Dual responsive curcumin loaded N-isopropylacrylamide/acrylated linseed oil copolymeric hydrogel films: tuned LCST with value-added properties

Abstract

Cross-linked poly(N-isopropylacrylamide), a typical representative of smart thermo-responsive polymers, usually shows a broad range of lower critical solution temperature (LCST) of 28–60 °C, which needs to be precisely fine-tuned in a narrow range to widen its applications. This work details the preparation of dual responsive (temperature and pH) flexible graft copolymeric hydrogel films through free radical polymerization of N-isopropylacrylamide (NIPAm) with acrylated epoxidized linseed oil (AELO) derived from linseed oil. The broad LCST of PNIPAm is fine-tuned more precisely to a narrow range of 30–33 °C with an optimized content of AELO. Further, temperature response is clearly demonstrated with the transmittance analysis of swelled gels above and below the LCST, which is also confirmed by dynamic mechanical analysis. Furthermore, different concentrations of curcumin were included in the responsive matrix to impart antioxidant properties and pH-dependent colour-changing abilities. The effect of AELO grafting and inclusion of curcumin on physicochemical properties of copolymeric hydrogel films, namely, swelling, morphology, and tensile strength, is investigated. In vitro cell studies showed that the resultant hydrogel films exhibited desirable biocompatibility with human keratinocyte and fibroblast cell lines. The results presented in this study demonstrate the potential of AELO-co-PNIPAm copolymeric hydrogel films as a viable functional material for medical patches, smart curtains, and other applications.