Study of thermal transitions of copolymers based on N-isopropylacrylamide and acrylic acid with potential for curcumin controlled release

Thermosensitive polymers based on poly(N-isopropylacrylamide) (pNIPAM) have been widely evaluated in a variety of biomedical applications due to their particular thermal behavior in aqueous solutions. Despite this, few works have focused on the complementary analysis of the thermal transitions of pNIPAM polymers in linear and crosslinked form. In this work, linear and crosslinked poly(N-isopropylacrylamide-co-acrylic acid) p(NIPAM-co-AA) copolymers were synthesized at similar NIPAM/AA feed composition and their thermosensitive behavior was studied by turbidimetric methods, FTIR spectroscopy analysis, and temperature-dependent swelling measurements. The intermolecular crosslinking hindered the hydrophobic aggregation of chain segments, leading to higher transition temperatures of synthesized polymers. AA units promoted the intersegment hydrogen bonds during heating and strengthened the hydrogen bond interactions water-network. The effect of the thermosensitive behavior of p(NIPAM-co-AA) copolymer on curcumin (CUR) release kinetic was also studied. The low uptake level of p(NIPAM-co-AA) hydrogel, partially shrunken at 37°C, produced a CUR sustained delivery, reaching the release equilibrium state up to 18 h. Hydrogels of p(NIPAM-co-AA) with a suitable composition exhibited a promising performance for the CUR controlled delivery at physiological conditions.