Preparation And Study Of Hydrogen Bond-enhanced Hydrogels

Developments of tough hydrogels greatly expand the applications of gels as load-bearing materials.However,the tough gels are much softer than the soft biotissues(e.g.skins with modulus up to 100 MPa).Designing hydrogels with high stiffness and toughness remains a big challenge.We report a series of ultrastiff and tough physical hydrogels facilely prepared by one-pot copolymerization of methacrylic acid and methacrylamide.The gels with water content of 45-70 wt%had remarkable mechanical properties,with tensile breaking stress of 1.2-8.3 MPa,breaking strain of 198-615%,elastic modulus of 2.3-217.3 MPa,and fracture energy of 2.9-23.5 kJ/m2,superior to most existing gels and comparable to the soft biotissues,especially in terms of modulus.Typical yielding and crazing were observed in the gel under tensile loading,indicating the forced elastic deformation of these glassy gels.The ultrahigh stiffness was attributed to the reduced segmental mobility by the hydrogen bonds that are stabilized by the hydrophobic methyl motifs in the aqueous environment.Due to the dynamic nature of noncovalent bonds,the physical gels also showed good shape memory and recyclability.The strategy by making gels in glassy state should be applicable for other systems to achieve high toughness and stiffness,meriting the applications of hydrogels as structural engineering and biomedical materials.Moreover,we synthesize a PAAc/PNIPAm double-network hydrogel by DN technology.Hydrogel bonds were formed between two networks.