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

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 mum, 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 degrees 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.

Visualization of alginate–poly‐L‐lysine–alginate microcapsules by confocal laser scanning microscopy

“…In this study, a high-G alginate was used, and hence PLL bound to the outer parts of the gel in accordance to the results of Thu. The thickness of the PLL layer increased with increasing exposure times, as expected (Thu et al, 1996a;Vandenbossche et al, 1993b). Figure 6 indicates that the initial binding of PLL is fast, to the very surface of the bead, but that it diffuses into the gel over longer exposure times.…”

Studies on small (<350 ?m) alginate-poly-L-lysine microcapsules. V. Determination of carbohydrate and protein permeation through microcapsules by reverse-size exclusion chromatography

“…These findings are in agreement with previous data obtained with standard >800 m microcapsules. 25,29,30 Brissova et al 31 have found that poly-L-lysine MW does not affect the permeability of standard microcapsules. Since they presented no data that address this particular issue, it is possible that they have studied only poly-L-lysine under 69.9 kDa, which are usually used to encapsulate cells.…”

“…This is in agreement with previous reports. 26,29,30 Using poly-L-lysine 0.08%, it was possible to produce microcapsules that excluded dextran 4400 Da and insulin (5700 Da). This is much smaller than what is required for immunoprotection and, in the case of microencapsulated islets of Langerhans, would be too small to allow effective insulin release.…”

“…The most widely used method consists of soaking capsules in a dextran solution and measuring the concentration variations of this soluble marker in the supernatant and/or inside the capsules. [25][26][27][28][29][30] The problems with these methods are (1) a low sensitivity and (2) the fact that marker adsorption on the membrane surface may be confused with absorption into microcapsules.…”

Immunoisolation to prevent tissue graft rejection: Current knowledge and future use

“…It was found that coating of the negatively charged alginate capsules with polycations, such as poly-L-lysine, poly-D-lysine, and poly-L-ornithine increases the mechanical stability and restricts permeability of immune cells. 31 However, coating with poly-L-ornithine and poly-D-lysine increased the inflammatory responses towards capsules, 32 while coating with poly-L-lysine has been shown to improve the biocompatibility and inhibit adhesion of inflammatory cells. 27,33 Adherent inflammatory cells secrete cytokines that amplify the local inflammatory reaction and lead to formation of a fibrotic capsule around the device.…”