Effects of unidirectional flow shear stresses on the formation, fractal microstructure and rigidity of incipient whole blood clots and fibrin gels

摘要

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