Investigation of blood rheology under steady and unidirectional large amplitude oscillatory shear.

We present new dynamic rheological tests of human blood that motivate an improved model for the thixotropic shear rheology of human blood. Unidirectional large amplitude oscillatory shear (UD-LAOS) is proposed as a dynamic test relevant for understanding <italic>in vivo</italic> arterial pulsatile blood flow, and data are presented for two healthy donors studied previously using more traditional steady and step-rate experiments. The model analyzes the overall extra stress of the system in two components. A thixotropic component is represented by a structure-kinetics model coupled with a stress expression containing both viscoelastic and thixotropic elements to account for the presence of linear aggregates of red blood cells, known as rouleaux, which form at low shear rates. Another component is viscoelastic, described through an extend White–Metzner approach. It corresponds to the stresses that arise due to the isolated red blood cells, which deform at high shear rates. The combined model is fit to experimental steady shear and UD-LAOS data for two healthy donors and is subsequently used to predict the stress response of the blood sample to UD-LAOS experiments over a broad range of strain amplitudes and frequencies. Comparison to the previous models for transient blood rheology shows a significantly improved fit over a range of physiologically relevant flow conditions. In addition, this analysis demonstrates the usefulness of UD-LAOS tests with regards to understanding the microstructural evolution in blood under transient flow. [ABSTRACT FROM AUTHOR]