Microscale blood flows and rheology – surface tension driven flow applications for point of care diagnostics

Abstract

Surface tension driven blood flow in microfluidic applications for blood diagnostics, is a simple and cost-effective approach, however, the flow and rheological characteristics of blood in such setups is not well understood. The aim of this work is to characterize the blood flow in such applications and to investigate the influence of erythrocyte deformability, aggregation and haematocrit, which dominate the non-Newtonian nature of blood. For this purpose, normal and super-hydrophilic microchannels were produced to accommodate the flow, and whole human blood, as well as erythrocyte suspensions were produced to provide various states of erythrocyte deformability, aggregation and sample haematocrit. The samples were imaged under flow, and their local and bulk velocity characteristics were assessed using micro-Particle Image Velocimetry setups and tracking techniques. Standard methods were utilised to assess the viscosity, aggregation and deformability of the samples, whereas image processing methods were developed to characterize the microstructure of the samples in the microchannel. Fluid mechanics and rheology theory was utilised to model the velocity and viscosity of the fluids. The results, show a clear influence of the viscosity, however, a complex non-monotonic influence of the aggregation, on the velocity in the microchannel affected by moderate to intense shearing conditions in the channel.