Studies on diffusion in alginate gels .1. Effect of cross-linking with calcium or zinc ions on diffusion of acetaminophen

The permeability of acetaminophen in hydrated alginate and alginic acid gels was measured using side-by-side glass diffusion cells. Gel films were prepared by cross-linking sodium alginate films in aqueous solutions (0.1 to 0.7 M) of calcium or zinc acetate for 1 to 30 min at 25 degrees C. Films prepared in 0.34 M cation solution for 15 min were either exposed to Simulated Gastric Fluid USP minus pepsin, or dried at 45 degrees C to constant weight and then rehydrated, prior to a diffusion study. Acetaminophen permeability in the gel films decreased with increasing divalent cation concentration and cross-linking time until an apparent optimum was reached. The decreased permeability was suggested to be due to increased cross-linking in the gelled structure. The permeability of acetaminophen in the gel films decreased in the order alginic acid gel films > acid-exposed alginate gel films > divalent alginate gel films. Dehydration decreased the permeability of acetaminophen in the Ca alginate gel films. Overall, there was little difference between the permeability of acetaminophen in Ca or Zn alginate gel films.