Control of pore sizes in macroporous chitosan and chitin membranes

A novel method for the preparation of macroporous chitosan and chitin membranes is suggested, which employs silica particles as porogen. The macroporous chitosan membranes were prepared by (1) casting an acidic chitosan solution that contains silica particles, (2) removing the solvent by evaporation, and (3) dissolving the silica particles by immersing the membranes into an alkaline solution. This simple method provides chitosan membranes with high porosity and satisfactory mechanical strength, the pore sizes of which can be easily controlled by varying the size of silica particles. The effects of various evaporation conditions and amount of silica on the flow rate of water through the membranes were investigated. In order to prevent their dissolution in acidic solutions, the chitosan membranes were cross-linked under alkaline conditions, using epichlorohydrin as the cross-linking agent. Macroporous chitin membranes were prepared by acetylating the chitosan membranes with acetic anhydride in methanol. In contrast to the uncross-linked chitosan membranes, which are soluble in dilute acidic solutions and insoluble in alkaline solutions, the chitin membranes are insoluble both in acidic and basic solutions. Both kinds of membranes can be employed in affinity or ion-exchange bioseparations.