Resumen:
The mechanisms of sorption and release of solutes from polymeric materials synthesised by cross-linking ß-cyclodextrin (ß-CD) with epichlorohydrin have been investigated. Gemfibrozil (pKa 4.7) was chosen as model solute. The polymers were obtained by suspension (P1) and block polymerisation (P2). Both P1 and P2 had similar ß-CD contents (65 and 64%) and their swelling capacities were 5.0 and 5.8 cm3/g, respectively. The sorption of gemfibrozil kinetic data in water and in aqueous solutions at pH 2.8 and 7.0 were fitted to a hyperbolic equation and they were studied by applying the Weber and Morris and the Elovich equations. P2 presented faster rates and higher sorption capacities in water and at pH 2.8. The mechanisms of sorption were pH-dependent. In water, the sorption rate was determined by the diffusion of gemfibrozil in the polymer network and fitted the Weber and Morris equation. At pH 2.8 a better adjustment to the Elovich equation suggested a significant influence of the inclusion in the ß-CD cavities. The release kinetics at pH 7.0 was controlled by drug solubilisation and presented maximum release values of 90 (P1) and 95% (P2), with a suitable regeneration of the loaded polymer. In water, the release was slower, fitted a hyperbole and the mechanism was controlled by drug solubility and also by the polymeric geometry. Finally, release assays were carried out from discs of loaded polymer in a medium that simulated the gastrointestinal tract.