Preparation of caffeic acid-grafted gelatin hydrogel and its antioxidant function

Objective To fabricate caffeic acid-grafted gelatin (CA-gel) hydrogels and investigate effects of the grafting ratios on the physicochemical properties of the hydrogels, and evaluate the antioxidant function of hydrogels. Methods CA-gel gelatin was synthesized by controlling the ratio of caffeic acid and gelatin, and the hydrogels were formed with laccase as the cross-linking agent. The molecular structure of caffeic acid-grafted gelatin was characterized by HPLC and 1H-NMR. The grafting degree of caffeic acid was determined by UV-Vis spectrophotometer and the gelation time of hydrogel was determined by vial-tilting method. The elastic modulus was measured by microsphere indentation method. The swelling ratio and degradation rate of the hydrogel were calculated according to mass change before and after swelling and degradation, and the scavenging effect on DPPH radical(DPPH·) was determined by the change of absorbance of DPPH radical solution. Cell counting kit-8 was used to evaluate the cytotoxicity of the hydrogels and the protective effect on fibroblasts in high oxidative stress microenvironment. Results Caffeic acid was grafted onto gelatin molecules with following respective parameters: grafting degrees were 33.0 μmol/g, 61.8 μmol/g and 74.4 μmol/g, the gelation time was 33 min, 42 min and 47 min, the swelling ratios of the hydrogels were 896.5%, 835.3% and 803.9%, the elastic modulus of the hydrogels were 7.2 kPa, 29.4 kPa and 34.5 kPa, and the scavenging effects on DPPH radical of the hydrogels were 38.5%, 41.9% and 49.8%, respectively. In addition, the degradation rate decreased with the increase of grafting degree. The hydrogels were non-cytotoxic and displayed protective effect on the fibroblasts in the peroxide-existing environment. Conclusions CA-gel hydrogels have adjustable gelation time, biodegradation rate, elastic modulus and free radical scavenging activity and show a significant protective effect against fibroblasts in high oxidative stress microenvironment as well.