Techniques for Preparing Hydrogel Membrane Capsules

Encapsulation techniques are fmding increasing interest in a variety of areas of biotechnology. Enzymes, living ceils, hormones, drugs, adsorbents and other bioactive materials can be encapsulated and used in bioreactors, artificial organs, controlled drug-release systems, bioseparation systems and etc (Chang, 1972; Kondo, 1979; Lira, 1984; Nigam, 1988; Nixon, 1976). Ideally, encapsulation of bioactive materials should be carried out in mild conditions and materials employed should be inert and non-toxic. However, a number of encapsulation techniques utilizing covalent binding hydrogel membranes require harsh conditions such as the use of non-aqueous solvents, extremes of pH, or high temperature. Recently ionotropic gels have been used for encapsulating bioactive materials under mild conditions. Lim et al. (1980; 1982; 1984) successfully encapsulated living ceils in poly (L-lysine)-alginate capsules. Cells are initially entrapped in calcium-alginate gel beads. Calcium ions in the outer skin of the beads are displaced by poly (L-lysine) to form a polyelectrolyte complex membrane and calcium alginate gel thus wrapped by the complex is liquified using a calcium chelating agent. Difficulties in reproducing the complicated procedures of microencapsulation and in scale-up may restrict the extension of this method to a variety of applications.