Tissue Viabil., 2013, 22, 112-121].

[0004] Gelatine has been explored for the synthesis of hydrogels with applications in skin tissue engineering and wound healing, since gelatine is a natural polymer obtainedfrom the hydrolysis of collagen, which is a constituent of the skin's extracellular matrix [A. Bigi et al. Bigi et al., Biomaterials, 2004, 25, 5675-5680; C.E. Campiglio et al., Materials, 2019, 12, 2476; S. Tavakoli, A.S. Klar. Biomolecules, 2020, 10, 1169]. However, gelatine has low mechanical strength and undergoes denaturation at relatively low temperatures (around 40 °C), with triple helices transitioning into individual coiled chains [D. Hardman et al., NPG Asia Mater., 2022, 14, 11]. Gelatine must therefore be modified to improve its properties so that it can be used in biomedical applications and electronic textiles without impairing the material at physiological temperatures of around 37 °C.

[0005] The use of electrostimulation through electroactive dressings is a promising strategy for skin regeneration, as the skin responds to electrical signals and has endogenous conductivity in the order of 0.01 mS / m [C. Korupalli et al., Adv. Healthcare Mater., 2021, 10, 2001384]. However, a zero electroconductivity value has been reported for gelatine hydrogels [Z.Qin et al., J. Mater. Chem. A, 2020, 8, 4447].

[0006] The application of an external electric field leads to the migration of skin cells such as fibroblasts [M.J. Brown, L.M. Loew, J. Cell Biol., 1994, 127, 117-128; Y. Wang et al. Wang et al, J. Tissue Eng. Reg. Medicine, 2017, 11, 1110-1121], keratinocytes [M. Zhao et al, Nature, 2006, 442, 457-460; K.S. Fang et al, J. Inv. Dermatol., 1998, 111, 751-756; A. Sebastian et al, J. Inv. Dermatol., 2015, 135, 1166-1174] and endothelial cells [G.P.A. Yen-Patton et al., J. Cell. Physiol., 1988, 134, 37-46; B. Song et al, Proceedings Nat. Acad. Sci. U.S.A., 2002, 99, 13577-13582] to the wound site, thus accelerating the regeneration ofskin tissue. However, the use of hydrogels as electroconductive dressings has not yet been explored due to their inferior mechanical properties, which make them fragile and prone to break.

[0007] On the other hand, there has been enormous growth in the flexible electronics market, particularly in flexible bioelectronics. To obtain a material that can interface between the human body and the electronic component, this material must have appropriate biocompatibility, mechanical, and electrical properties, and the poly (3,4- ethylenedioxythiophene ) and poly (styrene sulfonate) (PEDOT:PSS) mixture has been widely explored in this area [S. Zhang et al. Zhang et al., Adv. Mater., 2020, 32, 1904752; L.V. Kayser, D.J. Lipomi, Adv. Mater., 2019, 31, 1806133]. However, contrary to what would be desirable, PEDOT:PSS is mostly presented in the form of a brittle film and not as a hydrogel, although the latter is the most compatible form for interfacing with human tissues due to its high water content. However, PEDOT:PSS hydrogels that have been described in the literature have a Young's modulus of 1 kPa [S. Zhang et al., Adv. Mater., 2020, 32, 1904752]; and an elongation at break of less than 150%, while also containing a second synthetic polymer (polyvinyl alcohol) [L.V. Kayser, DJ Lipomi, Adv. Mater., 2019, 31, 1806133]. It is also known that PEDOT:PSS hydrogels can be obtained when mixed with other synthetic or non-synthetic polymers in aqueous solution.

[0008] The use of hydrogels for biomedical or flexible electronics applications requires attention to their self- healing properties, since when a material is applied to the human body it is subjected to various types of tension and pressure from the patient's movement, which can lead tofracture or breakage of the material, interrupting its therapeutic effect and requiring periodic replacement. As a result, there is a need to develop materials that are capable of self-regeneration through simple processes that are compatible with physiological conditions of use.

[0009] The cross-linking of a gelatine hydrogel, using riboflavin and UV radiation, has already been described, under conditions different from the present disclosure, but including glycerol as a dopant for gelation to occur, and without including PEDOT:PSS to give the material mechanical and electrical properties [J.M. Galdoporpora et al., Adv. Mater. Lett., 2019, 10, 324-328].

[0010] As for the electrical and electrochemical properties of PEDOT:PSS, document CN102621206A describes methods for preparing composites with PEDOT:PSS for applications in modified electrodes. However, they do not appear in the form of an elastic hydrogel and are not applicable in tissue engineering or bioelectronics.

[0011] Conversely, when the literature describes the development of PEDOT:PSS in hydrogel form, it is prepared with polyethylene terephthalate or polypropylene, which are synthetic polymers, and a solvent is added as a dopant (for example, dimethyl sulfoxide, ethylene glycol, dimethylformamide or tetrahydrofuran), an ionic liquid or a metal to increase the electrical conductivity as described in document CN109824915B. However, many of these compounds are toxic and hydrogels have a water absorption capacity of up to 140% of their mass. Owing to their lower capacity to absorb water, the hydrogels described in the literature lose their applicability at the interface with the human body. Furthermore, these hydrogels do not include self-healing properties .

[0012] Some methodologies for preparing PEDOT:PSS hydrogels with self-healing capacity do not include the use of gelatine to increase the hydrogel's biocompatibility, nor the use of cross-linking methodology using riboflavin and UV or blue radiation. As a result, these hydrogels have inferior mechanical properties, namely greater rigidity and less compatibility with the mechanical properties of biological tissues, with a Young's modulus of between 5 and 1000 MPa and an elongation at break of between 1 and 9% [Y. Li et al., Adv. Funct. Mater., 2020, 30, 2002853]. Other works have explored methodologies even more complex or limited than the present invention for achieving self-healing, as they use high temperatures, the application of pressure or electricity, and the addition of water in conjunction with high pressure and / or temperature [S. Zhang et al. Zhang et al., Adv. Mater., 2020, 32, 1904752; Y. Li et al., Adv. Funct. Mater., 2020, 30, 2002853; Y. Kikuchi et al, ACS Appl. Biomater., 2020, 3, 2507-2515].

[0013] These facts are described in order to illustrate the technical problem solved by the realisations in this document.GENERAL DESCRIPTION

[0014] This publication concerns the production of an electroconductive hydrogel made of poly (3,4- ethylenedioxythiophene ):poly (styrene sulphonate) (PEDOT:PSS) and gelatine, cross-linked with riboflavin, with the capacity to self-heal and recover its mechanical and electroconductive properties. This material has the potential to be used in biomedical applications, such as tissue engineering, and bioelectronics, such as sensors or electronic textiles.

[0015] In one embodiment, the present disclosure relates to obtaining an electroconductive hydrogel of PEDOT:PSS and gelatine, cross-linked with riboflavin and exposed to UV or blue light, preferably light with a wavelength between 200 and 500 nm, with the ability to self-heal when exposed to a certain range of temperatures between 0 °C and 110 °C, including preferably temperatures below 70 °C, most preferably 37 °C.

[0016] In one form, the composition of the hydrogel comprises 2-30% (w / v) gelatine, preferably 15% (w / v); a concentration of riboflavin between 5 mM and 750 mM, preferably 211 mM; and a concentration of 0.1-10% (w / w) PEDOT:PSS, preferably 1.3% (w / w), where the mass ratio between PEDOT and PSS varies from 1:10 to 2:1, preferably 1:2.5.

[0017] In the market for supports for biomedical applications, such as electroconductive patches, and in the flexible electronics market, such as bioelectronic interfaces, there is a difficulty in associating the biocompatibility characteristics of hydrogels, synthesised from compounds of non-synthetic origin, with more robust mechanical properties that are compatible with human tissues, and also in associating electroconductive properties with the capacity for self-healing under physiological conditions in the same material. The present disclosure includes the characteristics of high biocompatibility, mechanical properties compatible with human tissues, electroconductive properties compatible with electroactive tissues and the ability to self-heal under physiological conditions and over a wide range of temperatures .

[0018] The present disclosure describes a pre-hydrogel composition for forming an electroconductive and self- healing hydrogel, characterised by comprising: 0.1 to 10% (w / w) of a mixture of poly (3,4-ethylenedioxythiophene) and poly(styrene sulfonate); 2 to 30% (w / v) gelatine, preferably unmodified gelatine; and 5 to 750 mM riboflavin, wherein the composition is cross-linkable after exposure to UV light or blue light, preferably after exposure to light with a wavelength between 200 and 500 nm.

[0019] In one embodiment, the composition consists of 0.1 to 10% (w / w) of a mixture of poly(3,4- ethylenedioxythiophene) and poly (styrene sulphonate); 2 to 30% (w / v) gelatine, preferably unmodified gelatine; 5 to 750 mM riboflavin; and optionally an active compound.

[0020] In one embodiment, the composition comprises 1.3 to 2% (w / w) poly (3,4-ethylenedioxythiophene) and poly(styrene sulphonate); 15 to 20% (w / v) gelatine; and 211 to 230 mM riboflavin.

[0021] In one embodiment, the mass ratio between poly (3,4-ethylenedioxythiophene) and poly (styrene sulphonate) ranges from 1:10 to 2:1, preferably 1:2.5.

[0022] In one embodiment, the gelatine is type A gelatine.

[0023] The present disclosure also relates to an electroconductive and self-healing hydrogel characterised by comprising the disclosed composition.

[0024] In one embodiment, the hydrogel is selfregenerating at a temperature ranging from 0 to 100 °C, preferably from 35 to 70 °C, most preferably at 37 °C.

[0025] In one embodiment, the hydrogel has an electroconductivity of at least 0.1 mS / m. In anotherembodiment, the electroconductivity varies from 0.1 mS / m to 420 mS / m, preferably between 190 mS / m and 420 mS / m.

[0026] In one embodiment, the hydrogel has a Young's modulus of at least 10 kPa. In another embodiment, the hydrogel has a Young's modulus of between 10 and 100 kPa.

[0027] In one embodiment, the hydrogel has a breaking elongation capacity of at least 200%.

[0028] In one embodiment, the hydrogel has a water absorption capacity of 600% of its mass.

[0029] The present disclosure further describes a method for preparing an electroconductive and self-healing hydrogel from the pre-hydrogel composition described, characterised by comprising the following steps: preparing an aqueous polymer solution comprising a mixture of poly (3,4- ethylenedioxythiophene ) and poly (styrene sulfonate), and riboflavin; increasing the pH of the aqueous polymer solution until the riboflavin is completely dissolved; dissolving gelatine in the aqueous polymer solution with riboflavin in order to obtain a pre-hydrogel; cross-linking the pre-hydrogel by exposure to UV light or blue light to obtain the hydrogel.

[0030] In one embodiment, the composition is crosslinkable after exposure to light with a wavelength between 200 and 500 nm.

[0031] In one embodiment, the pH of the aqueous polymer solution is increased to a pH of at least 12.5.

[0032] In one embodiment, the aqueous polymer solution of poly (3,4-ethylenedioxythiophene) and poly (styrene sulphonate) has a concentration of 0.1 to 10% (rnpoiymer / mtotai), preferably 1.3 to 1.5% (rnpoiymer / mtotai).

[0033] In one embodiment, the pre-hydrogel is crosslinked by exposure to light for at least 30 minutes, preferably 35 to 45 minutes.

[0034] In one embodiment, the pre-hydrogel is crosslinked with light with a wavelength ranging from 350 to 500 nm, preferably 366 nm.

[0035] The present disclosure further describes a composition comprising the disclosed hydrogel, or the disclosed pre-hydrogel composition, characterised in that it is for use in medicine.

[0036] In one embodiment, the composition is administered in the form of a transdermal patch, compress or bandage.

[0037] In one embodiment, the composition is for use in tissue engineering, controlled drug delivery, and / or biosensors.

[0038] In one embodiment, the composition is for use in skin regeneration.

[0039] One aspect of the present disclosure relates to the use of a composition comprising the disclosed hydrogel, or the disclosed pre-hydrogel composition, in textiles or electronic sensors.

[0040] The present disclosure further describes a transdermal dressing, compress, or bandage characterised in that it comprises the disclosed hydrogel or pre-hydrogel composition.BRIEF DESCRIPTION OF THE FIGURES

[0041] For ease of understanding, figures are attached which represent preferred embodiment that are not intended to limit the subject of this description.

[0042] Figure 1: Representation of the infrared spectra of an electroconductive hydrogel made of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, non-cross-linked and cross-linked in the presence of 211 mM riboflavin and with 45 min exposure to light with a wavelength between 350 and 500 nm.

[0043] Figure 2: Representation of the elastic modulus of an electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, non-cross-linked and cross-linked in the presence of 211 mM riboflavin and with 45 min exposure to light with a wavelength between 350 and 500 nm.

[0044] Figure 3: Representation of the infrared spectrum of an electroconductive hydrogel of 15% (w / v) gelatine and 0.65% (w / w) PEDOT:PSS, non-cross-linked and cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm.

[0045] Figure 4: Representation of the elastic modulus of an electroconductive hydrogel made of 15% (w / v) gelatine and 0.65% (w / w) PEDOT:PSS, non-cross-linked and cross-linked in the presence of 211 mM riboflavin and with 45 min exposure to light with a wavelength between 350 and 500 nm.

[0046] Figure 5: Representation of the elastic modulus of an electroconductive hydrogel made of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, before cutting with a blade or applying mechanical breakage and after self-healing at 37 °C (1 or 2 cycles of cutting / breakage and self-healing) and 45 °C (1 cycle of cutting / breakage and self-healing).

[0047] Figure 6: Representation of the electroconductivity of an electroconductive hydrogel made of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linkedwith 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, before mechanical breakage and after self-healing at 37 °C (2 cycles of breakage and self-healing) and 45 °C (2 cycles of breakage and self- healing).

[0048] Figure 7: Representation of the cell count expressed as a percentage (%) of live cells per total cell count, in the incubation area vs. migration area after 2.5 h for the control and electrostimulation conditions in an electroconductive hydrogel of 15% (m / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked in the presence of 211 mM riboflavin and with 45 min exposure to light with a wavelength between 350 and 500 nm.DETAILED DESCRIPTION

[0049] The present disclosure relates to a pre-hydrogel composition for forming an electroconductive hydrogel of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate)(PEDOT:PSS) and gelatine, cross-linked with riboflavin, with the ability to self-heal, and recover its mechanical and electroconductive properties. The method for producing the hydrogel, as well as compositions for use in medicine that include the pre-hydrogel, or hydrogel, described, are also disclosed. In particular, compositions for use in tissue engineering, controlled drug delivery, and / or for biosensors are disclosed.

[0050] The present disclosure relates to a pre-hydrogel composition to form an electroconductive hydrogel of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate)(PEDOT:PSS) and gelatine, cross-linked with riboflavin, with the ability to self-heal and recover its mechanical andelectroconductive properties. This material and the resulting hydrogel have characteristics that have the potential to be exploited in biomedical applications such as tissue engineering, and bioelectronics such as sensors or electronic textiles.

[0051] In one embodiment, the hydrogel described in the present disclosure achieves electroconductivity values of 420 mS / m, a value higher than the zero reported in the state of the art for gelatine hydrogels. It is therefore applicable in electroactive dressings, which could be used in tissue engineering applications, notably to promote skin regeneration, since the skin responds to electrical signals and has endogenous conductivity in the order of 0.01 mS / m.

[0052] Surprisingly, the mechanical properties of the hydrogels of the present disclosure are superior to those of the hydrogels of the state of the art, which are softer materials with greater mechanical fragility than the present invention, which has a Young's modulus of between 10 and 100 kPa.

[0053] In one embodiment, the present disclosure relates to obtaining an electroconductive hydrogel from PEDOT:PSS and gelatine, cross-linked with riboflavin and exposed to UV or blue light, in particular light with a wavelength between 200 and 500 nm, with the ability to self-heal when exposed to a certain range of temperatures between 0 °C and 110 °C , including preferably at 37 °C and with high efficiency at physiological temperatures. In one embodiment, the composition of the hydrogel comprises 2-30% (w / v) gelatine, preferably 15% (w / v); a riboflavin concentration of between 5 mM and 750 mM, preferably 211 mM; and a PEDOT:PSS concentration of 0.1-10% (w / w), preferably 1.3% (w / w), in a PEDOT:PSS mass ratio of 2:1 to 1:10, preferably 1:2.5.

[0054] It is known that riboflavin and UV light are capable of promoting the cross-linking of gelatine in the presence of glycerol and at pH values of approximately 10, as described in document US38864341A. Surprisingly, in the present invention it has been found that gelatine crosslinking is possible without the addition of dopants such as glycerol, using only riboflavin in a basic medium and UV or blue light to obtain a cross-linked gelatine hydrogel.

[0055] In the present disclosure, basified riboflavin is referred to as a solution of riboflavin prepared in a solvent with the addition of a base until a final pH of the solution equal to or greater than 10.5 is reached, preferably equal to or greater than 12.5, which is surprising in view of what is described in the literature [M.A. Sheraz et al., Beilstein J. Org. Chem., 2014, 10, 1999-2012].

[0056] Surprisingly, it was found that replacing the water with an aqueous solution of PEDOT:PSS allows the preparation of a basified riboflavin solution without precipitation of the riboflavin. In one embodiment, a 1.3% (w / w) solution of PEDOT:PSS, in which the mass ratio between PEDOT:PSS varies from 1:10 to 2:1, preferably 1:2.5, allows for the preparation of a 211 mM solution of riboflavin, basified without the occurrence of riboflavin precipitation. After dissolving the gelatine in this PEDOT:PSS and riboflavin solution, the gelatine can be cross-linked by exposing the solution to UV or blue light to obtain a crosslinked gelatine and PEDOT:PSS hydrogel with electroconductive and self-healing properties, as described in the present invention.

[0057] The self-healing methodologies for PEDOT:PSS hydrogels previously described in the literature require the application of electric current, pressure, the addition ofwater or a temperature equal to or greater than room temperature, and the recovery of the hydrogels' mechanical properties has not been reported. Surprisingly, the hydrogel described in the present disclosure has the ability to self- heal just by the physical contact of the two parts that have been separated. In one embodiment, the self-healing of the hydrogel occurs within a temperature range of 0 °C to 110 °C, preferably 37 °C, and with high efficiency at physiological temperatures, and a relative humidity of more than 5%, preferably in the range of 50% to 60%. It should be noted that the mechanical and electroconductive properties are maintained after self-healing when compared with the state before breaking / cutting the hydrogel obtained as described in this invention.

[0058] The cross-linked gelatine and PEDOT:PSS hydrogel was prepared using the following steps: i) A solution of basified riboflavin and PEDOT:PSS(pH = 12.5) was prepared; ii) The gelatine was dissolved in the solution prepared in i); iii) The solution obtained in ii) was placed in a mould; iv) The gelatine was cross-linked by exposing the moulded solution (iii) to UV or blue light and waiting for the gel to form by gelling.

[0059] In one embodiment, the self-healing method of the present invention consisted of joining, i.e. encouraging physical contact between the two parts of a hydrogel that had previously been physically separated by cutting or by breaking through tension; this test was carried out at various temperatures and in atmospheres with specific relative humidity.Preparation of a solution of basified riboflavin andPEDOT:PSS

[0060] The present disclosure describes the preparation of a solution of riboflavin and PEDOT:PSS under conditions that allow the complete dissolving of riboflavin without the addition of solubilisation aids such as dextran, and which has been surprisingly successful.

[0061] To obtain a solution of basified riboflavin and PEDOT:PSS, riboflavin was added to an aqueous suspension containing PEDOT:PSS, yielding a riboflavin suspension. Subsequently, increasing amounts of NaOH were added until the riboflavin was completely dissolved, changing from a suspension to a solution, which occurred at a pH of 12.5 or higher.Dissolution of gelatine in solution of basified riboflavin and PEDOT:PSS

[0062] To dissolve gelatine in the basified riboflavin solution prepared in PEDOT:PSS, the mixture had to be heated to a temperature of between 50 °C and 60 °C. The gelatine was added gradually and, once it had been added, it was kept under manual mechanical stirring for at least 30 min.Moulding the solution of gelatine, basified riboflavin and PEDOT:PSS

[0063] In a comparative embodiment, the solution was used in a high-precision, fixed-thickness film applicator, which was moved on its own table to lay down a hydrogel film of uniform thickness. However, the viscosity of the solution did not allow this attempt to succeed.

[0064] In another comparative embodiment, the solution was poured onto acetate paper using the "drop casting" technique, but the high viscosity of the solution did not allow cross-linking and the formation of a homogeneous hydrogel .

[0065] In one embodiment, the solution was poured homogeneously into a plastic Petri dish (with a diameter of 90 mm). This made it possible to obtain a homogeneous moulding of the solution.Gelatine cross-linking and gelling

[0066] Surprisingly, the best gelatine cross-linking conditions were obtained for a riboflavin concentration of between 5 and 750 mM, preferably 211 mM, without riboflavin precipitation occurring, and exposure of the gelatine solution, basified riboflavin, and PEDOT:PSS to UV or blue light, preferably light with a wavelength between 200 and 500 nm, for 45 min. These parameters of gelatine concentration, riboflavin concentration, solution pH and exposure time are very different from those reported in a previous academic study [JM Galdoporpora JM, et al., Adv. Mater. Lett., 2019, 10, 324-328].Quantifying the electroconductivity of hydrogels

[0067] The electroconductivity of the hydrogels was measured by the four-point probe method, using a Keithley DC power source (Keithley Instruments, Cleveland, OH, USA) and an Agilent 34401A multimeter (Agilent Technologies, Santa Clara, CA, USA). To improve electrical contact between the samples and the measuring equipment, four 50 nm thick goldstrips were deposited on the hydrogels using an Edwards Coating System E 306A thermal evaporation system (Edwards, Irvine, CA, USA). Finally, the thickness of the fibre mats was measured using a calliper.ExamplesExample 1Synthesis of an electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm.

[0068] In one embodiment, 1.5876 g of riboflavin was added to 20 mL of a 1.3% (w / w) aqueous suspension of 1:2.5 PEDOT:PSS, obtaining a 211 mM riboflavin suspension. Subsequently, 1 pellet of NaOH was added until the riboflavin was completely dissolved, obtaining a pH value of 12.5 after 40 min. 3 g of type A gelatine of porcine origin was gradually added to the riboflavin solution, heating the mixture to a temperature of 60 °C under manual mechanical stirring, which was maintained for at least 40 min after the gelatine was added.

[0069] The mixture obtained was poured into a plastic Petri dish, the diameter of which allowed the solution to spread evenly throughout the dish. The Petri dish was irradiated for 45 min with light with a wavelength between 350 and 500 nm, and left to cool for a certain period of time at room temperature, preferably for 15 minutes.

[0070] In one embodiment, cross-linking was confirmed by infrared spectroscopy (IR) and by measuring the elasticmodulus in comparison with the non-cross-linked hydrogel, as shown in Figures 1 and 2, respectively.

[0071] Fourier transform IR spectroscopy (FTIR) was carried out using a Spectrum Two FT-IR Spectrometer equipped with an ATR accessory. The transmittance spectra were obtained in the region (400-4000) cm-1(resolution 4 cm-1, 8 scans) at room temperature and an automatic baseline correction treatment was applied.

[0072] For the scope and interpretation of this disclosure, it is defined that "ambient temperature" should be considered as a temperature between 15-30 °C, preferably between 18-25 °C, more preferably between 20-22 °C.

[0073] In one embodiment, the mechanical properties of the hydrogels were assessed by a uniaxial tensile test using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min, on samples with the following dimensions: length 20 mm and width 10 mm.Example 2.Synthesis of an electroconductive hydrogel of 15% (w / v) gelatine and 0.65% (w / w) PEDOT:PSS, cross-linked with 211 M riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm.

[0074] In one embodiment, 1.5876 g of riboflavin was added to 20 mL of a 0.65% (w / w) aqueous suspension of 1:2.5 PEDOT:PSS, yielding a 211 mM riboflavin suspension. Subsequently, 1 pellet of NaOH was added until the riboflavin was completely dissolved, yielding a pH value of 12.5 after 40 min. 3 g of type A gelatine of porcine origin was gradually added to the riboflavin solution, heating the mixture to a temperature of 50 °C under manual mechanical stirring, whichwas maintained for at least 40 min after the gelatine had been added.

[0075] The mixture obtained was poured into a plastic Petri dish, the diameter of which allowed the solution to spread evenly throughout the dish. The Petri dish was irradiated for 45 min with light with a wavelength between 350 and 500 nm, and left to cool for a few minutes at room temperature.

[0076] In one embodiment, cross-linking was checked by IR spectroscopy and by measuring the elastic modulus in comparison with the non-cross-linked hydrogel, as described in Example 1, as shown in Figures 3 and 4, respectively.Example 3.Self-healing test at 45 °C after cutting the gelatine andPEDOT:PSS electroconductive hydrogel with a blade

[0077] In one embodiment, the electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, prepared in Example 1, was completely cut into two symmetrical parts using a metal blade ("cut" condition). Subsequently, the two parts of the hydrogel were brought into contact without applying pressure and stored at 45 °C and relative humidity of 50% to 100%.

[0078] In one embodiment, between 30 and 45 min after cutting, preferably after 40 min, the two parts of the healed hydrogel were completely joined (1 cycle). The success of self-healing can be confirmed by recovering mechanical properties by measuring the elastic modulus and comparing it with the value before cutting and after self-healing, as shown in Figure 5.

[0079] In one embodiment, the recovery of the hydrogel's mechanical properties was assessed by a uniaxial tensile test using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min, on samples with the following dimensions: length 20 mm and width 10 mm.Example 4.Self-healing test at 45 °C after mechanical breakage of the gelatine and PEDOT:PSS electroconductive hydrogel

[0080] In one embodiment, the electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, prepared in Example 1, was completely broken into two parts using a texturometer to apply mechanical stress ("mechanical break" condition). Subsequently, the two parts of the hydrogel were brought into contact, without applying pressure, and stored at 45 °C and relative humidity of 50% to 100%.

[0081] In one embodiment, "mechanical breakage" is carried out using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min until the sample is completely broken, on samples with the following dimensions: length 20 mm and width 10 mm.

[0082] In one embodiment, between 30 and 45 min after mechanical breakage, preferably after 40 min, the two parts of the healed hydrogel were completely joined (1 cycle). The success of self-healing can be confirmed by the partial recovery of mechanical properties by measuring the elastic modulus and comparing it with the value before breakage and after self-healing, as shown in Figure 5.

[0083] In one embodiment, the recovery of electroconductivity obtained by the four-point probe method can be confirmed by comparing the electroconductivity value before breakage (420 mS / m) and the value after self-healing (2 cycles, 0.1 mS / m), as shown in Figure 6, both values being higher than the zero reported in the state of the art for gelatine hydrogels.

[0084] In one embodiment, the recovery of the hydrogel's mechanical properties was assessed by a uniaxial tensile test using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min, on samples with the following dimensions: length of 20 mm and width of 10 mm.Example 5.Self-healing test at 37 °C after cutting the gelatine andPEDOT:PSS electroconductive hydrogel with a blade

[0085] The electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, prepared in Example 1, was completely cut into two symmetrical parts using a metal blade ("cut" condition) . Subsequently, the two parts of the hydrogel were brought into contact, without applying pressure, and stored at 37 °C and relative humidity of 50% to 100%.

[0086] In one embodiment, between 30 and 45 min after mechanical breakage, preferably after 40 min, the two parts of the hydrogel were completely joined (1 cycle). The cutting and self-healing process was repeated under the same conditions (2 cycles). The success of self-healing can be confirmed by the partial recovery of the mechanicalproperties by measuring the elastic modulus, comparing the value before breakage with the value obtained after self- healing, as shown in Figure 5.

[0087] In one embodiment, the recovery of the hydrogel's mechanical properties was assessed by a uniaxial tensile test using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min, on samples with the following dimensions: length 20 mm and width 10 mm.Example 6.Self-healing test at 37 °C after mechanical breakage of the gelatine and PEDOT:PSS electroconductive hydrogel

[0088] In one embodiment, the electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, prepared in Example 1, was completely broken into two parts using a texturometer to apply mechanical stress ("mechanical break" condition). Subsequently, the two parts of the hydrogel were brought into contact, without applying pressure, and stored at 37 °C and relative humidity of 50% to 100%.

[0089] In one embodiment, "mechanical breakage" is carried out using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min until the sample is completely broken, on samples with the following dimensions: length 20 mm and width 10 mm.

[0090] In one embodiment, between 30 and 45 minutes after mechanical breakage, preferably after 40 minutes, the two parts of the hydrogel were completely joined (1 cycle). The mechanical breaking and self-healing process was repeatedunder the same conditions (2 cycles). The success of self- healing can be confirmed by the partial recovery of mechanical properties through the measurement of the elastic modulus, comparing the value before breaking with the value shown by the hydrogel after self-healing, as shown in Figure 5. The recovery of electroconductivity, obtained by the four- point probe method, can be confirmed by comparing the value before breakage (420 mS / m) and after self-healing (2 cycles, 190 mS / m), as shown in Figure 6, both values being higher than the zero reported in the state of the art for gelatine hydrogels.

[0091] In one embodiment, the recovery of the hydrogel's mechanical properties was assessed by a uniaxial tensile test using a texturometer equipped with 50 N tensile grips and at a constant speed of 0.25 mm / min, on samples with the following dimensions: length of 20 mm and width of 10 mm.Example 7.Biocompatibility and skin regeneration test on gelatine and PEDOT:PSS electroconductive hydrogel, cross-linked with 211 M riboflavin and 45 min exposure to UV or blue light.

[0092] In one embodiment, the electroconductive hydrogel of 15% (w / v) gelatine and 1.3% (w / w) PEDOT:PSS, cross-linked with 211 mM riboflavin and 45 min exposure to light with a wavelength between 350 and 500 nm, prepared in Example 1, was completely cut into two symmetrical parts using a metal blade, sterilised by immersion in an antimycotic and antibiotic solution and incubated in Dulbecco's Modified Eagle's Medium supplemented with foetal bovine serum (DMEM / FBS) at 37 °C overnight.

[0093] In one embodiment, a platinum wire was attached to one half of the hydrogel, while another platinum wire was submerged in DMEM / FBS medium and attached to a well of a cell culture plate. L-929 mouse fibroblast cells were incubated on the surface of the half of the hydrogel that was in contact with the platinum wire, at a cell density of IxlO6cells / cm2and incubated at 37 °C for 1 h; this half of the hydrogel was then submerged in culture medium. The cells were washed twice with phosphate-buffered saline (PBS) and marked for 20 min with 2 pM calcein red-orange in DMEM / FBS. After washing with PBS, the cells were incubated with DMEM / FBS at 37 °C for 1 h, and the other half of the hydrogel was placed in contact with the half containing the cells, also submerged in culture medium. The platinum wires (1 cm apart) which served as electrodes were connected to a voltage source and electrostimulation was carried out for 1 h using a square wave alternating current (-200 mV to 200 mV, frequency 100 Hz). A control state was prepared using the same protocol but without electrostimulation. After 1.5 h of rest, the morphology, proliferation, and migration of the cells was confirmed by the fluorescence of the outer membrane of the viable cells using a fluorescence microscope, as demonstrated by the cell count shown in Figure 7.

[0094] The term "comprises" or "comprising" when used in this document is intended to indicate the presence of the characteristics, elements, integers, steps, and components mentioned, but does not preclude the presence or addition of one or more other characteristics, elements, integers, steps, and components, or groups thereof.

[0095] The present invention is, of course, in no way restricted to the embodiments described in this document and a person with average knowledge of the field will be able toforesee many possibilities for modifying it and replacing technical characteristics with equivalent ones, depending on the requirements of each situation, as defined in the appended claims.

[0096] The following claims define additional embodiments of the present description.

Claims

C L A I M S1. Pre-hydrogel composition to form an electroconductive and self-healing hydrogel, characterised by comprising:0.1 to 10% (w / w) of a mixture of poly(3,4- ethylenedioxythiophene) and poly (styrene sulphonate);2 to 30% (w / v) gelatine, preferably unmodified gelatine; and5 to 750 mM riboflavin, in which the composition is cross-linkable after exposure to UV light or blue light.

2. Composition according to the preceding claim characterised in that it consists of:0.1 to 10% (w / w) of a mixture of poly(3,4- ethylenedioxythiophene) and poly (styrene sulphonate);2 to 30% (w / v) gelatine, preferably unmodified gelatine; and5 to 750 mM riboflavin; optionally an active compound.

3. Composition according to any of the preceding claims characterised in that it comprises:1.3 to 2% (w / w) of a mixture of poly(3,4- ethylenedioxythiophene) and poly (styrene sulphonate);15 to 20% (w / v) gelatine; and 211 to 230 mM riboflavin.

4. Composition according to any of the preceding claims characterised in that it is cross-linkable after exposure to light with a wavelength between 200 and 500 nm.

5. Composition according to any of the preceding claims characterised in that the mass ratio between poly (3,4-ethylenedioxythiophene) and poly (styrene sulphonate) ranges from 1:10 to 2:1, preferably it is 1:2.5.

6. Composition according to any of the preceding claims characterised in that the gelatine is type A gelatine.

7. Electroconductive and self-healing hydrogel characterised by comprising the composition described in any one of claims 1 to 6.

8. Electroconductive and self-healing hydrogel according to the previous claim characterised by being self-healing at a temperature ranging from 0 to 100 °C, preferably from 35 to 70 °C.

9. Electroconductive and self-healing hydrogel according to any of the preceding claims 7 to 8 characterised by having an electroconductivity of at least 0.1 mS / m.

10. Hydrogel according to any of the preceding claims 7 to9 characterised by having an electroconductivity ranging from 0.1 mS / m to 420 mS / m.

11. Hydrogel according to any of the preceding claims 7 to10 characterised in that it has a Young's modulus of at least 10 kPa.

12. Hydrogel according to any of the preceding claims 7 to11 characterised in that it has a Young's modulus ranging from 10 to 100 kPa.

13. Hydrogel according to any of the preceding claims 7 to12 characterised in that it has an elongation to breakage capacity of at least 200%.

14. Hydrogel according to any of the preceding claims 7 to13 characterised by having a water absorption capacity of 600% of its mass.

15. Hydrogel according to any of the preceding claims 7 to15 characterised in that the gelatine is type A gelatine.

16. Method for preparing a hydrogel as described in any one of claims 7 to 15 from the composition described in any one of claims 1 to 6, characterised by comprising the following steps: prepare an aqueous polymer solution comprising a mixture of poly (3,4-ethylenedioxythiophene) and poly(styrene sulphonate), and riboflavin; increase the pH of the aqueous polymer solution until the riboflavin is completely dissolved; dissolve the gelatine in the polymer solution with riboflavin to obtain a pre-hydrogel; transfer and distribute the pre-gel evenly into a mould; cross-linking the pre-hydrogel by exposure to UV light or blue light in order to obtain the hydrogel, preferably by exposure to light with a wavelength between 200 and 500 nm.

17. Method according to the previous claim characterised in that the pH of the aqueous polymer solution is increased to a pH of at least 12.5.

18. Method according to any of claims 16 to 17 characterised in that the aqueous polymer solution of poly (3,4- ethylenedioxythiophene) and poly (styrene sulphonate) has a concentration of 0.1 to 10% (mpoiymer / mtotai), preferably 1.3 tO 1.5-6 (mpolymer / mtotal)•19. Method according to any one of claims 16 to 18 characterised in that the pre-hydrogel is cross-linked by exposure to light for at least 30 minutes, preferably 35 to 45 minutes.

20. Method according to any one of claims 16 to 19 characterised in that the pre-hydrogel is cross-linked with light having a wavelength ranging from 350 to 500 nm, preferably 366 nm.

21. Composition comprising the hydrogel described in any one of the preceding claims 7-15 or the pre-hydrogel composition described in any one of the preceding claims 1 to 6 characterised in that it is for use in medicine.

22. Composition according to the preceding claim characterised in that it is administered in the form of a transdermal patch, compress or bandage.

23. Composition according to any of the preceding claims 21 to 22 characterised in that it is for use in tissue engineering, controlled drug delivery, and / or biosensors.

24. Composition for use according to any of the preceding claims 21 to 23 characterised in that it is for use in skin regeneration.

25. Use of a composition comprising the hydrogel described in any of the preceding claims 7-15 or the pre-hydrogel composition described in any of the preceding claims 1 to 6 in textiles or electronic sensors.

26. Transdermal dressing, compress, or bandage characterised in that it comprises the hydrogel described in any one of the preceding claims 7-15 or the pre-hydrogel composition described in any one of the preceding claims 1 to 6.

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