pH- and temperature-responsive poly(aspartic acid)-l-poly(N-isopropylacrylamide) conetwork hydrogel

Multiresponsive conetwork hydrogels, PASP-l-PNIPAAm, composed of pH-responsive, biodegradable poly(aspartic acid) (PASP) and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) were synthesized by the reaction of allylamine-grafted polysuccinimide and N-isopropylacrylamide in organic medium and a subsequent hydrolysis. The composition of allylamine-modified polymer was determined by nuclear magnetic resonance (NMR) and Fourier transformation infrared spectroscopy (FTIR). pH and temperature sensitivities were studied by measurement of swelling degrees. Scanning electron microscopic (SEM) analysis revealed that the pore size and the morphology of the PASP-l-PNIPAAm hydrogel could be controlled by the ambient pH and temperature. The volume phase transition temperature of the gels was determined by differential scanning calorimetry (DSC). A widely used non-steroidal anti-inflammatory drug, DiclofenacNa (DFS) was chosen as a model drug for drug release experiments. The hydrogel was non-toxic for human epithelial cells. According to the results these hydrogels are suitable for colon-specific controlled drug delivery.