A new protocol of rheology has been developed a couple of years ago at the LLB. This protocol uses wetting properties to facilitate access to the measurement of liquid elasticity in confined geometry [1-2].
We test this protocol with physiological fluids like blood plasma [3] and compare to results obtained with other wetting conditions. Blood contains living cells with different extrinsic (size, shape) and intrinsic (deformability, aggregability) properties that are embedded in blood plasma. Cells and plasma cannot be considered as separate entities without interaction between the two. Together with the cells, the different proteins (10% protein concentration) and small molecules in plasma enable the formation of adhesive layers, structuring, and phase separation, processes that are influenced by the material to which the sheared blood sample is exposed. We have found that different substrates, including those purchased from commercial suppliers, result in different shear moduli. Typical rheology artefacts like incomplete filling or asymmetrical meniscus can be excluded. The lowest modulus was found for steel that corresponds to conventional measurements, indicating the weakest contact between blood and test body. A transition from frequency-independent (elastic plateau) to frequency-dependent behavior is observed versus increasing shear strain. These findings indicate that blood plasma is a microstructural gel those interactions are significantly strong to impact the confinement response.
We raise the question which substrate is best suited for studying physiological fluids. Finally, we present new SANS data on the correlation between human plasma proteins that cannot be reconciled with the Newtonian behavior assumption from conventional rheometry.
- Noirez, L. Baroni, P. Mendil-Jakani, H. (2009). The missing parameter in rheology: hidden solid-like correlations in viscous liquids, polymer melts and glass formers, Polymer International 58, 962.
- Zaccone, A. and Trachenko, K. (2020). Explaining the low-frequency shear elasticity of confined liquids. PNAS, 117:1 9653-19655.
- Windberger, U., Baroni, P., Noirez, L. (2022). Capillary-size flow of human blood plasma : revealing hidden elasticity and scale dependence, J. Biomed Mater Research J. Biomed. Mater. Res. A 110, 298–303.