A method for preparing a skin-based conductive hydrogel based on polycationic electrolyte

Abstract

The present application relates to a kind of preparation method of skin-based conductive hydrogel based on polycation electrolyte.The method uses cationic monomer and initiator aqueous solution to impregnate treatment pickled bare skin, stir at 5~30 ℃ for 4~48 hours, then bare skin is heated at 40~70 ℃ for 2~12 hours, to obtain skin-based conductive hydrogel.The method uses high-strength pickled bare skin as the basic framework of conductive hydrogel, and the polyelectrolyte three-dimensional network formed by in-situ polymerization of cationic monomer forms network interpenetrating structure with the original collagen fiber three-dimensional network of bare skin, which gives skin-based conductive hydrogel high mechanical strength, effectively solves the defects of insufficient network structure stability, poor mechanical strength and easy leakage of conductive ions of traditional ion conductive hydrogel.The raw materials used in the present application can be easily obtained from the leather and chemical industry, and the price is cheap, and the preparation process is simple, easy to large-scale preparation.

Description

Technical Field

[0001] This invention relates to the field of conductive hydrogels and animal skin biomass materials, specifically to a method for preparing a skin-based conductive hydrogel based on polycationic electrolyte by using acid-impregnated naked skin as raw material, impregnating it with a solution composed of cationic monomers and initiators, and then polymerizing it in situ. Background Technology

[0002] Conductive hydrogels are a novel class of functional materials that combine the hydrophilicity of a three-dimensional network structure with mechanical flexibility and charge transport capabilities. Through the synergistic effect of the polymer matrix and conductive components, they achieve integrated "structure-function," demonstrating broad application value in flexible electronics, electrochemical energy storage, biomedicine, and sensor devices. Based on the different conductive components, conductive hydrogels can be classified into conductive polymer-based conductive hydrogels, carbon-based conductive hydrogels, metal-based conductive hydrogels, and ion-conductive hydrogels. Among these, the rigid conductive materials in conductive polymer-based, carbon-based, and metal-based conductive hydrogels are randomly distributed and easily aggregate in the flexible hydrogel matrix, severely affecting the electrochemical performance of the conductive hydrogel. In contrast, ion-conductive hydrogels do not require the addition of conductive fillers; their conductivity is formed by the migration of conductive ions uniformly distributed within the hydrogel framework, exhibiting stable electrochemical performance. Ion-conductive hydrogels are very similar to the ion conduction mechanism of human skin and possess good mechanical properties, stable conductivity, and high sensitivity, making them considered one of the best candidate materials for biomimetic electronic skin.

[0003] There are two main ways to construct conductive hydrogels with ion-conducting properties: (1) Introducing ion salt solutions into the hydrogel. For example, metal salts such as LiCl, NaCl, KCl, and FeCl3 have good water solubility and will generate metal ions (LiCl, NaCl, KCl, FeCl3) in water. + Na + K + Fe 3+ , to provide good conductivity for hydrogels, has been widely used in the preparation of ion-conducting hydrogels. (2) Introducing polymer electrolytes into hydrogels. The conductive hydrogel prepared by the former method is a salt ion-type ion-conducting hydrogel, whose conductivity mechanism is "free ion diffusion": the pore structure of the polymer network provides migration paths for ions, and water molecules act as a solvation medium to reduce the ion migration energy barrier. Ion concentration, network connectivity and water content are the key factors affecting conductivity efficiency. Ionic conductivity is usually between 0.5 and 18 mS / cm. The conductive hydrogel prepared by the latter method is a polyelectrolyte-type ion-conducting hydrogel, through the dissociable groups on the polymer backbone (anionic type: -COO) - -SO3 - Cationic type: -NH3+ -N + (CH3)3; zwitterionic type: containing both cation and anion groups) provides conductive ions, requiring no additional ionic salts. The conductivity mechanism is "polymer chain-mediated ion transport": dissociated ions (such as -COO) - with Na + A continuous transport path is formed within the polymer network. Ion migration depends on the local cooperative motion of polymer chain segments and the network pore structure. The ionic conductivity is usually between 1 and 34 mS / cm.

[0004] Salt ion-conducting hydrogels were widely used in early flexible sensing and aqueous batteries due to their simple preparation and low cost. However, the inherent characteristics of exogenous salt ions led to bottlenecks such as ion leakage, poor environmental stability, and insufficient biocompatibility. Polyelectrolyte-based ion-conducting hydrogels, through molecular design, "anchor" conductive ions to the polymer network, fundamentally solving the core defects of salt ion-conducting hydrogels and exhibiting superior overall performance. For example, the dissociative groups (such as sulfobetaine and carboxyl groups) of polyelectrolyte conductive hydrogels form strong hydrogen bonds with water molecules, which can firmly lock in water within the network and exhibit excellent resistance to dehydration. The dissociative groups of polyelectrolyte conductive hydrogels can disrupt the orderly arrangement of water molecules, inhibit ice crystal formation, and have good resistance to low-temperature freezing. The conductive ions of polyelectrolyte conductive hydrogels originate from the dissociation of the polymer backbone. There is a weak interaction between counter ions and dissociative groups, which significantly reduces the risk of leakage. Polyelectrolyte conductive hydrogels maintain the loose structure of the network through electrostatic repulsion and hydrogen bonding between dissociative groups, and the dynamic cross-linking mechanism can alleviate stress concentration, thus making the network structure more stable. The dissociative groups (such as carboxyl groups and sulfobetaine) of polyelectrolyte conductive hydrogels are mostly biocompatible functional groups, and there is no osmotic pressure damage from free salt ions, resulting in a cell survival rate that is generally higher than 90%.

[0005] Despite the significant advantages of polyelectrolyte-based ion-conductive hydrogels, they still suffer from insufficient mechanical strength. Currently, the main mechanisms for improving the mechanical properties (such as tensile strength, elongation at break, toughness, and fatigue resistance) of ion-conductive hydrogels are as follows: (1) Dual network reinforcement mechanism: constructing an interpenetrating structure of "rigid network-flexible network", the rigid network provides strength support, the flexible network ensures chain segment mobility and ion transport efficiency, and at the same time, energy dissipation is achieved through sacrificial bonds (such as hydrogen bonds and metal coordination bonds), thereby improving flexibility; (2) Filler reinforcement and toughening mechanism: improving mechanical properties by introducing nano-reinforcing phases (such as cellulose nanocrystals, metal-organic frameworks (MOFs), and carbon nanotubes); (3) Polymer chain structure optimization mechanism: optimizing the degree of entanglement and flexibility of polymer chains by adjusting parameters such as monomer molecular weight, copolymerization ratio, and crosslinking agent type; (4) Microphase separation structure design mechanism: utilizing the hydrophilic and hydrophobic differences of amphiphilic polymers, forming a dual continuous structure of "rigid hydrophobic phase-flexible hydrophilic phase" through water-induced microphase separation, the rigid hydrophobic phase bears the mechanical load, and the flexible hydrophilic phase provides ion transport channels, thereby achieving performance decoupling.

[0006] Nevertheless, the insufficient mechanical strength of polyelectrolyte-based ion-conducting hydrogels remains a significant limitation due to the inherently poor mechanical properties of the polymer's three-dimensional cross-linked network, thus restricting their application in high-load environments. Therefore, developing novel polyelectrolyte-based ion-conducting hydrogel materials with stable network structures and high mechanical strength is crucial and urgent, and is of great significance for promoting their high-value utilization in complex, high-load environments. Summary of the Invention

[0007] Animal hides (such as goatskin, sheepskin, cowhide, and pigskin), as raw materials for leather tanning, are a typical natural biomass material with outstanding advantages such as abundant resources, renewability, good biocompatibility, and biodegradability. Currently, the application of animal hides is undergoing an important transformation from traditional leather tanning to high-value-added functional materials. Their unique collagen fiber structure and excellent comprehensive properties are the foundation for their functional applications. Collagen fibers account for 99% of the connective tissue fibers in dermis and are the object of leather processing and functional applications. The microstructure of collagen fibers is highly ordered: collagen molecules (procollagen) consist of three polypeptide chains forming a triple helix structure. These molecules are arranged in parallel and covalently cross-linked to form primary protofibrils (diameter 12~17 Å). Primary protofibrils aggregate into protofibrils (diameter approximately 2~5 μm), and protofibrils recombine to form collagen fibers (diameter 20~150 μm). Finally, collagen fibers are woven into fiber bundles, forming the unique multi-level three-dimensional network structure of collagen fibers in animal hides. This multi-level, ordered hierarchical structure allows collagen fiber bundles to interweave and combine in three-dimensional space, forming a three-dimensional woven network that endows animal hides and leathers with excellent mechanical strength. The multi-level assembly structure and cross-linking characteristics of collagen fibers are the core factors determining the mechanical properties of animal hides, and the two work synergistically to regulate key mechanical indicators such as strength, toughness, and elasticity. Simultaneously, the three-dimensional porous network structure of collagen fibers (porosity 50%–80%) provides uniformly dispersed channels for functional components (such as conductive particles, drugs, and nanofillers), laying a natural foundation for the high-value utilization of animal hides.

[0008] Based on the above analysis, it can be seen that the multi-level structure (molecular-level triple helix, micro-level fiber bundle, macro-level three-dimensional network) and porous characteristics of the three-dimensional cross-linked network of animal skin collagen fibers provide sufficient physical space and reaction sites for the absorption of functional substances. Therefore, it can serve as the basic framework of conductive hydrogels, and its inherent high mechanical strength and high toughness will greatly enhance the mechanical strength and flexibility of the resulting skin-based conductive hydrogel. Therefore, to address the shortcomings of unstable network structure and insufficient mechanical strength in polyelectrolyte-type ion-conductive hydrogels, this invention adopts a "top-down" preparation route. First, an impregnation treatment is performed, immersing the acid-treated bare skin in an impregnation solution composed of cationic monomers and initiators, allowing these functional substances to penetrate into the three-dimensional network structure of the collagen fibers in the bare skin. Then, the cationic monomers undergo in-situ polymerization, resulting in a polyelectrolyte three-dimensional network that forms an interpenetrating network structure with the original three-dimensional collagen fiber network in the bare skin, yielding a skin-based conductive hydrogel. This further improves the mechanical strength of the skin-based conductive hydrogel, and the polycationic electrolyte imparts good and durable stable conductivity.

[0009] Specifically, the present invention aims to provide a method for preparing a skin-based conductive hydrogel, characterized by the following process flow: 1) Weigh the acid-impregnated bare skin and add it to an impregnation solution of 200%~800% of the weight of the bare skin, and stir at 5~30°C for 4~48 hours; 2) Take out the impregnated bare skin, place it between two smooth plates, and heat it at 40~70°C for 2~12 hours while keeping the bare skin flat to obtain the skin-based conductive hydrogel. The acid-treated raw hide used in this method is any one of acid-treated cowhide, acid-treated pigskin, and acid-treated sheepskin; the impregnation solution used to prepare the leather-based conductive hydrogel is composed of cationic monomer, initiator, and water, with a mass ratio of cationic monomer:initiator:water = 100:0.1~1.0:40~200; the cationic monomer in the impregnation solution is any one of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and methacrylamidopropyltrimethylammonium chloride; the initiator in the impregnation solution is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

[0010] The method for preparing skin-based conductive hydrogels provided by this invention has the following advantages: First, this invention uses acid-impregnated bare skin with high mechanical strength and high toughness as the basic framework of conductive hydrogel. The resulting skin-based conductive hydrogel not only inherits the original high mechanical strength and high flexibility of the bare skin, but also forms a three-dimensional polyelectrolyte network through in-situ polymerization of cationic monomers, which interpenetrates with the original collagen fiber three-dimensional network in the bare skin, further improving the mechanical strength of the skin-based conductive hydrogel. This effectively solves the defects of poor network stability and insufficient mechanical strength of traditional conductive hydrogels.

[0011] Secondly, the present invention uses cationic monomers to prepare polyelectrolyte-based conductive hydrogels through in-situ polymerization. The conductivity of the hydrogels comes from the conductive ions provided by the dissociated groups of the polymer backbone, so there is no problem of conductive ion leakage.

[0012] Third, the raw materials used in this invention are readily available and inexpensive from the leather and chemical industries, and the preparation process is simple and easy to carry out on a large scale. Detailed Implementation

[0013] The following embodiments are provided to illustrate the present invention in more detail. It should be noted that the following embodiments should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention are still within the scope of protection of the present invention.

[0014] Example 1 An impregnation solution was prepared using acryloyloxyethyltrimethylammonium chloride as a cationic monomer, potassium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.4:100. The acid-treated goatskin was weighed and added to the impregnation solution at 550% of its weight. The mixture was stirred at 22°C for 24 hours. Subsequently, the impregnated goatskin was removed and placed between two smooth plates. While maintaining the flatness of the goatskin, it was heated at 55°C for 10 hours to obtain a skin-based conductive hydrogel.

[0015] Example 2 An impregnation solution was prepared using methacryloyloxyethyltrimethylammonium chloride as a cationic monomer, potassium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.2:60. The acid-impregnated sheepskin was weighed and added to the impregnation solution, which was then stirred at 10°C for 40 hours. Subsequently, the impregnated sheepskin was removed and placed between two smooth plates. While maintaining the sheepskin's flatness, it was heated at 45°C for 11 hours to obtain a skin-based conductive hydrogel.

[0016] Example 3 An impregnation solution was prepared using methacrylamide propyltrimethylammonium chloride as a cationic monomer, potassium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.1:40. The acid-treated cowhide was weighed and added to the impregnation solution, which was 200% of the cowhide's weight. The mixture was stirred at 5°C for 48 hours. Subsequently, the impregnated cowhide was removed and placed between two smooth plates. While keeping the cowhide flat, it was heated at 65°C for 3 hours to obtain a leather-based conductive hydrogel.

[0017] Example 4 An impregnation solution was prepared using acryloyloxyethyltrimethylammonium chloride as a cationic monomer, ammonium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:1.0:200. The acid-treated pigskin was weighed and added to the impregnation solution, which was 700% of the pigskin's weight. The mixture was stirred at 30°C for 4 hours. Subsequently, the impregnated pigskin was removed and placed between two smooth plates. While maintaining the pigskin's flatness, it was heated at 70°C for 2 hours to obtain a skin-based conductive hydrogel.

[0018] Example 5 An impregnation solution was prepared using methacryloyloxyethyltrimethylammonium chloride as a cationic monomer, ammonium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.7:140. The acid-treated goatskin was weighed and added to the impregnation solution at 300% of its weight. The mixture was stirred at 15°C for 32 hours. Subsequently, the impregnated goatskin was removed and placed between two smooth plates. While maintaining the flatness of the goatskin, it was heated at 40°C for 12 hours to obtain a skin-based conductive hydrogel.

[0019] Example 6 An impregnation solution was prepared using methacrylamide propyltrimethylammonium chloride as the cationic monomer, ammonium persulfate as the initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.6:120. The acid-impregnated sheepskin was weighed and added to the impregnation solution, which was then stirred at 28°C for 8 hours. Subsequently, the impregnated sheepskin was removed and placed between two smooth plates. While maintaining the sheepskin's flatness, it was heated at 50°C for 8 hours to obtain a skin-based conductive hydrogel.

[0020] Example 7 An impregnation solution was prepared using acryloyloxyethyltrimethylammonium chloride as a cationic monomer, azobisisobutyramidine hydrochloride as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.5:110. The acid-treated cowhide was weighed and added to the impregnation solution at 500% of its weight. The mixture was stirred at 16°C for 44 hours. Subsequently, the impregnated cowhide was removed and placed between two smooth plates. While keeping the cowhide flat, it was heated at 60°C for 6 hours to obtain a leather-based conductive hydrogel.

[0021] Example 8 An impregnation solution was prepared using methacryloyloxyethyltrimethylammonium chloride as a cationic monomer, azobisisobutyramidine hydrochloride as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.3:80. The acid-treated pigskin was weighed and added to the impregnation solution at 350% of its weight. The mixture was stirred at 20°C for 20 hours. Subsequently, the impregnated pigskin was removed and placed between two smooth plates. While maintaining the flatness of the pigskin, it was heated at 58°C for 9 hours to obtain a skin-based conductive hydrogel.

[0022] Example 9 An impregnation solution was prepared using methacrylamide propyltrimethylammonium chloride as the cationic monomer, azobisisobutyramidine hydrochloride as the initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.9:180. The acid-treated goatskin was weighed and added to the impregnation solution at 600% of its weight. The mixture was stirred at 8°C for 36 hours. Subsequently, the impregnated goatskin was removed and placed between two smooth plates. While maintaining the goatskin's flatness, it was heated at 62°C for 5 hours to obtain a skin-based conductive hydrogel.

[0023] Example 10 An impregnation solution was prepared using acryloyloxyethyltrimethylammonium chloride as a cationic monomer, ammonium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.8:160. The acid-impregnated sheepskin was weighed and added to the impregnation solution, which was 750% of the sheepskin's weight. The mixture was stirred at 26°C for 12 hours. Subsequently, the impregnated sheepskin was removed and placed between two smooth plates. While maintaining the sheepskin's flatness, it was heated at 53°C for 7 hours to obtain a leather-based conductive hydrogel.

[0024] Example 11 An impregnation solution was prepared using methacryloyloxyethyltrimethylammonium chloride as a cationic monomer, potassium persulfate as an initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.5:70. The acid-treated cowhide was weighed and added to the impregnation solution, which was 450% of the cowhide's weight. The mixture was stirred at 25°C for 16 hours. Subsequently, the impregnated cowhide was removed and placed between two smooth plates. While keeping the cowhide flat, it was heated at 68°C for 4 hours to obtain a leather-based conductive hydrogel.

[0025] Example 12 An impregnation solution was prepared using methacrylamide propyltrimethylammonium chloride as the cationic monomer, azobisisobutyramidine hydrochloride as the initiator, and water in a mass ratio of cationic monomer:initiator:water = 100:0.8:130. The acid-treated pigskin was weighed and added to the impregnation solution at 650% of its weight. The mixture was stirred at 18°C ​​for 28 hours. Subsequently, the impregnated pigskin was removed and placed between two smooth plates. While maintaining the flatness of the pigskin, it was heated at 60°C for 5 hours to obtain a skin-based conductive hydrogel.

[0026] The tensile strength of the leather-based conductive hydrogel prepared in the above embodiments was determined by the method described in QB / T2710-2018 (Determination of tensile strength and elongation of leather physical and mechanical tests), and its conductivity was determined by an electrochemical workstation. The results are shown in Table 1.

[0027] Table 1

Claims

1. A method for preparing a skin-based conductive hydrogel, characterized in that... The process flow of this method is as follows: 1) Weigh the acid-impregnated bare skin and add it to an impregnation solution of 200%~800% of the weight of the bare skin, and stir at 5~30℃ for 4~48 hours; 2) Take out the impregnated bare skin and place it between two smooth plates. While keeping the bare skin flat, heat it at 40~70℃ for 2~12 hours to obtain the skin-based conductive hydrogel.

2. The method for preparing a skin-based conductive hydrogel according to claim 1, characterized in that... The acid-impregnated bare skin used to prepare the skin-based conductive hydrogel can be any one of acid-impregnated cowhide, acid-impregnated pigskin, and acid-impregnated sheepskin.

3. The method for preparing a skin-based conductive hydrogel according to claim 1, characterized in that... The impregnation solution used to prepare the skin-based conductive hydrogel consists of cationic monomer, initiator and water, with a mass ratio of cationic monomer:initiator:water = 100:0.1~1.0:40~200.

4. The method for preparing a skin-based conductive hydrogel according to claims 1 and 3, characterized in that... The cationic monomer in the impregnation solution used to prepare the skin-based conductive hydrogel is any one of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and methacrylamidopropyltrimethylammonium chloride.

5. A method for preparing a skin-based conductive hydrogel according to claims 1 and 3, characterized in that... The initiator in the impregnation solution used to prepare the skin-based conductive hydrogel is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

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