Transport of small anionic and neutral solutes through chitosan membranes: Dependence on cross-linking and chelation of divalent cations

摘要

Chitosan membranes were prepared by solvent casting and cross-linked with glutaraldehyde at several ratiosunder homogeneous conditions. The cross-linking degree, varying from 0 to 20%, is defined as the ratio betweenthe total aldehyde groups and the amine groups of chitosan. Permeability experiments were conducted using aside-by-side diffusion cell to determine the flux of small molecules of similar size but with different chemicalmoieties, either ionized (benzoic acid, salicylic acid, and phthalic acid) or neutral (2-phenylethanol) at physiologicalpH. The permeability of the different model molecules revealed to be dependent on the affinity of those structurallysimilar molecules to chitosan. The permeability of the salicylate anion was significantly enhanced by the presenceof metal cations commonly present in biological fluids, such as calcium and magnesium, but remained unchangedfor the neutral 2-phenylethanol. This effect could be explained by the chelation of metal cations on the aminegroups of chitosan, which increased the partition coefficient. The cross-linking degree was also correlated withthe permeability and partition coefficient. The change in the permeation properties of chitosan to anionic solutesin the presence of these metallic cations is an important result and should be taken into consideration when tryingto make in vitro predictions of the drug release from chitosan-based controlled release systems.