Electrokinetics and electromechanics in controlled release from ionizable gels: theory & experiments

Hydrogels containing weak acid or base pendant groups swell and release drugs differentially as a function of environmental pH and ionic strength. Also, the identity and concentration of buffering species in the release medium can affect swelling and drug release kinetics. A full understanding of factors affecting swelling and release would be reflected in a quantitative mathematical model of these processes. The authors develop a finite element computer model which predicts swelling and release profiles from spherical gels given specified values of mechanical and chemical parameters of the hydrogel, drug, and release medium. The code contains electromechanical and electrochemical components. Numerical computations based on a mathematical model predict gel swelling and stresses, charge density, solute concentrations, and solute and solvent fluxes. The model is validated by comparing its predictions with an experiment on controlled release of sodium salicylate