Biorheological methods employing the Weissenberg Rheogoniometer

Abstract

The theories and spatial concepts of Karl Weissenberg have been applied to the science of biorheology by employing the Weissenberg Rheogoniometer. Two main types of experimental methods have been used for the characterization of the bulk shear properties of biorheological fluids: (A) In continuous laminar shearing motion, the tangential and normal components of stress are measured at a series of rates of shear. From these parameters, the apparent viscosity, an elastic modulus and a recoverable strain, are calculated as functions of the rate of shear. In this continuous shear experiment, the physical structure present in the material at any given rate of shear may be quite different from the material in its rest state or at other rates of shear. (B) In harmonic oscillatory motion, the material is subjected to a harmonic laminar shear about its rest state at a number of frequencies and small strain amplitudes. From these experiments the dynamic moduli of viscosity and elasticity are calculated. Preparations of biological materials, such as whole blood and systems of blood components, both in health and disease states, have been investigated using methods A and B, together with studies of surface layers of plasma proteins at interfaces.