Mechanically Robust And Highly Elastic Polymeric Hydrogels With Self-Healing Ability

Hydrogels with high mechanical strength have attracted increasing attentions for decades due to their wide applications in intelligent actuators,flexible electronics and tissue engineering.In recent years,various energy dissipation strategies have been successfully developed to enhance the mechanical strength of hydrogels.However,the currently employed methods for the fabrication of hydrogels with high mechanical strength and toughness usually require multistep processes.Moreover,the significant improvements in both strength and deformability of hydrogels often lead to poor elastic-recovery property?needs long time and even external stimulation for partial or full recovery?and fatigue resistance,which is mainly attributed to the inefficient dissociation-association process of dynamic crosslinks.Therefore,it is necessary to develop facile and effective strategies to strengthen hydrogels and improve their elastic-recovery ability.Additionally,hydrogels are soft materials containing large amounts of water which are susceptible to physical damage such as accidental cut and fracture.Imparting self-healing/healable ability to mechanically robust and highly elastic hydrogels can effectively enhance their reliability and extend their lifetime.However,hydrogels with high strength have strong crosslinking interactions among polymer chains which can restrict the mobility of polymer chains and decrease the healing ability of the hydrogels.Therefore,the healing ability of hydrogels and their high strength are always contradictory.In this thesis,we focus on developing novel high-strength hydrogels and promoting their reliability and extending their service life.This thesis successfully developed a series of faile and effective strategies to improve the mechanical strength and elastic-recovery of hydrogels through tailoring the interactions among polymer chains and the micro-domains in hydrogels.Further,we endow high-strength hydrogels with rapid and efficient self-healing ability and investigate their corresponding functions.1.We developed a facile and effective drying-reswelling method to construct mechanically robust and highly elastic double-network hydrogels.The weak poly?vinyl alcohol??PVA?-polyacrylamide?PAAm??PAAm-PVA?compsite hydrogels were dried and reswollen in water to induce the formation of the crystalline domains of PVA.The tensile strength and compressive strength of the PAAm-PVA double-network hydrogels are 8.6 and 4.4 times higher than that of PAAm-PVA compsite hydrogels.2.We developed a new kind of weak-polyelectrolyte-based hydrogel with high strength,toughness,and excellent self-recovery by one-step polymerization of poly?ethylene glycol?methacrylate?MPEG?and weak electrolyre monomer acrylic acid?AA?in the presence of polyethylenimine?PEI?.Because of the synergy of electrostatic and hydrogen-bonding interactions and the reinforcement effect of the PAA-PEI complex nanoparticles,the PEI_0.15/AA/MPEG_0.04 hydrogels exhibit a high tensile strength of?4.7 MPa,toughness of?32.6 MJ m^-3,and excellent self-recovery such that the deformed or stretched hydrogels can fully recover to their initial states within 10 min at room temperature.3.We fabricated self-healing,mechanically strong and highly elastic hydrogels through constructing the dynamic rigid hydrophobic domains serving as nano-fillers in hydrogels.The hydrogels are synthesized by dialysis of dimethylsulfoxide solution of poly?vinyl alcohol?grafted with 4-carboxybenzaldehyde sequentially in ethanol and water.The in situ-formed hydrophobic domains cross-linked with hydrogen bonds significantly enhance the strength?5.8 MPa?and elasticity of the hydrogels and enable self-healing of fractured hydrogels to restore their original mechanical strength.