Hydrodynamic deposition: A novel method of cell immobilization

Abstract

A novel method of cell immobilization is described. The cell support consists of ceramic microspheres of approximately 50–75 μm diameter. The spheres are hollow, having a wall thickness of 10–15 μm and one entrance (ca. 20 μm diameter). The walls are porous with a mean pore size of approximately 90 nm. When a cell suspension (of S. cerevisiae) is passed through a column of such particles, cells are immobilized. Conditions are devised such that the overwhelming majority of cells are held in the central cavity of the support and not between the particles. Provided turbulence is avoided, the distribution of cells along the column length in the steady state is rather homogeneous. The facts that (a) essentially all particles, regardless of orientation, entrap cells, and (b) nonporous particles also entrap cells with high efficiency, indicate that filtration effects are irrelevant and that heretofore unrecognized hydrodynamic forces are alone responsible for the cell immobilization. Cells can be immobilized to high biomass densities, while the hydrodynamic properties of columns containing such immobilized cells are excellent. We describe an on-line electronic method for the real-time measurement of immobilized cellular biomass. Cell growth (so recorded) and metabolism continue to occur in such particles at high rates. Using the glycolytic production of ethanol by S. cerevisiae as a model reaction, volumetric productivities as great as any published are obtained. Thus the “lobster-pot effect” or “hydrodynamic deposition” represents a novel, promising, and generally applicable method of cell immobilization.