Investigation of oxygen transfer through the membrane of polymer hollowspheres by oxygen micro-electrodes

Estimation of oxygen transfer from an aqueous solution into polymer hollow spheres, as used for encapsulation of microorganisms, requires detection of the dissolved oxygen concentration inside the hollow sphere. Using microcoaxial needle electrodes, oxygen kinetics in different penetration depths within single cellulose-sulfate hollow spheres loaded with and without living yeast cells could be measured. Based on the reaction kinetics the diffusion coefficient for oxygen and the oxygen-uptake rate have been calculated. The diffusion coefficient DO2 within the thin membrane of cell-free spheres was in the order of 10(-10)m2s-1. Due to the liquid core of the hollow sphere the corresponding diffusion coefficient DO2 is in the range of the value for water. The oxygen-uptake rate QO2 in cell containing spheres could be estimated to 90 mmol l-1 h-1, which corresponds to a specific oxygen-uptake rate qO2 of 10 mmol g-1 h-1. It is to conclude that oxygen supply of the microorganisms inside the hollow spheres was, in this case, not critically influenced by the thin polymeric wall of the capsules.