Hofmeister effect-assisted one step fabrication of fish gelatin hydrogels

Natural gelatin-based hydrogels are usually soft and fragile, and the preparation of hydrogels with elastic structures normally requires modification of gelatin chains or addition of chemical crosslinking agents. In this study, fish gelatin hydrogels with strong structures were simply fabricated by soaking original tilapia gelatin hydrogel in (NH4)(2)SO4 solution at appropriate concentrations, and the effects of (NH4)(2)SO4 concentrations on hydrogels were explored. Results showed that (NH4)(2)SO4 solution with 15 wt% mass concentration could strengthen gel structure. Compared with original hydrogel, hardness, storage modulus and loss modulus of treated hydrogels were all increased. Microstructures of hydrogels were more compact and water binding capacity increased. Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM) indicated that (NH4)(2)SO4 which were kosmotropic ions in Hofmeister series could introduce stronger hydrophobic interaction and electrostatic interactions, causing the gelatin chains in the preformed hydrogel grid closely aggregated. Thus, the gel structure was enhanced.