11. Bioengineering and Bio-thermal Fluid Dynamics

Currently, there is a need for mass culture technology of cells required for organogenesis and cell therapy. Suspension culture is particularly suitable for mass culture because it does not depend on the adhesive area of the culture vessel. Agitation is necessary to generate a suspended state, to exchange gases, and to prevent excessive aggregation of cells. However, there is a problem of cell damage due to collision with the agitator blades and shear stress caused by their rotation. Suspension culture devices such as bag-type and rotating wall vessels have been devised, but the former is not easy to control the flow, and the latter requires a dedicated device for the power source to rotate the culture vessel, making it unsuitable for large scale culture. To solve the problem of cell damage, there are high expectations for a next-generation suspension culture technology using Vibration Induced Circulating Flow. Since this technology uses vibration-induced flow in a tube, it is easier to control the flow than other suspension culture systems and can more actively suppress shear stress invasion on cells. Furthermore, it has been reported that the addition of moderate shear stress promotes the growth of microalgae, a type of microorganism, and it is expected that the addition of moderate shear stress under controlled vibration conditions can control the growth rate and differentiation of microalgae. In this report, the formation mechanism of Vibration Induced Circulating Flow is elucidated by Particle Image Velocimetry (PIV) as a basic flow evaluation for large-scale culture and theoretical model building. The results showed that the circulating flow is induced by the viscosity of the liquid. It was shown that the flow is induced by shear stress from the tube wall, and that the flow is sustained by inertial force and then attenuated by viscous force.