DUAL STIMULI-RESPONSIVE POLY (N-ISOPROPYLACRYLAMIDE-co-ACRYLIC ACID) COPOLYMERS AND THEIR APPLICATIONS IN IBUPROFEN DELIVERY

A series of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) nanoparticles with different contents of acrylic acid were synthesized via free radical polymerization route. Their pH- and thermo-responsive behaviors were investigated using ¹H-NMR, FT-IR and SEM, dynamic light scattering, scanning calorimeter and zeta potential measurements. The results elucidated that the P(NIPAM-co-AA) exhibited dual stimuli performances both pH- and temperature- response, showing more sensitive than the pure poly(N-isopropylacrylamide). Their swollen/shrunken behaviors were strongly dependent on the various parameters, including content of acrylic acid monomers, pH value of solution, temperature and salt concentration. Particularly, the electrical repulsive force, surface charge distribution and hydrogen bonding were thought to determine their sensitive properties. Salt effect showed more obvious at high pH than that at low pH, leading to a significant change of particle size distribution and Zeta potential. In addition, the P(NIPAM-co-AA) as matrix loaded-ibuprofen delivery in vitro was also evaluated, exhibiting a faster release rate at pH 7.4 than that at pH 2.0, while the accumulative release amount was larger at 37 ºC than that at 25 ºC in the aqueous ammonia solutions (at pH 7.4). These results demonstrated that the resultant copolymer presented a smart pH and thermo-response in the potential application of controlled drug delivery system