Effect of thermal cycling on the properties of thermoresponsive poly(N-isopropylacrylamide) hydrogels.

Crosslinked poly(N-isopropylacrylamide) hydrogels have been widely studied for a variety of thermoresponsive applications, including chromatography, affinity precipitation, controlled biocatalysis, viable cell immobilisation, biomimetic actuators and, in particular, modulated drug delivery. The exploitation of crosslinked poly(N-isopropylacrylamide) hydrogels in all these applications relies on the well-known temperature-sensitive swelling properties of these hydrogels. The purpose of the current study was to determine the effects of repeated thermal cycling on the thermoresponsive swelling behaviour of crosslinked poly(N-isopropylacrylamide) hydrogels. The results show that repeated thermal cycling leads to the formation of cracks on the surface of the hydrogels. Repeated thermal cycling also results in a decreased degree of swelling in the crosslinked poly(N-isopropylacrylamide) hydrogels at temperatures below the volume phase transition temperature (VPTT).