Technology of mammalian cell encapsulation

Entrapment of mammalian cells in physical membranes has been practiced sinc e the early 1950s when it was originally introduced as a basic research too l. The method has since been developed based on the promise of its therapeu tic usefulness in tissue transplantation. Encapsulation physically isolates a cell mass from an outside environment and aims to maintain normal cellul ar physiology within a desired permeability barrier. Numerous encapsulation techniques have been developed over the years. These techniques are genera lly classified as microencapsulation (involving small spherical vehicles an d conformally coated tissues) and macroencapsulation (involving larger hat sheet and hollow-fiber membranes). This review is intended to summarize tec hniques of cell encapsulation as well as methods for evaluating the perform ance of encapsulated cells. The techniques reviewed include microencapsulat ion with polyelectrolyte complexation emphasizing alginate-polylysine capsu les, thermoreversible gelation with agarose as a prototype system, interfac ial precipitation and interfacial polymerization, as well as the technology of flat sheet and hollow fiber-based macroencapsulation. Four aspects of e ncapsulated cells that are critical for the success of the technology, name ly the capsule permeability, mechanical properties, immune protection and b iocompatibility, have been singled out and methods to evaluate these proper ties were summarized. Finally, speculations regarding future directions of cell encapsulation research and device development are included from the au thors' perspective. (C) 2000 Published by Elsevier Science B.V.