Dynamic mechanical measurements in a shear field include all cohesive and adhesive forces within the contained sample. Prerequisites for correct tests are the homogeneity of the sample in the rheometer gap during the entire measurement and the optimal stress transfer from the moving to the stationary plate. Due to the importance of adhesion we also test blood suspensions in contact with biological and otherwise coated surfaces in addition to classic rheometry on metallic plates, as this affects the transfer of the applied shear stress / shear strain through the sample.
We characterize biological and technical materials by means of rheology, and we work for the Medical University of Vienna, Austria.
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Fibrin networks show strain hardening, Mullins effect, and nonlinear stress-relaxation. This rich mechanical response can be accessed by rheometry. Viscoelastic tests together with treatment protocols based on cut-off values are already used for postoperative patient care, but since now only the linear behavior of clots is tested. Measuring at broader ranges of shear deformation will add valuable information because blood flow compels clots into a dynamic non-linear response that alters clot remodeling. We therefore looked for an easy-to-use rheological protocol to identify the mechanical phenotype of a blood clot at large strains. Our rheological protocol translates well to other gels that contain fibers, such as collagen hydrogels with or without embedded cells.