The effect of gelatin grade and concentration on the migration of solutes into and through glycerogelatin gels.

The diffusion of 4-hydroxybenzoic acid and phenobarbitone through glycerogelatin gels was found to be independent of the type of gelatin used. Three types of gelatin, two acid-processed and one alkali-processed were studied, and the bulk viscosities of gels prepared from them was seen to vary considerably. However, the microviscosities of the gels, as measured by ESR, showed no significant differences. Thus microviscosity was the factor governing diffusion. Gelatin concentration in aqueous solutions without glycerol influenced microviscosity and hence diffusion. This is believed to be caused by dissolution of water-soluble fractions of the gelatin. Interstices in the gelatin matrix, though reduced in size when gelatin concentration is raised, are still too large to act as physical barriers to diffusing molecules. It is suggested that hydrated gelatin forms the matrix of glycerogelatin mixtures and that the interstitial fluid, through which migration occurs, consists almost entirely of glycerol and water.