Study On Autonomous Self-healing Multifunctional Polyglutamic Acid Based Composite Hydrogel

As a functional polymer material,hydrogel has extensive application prospects in skin repair,biological adhesives,biosensors,drug release and tissue regeneration because of its soft,high water content and good histocompatibility.However,traditional hydrogels are difficult to be widely applied because of their single function.For this reason,the researchers used reversible covalent crosslinking and composite modification to build multifunctional hydrogels with high self-healing rate and excellent comprehensive properties.However,because most dynamic covalent crosslinks often need external stimulation,the corresponding self-healing process is"non autonomous".Therefore,such hydrogels need appropriate external energy and stimulation to achieve self-healing,thus limiting their application in biomedicine.In this study,we focused on"achieving the integration of autonomous self-healing and multifunction of hydrogels".Aiming at the key difficulties of self-healing and mechanical properties,we seeked to build an"autonomous"self-healing system by exploring a reversible covalent bond under mild conditions.A hydrogel with excellent mechanical properties,which can be quickly and efficiently healed under mild conditions,was developed without any external stimulation.Meanwhile,its conductivity and antifreeze properties were also improved by compound modification.It provides a theoretical basis for the design and development of new multifunctional hydrogel with high strength and high self-healing property.1.In this study,polyglutamic acid（PGA）and tyramine hydrochloride（Tyr）were selected as a research platform.Firstly,PGA is an amino acid polymer with good biocompatibility.In addition,compared with other polyaminoacids,polyglutamic acid has higher molecular weight and longer molecular chain,which makes it easier to form network structure when cross-linked with other materials,Moreover,polyglutamic acid is a flexible molecular chain,which has better mobility compared with rigid chains such as alginate and chitosan,which can give better hydrogels’ductility,toughness and adhesion.In this study,the feasibility of inducing oxidative coupling reaction of Tyr under mild and atmospheric conditions was explored.The dynamic free radical coupling reaction between Tyr would be proposed and applied using a nonenzymatic catalysis,to achieve a reversible covalent bond,and then a self-healing hydrogel at room temperature has been seen in an O₂ environment.The compressive strength of 15 MPa and the elongation of over 4000%,the highest adhesion strength（to pigskin）of 453 k Pa and the autonomous self-healing ratio of 99%in mild conditions were achieved for the as-obtained hydrogels.The introduction of such chemical crosslinking can provide a theoretical basis for the design and development of new hydrogel with high strength and self-healing.2.On this basis,we explored to introduce ionic liquids with better amphiphilic properties into hydrogels to achieve ionic conductivity.In order to further give the system additional antibacterial properties,we chose those ionic liquid system with positively charged imidazole and used it to destroy the bacterial cell membrane by its electrostatic action with negatively charged phosphate groups on the bacterial cell membrane.At the same time,the negatively charged[BF₄]^-can form hydrated ions with water through hydrogen bonding,so as to construct a three-dimensional conductive network structure and endow the system with conductive properties.Moreover,glycerol was also introduced into the system,and then the hydrogen bonding network was constructed by means of its abundant hydroxyl groups.As a result,more free water would be converted into strongly bound water,which would reduce the freezing point of the system and allow the hydrogel to have excellent antifreeze performance.At the same time,its large number of active groups enhanced not only the self-healing properties of the hydrogels but also the adhesion properties.Through these strategies,we developed a multifunctional composite hydrogel with electrical conductivity,antibacterial property,frost resistance,adhesion,oxidation resistance,mechanical and electrical self-healing properties.At last,it can integrate multi-functions in one platform and thus,expand the scope of its application.3.In this study,the function of the multifunctional composite hydrogel as wound dressings to assist wound healing was explored.The wound healing rate of the composite hydrogel group loaded with electric stimulation reached 94%at fifteenth days,much higher than the healing rate of 63.2%in the medical gauze group.The hair follicle tissue could be observed,showing the same structure as the surrounding normal skin tissue.The stratum corneum of the composite wound was intact,and the keratinocytes on the wound surface were arranged closely,showing excellent skin repair ability.The electrical-stimulation-strategy-based conductive hydrogel also shows great potential in the treatment of large area trauma.4.In this study,the application of the multifunctional composite hydrogel as wearable strain sensor in electronic skin was further explored.Under tensile stress,when the tensile rate was 200%,the conductivity of the hydrogel after healing was 99%of the original hydrogel.When the tensile rate reached 400%,the conductivity of the hydrogel remained at 95%of the original hydrogel.However,the conductivity of the hydrogel after healing was not different from that of the original hydrogel under different compressive stress.Under bending stress,when the curvature was 90 degrees,the conductivity of the hydrogel after healing remained98%of the original hydrogel.Furthermore,we examined the conductive self-healing properties of the self-healing hydrogels under a variety of complex strains in daily life,such as wrist bending,arm bending,neck bending,knee bending and laryngeal movement during speaking different words.The conductivity of the self-healing hydrogel was basically consistent with that of the original hydrogel.These hydrogels have exhibited excellent electrical stability,high strain sensitivity and super-fast response capability.Benefiting from their excellent mechanical self-healing properties and electrical self-healing properties,and because they can restore their original sensing properties,these hydrogels will have higher reliability and durability when used as sensors.5.Finally,in order to further verify the mechanism of the oxidative coupling reaction without enzyme and expand its application,poly（glutamic acid）dopamine（PGA-DA）hydrogel was prepared,and the properties similar to that of PGA-Tyr hydrogel were obtained.In sum,by introducing such mild coupling reaction,conductive and antifreeze agents,high mechanical,self-healing conductivity and adhesion properties and other properties can be integrated into the same hydrogel system.Such multifunctional integration of hydrogels will provide a new idea for designing self-healing materials and multifunctional hydrogels.