Synthesis and properties of biodegradable thermo- and pH-sensitive poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels

Thermo- and pH-sensitive hydrogels were synthesized via the copolymerization of N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) crosslinked with a biodegradable PEG-co-PCL macromolecular crosslinker under UV irradiation. Swelling measurements showed that temperature and pH sensitivity of the resultant hydrogels were highly dependent on the composition of the hydrogels as well as temperature and pH of the local medium. The pH and temperature dependence of the hydrogels displayed good reversibility. The hydrolytic degradation studies showed that the degradation rate of the hydrogels increased with the increasing content of MAA introduced in the hydrogels in pH 7.4 PBS solutions at 37 °C. The study on the release of BSA indicated that the release rate of BSA was higher at pH 7.4 than at pH 2.0, and increased with the increase of the MAA content in the hydrogels in pH 7.4 PBS solutions at 37 °C. These hydrogel materials are desirable for potential applications as smart drug delivery systems.