Alginate impression materials.

Inverse aqueous size exclusion chromatography (SEC) was adopted to measure the permeability of microcapsules (hollow hydrogel spheres with diameter < 1 mm) using dextran molecular weight standards. Alginate/poly(L-lysine)/alginate microcapsules were chosen as a column substrate. Data from column SEC experiments were verified by kinetic studies of solute size exclusion. The permeability of tested microcapsules was modified by the reaction time with 0.05wt.% poly(L-lysine) (PLL). The exclusion limit of the microcapsules prepared at 5-min reaction time was found to be 100,000, while the microcapsules that were allowed to react with PLL for 20 min became less permeable and their exclusion limit was approximately 50,000. Based on relationships between solute size and molecular weight, the exclusion limits determined with dextrans were converted to the size and approximate molecular weight of protein presumably excluded by the capsular membrane at "ideal" conditions. The results from both column SEC and batch experiments suggest that the standard alginate/PLL/alginate capsules are permeable to immunoglobulins of IgG class. Unlike other techniques which utilize only a limited number of solutes, inverse SEC enables one to examine the capsule permeability to a homologous series of molecular weight standards. Inverse SEC also provides an opportunity to evaluate the properties of a large series of capsules directly by comparing their calibration curves. In addition, undesirable enthalpic effects in permeability studies with globular proteins as test solutes can be minimized or eliminated by using the inert molecular weight standards such as polysaccharides.

Alginates↗

PubMed1996

Factors influencing the adequacy of microencapsulation of rat pancreatic islets.

The observation that only a portion of all alginate-polylysine microcapsules are overgrown after implantation suggests that physical imperfections of individual capsules, rather than the chemical composition of the material applied, are responsible for inducing insufficient biocompatibility and thereby fibrotic overgrowth of those capsules. We recently developed a lectin binding assay that allows for quantifying the portion of inadequately encapsulated islets, and demonstrated that inadequately encapsulated islets induce a fibrotic response associated with graft failure. The present study investigates factors influencing the adequacy of encapsulation of pancreatic islets. We applied our lectin binding assay and found that the number of inadequate, and particularly incomplete, capsules is influenced by the following factors. (1) A capsule diameter of 800 micrometers is associated with a lower percentage of inadequate capsules than smaller (500 micrometers and 600 micrometers) or larger (1800 micrometers) capsules. (2) A high rather than low guluronic acid content of the alginate is associated with a lower percentage of inadequate capsules. This can be explained, at least in part, by smaller ranges of swelling and subsequent shrinkage during the encapsulation procedure. (3) An increase in viscosity caused by applying a higher alginate concentration compensates for a low guluronic acid content. This effect of increased viscosity cannot be explained by a reduced range of swelling and shrinkage during the encapsulation procedure. We conclude that alginates with a high guluronic acid content and a viscosity near the filtration limit are preferable in order to minimize the number of inadequate capsules.

Alginates↗