Determination of pore diameter and molecular weight cut-off of hydrogel-membrane liquid-core capsules for immunoisolation

The exclusion limit expressed as the largest pore size of capsules composed of hydrogel Ca-alginate membrane and hydroxy-propyl-ammonium starch liquid core considered as the immunoprotective system has been determined by means of inverse size exclusion chromatography with dextran molecular weight standards. The exclusion limits of the capsules were not influenced by the change of starch concentration in the core solution from 4 to 6% but were influenced by the change in alginate concentration in the membrane from 0.5 to 1.0%, causing the membranes to be less permeable. It was found that the diameter of the largest pores in hydrogel membranes was in the range 7.2-8.0 nm. Based on the relationship between solute size and its molecular weight, the capsules had an approximate exclusion limit of 21-25 kD for dextran and 78-103 kD for protein, which is sufficient to block the antibodies penetrating through the membrane.