Oxygen transfer performance of unbaffled stirred vessels in view of their use as biochemical reactors for animal cell growth

Cultivation of microorganisms, plants or animal cells requires liquid agitation in order to ensure oxygen and nutrient transfer and to maintain cell suspension. However, In such suspensions both mechanical agitation and sparging aeration can cause cell death. Many studies on animal cell damage due to mechanical agitation and sparging aeration have shown that mechanical damage of freely suspended animal cells is in most cases associated with bursting bubbles at the air–liquid interface (Barrett et al., 2010, Nienow et al., 1996). Gas bubbles are usually generated by direct air sparging to propagate oxygen in a culture suspension. Mechanical agitation may also introduce gas bubbles to the culture fluid through vortexing entrainment from the free surface. In this work oxygen transfer performance of an unbaffled stirred vessel is presented in view of its use as biochemical reactor for animal cell growth. As a matter of fact, oxygen mass transfer can occur through the free surface deep vortex which takes place when agitation is started. If this is not allowed to reach impeller blades, bubble formation and subsequent bursting inside the reactor is avoided. Experimental results showed that this kind of bioreactor can provide sufficient oxygen mass transfer for animal cell growth, so resulting in a valid alternative to more common sparged reactors.