THE MOLECULAR-WEIGHT CUTOFF OF MICROCAPSULES IS DETERMINED BY THE REACTION BETWEEN ALGINATE AND POLYLYSINE

Mammalian cells encapsulated in alginate-polylysine microcapsules are used as artificial organs in cancer research and in biotechnology. The se applications require microcapsules with a reproducible mol. wt. cut -off. The high cost of the polycation, polylysine, requires an efficie nt preparation procedure. This article shows that the overall reported contact time of 5 minutes at ambient conditions should be increased s everal times in order to reach a maximal binding between the calcium a lginate 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 fast er maximal binding, but the amount of polylysine bound increased also. Immersion of calcium alginate beads with a diameter of 750 mum, prepa red 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 i nteraction zone between calcium alginate beads and fluorescein isothio cyanate-labeled polylysine solutions was visualized with a confocal la ser scanning microscope as a function of time. Microcapsules, prepared at 40-degrees-C with 0.1% (w/v) polylysine solutions with mol. wts. b etween 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 th an 4.7 kD.