Cell adhesion kinetics varies with position in the cone-plate viscometer

Cone-plate viscometry is used extensively to study platelet and neutrophil aggregation kinetics. Conventional studies assume that flow in the viscometer is linear and that the nature of cell adhesion is independent of position in the device. However, at higher shear rates centrifugal forces result in radial motion of the liquid and hence significant secondary flow. We examined how this secondary flow may alter cellular adhesion kinetics. The Navier Stokes equation was solved numerically to determine the flow profile in the viscometer upto a shear rate (G) of 1500 s^-1. These results were coupled with a theoretical analysis of two-body particle hydrodynamics to estimate how the magnitude of inter-particle forces and contact duration vary with position in the viscometer. While positional variations within the inner half region of the viscometer were small and close to that predicted by linear flow analysis, the variations were more pronounced near the edge. Increasing the shear rate and the sample volume caused an increase in secondary flow effects. A bimolecular kinetic model was applied to estimate the overall cell adhesion efficiency under these conditions. Results indicate that, secondary flow at G = 1500 s^-1, caused decreases in adhesion efficiency of upto 30% relative to linear flow analysis. In addition to the mathematical model, experimental validation of theoretical predictions are also presented.