Effects of charge density on drug permeability through alginate gel membranes

Preparation methods for the alginate (Alg) gel membranes were developed and characterized, Three kinds of Alg gel membrane (mannuronate/guluronate rat io (M/G ratio)=1.00, 0.43, and 0.19) were prepared by a casting method, and the effects of M/G on characteristics such as transmittancy, viscoelastici ty, effective charge densities, and drug permeability were investigated. Th e water content and membrane thickness of the Alg gel membranes were not af fected by the M/G ratio, however, transmittancy and viscoelasticity were fo und to be significantly affected by them. Charge densities (theta) were obt ained using a membrane potential method, and these theta values increased w ith M/G ratio, and dissociation of the carboxylic groups of uronates was fo und to be suppressed significantly in the network, The permeability coeffic ients (P) of sodium benzoate through the membranes decreased with increasin g M/G ratio, The P values are discussed in terms of electrostatic interacti on, structure of the gel network, and bound and restricted water.