Mass Transfer in Immobilized Cell Systems

Abstract

Immobilized cell/bioactive agent systems have found applications in a variety of areas, including encapsulated cell therapy (Colton 1996, DeVos et al 1996, Lanza et al 1996, Stegemann and Sefton 1996), immobilized biocatalysts (Svec and Gemeiner 1995, Takizawa et al 1996), and polymeric drug-delivery systems (Gan et al 1996, Yao et al 1994). All, however, suffer from specific mass transfer problems. In the case of immobilized cells, oxygen must be able to reach the viable cells at a sufficient rate to keep the cells alive, while the desired prodduct, such as insulin in the case of diabetes treatment, must be able to diffuse out of the capsule, along with low molecular weight waste products With biocatalysts, whether they be enzymes or cells, the substrate must be able to reach the bead/capsule interior to allow the biochemical reaction to occur, and the desired products must be able to diffuse out of the bead. Similarly with drug-delivery systems, the release of the bioactive agent from the polymer matrix or capsule must be controlled so as to give a constant steady release rate.