Fluid Dynamics of a Micro-Bioreactor for Tissue Engineering

Abstract

A numerical model is developed for the in- vestigation of flow field and mass transport in a micro- bioreactor, of working volume below 5 ml, in which mediummixing is generated by amagneticstirrer-rod ro- tating on the bottom. The flow-field results show that a recirculation region exists above the stirrer rod and ro- tates with it; the related fluid mixing is characterized by a circulation coefficient of up to 0.2 which is about five times smaller than that of a one-litre stirred-tank bioreactor. The oxygen transfer coefficient is less than 5h −1 which is two orders smaller than that of a 10- litre fermentor with aeration, hence the oxygen transfer rate is insufficient for bacteria culture and bubble aer- ation is needed as was used in the prototype by Kos- tov et al. (2001). However, it is shown that for certain animal cell cultures, the oxygen concentration level in the micro-bioreactor can become adequate without using bubbleaeration, provided that themagnetic rod is rotated at a high speed (rod Reynolds number of 716). At such high rotation-speed, the micro-bioreactor exhibits a peak shear-stress below 0.5 N m −2 that is acceptable for ani- mal cell culture. The maximum local-energy dissipation rate is below 18 kW m −3 which is five times smaller than