RHEOLOGICAL PROPERTIES OF PLANT-CELL SUSPENSIONS

Packed cell and concentrated cell suspension cultures of Datura stramonium were exposed to oscillatory and steady shear on a Weissenberg rheogoniometer with a modified parallel plate geometry and to steady shear using other rotational viscometers. The viscoelastic properties of the cell suspensions were measured over a frequency range from 0.01 to 4 rad/s at low and high amplitudes. The applied strains were in the range of 1%-36%. Increasing the strain caused cell damage (e.g., approximately 20% at a strain of 36% during 3 h of shearing). Cell cultures exhibited both viscoelastic and shear thinning behavior. The concentrated cell suspension cultures showed much lower dynamic viscosities and elastic moduli than the packed cell cultures. From the measured viscoelastic properties, yield stresses were calculated. The maximum calculated average yield stress was 4 x 10(4) dyn/cm2 for the packed cells and 325 dyn/cm2 for the concentrated cell suspension having a cell volume fraction (PCV, packed cell volume) of 0.9 mL/mL. From the steady shear experiments, yield stresses were also determined. The maximum calculated yield stress was 360 dyn/cm2 for a concentrated cell suspension (PCV = 0.9 mL/mL) and 95 dyn/cm2 for the less concentrated cell suspension (PCV = 0.6 mL/mL). It was confirmed that D. stramonium cell suspension cultures at high cell concentrations exhibit yield behavior which can be determined by either oscillatory or steady shear. The yield stress values determined in this study will be of some value to the bioprocess engineering of plant cells for high density cell cultivation and product recovery. In particular, these values will be important to determine bioreactor operating conditions such as agitation and aeration rates.