The application of large amplitude oscillatory stress in a study of fully formed fibrin clots

T F Lamer,N Badiei,K Hawkins,P R Williams,D J Curtis,B R Thomas

doi:10.1063/1.4999991

Abstract

The suitability of controlled stress large amplitude oscillatory shear (LAOStress) for the characterisation of the nonlinear viscoelastic properties of fully formed fibrin clots is investigated. Capturing the rich nonlinear viscoelastic behaviour of the fibrin network is important for understanding the structural behaviour of clots formed in blood vessels which are exposed to a wide range of shear stresses. We report, for the first time, that artefacts due to ringing exist in both the sample stress and strain waveforms of a LAOStress measurement which will lead to errors in the calculation of nonlinear viscoelastic properties. The process of smoothing the waveforms eliminates these artefacts whilst retaining essential rheological information. Furthermore, we demonstrate the potential of LAOStress for characterising the nonlinear viscoelastic properties of fibrin clots in response to incremental increases of applied stress up to the point of fracture. Alternating LAOStress and small amplitude oscillatory shear measurements provide detailed information of reversible and irreversible structural changes of the fibrin clot as a consequence of elevated levels of stress. We relate these findings to previous studies involving large scale deformations of fibrin clots. The LAOStress technique may provide useful information to help understand why some blood clots formed in vessels are stable (such as in deep vein thrombosis) and others break off (leading to a life threatening pulmonary embolism).

Highlights

Characterisation of the nonlinear rheological properties of biopolymer gels has important implications for understanding their structure-function relationships under large stress and strain regimes
For the first time, that artefacts due to ringing exist in both the sample stress and strain waveforms of a LAOStress measurement which will lead to errors in the calculation of nonlinear viscoelastic properties
We investigated the applicability of LAOStress in studying the nonlinear viscoelastic properties of fully formed fibrin clots

Summary

INTRODUCTION

Characterisation of the nonlinear rheological properties of biopolymer gels has important implications for understanding their structure-function relationships under large stress and strain regimes. Marked changes in the structure and rheological properties of the clot can arise as a consequence of shear stress through several different mechanisms including strain-stiffening of the fibrin network,[11] strain-stiffening of individual fibrin fibres,[12,13] protein unfolding of stretched fibres,[14] unfolding of fibrin monomers,[15] yielding of branching points,[16] slippage of protofibrils within fibres,[17] and breakage of individual fibrin fibres.[18,19]. Several studies have reported the application of a pre-stress followed by the superposition of small amplitude oscillatory shear stress to probe the rheological properties in terms of differential moduli.[15,23,24] Using this approach, Piechocka et al.[15] identified distinct regimes of elastic response. Controlled stress LAOS (LAOStress) is arguably a more suitable technique than controlled strain LAOS for studying the nonlinear properties of fully formed fibrin clots. We combine alternating LAOStress and linear viscoelastic measurements in order to study reversible and irreversible changes in fibrin clot microstructure as a consequence of different levels of stress

Materials

Rheometry

Analysis of LAOStress waveforms

LAOStress data processing

Nonlinear and linear viscoelastic properties

CONCLUSIONS