Preparation And Properties Of Ultrastretchable Self-healing Adhesive Hydrogels Based On Small Molecule Adhesion Factors

Hydrogel is a kind of water-rich polymer material with three-dimensional network,which was similar to biological tissue.Adhesive hydrogels could be widely used in smart wearable materials,human health monitoring and biological tissue repair.However,adhesive hydrogels still have some shortcomings,such as monotypic adhesion factor group,poor mechanical properties,poor self-healing properties,complex preparation methods,and lack of multi-functionality,including biocompatibility,antibacterial,fluorescence,etc.Therefore,we introduced a variety of adhesion factors into the polymer network to improve the cross-linking density through multiple reversible interactions in this paper,endows hydrogels with high adhesion and excellent self-healing properties,realized the multiple functions of hydrogels.（1）Hydrogel material has some shortcomings such as poor tissue adhesion,poor tensile property and insufficient tensile stress as a wound dressing.Poly（acrylamide-histidine methylacrylamide）（P（AM-His MA））hydrogel was prepared by polymerizing histidine methylacrylamide（His MA）,biocompatible amino acid derivative and acrylamide（AM）.The hydrogels had properties of self-healing（tensile strength recovery>84%）,adhesion（porcine skin 4.1 k Pa）,excellent mechanical properties(tensile strength 77 k Pa compared to polyacrylamide（PAM）hydrogels,tensile elongation（5800%）and compressive stress（2.0 MPa）since amino acid His MA brought more physical crosslinking to P（AM-His MA）hydrogels.Then,P（AM-His MA）-Fe³⁺hydrogel was prepared by introducing Fe³⁺ions into P（AM-His MA）hydrogel.The mechanical properties（tensile strength of 89 k Pa,elongation of 4900%）,adhesion strength（pig skin of 11.9 k Pa）,and self-healing properties（within 5 minutes at room temperature）were enhanced by the construction of coordination bonds and a variety of non-covalent bonds.P（AM-His MA）-Fe³⁺hydrogels showed significant biocompatibility,excellent antibacterial properties（100%bactericidal effect）and accelerated wound healing process.Therefore,P（AM-His MA）-Fe³⁺hydrogel has a broad application prospect as a dressing for joint skin wound healing.（2）The preparation of hydrogels with high adhesion,high tensile strength,high tensile strength and electrical conductivity still has some problems,such as complicated technology（usually using multi-layer hydrogels composite）and difficult compatibility of multiple functions.In this work,we firstly synthesized arginine derivative monomer and ionic liquid imidazole salt derivative monomer,and then copolymerized with acrylic acid（AA）to prepare P（MArg-FHVI-AA）hydrogel.The hydrogel had properties of high transparency（visible light transmittance>85%）,super tensile（2613%）,high elasticity（1000%strain 10 cycles）,fatigue resistance（200 cycles under 80%compression deformation）,self-healing,good adhesion（adhesion strength of 37 k Pa and 32 k Pa to pig skin in air and water）and electrical conductivity.When metal ions were added into the P（MArg-FHVI-AA）hydrogel,the mechanical properties of the hydrogel were enhanced（tensile strength was from 109 to 352 k Pa,tensile strain was from 1707 to 1942%）,and the hydrogel exhibits stronger adhesion strength（68 k Pa for Pig skin）,good biocompatibility（99%）,excellent antibacterial properties（100%antibacterial effect against Escherichia coli and Staphylococcus aureus）,shape memory,fluorescence writing（its fluorescence intensity is 1099%of the initial）and message transmission function.In addition,P（MArg-FHVI-AA）hydrogel showed real-time detection performance for various sports.This work provides an idea for constructing multi-functional and intelligent adhesive conductive hydrogel materials.（3）The preparation of adhesive hydrogels with supertensile and self-repairing properties based on hydrophobic interaction was still a great challenge.In this paper,hydrophobic salicylaldehyde monomer was designed and prepared,and P（AA-MA-OA-FHMA）hydrogel was prepared by copolymerization with hydrophilic monomer and alkyl ester monomer.The hydrogel showed supertensile（4023%）,strong mechanical properties（278 k Pa）,high elasticity（10 cycles at 1000%strain）,fatigue resistance（150 cycles at 80%compression deformation）,self-healing,adhesion（40 k Pa）and electrical conductivity.Metal complexation or Schiff base reaction could occur with the addition of Al³⁺ions,Zn²⁺ions and hydrazine hydrate aqueous solution,enhanced the colorful fluorescence of hydrogels,which could be used for colorful painting and information transmission.In addition,P（AA-MA-OA-FHMA）-Al³⁺hydrogels had excellent antibacterial properties（100%）when Al³⁺ions were metal-complexed with salicylaldehyde and carboxyl group.The hydrogel could also monitor the activities of various joint parts of the human body,and even small strain changes such as throat vibration when speaking could be accurately identified and detected with high sensitivity and real-time performance.This work provided a more efficient and simple preparation scheme for constructing hydrophobic interaction of colorful fluorescent hydrogels.（4）Multiple interactions could be constructed between the catechol groups and the adhered interface,which played an important role in the construction of adhesive hydrogels.In this paper,Schiff base catechol monomer with ammonium salt was designed and prepared,and CMP-P（AA-APB-DHMDA）hydrogel was constructed by free radical polymerization method with small nucleotide molecules,phenylboric acid and acrylic monomer.The hydrogel exhibited excellent mechanical properties,including strong tensile properties（2720%）,high tensile stress（261 k Pa）,strong toughness and fatigue resistance（15 cycles at 500%fixed tensile strain and 150 cycles at 90%compressive strain）.In addition,the hydrogel also showed good properties such as self-healing（tensile strength recovery>70%）,high adhesion（105 k Pa）and electrical conductivity.When Al³⁺was added to the hydrogel,the antibacterial activity was greatly improved（>95%）.In addition,hydrogels showed signal sensitivity and real-time monitoring in both large strain and small strain monitoring of human activities as a strain sensor.Therefore,CMP-P（AA-APB-DHMDA）hydrogels had the potential to become intelligent wearable sensing materials.