Phosphated crosslinked guar for colon-specific drug delivery I. Preparation and physicochemical characterization

Guar gum (GG) was crosslinked with increasing amounts of trisodium trimetap hosophate (STMP) to reduce its swelling properties for use as a vehicle in oral delivery formulations, especially drug delivery systems aimed at local izing drugs in the distal portions of the small bowel. Swelling of GG in ar tificial gastrointestinal fluids was reduced from 100 to 120-fold (native G G) to 10-35-fold depending on the amount of crosslinker used, showing a bel l-shape dependency. As a result of the crosslinking procedure GG lost its n on-ionic nature and became negatively charged. This was demonstrated by met hylene blur (MB) adsorption studies and swelling studies in sodium chloride solutions with increasing concentrations in which the hydrogels' network c ollapsed. The adsorption of MB was also used to characterize the degree of the GG crosslinking, from which the effective network density was calculate d. In addition, effective network density was calculated from elasticity me asurements, Both measurements showed that the crosslinking density (but not swelling) of the new products was linearly dependent on the amount of STMP used in the reaction. (C) 2000 Elsevier Science B.V. All rights reserved.