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Novel bio-based hydrogels were prepared by cross-linking of microbial poly(gamma-glutamic acid) (PGA) with saccharides such as glucose, maltotriose, and cyclodextrin (CD) in the presence of water-soluble carbodiimide in dimethyl sulfoxide (DMSO) by one-pot synthesis at 25 degrees C for 24 h. The degradation of the gels in alkaline solution (pH 9) at 37 degrees C was also investigated. The PGA gels cross-linked with various neutral saccharides were obtained in relatively high recovery yields by use of a base like 4,4-(dimethylamino)pyridine. The PGA gel cross-linked by glucose showed the highest water absorption of 3000 g/g. The PGA gels cross-linked by CDs showed higher water absorption than those cross-linked by the corresponding linear saccharides. It was revealed that the water absorption of the PGA gel was affected by the cross-linker content and also the structure of cross-linkers as they had an effect on the cross-linking density of the PGA gel. The PGA gels were hydrolyzed under alkaline condition (pH 9) at 37 degrees C. The degradation rate was higher when the cross-linker content of the gel was lower.

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Bio-based biodegradable hydrogels were prepared by crosslinking microbial homo poly(amino acid), poly(c-glutamic acid) (PGA), with L-lysine in a one-pot synthesis in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) at 25 1C. The crosslinking was carried out in aqueous solution and the yields of the gels prepared with DMT-MM were higher than those prepared with water-soluble carbodiimide. The water absorption of the PGA gels crosslinked with L-lysine ranged from 300 to 2100 g/g. The water absorption of the PGA gel was affected by the amount of crosslinker and DMT-MM, which had an effect on the crosslinking density of the PGA gel. It was confirmed in a hydrolysis test in a buffer of pH 9 at 37 1C that the obtained gel that was crosslinked with L-lysine by amide bonds was more resistant to hydrolysis than the gel crosslinked by ester bonds. biochemical oxygen demand-biodegradability of the PGA gel crosslinked with L-lysine reached 60% in activated sludge at 25 1C.