Microencapsulation: a review of polymers and technologies with a focus on bioartificial organs

Various immunoisolation technologies including arteriovenous shunts, diffusion chambers and microcapsules are reviewed and various microcapsule production techniques are discussed. This encompasses syringe based droplet generation devices, various emulsion techniques and rotating discs. Polymers used for the formation of permselective microcapsules and capsular membranes are also presented. In particular, the immunoisolation of islets for the production of a bioartificial pancreas is evaluated. Screening of polyelectrolytes with respect to cell cytotoxicity is discussed along with a summary of various polymer chemistries, mechanisms of membrane formation and microencapsulation technologies. A systematic categorization is proposed and four cases are compared in detail: Sun's alginate/calcium chloride-based precast beads (Type I-B-chi), Dautzenberg's binary polyanion/polycation coacervation systems (Type II-A-alpha), Sefton's phase inversion systems based on non-ionic, elastic, hydrophobic copolymers (Type IV-F-delta), and a new multicomponent polyelectrolyte capsule with gel precasting and oligocation diffusion to control the cutoff (Type III-E-chi). In vitro and in vivo testing of xenograft functioning in the Type III-E-chi system will be reported.