Release of vitamin B-12 from poly(N-vinyl-2-pyrrolidone)-crosslinked polyacrylamide hydrogels: A kinetic study

Hydrogels, composed of poly(N-vinyl-2-pyrrolidone) and crossed polyacrylami de, were synthesized and the release of vitamin Bit from these hydrogels wa s studied as a function of the degree of crosslinking and pH of the externa l swelling media. The three drug-loaded hydrogel samples synthesized with d ifferent crosslinking ratios of 0.3, 0.7, and 1.2 (in mol %) follow differe nt drug-release mechanisms, that is, chain relaxation with zero-order, non- Fickian and Fickian, or diffusion-controlled mechanisms. To establish a cor relation between their swelling behavior and drug;release mechanism, the fo rmer was studied by the weight-gain method and, at the same time, the conce ntration of the drug released was studied colorimetrically, Various swellin g parameters such as the swelling exponent n, gel-characteristic constant i t, penetration velocity v, and diffusion coefficient D were evaluated to re flect the quantitative aspect of the swelling behavior of these hydrogels. Finally, the drug-release behavior of the hydrogels was explained by propos ing the swelling-dependent mechanism. (C) 2000 John Wiley & Sons, Inc.