Study On The Fabrication And Mechanical Properties Of Tough Hydrogels Based On Non-covalent Physical Interaction

Polymer hydrogels are the three-dimensional network formed by cross-linking polymer chains dispersed in an aqueous medium through a myriad of mechanisms,which have numerous applications in tissue engineering,wound dressing,medical electrode,flexible devices and other fields.However,the conventional chemical crosslinking hydrogels usually often cause permanent rupture originated from the lack of an efficient energy dissipation mechanism in the network,resulting in limited their applications.Therefore,taking into consideration the improvement of mechanical property for hydrogels,this article will introduce the non-covalent dynamic physical interactions to regulate the crosslinking structure of hydrogels,and investigate the relationships between mechanical properties and network structure of hydrogels.Specifically,this article include three parts as follows.In the first part of the article,cationic polystyrene(PS)microspheres composite hydrogels with excellent mechanical properties were fabricated by introduced the cationic PS microspheres were introduced into the pure hydrophobic association system to achieve the gather of hydrophobic component.First,the hydrophobic hexadecyl methacrylate are adsorbed on the surface of PS microspheres and stabilized in the presence of CTAC,forming hydrophobic association centers.Meanwhile,KPS are attracted towards the quaternary ammonium salt group of microspheres through ionic interactions,initiate the copolymerization,and dual physically cross-linked network was constructed.The fabricated hydrogel exhibited high tensile strength of 1.32 MPa,toughness of 4.53 MJ/m~3,fracture strain of 1300%,excellent self-recovery properties and fatigue resistance.In the second part of the article,we report the fabrication of hybrid cross-linked polyacrylamide(PAAm)/CTAC micelle hydrogels.The CTAC micelles act as physical cross-linker in the covalent chemical cross-linked PAAm network.In the hybrid cross-linked network,covalent crosslinking could effectively inhibit the hysteresis of hydrogel,meanwhile,the physical crosslinking could dissipate energy through reversible dissociation.The results of dynamic rheological measurement showed that CTAC micelles ameliorate the network structure of hybrid hydrogels,resulting in few defects of the polymer gel network.Therefore,the mechanical properties of hybrid hydrogels could be significantly enhanced by synergetic effects of physical and chemical cross-linking.The resulting hydrogel exhibits tensile stress of 481 kPa,facture strain of 1220%,fracture toughness of 1.65 MJ/m~3,excellent elasticity and self-recovery properties.In the third investigation,hydrophobic association hydrogels(HA gels)were successfully prepared through micellar copolymerization of acrylamide and a small amount of lauryl methlacrylate(or n-lauryl acrylate)in an aqueous solution containing sodium dodecyl sulfate.The tensile properties of HA gels were conducted under the different experiment conditions,and on the basis of the Mooney-Rivlin theory,the elastic parameters of cross-linked network of HA gels were investigated,and the effect of methyl of hydrophobic monomer on the mechanical properties of HA gels was discussed.The results of measurement showed that the methyl of hydrophobic monomer increased the rigidity of polymer chains in the association domain,increasing the degree of limitation of polymer chains,which leads to slower response of the HA gel to the tensile rate.In contract,the HA gels without methyl exhibited better elasticity and self-recovery.