The molecular weight cut‐off of microcapsules is determined by the reaction between alginate and polylysine

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Abstract
Mammalian cells encapsulated in alginate‐polylysine microcapsules are used as artificial organs in cancer research and in biotechnology. These applications require microcapsules with a reproducible mol. wt. cut‐off. The high cost of the polycation, polylysine, requires an efficient preparation procedure. This article shows that the overall reported contact time of 5 minutes at ambient conditions should be increased several times in order to reach a maximal binding between the calcium alginate beads and 0.1% (w/v) polylysine solutions. An increase of the polylysine concentration from 0.0125% to 0.8% (w/v) resulted in a faster maximal binding, but the amount of polylysine bound increased also. Immersion of calcium alginate beads with a diameter of 750 μm, prepared from 1 mL alginate, in 30 mL of a 0.8% (w/v) polylysine solution, resulted in a polylysine spill of more than 89%. The time required to reach a maximal binding was related to the reaction temperature. The interaction zone between calcium alginate beads and fluorescein isothiocyanate‐labeled polylysine solutions was visualized with a confocal laser scanning microscope as a function of time. Microcapsules, prepared at 40°C with 0.1% (w/v) polylysine solutions with mol. wts. between 12 and 249.2 kD, were permeable for fluorescein isothiocyanate‐labeled dextran, mol. wt. 4.7, but not for 40.5 kD. Higher polylysine concentrations resulted in a membrane with a mol. wt. cut‐off lower than 4.7 kD. © 1993 John Wiley & Sons, Inc.