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Effects of unidirectional flow shear stresses on the formation, fractal microstructure and rigidity of incipient whole blood clots and fibrin gels
Incipient clot formation in whole blood and fibrin gels was studied by the rheometric techniques of controlled stress
parallel superposition (CSPS) and small amplitude oscillatory shear (SAOS). The effects of unidirectional shear stress on incipient
clot microstructure, formation kinetics and elasticity are reported in terms of the fractal dimension (df ) of the fibrin network,
the gel network formation time (TGP ) and the shear elastic modulus, respectively. The results of this first haemorheological
application of CSPS reveal the marked sensitivity of incipient clot microstructure to physiologically relevant levels of shear
stress, these being an order of magnitude lower than have previously been studied by SAOS. CSPS tests revealed that exposure
of forming clots to increasing levels of shear stress produces a corresponding elevation in df , consistent with the formation of
tighter, more compact clot microstructures under unidirectional flow. A corresponding increase in shear elasticity was recorded.
The scaling relationship established between shear elasticity and df for fibrin clots and whole blood confirms the fibrin network
as the dominant microstructural component of the incipient clot in terms of its response to imposed stress. Supplementary studies
of fibrin clot formation by rheometry and microscopy revealed the substantial additional network mass required to increase df
and provide evidence to support the hypothesis that microstructural changes in blood clotted under unidirectional shear may be
attributed to flow enhanced thrombin generation and activation. CSPS also identified a threshold value of unidirectional shear
stress above which no incipient clot formation could be detected. CSPS was shown to be a valuable haemorheological tool for
the study of the effects of physiological and pathological levels of shear on clot properties