pH-sensitive shrinking of a dextran sulfate/chitosan complex gel and its promotion effect on the release of polymeric substances

A pH-sensitive gel was prepared by polyelectrolyte complex formation between dextran sulfate and chitosan. When the complex gel contained more amino groups than sulfate groups, it shrank pronouncedly at around pH 7 in NaCl solutions of various concentrations, probably because of the deionization of protonated amino groups remaining free from electrostatic interaction with the sulfate groups. Using the complex gel loaded with dextran by absorption, releasing behaviors were studied under various conditions. It was shown that shrinking of the complex gel had a promotion effect on the release of dextran. In 170 mM NaCl solution, the complex gel released dextran more rapidly at pH 8 than at pH 2, because the degree of shrinking was greater at pH 8. Thus, the promotion effect of the complex gel on the release of dextran was pH dependent, though the release rates at the two pHs became closer as the average molecular weight of dextran loaded was lowered. (C) 2001 John Wiley & Sons, Inc.