Synthesis and characterization of partially biodegradable, temperature and pH sensitive Dex-MA/PNIPAAm hydrogels

The objective of the study is to impart temperature and pH-sensitive capabilities to polysaccharide-based hydrogels, so that they can change their swelling property upon external stimulation like temperature or/and pH. Dextran was chosen as the model polysaccharide compound for such a demonstration. A novel class of dextran-maleic anhydride (Dex-MA)/poly(N-isopropylacrylamide) hybrid hydrogels was designed and synthesized by UV photocrosslinking. The dextran-based precursor (Dex-MA) was prepared by substituting the hydroxyl groups in Dex by MA. This Dex-MA precursor was then photocrosslinked with a known temperature sensitive precursor (N-isopropylacrylamide, NIPAAm) to form hybrid hydrogels having a wide range of composition ratio of Dex-MA to NIPAAm precursors. Due to the biodegradable nature of dextran, these Dex-MA/PNIPAAm hybrid hydrogels are partially biodegradable. These smart hybrid hydrogels were characterized by Fourier transform infrared spectroscopy for structural determination, differential scanning calorimetry for thermal property, maximum swelling ratio, swelling kinetics, temperature response kinetics, and effect of pH. The data obtained clearly show that these new smart hybrid hydrogels were responsive to the external changes of temperature as well as pH. The magnitude of smart and hydrogel properties of these hybrid hydrogels were found to depend on the feed composition ratio of the two precursors. By changing the composition ratio of these two precursors, the phase transition temperature (lower critical solution temperature) of the hybrid hydrogels could also be adjusted to be or near the body temperature for the potential applications in bioengineering and biotechnology fields. (C) 2003 Published by Elsevier Ltd.