Early stage of Erythrocyte Sedimentation Rate test: Fracture of a high-volume-fraction gel

TL;DR

This study investigates the initial fracture process of RBC gels in ESR tests, providing a physical model that explains how cell interactions influence gel stability and sedimentation delay, with implications for clinical accuracy.

Contribution

It introduces a fracturing model for RBC gels during ESR onset, linking microscopic interactions to macroscopic gel behavior and improving understanding of sedimentation dynamics.

Findings

Fracture dynamics of RBC gels are influenced by cell attraction strength.

The proposed model accurately describes the gel interface motion during early sedimentation.

Increased RBC attraction reduces gel delay time by increasing fracture density.

Abstract

Erythrocyte Sedimentation Rate (ESR) is a clinical parameter used as a non-specific marker for inflammation, and recent studies have shown that it is linked to the collapse of the gel formed by red blood cells (RBCs) at physiological hematocrits (i.e. RBC volume fraction). Previous research has suggested that the delay time before the sedimentation process is related to the formation of fractures in the gel. Moreover, RBC gels present specific properties due to the anisotropic shape and flexibility of the RBCs. Namely, the onset of the collapse is reached earlier and the settling velocity of the gel increases with increasing attraction between the RBCs, while gel of spherical particles show the opposite trend. Here, we report experimental observations of the gel structure during this onset and suggest an equation modeling this initial process as fracturing of the gel. We demonstrate that this equation provides a model for the motion of the interface between blood plasma and the RBC gel, along the whole time span. We also observe that the increase in the attraction between the RBCs modifies the density of fractures in the gel, which explains why the gel displays a decrease in delay time when the aggregation energy between the RBCs increases. Our work uncovers the detailed physical mechanism underlying the ESR and provides insights into the fracture dynamics of a RBC gel. These results can improve the accuracy of clinical measurements.