Synthesis of Chitosan-Alginate Microcapsule Membranes

Abstract

A polysaccharide, chitosan, was chemically modified to form a polyelectrolyte complex membrane with calcium alginate beads. A key factor in membrane for mation was found to be the viscosity average molecular weight (M v ) of the chitosan. While unmodified chitosan (M v = 12.1 x 10 5 ) formed thin and weak microcapsule membranes, when the M v of the chitosan was reduced to 2.4 x 10 5 , the polymer exhibited optimum membrane forming characteristics in terms of capsule strength and flexibility. The degree of deacetylation of chi tosan varied from 94.3% for the unmodified polymer to 93.2% for chitosan of M v = 1.6 × 10 5 . A substitution reaction sequence was developed in an attempt to modify the pendant amine of the practical grade polysaccharide. Reactive groups were coupled to the chitosan main chain following a two-step process; activation with a bromoacetyl halide and termination with a diamine [(NH 2 (CH 2 ) n NH 2 )] or methyl containing amine compound. Initial studies indicated that thin capsule membranes formed regardless of application of reaction se quence, distance of reactive groups from the main chain, or type of reactive group inserted. The permeability of the chitosan-alginate capsules was assessed, with various diffusing proteins. Membranes formed with chitosan M v =0.5 × 10 6 excluded beta amylase, suggesting a membrane molecular weight cut-off of approximately 200,000.