Thermosensitivity and release from poly N-isopropylacrylamide–polylactide copolymers

A series of thermoresponsive-co-biodegradable polymers, containing varying molar ratios of N-isopropylacrylamide (NIPA) and poly-lactic acid diacrylate macromer (PLAM) were prepared and characterised. Chemical structures were confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR). The hydrogels were thermoresponsive, exhibiting an increase in the lower critical solution temperature (LCST) the higher the percent of PLAM present. Swelling properties were dependant on both temperature and PLAM content. The degradation behaviour of the three-dimensional polymeric networks formed was dependent on both structural (mesh size, molecular weight distribution, composition) and environmental parameters (temperature). Swelling and in vitro biodegradation-induced morphological structural changes were examined using scanning electron microscopy (SEM). A greater rate of degradation and disruption to the porous network could be seen with increasing lactide content. Degradation was faster below the LCST, demonstrated by FTIR, pH decrease and acid release, consistent with the increased hydrophilicity of the network. The release profiles of the model drug indomethacin (IDM), from these thermoresponsive-co-biodegradable polymers, were found to be dependant on copolymer composition, drug loading and temperature, more rapid release occurring below the LCST.