Chemically modified polyacrylamide-g-guar gum-based crosslinked anionic microgels as pH-sensitive drug delivery systems: preparation and characterization

New spherically shaped cross-linked hydrogels of polyacrylamide-grafted gua r gum were prepared by the emulsification method. These were selectively de rivatized by saponification of the -CONH2 group to the -COOH group. The der ived microgels were characterized by FTIR and elemental analyses. The deriv atized microgels were responsive to PH and ionic strength of the external m edium. The swelling of microgels increased when the pH of the medium change d from acidic to alkaline. Transport parameters, viz., solvent front veloci ty and diffusion coefficients were calculated from a measurement of the dim ensional response of the microgels under variable pH conditions. The variat ion in pH changed the transport mechanism from Case II (in 0.1 N HCl) to no n-Fickian (in pH 7.4 buffer), and these processes are relaxation-controlled . Ionic strength exerted a profound influence on the swelling of the microg els. Swelling was reversible and pulsatile with the changing environmental conditions. The pH-sensitive microgels were loaded with diltiazem hydrochlo ride and nifedipine (both anti hypertensive drugs) and their release studie s were performed in both the simulated gastric and intestinal pH conditions . The release was relatively quicker in pH 7.4 buffer than observed in 0.1 N HCl; the release followed non-Fickian transport in almost all the cases. (C) 2001 Published by Elsevier Science BY.