Shear effects on suspended cells

Shear has been mainly considered in the technical literature as a destructive element, when applied to microorganisms and cells. Indeed, most of the research work addressing the subject aims at the identification of damaging levels of shear on a given culture. The present work is focused on the effects of shear on suspended cultures before the damaging levels are attained. Inspection of the literature reveals that shear may influence growth rate, cellular volume, metabolite production rate and distribution, and membrane permeabilities. Available devices for study and evaluation of shear effects on suspended cultures are described and critically reviewed. The review reveals the possibility of an influence of the liquid dynamics on the kinetics of the biochemical process. This is relevant for bioreactor design and scale up, and stresses the importance of using structural bioreactor models in order to describe the hydrodynamics of the system.