Bio-based hydrogels prepared by cross-linking of microbial poly(gamma-glutamic acid) with various saccharides

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.