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

Abstract

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.

Fibrin mechanical properties and their structural origins

“…Based on viscoelastic properties of incipient blood clots, a new biomarker of healthy, bleeding or prothrombotic clot microstructure was proposed, named the fractal dimension, which has been shown to have clinically important correlations [31-33]. Clots derived from the blood of subjects with pulmonary embolism showed accelerated establishment of viscoelastic properties compared to healthy donors [34].…”

Effects of exercise intensity on clot microstructure and mechanical properties in healthy individuals

“…These changes were confirmed by increases in G`G P , a measure of functional clot properties including viscoelastic strength, polymerisation and crosslinking, following both submaximal exercise and maximal exercise, suggesting that the resulting clot has increased viscoelastic strength following both exercise intensities. We have previously reported that d f has accurately quantifies the effects of acute and chronic vascular inflammatory changes [21][22][23], sheer stress [29], temperature [25] and haemoconcentration/dilution [24] on clot structure, all of which are established to occur during high intensity exercise [1,2].…”

Substoichiometric molecular control and amplification of the initiation and nature of amyloid fibril formation: lessons from and for blood clotting

“…Increases in fibre thickness. Hints of β-sheet formation induced by flow can be seen in [269], while in a very striking study, Campbell et al [270] saw a huge increase in the flow-induced diameter of fibrin fibres, from a mean of 79 to 226nm.…”