Manipulating degradation time in a N-isopropylacrylamide-based co-polymer with hydrolysis-dependent LCST.

A thermosensitive, bioresorbable and in situ gelling co-polymer, poly(N-isopropylacrylamide-co-dimethyl-gamma-butyrolactone acrylate-co-acrylic acid), was synthesized by radical co-polymerization with varying dimethyl-gamma-butyrolactone acrylate (DBA) content. The materials properties were characterized using differential scanning calorimetry, gel-permeation chromatography in conjunction with static light scattering, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and acid titration. The initial lower critical solution temperature (LCST) of the synthesized co-polymer is between room temperature and body temperature. With the increase of DBA content, the LCST decreases, but then increases after the ring-opening hydrolysis of the DBA side-group. The FT-IR and NMR spectra show the co-polymerization of three monomers, as well as the hydrolysis-dependent ring-opening of the DBA side-group. The addition of acrylic acid increases the initial LCST and accelerates the degradation rate of the co-polymer. An indirect cytotoxicity test indicated that this co-polymer has relatively low cytotoxicity as seen with 3T3 fibroblast cells.