EFFECT OF FLUID SHEAR FORCES ON PLANT-CELL SUSPENSIONS

The sensitivity of plant cell culture to fluid forces, or fluid-mechanical sensitivity, in a stirred bioreactor is evaluated by shearing the cells in viscometers for short duration under a range of laminar and turbulent conditions. This short-term evaluation is compared with the experiments in a stirred bioreactor under chemostat mode at various agitation speeds. Fluid-mechanical sensitivity was quantified by measuring various biological parameters including regrowth ability, membrane integrity, mitochondrial activity, aggregate size and lysis. A critical hydrodynamic variable was derived based on a model whereby the biological activity of cells after a given period in a defined shearing environment was a cumulative effect of the total work done by fluid forces on the cells. This hydrodynamic variable, calculated as total energy dissipation on,cells per unit volume, was used as a common basis to quantify the agitation-based shear forces under laminar and turbulent flow conditions. Fluid-mechanical sensitivity data for plant cell suspensions under different flow conditions was successfully correlated with this hydrodynamic variable. This correlation established a hierarchy of response, ranging from a subtle biological inhibitory effect on regrowth ability or sublytic effect, to the gross physical effect of aggregate breakup and lysis. Inhibition of growth rather than lysis was found to dictate the performance of plant cell culture in the bioreactor.