NEW CAPSULE WITH TAILORED PROPERTIES FOR THE ENCAPSULATION OF LIVING CELLS

A new capsule for the encapsulation and transplantation of pancreatic islets has been developed. Five active ingredients are involved in the capsule formation process: high viscosity sodium alginate (SA-HV), ce llulose sulfate (CS), poly(methylene-co-guanidine) hydrochloride (PMCG ), calcium chloride, and sodium chloride. Complexation reaction exhibi ts several unique features: (1) solution of SA-HV with CS represents a physical mixture of two entangled polyanions that provide both pH-sen sitive (carboxylic) and permanently charged (sulfate) groups; (2) pres ence of CaCl2 in the cation solution ensures formation of the gelled b ead after the drop of polyanion solution is immersed in the cation sol ution; (3) character of the polycation (PMCG), i.e., low molecular wei ght and unusually high charge density, combines both high mobility and reactivity; (4) presence of PMCG in cation solution, together with Ca Cl2, gives rise to the competitive binding of these two cations based on their diffusion and affinity towards the anion groups; and (5) NaCl provides the anti-gelling sodium ions that significantly affect the r eaction of CaCl2 with the polyanion matrix, thus altering the final pr operties of the capsule surface, shape, and permeability. The capsule size, mechanical strength, membrane thickness, and permeability can be precisely adjusted and quantified. Detailed information on the permea bility aspects is given in another paper by Brissova et al. [J. Biomed . Mater. Sci., 39, 61 (1998)]. The new features concerning capsule pro cessing and testing are presented. We believe that the capsule charact eristics can be optimized in the next step to meet the biological crit eria. The initial transplantation results suggest that this capsule is biocompatible and noncytotoxic and is a promising candidate for the i mmunoisolation of cells such as pancreatic islets. (C) 1998 John Wiley & Sons, Inc.