Photo-catalyzed formation of conductive hydrogels

Abstract

Disclosed herein are compositions that can change their electrical and mechanical properties in response to light irradiation. The compositions can include one or more of a random copolymer derived from at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer; an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization; an oxidant; and a solvent containing water. Methods for preparing conductive hydrogels are also disclosed.

Description

[0001] PHOTO-CATALYZED FORMATION OF CONDUCTIVE HYDROGELS

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims priority to United States Provisional Application No. 63 / 492,860, filed March 29, 2023, and the contents of which are incorporated herein by reference in their entireties for all purposes.

[0004] FIELD

[0005] The present disclosure relates to compositions that can change their electrical and mechanical properties in response to light irradiation. Methods for producing electrically conductive hydrogels are also disclosed.

[0006] BACKGROUND

[0007] Implantable and wearable bioelectronic devices can enable seamless communication and interaction between biological systems and machines. Among these devices, bioelectronics based on electrically conductive hydrogels are of a particular interest. Electrically conductive hydrogels consist of cross-linked polymeric networks percolated with electrically conductive nanoparticles or polymers.

[0008] Conductive hydrogels offer several advantages over traditional electronic materials. First, because of the cross-linked polymeric network, the elastic modulus of soft conductive hydrogels can be tuned to match those of biological tissues and the human body. Second, due to the presence of an electrically conductive phase and solvated ions in the porous network, conductive hydrogels can transduce ionic biological signals to electronic devices for sensing and vice versa for stimulation.

[0009] Conductive hydrogels made from conducting polymers (CPs), such as poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), or polyaniline (PANI), offer superior compatibility with biological systems compared to conventional nanocomposite hydrogels like metal nanowires (NWs) and carbon nanotubes (CNTs). The enhanced compatibility arises from the conductive polymers’ inherent flexibility and their ability to facilitate both ionic and electronic conductivity, making them ideal candidates for advanced bioelectronic interfaces. Unfortunately, bioelectronic devices made from conductive hydrogels are currently limited by their fabrication methods and our ability to control the shape and position of the hydrogel.

[0010] Conventional methods, such as molding, have been frequently used to fabricate conductive hydrogels but can only provide simple structures with low resolution (>100 m). This large size may not be compatible with bioelectronic applications requiring small electrodes. Alternatively, 3D-printing technologies, including nozzle-based printing and light-based printing, are capable of achieving more complex architectures with higher resolution. In nozzle-based printing, nozzles are used to extrude conductive polymer ink into a desired architecture. The structure and resolution of the desired architecture greatly depends upon the rheological properties of the precursor inks. Nozzle-based printing can ultimately compromise the quality and structural integrity of the desired architecture because the choice of nozzle radius, polymer ink, and heating temperature can lead to reduced homogeneity in the structure and the introduction of voids in the final printed products.

[0011] To achieve high-resolution spatial and temporal control, light-based printing methods of conductive hydrogels are emerging. This method of photogelation simultaneously patterns and cross-links conducting polymer solutions by light irradiation. However, photoprinting conductive hydrogels is still a challenging task because the conductive polymer in the hydrogel solution absorbs UV light which can prevent photoactivation and cross-linking. Though several studies have reported that the fabrication of composite hydrogels of PEDOT:PSS and polyethylene glycol diacrylate (PEGDA) (which serves as a photocurable crosslinker) using a visible-light photoinitiator system is possible; the resulting hydrogels have been found to suffer from low electrical conductivity. This low electrical conductivity could be due to low loadings of conductive polymer in the insulating scaffold.

[0012] The preparation of 3D-printed conductive hydrogels by photopolymerization of the 3,4-ethylenedioxythiophene (EDOT) monomer has been reported; however, the method used to prepare these hydrogels does not involve direct photoprinting, but a multistep process where the precursor ink is first extruded and then crosslinked by blue-light irradiation on nozzles under a phenol-coupling mechanism. Ruthenium [Ru] is used to catalyze both the photopolymerization and the phenol-coupling reaction in these methods. The use of [Ru] can cause potential incompatibility with biological tissues due to its cytotoxicity.

[0013] Most of the photo-crosslinking methods explored to date to generate conductive hydrogels rely on the use of photoactive catalysts to generate radicals that will subsequently trigger cross-linking by radical addition or polymerization. The addition of photocatalysts, however, often complicates the process as it requires the removal of oxygen and either needs to be biocompatible or removed after the hydrogel formation. Alternatively, hydrogels based on covalent chemistry processes that include dimerization under light irradiation without the need of a chemical catalyst, such as covalent chemistry processes that involve the use of coumarins, could address this problem. Under long-wave UV irradiation (365 nm), coumarins can undergo a [2 + 2] cycloaddition. Therefore, attaching coumarin groups on a polymer backbone could enable the production of cross-linked hydrogels through the formation of coumarin dimers. While the use of coumarins has been reported before for nonconductive hydrogels, their use in systems involving conductive polymers has not been shown. A possible reason for this could be because the conducting polymers absorb light at around the same wavelength that causes the coumarins to dimerize, thereby preventing cross-linking.

[0014] Thus, to address the foregoing issues, we disclose herein compositions and methods that are capable of simultaneous photo-crosslinking of a polymeric scaffold and polymerization of a conducting polymer under light irradiation. SUMMARY

[0015] Disclosed herein is a composition including (i.e., comprising) one or more of: a random copolymer derived from at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer; an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization; an oxidant; and a solvent containing water.

[0016] Also disclosed herein is a hydrogel composition including one or more of: a photo-crosslinked copolymer, derived from at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer, wherein the photo- crosslinkable polymeric units are photo-crosslinked; a polycationic conductive polymer derived from an aromatic heterocycle monomer polymerized by oxidative polymerization; and a solvent containing water.

[0017] Disclosed herein is also a medical device including any of the compositions disclosed herein, wherein the medical device is an implantable medical device, a wearable medical device, or a theranostic device.

[0018] Also disclosed herein is a method including one or more of the following steps: providing a composition including (a) a random copolymer, wherein the copolymer includes at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer, (b) a polycationic conductive polymer derived from an aromatic heterocycle polymerized by oxidative polymerization, (c) an oxidant, and (d) a solvent containing water; exposing the composition to UV light in a range of 300 to 400 nm, or 310 to 390 nm, or 340 to 380 nm for an amount of time in a range of 1 to 180 minutes, or 25 to 150 minutes, or 50 to 125 minutes to form a hydrogel composition; and washing the hydrogel composition by soaking the hydrogel in a solution containing distilled water or phosphate buffer solution (pH = 7) for 24 hours and changing the solution a minimum of three times.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other features and advantages of the compositions, devices and methods disclosed herein will be apparent to those skilled in the art reading the following detailed description in conjugation with the exemplary embodiments illustrated in the drawings, wherein:

[0021] FIG. 1 depicts an overview of an exemplary photo-catalyzed formation of conductive hydrogels, (a) Photographs and schematics of an exemplary precursor solution (left) and the resulting exemplary conductive hydrogel after irradiation (right), (b) Simultaneous photo-crosslinking of exemplary coumarin-derived copolymers, which can undergo a [2+2] cycloaddition, and photocatalyzed oxidative polymerization of EDOT.

[0022] FIG. 2 depicts an exemplary UV-Vis study of the cross-linking of P(SS-co- CoumAc). (a) UV absorption spectra of a solution of P(SS-co-CoumAc) in water (0.05 wt %) irradiated at 365 nm over 120 min. (b) Calculated percentage of coumarin dimerization as a function of irradiation time at 365 nm.

[0023] FIG. 3 depicts photorheology measurements at 365 nm as a function of irradiation time of exemplary solutions of P(SS-co-CoumAc) in water (50 wt %) with SS:CoumAc cross-linker ratios of (a) 100:5, (b) 100:10, and (c) 100:20.

[0024] FIG. 4 depicts the results from an exemplary experiment examining the photomediated formation of PEDOT:PSS-co-CoumAc gels with time. A synthetic scheme for the photomediated formation of PEDOT:PSS-co-CoumAc gels is provided, (a) Experimental conditions: P(SS-co-CoumAc) 100:10, ammonium persulfate (APS), ruthenium catalyst, and light irradiation at 365 nm. (b) Experimental conditions: PSS, APS, ruthenium catalyst, and light irradiation at 365 nm. (c) P(SS-co-CoumAc) 100:10, ammonium persulfate (APS) and ruthenium catalyst, (d) Experimental conditions: P(SS-co-CoumAc) 100:10, ruthenium catalyst, and light irradiation at 365 nm. (e) P(SS-co-CoumAc) 100:10, APS and light irradiation at 365 nm. (f) Experimental conditions: P(SS-co-CoumAc) 100:10, ammonium persulfate (APS), ruthenium catalyst, heating at 50°C.

[0025] FIG. 5 depicts the electrochemical impedance spectroscopy (EIS) of exemplary solutions and hydrogels as a function of the loading of EDOT in P(SS- co-CoumAc) at a 100:10 ratio, (a) Bode plots of precursor solutions and conductive hydrogels after 120 min of light irradiation and washed with both DI water and PBS solution, (b) Nyquist plots of the conductive hydrogels, (c) Equivalent circuit model used to fit the experimental data.

[0026] FIG. 6 depicts photorheology measurements at 365 nm as a function of irradiation time of exemplary solutions of P(SS-co-CoumAc) (50 wt %), EDOT, and APS in water with SS:CoumAc:EDOT ratios of (a) 100:5:13, (b) 100:10:13, and (c) 100:20:13.

[0027] FIG. 7 depicts the effect that the proportion of CoumAc cross-linker has on the mechanical and electronic properties of exemplary PEDOT:P(SS-co-CoumAc) conductive hydrogels, (a) Representative tensile test, (b) Bode plots, and (c) Nyquist plots from EIS studies.

[0028] FIG. 8 depicts SEM images of cross sections of exemplary freeze-dried conductive hydrogels with SS:CoumAc ratios of (a) 100:5, (b) 100:10, and (c) 100:20.

[0029] FIG. 9 depicts the comparison of sEMG signals collected by a photocrosslinked electrode (top) and a commercial 3 M electrode (bottom) adhered to a forearm (a) during different finger motions and (b) during repeated fist closing motions. The insets show photographs of the two electrodes and different finger / hand motions.

[0030] DETAILED DESCRIPTION

[0031] One aspect of the present disclosure is a composition including one or more of: a random copolymer derived from at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer; an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization; an oxidant; and a solvent containing water.

[0032] As used herein, the phrase "photo-crosslinkable" refers to a monomer that can create bonds between polymer chains under light irradiation. These monomers can possess functional groups capable of forming cross links with other polymers and / or monomers, such as but not limited to, primary amines, sulfhydryls, carbonyls, carbohydrates and carboxylic acids.

[0033] As used herein, the phrase "polycationic conductive polymer" refers to an electrically conductive, pi-conjugated polymer in its oxidized state that is positively charged.

[0034] In exemplary embodiments, the photo-crosslinkable monomer is selected from one or more of coumarin acrylate, 4-phenylazophenyl acrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, or a blend thereof.

[0035] In exemplary embodiments, the water-soluble anionic monomer is selected from one or more of styrene sulfonate, maleic acid, acrylic acid, or a blend thereof.

[0036] In exemplary embodiments, the aromatic heterocycle monomer is selected from one or more of 3,4-ethylenedioxythiophene, pyrrole, aniline, thiophene, 3,4- propylenedioxythiophene, 3,4-phenylenedioxythiophene, or a blend thereof.

[0037] In exemplary embodiments, the random copolymer includes one or more of poly(styrene sulfonate-co-coumarin acrylate), poly(styrene sulfonate-co-4- phenylazophenyl acrylate), poly(styrene sulfonate-co-triethylene glycol diacrylate), poly(styrene sulfonate-co-tetraethylene glycol dimethacrylate), or a blend thereof.

[0038] In exemplary embodiments, the oxidant is selected from one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, iron (III) sulfate, iron (III) chloridepersulfates, peroxides, iron (III) oxidants, or a combination thereof.

[0039] In exemplary embodiments, the random copolymer is derived from a mixture containing the water-soluble anionic monomer and the photo-crosslinkable monomer in a molar ratio in a range of 1 :1 to 50:1 , 2:1 to 40: 1 , or 4:1 to 25:1.

[0040] In exemplary embodiments, the random copolymer is derived from a mixture containing the water-soluble anionic monomer and the aromatic heterocycle monomer in a mass ratio in a range of 1 :1 to 50:1 , or 2:1 to 40:1 , or 5:1 to 35:1 .

[0041] In exemplary embodiments, the random copolymer has a molecular weight in a range of 10 to 100 kDa, 15 to 60 kDa, or 20 to 45 kDa, measured by size exclusion chromatography (SEC) using a refractive index detector, in water bufferDMF calibrated against poly(styrene sulfonate) (PSSNa) standards. PSSNa standards can be found in Lo et al (Lo, C. et al, "Influence of the molecular weight and size distribution of PSS on mixed ionic-electronic transport in PEDOT:PSS", Polym. Chem., 2022,13, 2764-2775) and Kayser et al (Kayser, L. et al, "RAFT Polymerization of an Intrinsically Stretchable Water-Soluble Block Copolymer Scaffold for PEDOT", Chem. Mater. 2018, 30, 13, 4459-4468).

[0042] In exemplary embodiments, the composition exhibits a sol-gel transition and forms a hydrogel upon exposure to UV light in a range of 300 to 400 nm, 310 to 390 nm, or 340 to 380 nm.

[0043] In exemplary embodiments, the composition is electrically conductive in the hydrogel state.

[0044] Another aspect of the present disclosure is a hydrogel composition including one or more of: a photo-crosslinked copolymer, derived from at least one photo- crosslinkable monomer and at least one water-soluble anionic monomer, wherein the photo-crosslinkable polymeric units are photo-crosslinked; a polycationic conductive polymer derived from an aromatic heterocycle monomer by oxidative polymerization; and a solvent containing water.

[0045] In exemplary embodiments, the photo-crosslinkable monomer in the hydrogel composition is selected from one or more of coumarin acrylate, 4- phenylazophenyl acrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, or a blend thereof.

[0046] In exemplary embodiments, the at least one water-soluble anionic monomer that the photo-crosslinked copolymer in the hydrogel composition is derived from is selected from one or more of styrene sulfonate, maleic acid, acrylic acid, or a blend thereof.

[0047] In exemplary embodiments, the photo-crosslinked copolymer in the hydrogel composition is derived from a mixture containing the at least one water-soluble anionic monomer and the at least one photo-crosslinkable monomer in a molar ratio in a range of 1 : 1 to 50: 1 , 2: 1 to 40: 1 , or 4: 1 to 25: 1 .

[0048] In exemplary embodiments, the water-soluble anionic monomer and the aromatic heterocycle monomer are present in the hydrogel composition in a mass ratio in a range of 1 : 1 to 50: 1 , 2: 1 to 40: 1 , or 5: 1 to 35: 1 .

[0049] In exemplary embodiments, the polycationic conductive polymer in the hydrogel composition is derived from a random copolymer including one or more of poly(styrene sulfonate-co-coumarin acrylate), poly(styrene sulfonate-co-4- phenylazophenyl acrylate), poly(styrene sulfonate-co-triethylene glycol diacrylate), poly(styrene sulfonate-co-tetraethylene glycol dimethacrylate), or a blend thereof. In exemplary embodiments, the polycationic conductive polymer in the hydrogel composition includes one or more of poly(3,4-ethylenedioxythiophene), polypyrrole, polyaniline, polythiophene, poly(3,4-propylenedioxythiophene), poly(3,4-phenylenedioxythiophene), or a blend thereof.

[0050] In exemplary embodiments, the polycationic conductive polymer in the hydrogel composition is derived from a random copolymer having a molecular weight in a range of 10 to 100 kDa, 15 to 60 kDa, or 20 to 45 kDa, measured, by size exclusion chromatography (SEC) using a refractive index detector, in water bufferDMF calibrated against PSSNa standards.

[0051] In exemplary embodiments, the hydrogel composition is electrically conductive. As used herein, the phrase "electrically conductive" refers to compositions (e.g., hydrogel compositions) capable of transporting electrical charges from one location to another.

[0052] In exemplary embodiments, the hydrogel composition produces a hydrogel that exhibits electrical conductivity in a range of 0.1 to 25 S / m, or 0.2 to 20 S / m, or 0.4 to 15 S / m.

[0053] In exemplary embodiments, under UV light (365 nm), the compositions disclosed herein transform from transparent, non-conducting solutions to dark blue, electronically conducting hydrogels. In exemplary embodiments, the nonconducting solutions are comprised of poly(styrene sulfonate)-co-poly(coumarin acrylate) (P(SS-co-CoumAc)) and dispersed 3,4-ethylene dioxythiophene (EDOT) monomer in water.

[0054] Another aspect of the present disclosure is a medical device including any of the compositions disclosed herein, wherein the medical device is an implantable medical device, a wearable medical device, or a theranostic device.

[0055] In exemplary embodiments, the medical device contains any compositions disclosed herein in an injectable scaffold, a 3D printed scaffold, a biomedical implant, an injectable electrode, a wearable electrode, a biosensor, an actuator, an electrochemical transistor, or soft electrodes for surface biopotential applications (e.g., electrocardiogram (ECG), electroencephalogram (EEG), and electromyography (EMG)).

[0056] Another aspect of the present disclosure is a method including one or more of the following steps: providing a composition including (a) a random copolymer, wherein the copolymer includes at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer, (b) an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization, (c) an oxidant, and (d) a solvent containing water; exposing the composition to UV light in a range of 300 to 400 nm, or 310 to 390 nm, or 340 to 380 nm for an amount of time in a range of 1 to 180 minutes, or 25 to 150 minutes, or 50 to 125 minutes to form a hydrogel composition; and washing the hydrogel composition by soaking the hydrogel in a solution containing distilled water or phosphate buffer solution (pH = 7) for 24 hours and changing the solution a minimum of three times.

[0057] In exemplary embodiments, the oxidant contained in the composition used in the method is selected from one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, iron (III) sulfate, iron (III) chloride persulfates, peroxides, iron (III) oxidants, or a combination thereof.

[0058] In exemplary embodiments, the oxidant and an aromatic heterocycle monomer contained in the composition used in the method are present in the composition in a molar ratio in a range of 1 :1 to 1.5:1 , 1 :1 to 1.4:1 , or 1.1 :1 to 1.3:1.

[0059] In exemplary embodiments, the method further comprises a step of washing the hydrogel with a solvent containing water.

[0060] In exemplary embodiments, the method includes a step of 3D printing the composition during the step of exposing the composition to UV light.

[0061] It has now been surprisingly discovered that the compositions and methods disclosed herein can, under UV radiation, form an electronically conducting hydrogel without the need of a photocatalyst. In an exemplary embodiment, the formation of the conductive hydrogels relies on the simultaneous, photo-mediated covalent photo-crosslinking of polystyrenesulfonate (PSS) copolymers with coumarin-derived monomers and the oxidative polymerization of EDOT (see FIG. 1). Without wishing to be bound by any particular theory, it is believed that the orthogonal photochemistry, involving the polymerization of EDOT and the [2 + 2] cycloaddition of coumarin, leads to the conducting hydrogel in this exemplary embodiment.

[0062] The conductive hydrogels produced from the compositions and methods disclosed herein can exhibit both ionic and electronic conductivity, possess tunable elastic moduli in the MPa range, and display a reasonable strain at break (up to 16%). The conductive hydrogels also showed that they can be photoprinted using a conventional photolithography system. This photo-mediated formation of conducting hydrogels can be applied to lithography or stereolithography to enable the printing of 2D or 3D networks with a controlled microstructure and provide materials for new applications in bioelectronics.

[0063] The printable conductive hydrogels also have potential applications in areas including, but not limited to, minimally-invasive bioelectronic implants, scaffolds for tissue engineering, electrostimulation, soft electrodes for surface biopotential applications, such as electrocardiogram (ECG), electroencephalogram (EEG), and electromyography (EMG), flexible displays, high performance electrolytic capacitors, high performance electrolytic capacitors, OLEDs, organic and hybrid photovoltaics, printed electronics, neural interfaces, actuators, cartilage repair, neural tissue engineering, cell capture and release, injectable electronics, injectable conductive hydrogels, biomedical devices, chemical sensors, drug delivery, temperature-sensitive displays, neuromorphic computing, electrochemical transistors, electronically-conductive fabrics, wearable and adaptable devices, and biosensors.

[0064] Examples

[0065] The present disclosure will be described in more detail with reference to the following Examples, which shows exemplary embodiments in accordance with the present disclosure. The present disclosure is not limited to these exemplary embodiments.

[0066] Example 1 : One Pot Photomediated Formation of Electrically Conductive Hydrogels

[0067] This experimental study was supported by a Beckman Young Investigator award to Laure Kayser from the Arnold and Mabel Beckman Foundation. The goal of this experimental study was to achieve photogelation of PEDOT:PSS-based conductive hydrogels. As such, a PSS copolymer was first synthesized with a photo-cross-linkable monomer, CoumAc. The P(NaSS-co-CoumAc) copolymers were synthesized by free-radical polymerization in a mixture of water and 1 ,4- dioxane at 70 °C with three different ratios of NaSS to CoumAc (100:20, 100:10, and 100:5, see Table 1) to determine the impact of the cross-linker density on the mechanical properties of the resulting hydrogels and the gelation time.

[0068] Table 1 : Synthesis of the P(SS-co-CoumAc) copolymers.

[0069] Polymer [SSNa]:[CoumA [SS]:[CoumAc] „c£>cname c] feedaactualb n indicating (kg

[0070] SS:CoumAc mol-1) molar ratio

[0071] 100:20 100:22.2 100:18 24.5 1.92

[0072] 100:10 100:11.1 100:10 30.2 2.33

[0073] 100:5 100:5.6 100:4.3 37.8 3.44 a The initial molar feed ratio of SSNa to CoumAc as measured by1H NMR spectroscopy. b Ratio of SSNa to CoumAc as measured by1H NMR spectroscopy of the purified copolymer. c Measured by SEC in a mixture of a water buffer and DMF calibrated against PSSNa standards using a refractive index detector.

[0074] As determined by proton nuclear magnetic resonance (1H NMR), the incorporation of CoumAc in the final polymer was a slightly lower than the [SSNa]: [CoumAc] feed ratio, which could have been due to the slightly lower reactivity of the acrylate CoumAc monomer compared with the styrenic NaSS. Interestingly, the synthesis of the P(SS-co-CoumAc) copolymers were able to achieve CoumAc loadings as high as 20 mol % without macroscopic gelation, which was previously observed to be unachievable with copolymers of N,N- dimethylacrylamide with over 5 mol % CoumAc. The molecular weight and size distribution of the copolymers, as measured by size exclusion chromatography (SEC), ranged from 24.5 kg mol-1for the 100:20 copolymer to 37.8 kg mol-1at lower CoumAc loadings. The higher viscosity of the reaction mixture at higher loadings of CoumAc could explain the slightly lower molecular weights obtained. After the formation of the P(NaSS-co-CoumAc) copolymer and in preparation for the incorporation of PEDOT, the P(NaSS-co-CoumAc) copolymer was stirred over an acidic resin to replace sodium ions with protons, resulting in P(SS-co-CoumAc).

[0075] Given that P(SS-co-CoumAc) had not been reported previously, the next step in this experimental study was to establish whether photo-gelation by [2+2] cycloaddition and crosslinking was feasible. In its monomeric form, coumarin exhibits strong absorbance at 320 nm. When exposed to UV light (e.g., 365 nm), coumarin undergoes a [2+2] cycloaddition reaction, resulting in the formation of a cyclobutane ring (see FIG. 1), which is not UV active. This dimerization can lead to a decrease in the UV-Vis absorption peak at 320 nm during the reaction. The photo-crosslinking of coumarin in P(SS-co-CoumAc) was therefore first investigated by UV-vis spectroscopy. A diluted solution of P(SS-co-CoumAc) with a ratio of 100:10 (0.05 wt% in water) was prepared and exposed to 365 nm light (25 mW cm- ~2). FIG. 2 shows the change in UV-vis absorption over the course of irradiation.

[0076] The absorbance at 320 nm diminished as the coumarin groups dimerized. After one hour, approximately 75% of the coumarin moieties had dimerized and reached their maximum (see FIG. 2). However, due to the low concentration needed as to not saturate the UV-vis, these solutions did not form a gel.

[0077] The cyclobutane formed through dimerization can be cleaved back to the monomeric coumarin by irradiating the solution at a wavelength of 254 nm. For P(SS-co-CoumAc), this reversible process was also feasible since an increase in the 320 nm peak after irradiation at 254 nm for 5 min was observed. However, the absorption intensity did not fully return to its original level. After 15 minutes of irradiation, approximately 5% of the dimer still remained. This phenomenon can be explained by the formation of an equilibrium between the open and closed form of the coumarin at this wavelength.

[0078] Based on these results, the polymer concentration was increased to investigate the gelation behavior. At 40 wt%, the solution of P(SS-co-CoumAc) became a soft gel when exposed to 365 nm. In view of this observation, the polymer concentration was increased to 50 wt%. At that concentration, the formation of a stable gel was observed within approximately an hour. To achieve a more quantitative assessment of the gelation time, real-time changes in storage modulus (G1) and loss modulus (G") were monitored by photo-rheology under irradiation at 365 nm (see FIG. 3). In all three copolymers, the initial state was liquid, with G' lower than G". However, upon light exposure, both G1and G" increased, until G1surpassed G", indicating the transformation of the liquid precursor into a hydrogel state. Consequently, the time at which G' equaled G" was defined as the gelation time (tgei) of the hydrogels. The gelation times for the pristine hydrogels with ratios 100:5, 100:10, and 100:20 were 117 minutes, 115 minutes, and 63 minutes, respectively. As the amount of coumarin crosslinker increased, the gelation time decreased, leading to a faster conversion of the precursor liquid to a hydrogel state. However, the storage modulus remained similar in all three cases at around 7 MPa.

[0079] Having confirmed that the precursor copolymer can be photo-crosslinked, the experimental study next examined whether the incorporation of the conducting polymer PEDOT+into the precursor polymer could be achieved. PEDOT was chosen for its high conductivity and stability in water and oxygen. To achieve the one-pot photo-mediated preparation of conductive hydrogels, a long-wave UV light (365 nm) was used since it could simultaneously enable the photo-crosslinking of the coumarin-derived copolymer P(SS-co-CoumAc) and drive the oxidative polymerization of EDOT.

[0080] Previous studies have shown that EDOT monomers and other aromatic heterocycles, such as pyrrole and thiophene derivatives, can be oxidatively polymerized in the presence of a photoredox catalyst, such as [Ru(bpy)s]2+. Upon long-wave light irradiation, [Ru(bpy)s]2+reaches a photoexcited state *[Ru(bpy)s]2+which, in the presence of electron acceptors, generates a strong oxidant, [Ru(bpy)s]3+, capable of triggering the oxidative polymerization of aromatic heterocycles. Therefore, to first determine whether photo-mediated formation of PEDOT:PSS-co-CoumAc gels could be achieved, similar reaction conditions as those previously reported were used for the photo-polymerization of EDOT in P(SS- co-CoumAc) ( / .e., a ratio of P(SS-co-CoumAc) to EDOT of 100:10 in 50 wt% water with 0.33 mM of [Ru(bpy)s]2+, 93 mM EDOT, 110 mM of ammonium persulfate (APS), and light irradiation at 365 nm (25 mW cm-2)). The gelation of the solution was initially monitored visually and the polymerization of PEDOT+was seen by a characteristic color change to dark blue. Under these conditions, the formation of a dark blue gel in 90 min was observed with the solution turning dark blue in less than 15 min, thereby demonstrating that a one-pot, photo-mediated, formation of PEDOT hydrogels was possible (see FIG. 4). The relatively long gelation time was consistent with that necessary for the coumarin photo-dimerization (see FIG. 3).

[0081] In control experiments, the impact of the presence of coumarin crosslinker, UV light, APS, and Ru(ll) catalyst on the formation of PEDOT+hydrogels was investigated. In the absence of coumarin units (only PSS, FIG. 4), the solutions turned dark blue but did not gel within a 90 min timeframe despite an apparent increase in the viscosity of the solution. In the absence of light, no gelation was observed and the PEDOT polymerization proceeded very slowly with a faint green coloration only seen after 30 min (FIG. 4). This experiment indicated that light is crucial for both the crosslinking and the polymerization. Without APS, polymerization still proceeded, but more slowly, and no gelation was observed within 90 min (FIG. 4). This effect could be explained by a synergistic effect from the coumarin dimerization and PEDOT polymerization within the covalently crosslinked network to form gels faster, possibly in the form of an interpenetrating network.

[0082] The last control experiment in the absence of added Ru(ll) catalyst was the most surprising (FIG. 4). PEDOT polymerization proceeded roughly at the same rate and gelation was observed within the same time frame as with the Ru(ll) photoredox catalyst. Two possibilities can explain this observation. There could have been traces of catalytic oxidant in the reaction mixture, or oligomeric PEDOT — formed by early-stage oxidation with APS — could have acted as a photocatalyst and led to further polymerization via a self-catalyzed reaction pathway. Regardless, the surprising result remains that additional photoredox catalysts are not needed for the photo-mediated formation of conductive hydrogels. Given the potential cytotoxicity of ruthenium and difficulty in removing traces of metals in hydrogels, this experimental study continued without the use of [Ru(bpy)s]2+.

[0083] With general reaction conditions in hand to obtain photo-crosslinked hydrogels, the effect of the loading of EDOT on the electronic properties of the conductive hydrogels was investigated by electrochemical impedance spectroscopy (EIS) and 2-point parallel plate resistance measurements. From a molar ratio of SS: EDOT of 100:4 in initial studies, the loading of EDOT was increased to 100:9, 100:13, and 100:21 . The solutions were irradiated for 120 min to ensure complete gelation and EDOT polymerization, then washed with deionized water and a phosphate buffer saline (PBS) solution. The Bode plots from EIS (FIG. 5) showed that, compared to precursor solutions, all the conductive hydrogels displayed significantly lower impedance (over two orders of magnitude), especially in the low- frequency range. This decrease in impedance is consistent with the incorporation of interconnected conducting polymer chains (PEDOT+) in the resulting hydrogels. Notably, the hydrogel with a 100:13 ratio of SS to EDOT displayed the lowest impedance magnitude at an identical gel volume. The Nyquist plot of the hydrogels (FIG. 5) was analyzed and fitted to the equivalent circuit model commonly used for PEDOT-based conductive hydrogels (FIG. 5). The tabulated values extracted from this model are presented in Table 2 and show small %2values indicating a good fit for the model.

[0084] Table 2: Electronic properties of the conductive hydrogels

[0085] SS:EDOT [EDOT]

[0086] Molar ratio (mM)

[0087] 100:4 93 100:4.2 0.57 ± 0.006 136 17 0.03

[0088] 4

[0089] 100:9 186 100:6.9 1.69 ± 0.03 473 14 0.01

[0090] 100:13 279 100:8.3 4.58 ± 0.12 160 11 0.05

[0091] 100:21 465 100:10.5 1.15 ± 0.06 341 5 0.04aObtained by XPS.bObtained by two-point parallel plate measurement.cObtained by fitting EIS data against equivalent circuit model in Figure 5c.

[0092] The values of Rc, Re, and Ri are, respectively, the resistive contributions from the assembled cell used for the test, and the electronic and ionic resistance from the conductive hydrogel. Cgis the ideal geometric capacitance of conductive hydrogels and Qdi is the constant phase element describing the non-ideal doublelayer capacitance. The values reported in Table 2 represent the average values for Reand Ri from three independently prepared samples, with Rebeing the lowest for the 100:13 ratio (160 Q) and Ri being lowest for the 100:21 ratio (5 Q). Additionally, the conductivity, measured using the 2-point parallel plate method, showed the highest value for the 100:13 ratio (4.58 ± 0.12 S m-1), comparable to other PEDOT- based hydrogels.

[0093] In addition to the color change, the presence of PEDOT+in the bulk of resulting hydrogels was also confirmed by X-Ray photoelectron spectroscopy (XPS) of freeze-dried samples. The S(2p) electrons of PEDOT and PSS have different binding energies, so the ratio of PSS / PEDOT can be analyzed by XPS. In the XPS data, the S (2p) peaks at a binding energy of 169 eV correspond to the sulfur in the sulfonate groups of PSS and the S(2p) signals at 165 eV correspond to the sulfur in the thiophene fragment of PEDOT. The area ratio of the S(2p) peaks in the XPS data can therefore be used to estimate the relative composition of PSS to PEDOT of samples. The ratios are just slightly lower than the ratio of SS to EDOT added (Table 2), indicating that some fraction of EDOT / PEDOT is washed away during the hydrogel work-up steps. Importantly, these electrically-conductive hydrogels did not contain secondary additives or metal catalysts reducing the potential risk of cytotoxicity in bioelectronics applications. Based on the EIS and conductivity measurements, SS:EDOT ratio of 100:13 was optimized for the preparation of subsequent conductive hydrogels. The sol-gel transition during photo-irradiation was then monitored using photo-rheology measurements at a constant SS:EDOT ratio of 100:13 but with a varying loading of CoumAc in P(SS-co-CoumAc) (FIG. 6). Compared to the hydrogels without PEDOT, the gelation process of conductive hydrogels was significantly accelerated (approximately 50 minutes faster). This result was consistent with previous experiments showing that gelation was not only due to coumarin crosslinking but also the formation of interconnected PEDOT chains. The gelation times for the conductive hydrogels with SS:CoumAc ratios of 100:5, 100: 10, and 100:20 were 62 min, 68 min, and 14 min, respectively. As the amount of coumarin crosslinker increased, the gelation time decreased, resulting in a more rapid conversion of the precursor liquid into a hydrogel state. Notably, the conductive hydrogel with a ratio of SS:CoumAc:EDOT of 100:20:13 achieved gelation within a timeframe which could be suitable for stereolithography (14 min for 0.5 mL) (FIG. 6). At low loadings of CoumAc (FIG. 6), the moduli did not reach a plateau within the 240 min experiment. But, both 100:10:13 (FIG. 6) and 100:20:13 (FIG. 6) reached equilibrium at roughly 120 min indicating that both the coumarin crosslinking and PEDOT polymerization were completed within this time.

[0094] The influence of the proportion of coumarin crosslinker on the mechanical properties of conductive hydrogels was examined through tensile tests. Still keeping a SS:EDOT ratio of 100:13, the solutions were irradiated for 120 min in a mold, and the hydrogels were washed with DI water and PBS prior to the tensile test. FIG. 7 illustrates the stress-strain curves obtained from the tensile elongation of hydrogels with different SS:CoumAc ratios. The hydrogels exhibited varying elastic moduli: 4.6 MPa, 5.4 MPa, and 10.5 MPa for ratios of 100:5, 100:10, and 100:20 respectively (Table 3).

[0095] Table 3. Tabulated mechanical and electronic properties showing the effect of the amount of CoumAc crosslinker.

[0096] __ _ . Elas . ti .c Strain atT. Cond .uct ..iv ..

[0097] SS:CoumA modulu . . Toughness it _ Re _ Ri2c ratio s a (kJ nr3)3fS-nb Wc(«)c X

[0098] (MPa)a ( / o) (S m'

[0099] 100:20 7.2 ± 3.0 6 ± 2 6.0 ± 2.4 2.8 ± 0.1 293 ± 61 4.7 ± 0 00

[0100] 0.6 8

[0101] 100:10 5.4 ± 3.6 13 ± 5 9.0 ± 3.2 4.6 ± 0.1 166 ± 6 9.2 ± 0 00

[0102] 1.7 6

[0103] 100:5 4.6 ± 2.0 16 ± 1 16.2 ± 3.0 9.2 ± 0.7 198 ± 24 9.0 ± 0 03

[0104] 2.5aMeasured by tensile tests.bObtained by two-point parallel plate measurements. •Obtained by EIS by fitting to the equivalent circuit model shown in Figure 4c. Average of three separate samples.

[0105] As the amount of crosslinker increased, the elastic modulus of the hydrogels increased, while the toughness and strain at break decreased. Among the ratios tested, the hydrogel with a ratio of 100:5 displayed the highest strain at break (16%). However, at 120 min irradiation, relatively lower elastic modulus was observed. These relatively lower elastic modulus could possibly be caused by the hydrogel network not being fully crosslinked.

[0106] To gain further insights into the effect of the proportion of coumarin crosslinker on the ionic and electronic conductivities, EIS and parallel plate resistance measurements were conducted. The Bode plots (FIG. 7) showed that the impedance magnitude was just slightly lower in the formulations with less coumarin crosslinker. The Nyquist plots (FIG. 7) of the hydrogels were analyzed and fitted to the equivalent circuit model shown in FIG. 5. For all three ratios tested, Re and Ri were roughly the same with Re around 200 Q and Ri of 5-9 Q. The electronic conductivities, measured through 2-point parallel plate measurements, showed only a slightly higher value (9.22 S rrr1) in the hydrogels with the lowest amount of crosslinker (SS:CoumAc 100:5). The lack of major differences between the three formulations was not surprising, because the ratio of PEDOT:PSS was kept constant at 13:100, and PEDOT+was the only contributor to electronic conductivity in the hydrogels.

[0107] Next, the microstructure of the hydrogels was studied by scanning electron microscopy (SEM) on freeze-dried cross-sections. The SEM images of PEDOT:P(SS-co-CoumAc) hydrogels with a SS:CoumAc crosslinker ratio 100:5, 100:5, and 100:20 (FIG. 8) revealed a 3D interconnected porous structure. The cross-sections SEM of all hydrogels showed a dense but relatively homogeneous network. The average pore size, as determined by image analysis, of the conductive hydrogels of ratio 100:5, 100:10, 100:20 were 1 .15 ± 0.47 pm, 0.63 ± 0.26 pm, 0.77 ± 0.27 pm, respectively. These values are consistent with an increase in network density at higher degrees of crosslinking. As the degree of coumarin crosslinker increased, a change from a fibrillar network morphology to the formation of denser aggregates was observed. This change in morphology could explain the difference in the mechanical behavior under tensile tests (FIG. 7), where the fibrillar networks are more elastic (100:5 ratio) and the aggregated networks are getting more plastically deformed (100:20).

[0108] As a proof of concept of the utility of the photo-mediated formation of conductive hydrogels, a commercial laser writer was used to test if the exemplary formulations could achieve photo-patterned conductive hydrogels. For this experiment, the formulation with the fastest gelation time was chosen, i.e., SS:CoumAc:EDOT of 100:20:13. The precursor solution was drop-casted and spread manually on a glass slide pre-treated with plasma to increase its hydrophilicity. The glass slide was then placed under the laser writer which used a wavelength of 385 nm with an intensity of 2 W cm-2to create a design with features that had a minimum width of 100 pm through 45s exposure times. The total printing time to achieve the desired pattern was 13.5 min.

[0109] Blue patterns with good resolution were obtained. No ‘bleeding’ of PEDOT was observed outside the patterned features, which suggests that its diffusion is limited by the formation of a crosslinked network even at these short exposure times. While this photo-printing experiment was not fully optimized, it showed that patterns of conductive hydrogels with micron-scale resolution could be achieved.

[0110] The photo-crosslinked hydrogels have good conductivities and elastic moduli similar to that of skin, which should enable conformal contact between the electrodes and skin. To demonstrate this, the photo-crosslinked hydrogels, with SS:CoumAc:EDOT ratio of 100:20:13 (same formulation as above for the photopatterning), were compared to a commercial 3M™ Ag / AgCI hydrogel sEMG electrode (FIG. 9). The hydrogels were applied as electrodes wearable on the arm for surface electromyography (sEMG) to measure finger movements. For ease of fabrication and wiring, the PEDOT-based conductive hydrogel was photocrosslinked for 120 min directly into the electrode reservoir emptied from the commercial product. The electrodes were adhered firmly onto the skin of the forearm to ensure good contact. The sEMG signals obtained with the photocrosslinked hydrogel electrode closely resembled those recorded using commercial gel electrodes, but with a slightly higher potential amplitude. The photo-crosslinked electrode showed good sensitivity by detecting changes in sEMG signal when different finger movements were made, highlighting its potential as a wearable electrode.

[0111] Experimental Methods for Example 1 Materials

[0112] 4-Methylumbelliferone, 2-bromoethanol, triethylamine, sodium 4- styrenesulfonate (NaSS), 4,4'-azobis(4-cyanovaleric acid) (ACVA), 3,4- ethylenedioxythiophene (EDOT), ammonium persulfate ((NH4)2S20s), acidic resin (Dowex Marathon C hydrogen form) were purchased from Sigma-Aldrich and used without further purification. Potassium carbonate (K2CO3), anhydrous N,N- dimethylformamide (DMF), chloroform (CHC ), dioxane, dichloromethane (CH2CI2), sodium sulfate (Na2SO4) were purchased from Fisher Scientific. Acryloyl chloride was purchased from Sigma-Aldrich and passed through a column of basic alumina to remove inhibitors and acidic impurities prior to the reaction. 3M™ Ag / AgCI Red Dot Monitoring Electrodes were purchased from Amazon.

[0113] Synthesis of 7-(2-hydroxyethoxy)-4-methylcoumarin (CoumOH).

[0114] 4-Methylumbelliferone (4.00 g, 22.7 mmol, 1 equiv.) and potassium carbonate (6.23 g, 45.4 mmol, 2 equiv.) were mixed in anhydrous DMF (40 mL) under nitrogen atmosphere. 2-Bromoethanol (2.42 mL, 34.0 mmol, 1.5 equiv.) was added, and the reaction was heated at 90 °C for 18 h. The reaction mixture was cooled to room temperature and poured into ice-cold water. The white precipitate was collected by vacuum filtration and dried in vacuo. Yield: 4.50 g (90%).1H NMR (600 MHz, DMSO-de): 5 (ppm) 7.70-7.68 (dd, 1 H), 6.99-6.97 (m, 2H), 6.21 (d, 1 H), 4.92 (t, 1 H), 4.10 (t, 2H), 3.75 (m, 2H), 2.40 (d, 3H).

[0115] Synthesis of 7-(2-acryloyloxyethoxy)-4-methylcoumarin (CoumAc).

[0116] 7-(2-Hydroxyethoxy)-4-methylcoumarin (4.00 g, 18.2 mmol, 1 equiv.) was suspended in chloroform (75 mL) and triethylamine (5.06 mL, 36.3 mmol, 2 equiv.) was added. Acryloyl chloride (2.94 mL, 36.3 mmol, 2 equiv.) was added portionwise under argon and the reaction was stirred at room temperature. After 1 h, additional triethylamine (2.53 mL, 18.2 mmol, 1 equiv.) and acryloyl chloride (1.47 mL, 18.2 mmol, 1 equiv.) were added and the solution was stirred overnight. The reaction mixture was diluted with dichloromethane, washed with brine (100 ml_ x 2), dried over sodium sulfate, filtered, and concentrated in vacuo. The crude product was recrystallized twice from ethanol to yield CoumAc as a white powder. Yield: 1 .83 g (37%).1H NMR (600 MHz, CDCI3): 5 (ppm) 7.45 (d, 1 H), 6.82 (dd, 1 H), 6.77 (d, 1 H), 6.39 (dd, 1 H), 6.11 (m, 2H), 5.81 (dd, 1 H), 4.48 (t, 2H), 4.21 (t, 2H), 2.34 (s, 3H).

[0117] Synthesis of P(SS-co-CoumAc) copolymer.

[0118] CoumAc (307.5 mg, 1.12 mmol), sodium styrene sulfonate (NaSS) in different amounts according to the desired ratio of PSS to PCoumAc (1.04 g-5 mmol, 2.08 g-10.1 mmol, and 4.16 g-20.2 mmol for ratio of 100:20, 100:10, and 100:5, respectively), and ACVA (147 mg, 0.52 mmol) were dissolved in a mixture of 16 mL of water and 8 mL of dioxane, degassed under a flow of nitrogen for 30 min. The reaction mixture was placed in an oil bath at 70 °C for 18 h. The reactions were stopped by rapid cooling and exposure to air. P(SSNa-co-CoumAc) was purified by dialysis against water for 2 days with multiple water bath changes. The purified solution was rotovapped and dried under vacuum to yield a solid product. Next, P(SSNa-co-CoumAc) was dissolved in water (0.1 g mL-1) and stirred over an acidic resin (Dowex Marathon C hydrogen form) for 6 h at room temperature to afford the acid form of P(SS-co-CoumAc). Then, P(SS-co-CoumAc) was filtered through a 0.45 pm Nylon syringe filter and dried under vacuum.

[0119] Preparation of PEDOT:P(SS-co-CoumAc) conductive hydrogels. P(SS-co-CoumAc) (150 mg, 50 wt%) was dissolved in 0.3 mL of water. Depending on the ratio of PSS to PCoumAc, different amount of EDOT and APS were added to the solution to keep the optimized mole ratio of APS to EDOT 1.2:1 , and the mole ratio of PSS to EDOT 100:13. For the ratio of PSS to PCoumAc 100:20, EDOT (8.25 pL, 0.078 mmol) and APS (21 .3 mg, 0.093 mmol) were added. For the ratio of PSS to PCoumAc 100: 10, EDOT (9 pL, 0.085 mmol) and APS (22.5 mg, 0.099 mmol) were added. For the ratio of PSS to PCoumAc 100:5, EDOT (9.45 pL, 0.0089) and APS (24.4 mg, 0.107 mmol) were added. The solutions were stirred vigorously at room temperature for 5 mins, then irradiated with long-wave UV (A = 365 nm) for 150 mins until gelation was complete.

[0120] Nuclear magnetic resonance (NMR).

[0121] 1H NMR spectrum were recorded on a Bruker 600 MHz spectrometer at room temperature.

[0122] Size exclusion chromatography (SEC).

[0123] Number-average (Mn) and weight-average (Mw) molecular weights and dispersity (£>) were determined by SEC using a Tosoh HLC-8420 GPC EcoSEC LC system equipped with a PSS GRAM column (10 pm, 8 x300 mm) running in 10 vol% deionized water and 90% dimethylformamide (DMF) with 0.1 wt% lithium bromide (LiBr) at 25 °C with a flow rate of 0.8 mL min-1, and calibrated against narrow dispersity polystyrene sulfonate standards (purchased from Polymer Standards Service).

[0124] UV-Vis Spectroscopy.

[0125] UV-Vis measurements were taken using a Shimadzu UV-3600 Spectrometer at 25 °C. Absorbance measurements were conducted with 2 mL of sample in quartz cuvettes.

[0126] Photo-rheometer.

[0127] The gelation process of the hydrogel precursor under UV light (365 nm) was evaluated by an oscillatory rheometer (AR-G2, TA Instrument) assembled with an OmniCure Series 2000 light source (25 mW cm-2), a sample chamber, and an 8- mm diameter steel parallel-plate geometry. The testing was conducted at room temperature with a strain of 1 %, and an axial force control of 0 ± 0.5 N.

[0128] Electrochemical impedance spectroscopy (EIS).

[0129] EIS measurements were performed on a Metrohm Autolab PGSTAT128N in a Faraday cage. Impedance magnitude and phase were scanned over a frequency range of 0.1 to 1x105Hz at 0 V bias with 10 mV amplitude.

[0130] Resistance measurements.

[0131] The resistance was measured between two parallel stainless steel electrodes and was measured using a Keithley 2400 source meter. The conductivity o was calculated by using equation (1 ) where L is length, t is thickness, and w is width of hydrogel. L <y = R -x t x w (1)

[0132] Tensile tests.

[0133] The mechanical tests (stress-strain curves) on the conductive hydrogels (4 mm x 25 mm x 2 mm) were performed on a tensile tester (MTS, Tytron 250) at a speed of 9 mm min-1at room temperature. Toughness was calculated from the integration of the stress-strain curves.

[0134] X-ray photoelectron spectroscopy (XPS).

[0135] The elemental composition of the hydrogels was analyzed by X-ray photoelectron spectroscopy on a Thermo Scientific K-Alpha XPS system. The hydrogels were lyophilized and grinded into powder before taking XPS.

[0136] Scanning electron microscopy (SEM).

[0137] Cross-sectional images were obtained using an Auriga 60 SEM. The hydrogels were lyophilized and broken in half then the surface of the samples was sputter-coated with Palladium for 60 seconds before recording the SEM images.

[0138] Optical microscopy.

[0139] Optical microscopy images of the photo-printed hydrogels were taken on a Zeiss Axiovert200M microscope.

[0140] Electrode fabrication and surface electromyography (sEMG) measurements To fabricate photo-crosslinked electrodes, we carved out the gels in the commercial 3M™ Ag / AgCI Red Dot Monitoring electrodes. Then, we placed the precursor solution with a SS:CoumAc:EDOT ratio of 100:10:13 into the electrode mold and photo-irradiated it for 120 min. The photo-crosslinked gels were then washed multiple times with deionized water and PBS before conducting the sEMG measurements.

[0141] The EMG measurements were performed using the methods described by Blau et. al. (Blau, R.; Chen, A. X.; Polat, B.; Becerra, L. L.; Runser, R.; Zamanimeymian, B.; Choudhary, K.; Lipomi, D. J., Intrinsically Stretchable Block Copolymer Based on PEDOT:PSS for Improved Performance in Bioelectronic Applications. ACS Appl. Mater. Interfaces 2022, 14 (4), 4823-4835). The electrodes were adhered firmly onto the skin of the forearm to ensure good contact. The electrodes were connected to the ECG channel of a MAX30001- EVSYS evaluation board (Maxim Integrated Products, Inc.). The reference electrode (3M™ Ag / AgCI Red Dot Monitoring Electrode) was placed on the elbow of the same arm and connected to the Body Bias pin of the board. The ECG channel was configured to have a gain of 20 V / V and a sampling rate of 512 readings s-1. Post-ADC digital filters were used during the recordings. The low pass filter cutoff was 40 Hz, and the high pass filter cutoff was 0.5 Hz. A Butterworth notch filter with a width of 59 to 61 Hz was applied post-measurement to eliminate 60 Hz power-line noise.

[0142] Laser writer

[0143] The patterned polymer was made by laser writing using a commercial maskless photolithography tool (microlight3D). The pattern was designed in the mask design software Klayout. Then the pattern file was imported into the Phaos, which is a dedicated software to configure the maskless photolithography tool. The designed pattern was split into 18 stitches and the exposure time was set to 45 seconds for each stitch. The precursor ink solution with a SS:CoumAc:EDOT ratio of 100:20:13 was spread onto a microscope glass slide and the glass slide was placed onto the exposure stage of the photolithography tool. The wavelength of the UV light was 385 nm and the light power density was 2072 mW cm-2.

[0144] It will be appreciated by those skilled in the art that the present disclosure can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the disclosure is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

Claims

CLAIMS:1 . A composition comprising:(i) a random copolymer derived from at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer;(ii) an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization;(iii) an oxidant; and(iv) a solvent comprising water.

2. The composition according to claim 1 , wherein the photo-crosslinkable monomer is selected from the group consisting of coumarin acrylate, 4- phenylazophenyl acrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, or a blend thereof.

3. The composition according to claim 1 , wherein the water-soluble anionic monomer is selected from the group consisting of styrene sulfonate, maleic acid, acrylic acid, or a blend thereof.

4. The composition according to claim 1 , wherein the aromatic heterocycle monomer is selected from the group consisting of 3,4- ethylenedioxythiophene, pyrrole, aniline, thiophene, 3,4- propylenedioxythiophene, 3,4-phenylenedioxythiophene, or a blend thereof.

5. The composition according to claim 1 , wherein the random copolymer comprises poly(styrene sulfonate-co-coumarin acrylate), poly(styrene sulfonate-co-4-phenylazophenyl acrylate), poly(styrene sulfonate-co- triethylene glycol diacrylate), poly(styrene sulfonate-co-tetraethylene glycol dimethacrylate), or a blend thereof.

6. The composition according to claim 1 , wherein the oxidant is selected from the group consisting of ammonium persulfate, potassium persulfate, hydrogen peroxide, iron (III) sulfate, or iron (III) chloridepersulfates, peroxides, iron (III) oxidants, or a combination thereof.

7. The composition according to claim 1 , wherein the random copolymer is derived from a mixture containing the water-soluble anionic monomer and the photo-crosslinkable monomer in a molar ratio in a range of 1 :1 to 50:1 , or 2:1 to 40:1 , or 4:1 to 25:1.

8. The composition according to claim 1 , wherein the random copolymer is derived from a mixture containing the water-soluble anionic monomer andthe aromatic heterocycle monomer in a mass ratio in a range of 1 :1 to 50: 1 , or 2:1 to 40:1 , or 5: 1 to 35:1.

9. The composition according to claim 1 , wherein the random copolymer has a molecular weight in a range of 10 to 100 kDa or 15 to 60 kDa, or 20 to 45 kDa, measured, by size exclusion chromatography (SEC) using a refractive index detector, in water buffenDMF calibrated against PSSNa standards.

10. The composition according to claim 1 , wherein the composition exhibits a sol-gel transition and forms a hydrogel upon exposure to UV light in a range of 300 to 400 nm, or 310 to 390 nm, or 340 to 380 nm.

11. The composition according to claim 10, wherein the composition is electrically conductive in the hydrogel state.

12. A hydrogel composition comprising:(i) a photo-crosslinked copolymer, derived from at least one photo- crosslinkable monomer and at least one water-soluble anionic monomer, wherein the photo-crosslinkable polymeric units are photo-crosslinked; and(ii) a polycationic conductive polymer derived from an aromatic heterocycle monomer by oxidative polymerization; and(iii) a solvent comprising water.

13. The hydrogel composition according to claim 12, wherein the photo- crosslinkable monomer is selected from the group consisting of coumarin acrylate, 4-phenylazophenyl acrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, or a blend thereof.

14. The hydrogel composition according to claim 12, wherein the water-soluble anionic monomer is selected from the group consisting of styrene sulfonate, maleic acid, acrylic acid, or a blend thereof.

15. The hydrogel composition according to claim 12, wherein the water-soluble anionic monomer and the photo-crosslinkable monomer are present in a molar ratio in a range of 1 :1 to 50:1 , or 2:1 to 40:1 , or 4:1 to 25: 1.

16. The hydrogel composition according to claim 12, wherein the water-soluble anionic monomer and the aromatic heterocycle monomer are present in a mass ratio in a range of 1 :1 to 50:1 , or 2:1 to 40: 1 , or 5: 1 to 35:1.

17. The hydrogel composition according to claim 12, wherein the random copolymer comprises poly(styrene sulfonate-co-coumarin acrylate),poly(styrene sulfonate-co-4-phenylazophenyl acrylate), poly(styrene sulfonate-co-triethylene glycol diacrylate), poly(styrene sulfonate-co- tetraethylene glycol dimethacrylate), or a blend thereof.

18. The hydrogel composition according to claim 12, wherein the polycationic conductive polymer comprises poly(3,4-ethylenedioxythiophene), polypyrrole, polyaniline, polythiophene, poly(3,4-propylenedioxythiophene), poly(3,4-phenylenedioxythiophene), or a blend thereof.

19. The hydrogel composition according to claim 12, wherein the random copolymer has a molecular weight in a range of 10 to 100 kDa or 15 to 60 kDa, or 20 to 45 kDa, measured, by size exclusion chromatography (SEC) using a refractive index detector, in water buffer: DM F calibrated against PSSNa standards.

20. The hydrogel composition according to claim 12, wherein the hydrogel composition is electrically conductive.

21. The hydrogel composition according to claim 20, wherein the hydrogel exhibits electrical conductivity in a range of 0.1 to 25 S / m, or 0.2 to 20 S / m, or 0.4 to 15 S / m.

22. A medical device comprising the composition or hydrogel composition according to any one of claims 1 to 21 , wherein the medical device is an implantable medical device, a wearable medical device, or a theranostic device.

23. The medical device of claim 22, wherein the composition or hydrogel composition are present in an injectable scaffold, a 3D printed scaffold, a biomedical implant, an injectable electrode, a wearable electrode, a biosensor, an actuator, or an electrochemical transistor, or a soft electrodes for surface biopotential applications, including electrocardiogram (ECG), electroencephalogram (EEG), and electromyography (EMG).

24. A method comprising the steps of:(i) providing a composition comprising: a. a random copolymer, wherein the copolymer comprises at least one photo-crosslinkable monomer and at least one water-soluble anionic monomer, b. an aromatic heterocycle monomer for synthesizing a polycationic conductive polymer by oxidative polymerization,c. an oxidant, and d. a solvent comprising water;(ii) exposing the composition to UV light in a range of 300 to 400 nm, or 310 to 390 nm, or 340 to 380 nm for an amount of time in a range of 1 to 180 minutes, or 25 to 150 minutes, or 50 to 125 minutes to form the hydrogel composition according to any one of claims 12-21 ; and(iii) washing the hydrogel composition by soaking the hydrogel in a solution comprising distilled water or phosphate buffer solution (pH = 7) for 24h and changing the solution a minimum of three times.

25. The method according to claim 24, where the oxidant is selected from the group consisting of ammonium persulfate, potassium persulfate, hydrogen peroxide, iron (III) sulfate, or iron (III) chloridepersulfates, peroxides, iron (III) oxidants, or a combination thereof.

26. The method according to claim 24, wherein the oxidant and the aromatic heterocycle monomer are present in a molar ratio in a range of 1 : 1 to 1.5:1 , or 1 :1 to 1.4:1 , or 1.1 :1 to 1.3:1.

27. The method according to claim 24, further comprising a step of 3D printing the composition during the step of exposing the composition to UV light.

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