Preparation of poly(N-isopropylacrylamide)-grafted PLCL films and nanofibers using -ray irradiation and their swelling behaviors

Abstract

Recently, copolymers of lactide (LA) and ε-caprolactone (CL) have been investigated as biodegradable elastomeric materials. Poly(L-lactide-co-ε-caprolacton)(PLCL) is a semicrystalline polymer in which certain fraction of the polymer is still amorphous when the polymer is cobbled down and thereby becomes entrapped between crystalline regions. This self-reinforcement, also observed in natural rubber, is the origin of high tensile strength and maximal extensibility. Due to these unique morphological properties, the rate of degradation of PLCL is dependent on their degree of crystallinity and glass transition temperatures. Poly(N-isopropylacrylamide)(PNIPAAm) is a well-known temperature-responsive polymer, exhibiting a lower critical solution temperature (LCST) at 32℃ in water. The objectives of this study were to prepare stimuli-responsive biodegradable and elastic polymers by grafting of NIPAAm on PLCL. N-isopropylacrylamide (NIPAAm) was grafted on to the elastomeric PLCL films and nanofibers using γ-ray irradiation with various doses. The grafted polymers were characterized by examining graft ratio, mechanical strength, swelling kinetics and ratio, and drug release behavior. NIPAAm graft yield was increased in irradiation dose and aqueous solution was preferred for higher graft yield as compared with methanol. The mechanical strength of NIPAAm grafted PLCL increased with increase in graft yield of NIPAAm. In the swelling kinetics, all hydrogels reached equilibrium swollen state within three hours. The equilibrium swelling ratio of the hydrogels decreased with increasing irradiation dose. The swelling ratio of the hydrogels dramatically decreased as temperature increased from 25 °C to 40 °C, which was reversible because of the temperature-induced phase separation of NIPAAm at 32℃.