Early studies by Pendleton and West (1) in 1932 demonstrated that urea moved from the blood into the small intestine in uremic dogs. In 1946, Twiss and Kolff (2) showed in uremic patients that urea could be removed when an isotonic solution was perfused through an isolated in- testinalloop. Since these early studies had demonstrated the presence of urea and its removal from the gastrointestinal tract, Yatzidis (3) in 1964 investigated the use of activated charcoal for the removal of uremic wastes from the intestinal tract. In addition to Yatzidis' studies with char- coal, other investigations with charcoal have been unable to confirm any significant reduction in serum levels of urea, creatinine, uric acid, or guanidines (4,5) via this approach. At the same time that Yatzidis proposed the use of charcoal for re- moval of nitrogenous wastes from the intestinal tract, he also proposed using charcoal in a hemoperfusion microapparatus as an effective artifi- cial kidney. However, clinical studies performed with the Yatzidis char- coal artificial kidney showed an adverse affect on platelets and the re- lease of embolizing particles (6,7). To overcome these platelet and emboli problems, Chang's group (8) proposed the general idea of "artificial cells," Le., microcapsules con- taining adsorbents. Since the charcoal particles were now encased within blood compatible membranes, they could not leave the microcapsules to cause embolism, and platelets did not now come in direct contact with the charcoal. In their early clinical hemoperfusion studies, Chang et al.

The concept of using encapsulation for the immunoprotection of transplanted cells was introduced for the first time in the 1960s. "[Microencapsulated cells] might be protected from destruction and from partici- pation in immunological processes, while the enclosing membrane would be permeable to small molecules of specific cellular product which could then enter the general extracellular compartment of the recipient. For instance, encapsulated endocrine cells might survive and maintain an effective supply of hormone." (Chang, Ph.D. Thesis, McGill University, 1965; Chang et aI., Can J Physiol PharmacoI44:115-128, 1966). We asked Connaught Laboratories, Ltd., in Toronto to put this concept into practice. In 1980, Lim and Sun from Connaught Laboratories reported on the successful implantation of poly-I-Iysine-alginate encapsu- lated rat islets into a foreign host. [Lim and Sun, Science 210:908-909, 1980]. Now many groups around the world are making tremendous progress in the encapsulation of a multitude of cell types. Kiihtreiber, Lanza, and Chick have invited many cell encapsulation groups from around the world to contribute to this book. The result is a very useful reference book in this rapidly growing area. With so many excellent au- thors describing in detail the different areas of cell encapsulation, my role here will be to briefly discuss a few points.

Early studies by Pendleton and West (1) in 1932 demonstrated that urea moved from the blood into the small intestine in uremic dogs. In 1946, Twiss and Kolff (2) showed in uremic patients that urea could be removed when an isotonic solution was perfused through an isolated in- testinalloop. Since these early studies had demonstrated the presence of urea and its removal from the gastrointestinal tract, Yatzidis (3) in 1964 investigated the use of activated charcoal for the removal of uremic wastes from the intestinal tract. In addition to Yatzidis' studies with char- coal, other investigations with charcoal have been unable to confirm any significant reduction in serum levels of urea, creatinine, uric acid, or guanidines (4,5) via this approach. At the same time that Yatzidis proposed the use of charcoal for re- moval of nitrogenous wastes from the intestinal tract, he also proposed using charcoal in a hemoperfusion microapparatus as an effective artifi- cial kidney. However, clinical studies performed with the Yatzidis char- coal artificial kidney showed an adverse affect on platelets and the re- lease of embolizing particles (6,7). To overcome these platelet and emboli problems, Chang's group (8) proposed the general idea of "artificial cells," Le., microcapsules con- taining adsorbents. Since the charcoal particles were now encased within blood compatible membranes, they could not leave the microcapsules to cause embolism, and platelets did not now come in direct contact with the charcoal. In their early clinical hemoperfusion studies, Chang et al.