Polymeric genipin macromers, prepared by ring-opening polymerization at various pH values, are used as crosslinking agents to fix collagen hydrogels. The results indicate that as the dark color of polymeric genipin itself and the networks formed by long-range intermolecular crosslinking, the genipin-fixed collagen hydrogels displace darker color. The polymeric genipin prepared at higher pH value needs longer time to fully crosslink with collagen molecules. Moreover, polymerization of genipin reduces the yield of genipin-fixed collagen hydrogels due to low extent of crosslinking. Specially, the microscope photographs present the porous networks structures of genipin-fixed collagen hydrogels. The pore size increases with the increase in polymerization degree of genipin. The data of FTIR indicate the likely transition of -NH(2) groups in collagen chains into C=N. Owning to much more number of hydrophilic groups and more porous networks, collagen hydrogels fixed by genipin with higher polymerization degree have higher water absorption capacity. The equilibrium swelling of genipin-fixed collagen hydrogels is pH-responsive, which show "M" type changes with the pH values. The results obtained in the study suggest that the polymeric genipin prepared at various pH values lead to significant influence to the crosslinking characteristics and properties of collagen hydrogels.
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