A diffusion model and optimal cell loading for immobilized cell biocatalysts

A diffusion model based on the random pore model is derived for immobilized cell biocatalysts and verified with 19 sets of experimental diffusion data . The predicted effective diffusivity relative to that for the support matr ix reflects a quadratic dependence on the cell loading and contains a singl e parameter that depends on the intracellular diffusivity and the chemical partitioning coefficient. The model is used to predict optimal cell loading s that maximize the total reaction rate in an immobilized cell biocatalyst. A rule of thumb based on the diffusion model is obtained to the effect tha t the cell loading should be at least 1/3 for single reactions regardless o f the kinetics and diffusional resistances. A means of calculating improved lower bounds is provided for cases where the cellular diffusional resistan ce is known but the kinetics are not. The optimal cell loadings for reversi ble first-order and for Michaelis-Menten kinetics are presented and demonst rated to be within the range of conditions of practical interest. (C) 2000 John Wiley & Sons, Inc.