Chitosan-polyelectrolyte complexation for the preparation of gel beads andcontrolled release of anticancer drug. II. Effect of pH-dependent ionic crosslinking or interpolymer complex using tripolyphosphate or polyphosphate as reagent

Chitosan gel beads were prepared using an in-liquid curing method by ionotr opic crosslinking or interpolymer Linkage with tripolyphosphate (TPP) or po lyphosphate (PP). The ionic interaction of chitosan with TPP or PP is pH-de pendent due to the transition of "ladder-loop" complex structures. Chitosan gel beads cured in a pH value lower than 6 of a TPP solution was a control led homogeneous ionic-crosslinking reaction, whereas chitosan gel beads cur ed in a lower pH PP solution was a nonhomogeneous interpolymer complex reac tion due to the mass-transfer resistance for the diffusion of macromolecula r PP. According to the results of FTIR and EDS studies, it was suggested th at significantly increasing the ionic-crosslinking density or interpolymer linkage of a chitosan-TPP or chitosan-PP complex could be achieved by trans ferring the pH value of curing agent, TPP or PP, from basic to acidic. The swelling behavior of various chitosan heads in acid medium appeared to depe nd on the ionic-crosslinking density or inter-polymer linkage of the chitos an-TPP or chitosan-PP complex, which were deeply affected by the in-liquid curing mechanism of the chitosan gel beads. By the transition of the in-liq uid curing mechanism, the swelling degree of chitosan-TPP or chitosan-PP be ads was depressed and the disintegration of chitosan-TPP or chitosan-PP bea ds did not occur in strong acid. The drug-release patterns of the modified chitosan gel beads in simulated intestinal and gastric juices were sustaine d for 20 h. These results indicate that the sustained release of anticancer drugs could be achieved due to the variation of the reaction mechanism of a chitosan-polyelectrolyte pH-dependent ionic interaction. (C) 1999 John Wi ley & Sons, Inc.