Permeability characteristics of calcium alginate films

The permeability of acetaminophen in hydrated calcium alginate films was measured in side-byside glass diffusion cells. The films were prepared by ionically crosslinking dry sodium alginate films by immersion in aqueous solutions of calcium acetate (0.1 to 1.0 M) for 1 to 15 minutes. Permeability of acetaminophen in hydrated calcium alginate films varied approximately 14.6-fold, depending upon calcium acetate concentration and immersion duration used in the cross-linking process. Permeability of acetaminophen in calcium alginate films prepared by immersion of dry sodium alginate in aqueous solutions of calcium acetate for 3 to 8 minutes reached a limiting value at all calcium acetate concentrations. However, the magnitude of the limiting value was dependent upon the concentration of calcium acetate used in the crosslinking procedure. The highest limiting permeability was observed in films prepared using the lowest concentration of calcium acetate, whereas the lowest limiting permeability was observed in films prepared using the highest concentration of calcium acetate. When calcium alginate films were prepared by immersion in calcium acetate solutions of greater concentration than 0.5 M and immersion times less than 10 minutes, permeability coefficients were higher for the higher calcium acetate concentrations. Only when immersion times were greater than 10 minutes did permeability decrease as calcium acetate concentration increased. It is suggested that this is a result of the rapid crosslinking of sodium alginate at the surface, which in turn slows the diffusion of calcium ions into the film. Because of the relatively short immersion time, a high degree of crosslinking is not attained and this results in a calcium alginate film that is more permeable.