Influence of molecular weight and structure on diffusion rates and mechanisms of dextran polyelectrolyte complexes

The release profiles of fluorescein isothiocyanate-dextran (FD) at various molecular weights (20-500 kDa) and the swelling behaviors of polyelectrolyte complex-forming tablets were investigated. Four types of tablets were prepared using different combinations of the following chemicals: carboxymethyl dextran (CMD), dextran sulfate (DS), 2-diethylaminoethyl dextran (EA), and 2-hydroxypropyltrimethylammonium dextran (CDC). Release tests were conducted via the rotating basket method at pH 6.8. Swelling behaviors were analyzed via the front movement method. For all FDs, release rates decreased with decreasing density of charged groups in the matrix, as follows: CMD-EA, CMD-CDC, DS-EA, and DS-CDC. Front movement profiles showed that the dried core disappeared within 3 h, leaving the swollen matrix. Results revealed that the tablets rapidly formed hydrated matrices, with release of the incorporated FDs by diffusion and erosion. The tablets successfully released the macromolecules, and we determined that the release rates could be controlled with a combination of dextran derivatives.