Viscoelastic properties of blood studied through piezoresistance measurements

Piezoresistance describes the change of electrical resistance in a material undergoing deformation. Heterogeneous materials having different resistivities of dispersed and continuous matrix phases, such as blood (comprised of red and white blood cells and platelets suspended in plasma), can exhibit the piezoresistance effect. For an initially isotropic material, two independent intrinsic material coefficients, λ ₁ and λ ₂, would uniquely describe the piezoresistance phenomenon. Materials undergoing deformation affect a material's resistivity in two ways: (a) by introducing anisotropy in the material, which is characterized by λ ₁ and (b) by changing the volume density of the inclusions, which is associated with (1/3λ ₁+λ ₂). In this paper, the piezoresistance effect in bovine blood samples is studied under oscillatory shear flow with a planar sensor rosette. The first piezoresistance coefficient, λ ₁, was measured at various frequencies and shear rates in the blood flow and compared with cosδ (equal to G′/G ^*, where G′ and G ^* are the storage and complex moduli, respectively), which reflects the degree of elasticity. The coefficient λ ₁ was found to have a trend similar to that of cosδ under all conditions tested. Thus λ ₁ might potentially be used to characterize the viscoelastic properties of blood and the deformability of red blood cells, thus clarifying pathophysiology and facilitating diagnosis.