Erythrocyte sedimentation: Effect of aggregation energy on gel structure during collapse

TL;DR

This study investigates how the microstructure and aggregation energy of erythrocyte gels influence sedimentation rates, supporting the view that blood sedimentation behaves like gel collapse rather than simple cell aggregation.

Contribution

It provides experimental and simulation evidence linking erythrocyte microstructure, aggregation energy, and sedimentation rate, emphasizing the gel collapse mechanism over aggregate settling.

Findings

Increased attraction strength leads to larger voids in the gel network.

Larger voids result in higher gel permeability and faster sedimentation.

Results support the gel hypothesis for blood sedimentation interpretation.

Abstract

The erythrocyte (or red blood cell) sedimentation rate (ESR) is commonly interpreted as a measure of cell aggregation and as a biomarker of inflammation. It is well known that an increase of fibrinogen concentration, an aggregation-inducing protein for erythrocytes, leads to an increase of the sedimentation rate of erythrocytes, which is generally explained through the formation and faster settling of large disjoint aggregates. However, many aspects of erythrocyte sedimentation conform well with the collapse of a colloidal gel rather than with the sedimentation of disjoint aggregates. Using experiments and cell-level numerical simulations, we systematically investigate the dependence of ESR on fibrinogen concentration and its relation to the microstructure of the gel-like erythrocyte suspension. We show that for physiological aggregation interactions, an increase in the attraction strength between cells results in a cell network with larger void spaces. This geometrical change in the network structure occurs due to anisotropic shape and deformability of erythrocytes and leads to an increased gel permeability and faster sedimentation. Our results provide a comprehensive relation between the ESR and the cell-level structure of erythrocyte suspensions and support the gel hypothesis in the interpretation of blood sedimentation.