Acid-Induced and Calcium-Induced Gelation of Alginic Acid: Bead Formation and pH-Dependent Swelling

Abstract

The bead formation of alginic acid in the acidic medium (pH 1.0) was investigated in comparison with that of calcium-induced gel beads. The acid-induced gel beads could be visually observed in a few minutes as the transparent spherical figures were detected with a clear boundary between the gel bead and the bulk aqueous phase. The weight change of acid-induced curing beads was as fast as that of the calcium-induced during the initial several hours. But the acid-induced bead lost 15% of its weight at the full stage of gelation, while the calcium-induced lost 37%. The respective beads were incubated at various pHs of 1.0 to 5.0. In the acidic region up to 2.5, the physical integrity of both beads was well maintained. As the pH was raised, they swelled in a sigmoid manner with an inflexion point at about pH 3.2 for the acid-induced beads and at pH 2.8 for the calcium-induced. However, the acid-induced bead disintegrated at a pH of more than 3.5, while the calcium-induced was kept well. The acid-induced beads would be advantageous for some drugs to be incorporated that calcium ions used for alginate gelation might cause undesirable effects such as insoluble salt formation and inactivation due to metal-drug chelation. © 1991, The Pharmaceutical Society of Japan. All rights reserved.