Physicochemical characteristics of thermo-responsive gelatin membranes containing carboxymethyl chitosan and poly(N-isopropylacrylamide-co-acrylic acid)

Gelatin has many superior biological properties and can absorb a large volume of water to form hydrogels, making it a promising material for skin wound care. In this study, gel membranes were prepared based on gelatin and added with different amounts of the synthesized carboxymethyl chitosan (CMCS) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NI-co-AA)) copolymer for providing antibacterial and thermo-responsive properties, respectively. The synthesized CMCS had a degree of carboxymethyl substitution at 0.77 and the P(NI-co-AA) had an AA content of 5.7 mol %. Both CMCS and P(NI-co-AA) had carboxylate groups that could further provide ionic-crosslinking sites for the membranes. Though the P(NI-co-AA) copolymer had a higher phase transition temperature than poly(N-isopropylacrylamide) (PNIPAAm) owing to its hydrophilic carboxylate groups, the prepared gelatin/CMCS/P(NI-co-AA) membranes had similar phase transition temperatures to the PNIPAAm at around 30.5 − 32.4 °C because of ionic crosslinking. Moreover, the equilibrium swelling ratio and water vapor transmission rate of the gel membranes were in the range of 769 − 1226% and 1678 − 2496 g/m²- day, respectively. These membranes could promote cell proliferation of human keratinocytes (HaCaT) and mouse fibroblasts (L-929), indicating they were non-toxic to the cells. They also had antimicrobial properties against S. aureus and E. coli, where the antibacterial efficacy increased with increasing the CMCS content. These hydrogel membranes had good biocompatibility, suitable swelling ratio and water vapor transmission rate, antibacterial and thermo-responsive properties. Therefore, they have potential to be applied as functional wound dressing material.