A novel strategy to fabricate water-soluble collagen using poly(γ-glutamic acid)-derivatives as dual-functional modifier

Native collagen cannot be dissolved in neutral pH buffer, limiting its application in many fields. The traditional method to prepare water-soluble collagen is succinylation modification, which causes the decrease in the thermal stability. Therefore, poly(γ-glutamic acid)- N -hydroxysuccinimide (γ-PGA-NHS) esters were used as a novel modifying agent of collagen. FTIR results indicated the intact retention of native triple-helix structure after modification. Isoelectric point of the modified collagens shifted continuously to lower values with increasing the γ-PGA-NHS/collagen ratios (w/w). Consequently, the modified collagen can form a clear solution in neutral pH buffer. Furthermore, the denaturation temperature (T d ) of the modified collagens reached 44.8–49.9   °C, which were 6.0–11.1   °C higher than that of native collagen. However, it should be noted that gelation occurred when modifier/collagen ratio (w/w)   =   50% as γ-PGA-NHS with a relatively high esterification degree was used. As a whole, these results indicated that dual-functional modification in regards to both of water solubility and thermal stability on collagen can be achieved using γ-PGA-NHS esters with a relatively low esterification degree. In addition, the proliferation of fibroblasts could be promoted as reflected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay and 4′,6-diamidino-2-phenylindole (DAPI) method, suggesting the excellent cytocompatibility of the modified collagens. The present study provided useful information to the design of novel water-soluble collagen, which could be applied in the fields including biomaterials, cosmetics etc.