Blood linear viscoelasticity by small amplitude oscillatory flow

Abstract

Blood is a complex fluid with non-Newtonian characteristics and consists primarily of a concentrated suspension of red blood cells (RBCs) characterized by high deformability and aggregability. The majority of both research and clinical investigations on blood rheology is based on steady shear measurements aimed at determining blood viscosity as a function of shear rate. On the other hand, investigations of blood rheology in the linear viscoelastic regime are sparse in the literature and currently limited. In principle, small amplitude oscillatory flow is best suited to study blood microstructure and rheology under quasi-static conditions, which are relevant in a range of applications, from blood storage to blood aggregability testing. Here, we present the first systematic experimental investigation of blood rheological behavior in the linear viscoelastic regime, by performing oscillatory shear measurements by conventional bulk rheology. The storage (G′) and loss (G″) moduli of whole human blood have been measured over an extended range of frequencies [0.1–30 rad/s]. Data show that G″ predominates over G′ across the entire tested range of frequency. By comparing steady and oscillatory shear viscosity, it was found that the Cox-Merz rule is followed to a good approximation, with higher deviations at small shear rate/frequencies. The effects of RBC volume fraction and of aggregating media (i.e., dextran solution at two different concentrations) have been also investigated. Overall, our results are consistent with the behavior of a weakly attractive suspension, where RBCs form reversible aggregates that can be broken by the action of flow

Representative subsampling of sedimenting blood

“…We recognize that this description is only approximate since blood is a complex fluid that is shear-thinning, slightly viscoelastic and has a small yield stress (1-10 mPa) [34]. However, its rheology is often well described by a Casson law [35,36], which, in the limit of a small yield stress, reduces to an Newtonian effective-viscosity description such as the one used above.…”

Dynamic and Quantitative Assessment of Blood Coagulation Status with an Oscillatory Rheometer

“…Repeated measurements (n = 10) of Thromborel-activated blood from the same donor are shown over time (300 s). The data of uncoagulated blood were taken from literature, where an elastic shear modulus of 0.02 Pa (blue dashed line) and a viscous shear modulus of 0.05 Pa (red dashed line) at 1 Hz are given and shown here as a constant dashed line in the diagram [22]. Upon addition of Thromborel coagulation is initiated and the means of viscous and elastic shear modulus increase (Figure 1a).…”

Strain rate sensitivity of polycarbonate and vinyl ester from dynamic mechanical analysis experiments

“…Dynamic mechanical analysis (DMA) is a widely used technique in polymer science for determining thermal properties of materials, such as polymeric solids [1][2][3] and complex fluids [4]. The technique involves applying an oscillatory deformation to a specimen and measuring the resulting stresses.…”

“…There is also difficulty in converting from frequency to a nominal strain rate and assuming the storage modulus at that frequency to be equivalent to the Young's modulus at that strain rate [16]. This can be interpreted as attempting to find an analogy to the empirical Cox-Merz rule from rheology, which works well for complex fluids including blood [4,17]. However, the relaxation process in fluid flow is not the same as in deformation of a solid; therefore, a different approach is used in the present work.…”