Diffusion phenomena in the spherical matrices used for cell immobilization

A transient method was used to determine the effective diffusion coefficient D(eff) of glucose and ethanol in a 3.5% calcium alginate matrix under various operating conditions. A known quantity of alginate beads was suspended in a known volume of stirred solution and the variation in the solute concentration was followed over time. D(eff) values were determined by minimizing the sum of the deviation between the experimental points and those predicted by a model in which the Biot number was used to allow for the external diffusional resistance in the liquid surrounding the beads. The experimental results obtained by this method are examined and discussed for the purpose of understanding the behaviour of the matrix in the presence of a bioreaction.