Supercritical drying of thermoresponsive gels based on N-isopropylacrylamide

Abstract

Thermoresponsive materials are of great interest for medicine, pharmacy and food industry. During the production of these materials they are often taken into their dry state, requiring gentle processes with minimum effect over their properties. In this study, supercritical drying process was used to obtain dry products from thermoresponsive N-Isopropylacrylamide based gels and compared to other typical drying processes like hot air- and freeze- drying. Depending on the method, different degrees of modification of the structure were observed, which have a significant influence on the final properties of the materials and on their rehydration. Results show that supercritical technology can be used to produce dry porous materials with less collapsed structure or modified properties than conventional or freeze drying techniques while keeping the thermoresponsive nature, which is translated into materials with higher porosity and surface area, and slightly improved swelling degree. Swelling kinetics results showed that materials dried by conventional drying displayed sigmoidal anomalous behavior, those dried by freeze-drying exhibited a two-stage anomalous behavior, and materials obtained by supercritical drying presented behaviors close to Fickian which is of great interest for further drug release applications.