Microfluidic Red Blood Cell Analysis

A Cytometric instrument which incorporates a combined macrofluidic and microfluidic system has been developed for the quantification of erythrocyte (red blood cell) rheology.

It is postulated that erythrocytes, displaying abnormal cell-mechanical properties, may be present in pathologies such as Diabetes, Thalassaemia and Sickle Cell Anaemia, however the existing haemorheological techniques lack sufficient specificity to verify the presence of such cells.

The STRC's Microfluidics and Microengineering Research Group initiated collaboration with the Department of Physiology and Biophysics at Imperial College School of Medicine, St Mary’s Hospital, London in 1994 in order to asses the feasibility of employing microfabricated silicon structures for haemorheological measurement.

Haemocytometer.


Multilayer microfluidic device packaged with electronic heating control circuitry.	View of the top of the Si layer. Shows 1600 flow channels surrounding a central feed shaft.	Close up of an array of 100µm long flow channels whose width varies sinusoidally between 3µm and 5µm.

Accordingly, the cytometric instrument presented has been developed. The instrument is composed of an optimised macroscopic fluid controlling system and a micromachined silicon continuous flow microfluidic device, which utilizes mesofluidic manifolding for optimized connection of the two assemblies. Real-time video data extraction and processing techniques (developed in-house), perform accurate, detailed measurements of statistically significant samples of erythrocytes (circa 1000) on a cell-by-cell basis. Erythrocytes are measured whilst flowing through precisely defined microfabricated capillary flow channels, under physiologically equivalent conditions of temperature and pressure.

Video of Precision control of erythrocytes through silicon flow whose channels width varies sinusoidally.

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Plot of cell velocity through straight 3.5µm wide channels as a function of Volume index for 1557 cells from a control sample.

Plot of cell velocity through straight 3.5µm wide channels as a function of volume index for 1347 cells from a 10% hardened 90% control sample.

The architecture of the system provides: precise control of the delivery of erythrocyte suspensions to, and subsequently from, the measurement area of the microfluidic device; accurate and highly reproducible setting of operating pressures, to 0.05mm H₂O (»0.5Pa); and rapid and reliable priming, cleaning and flushing procedures, thereby minimizing cross-contamination and biological fouling.

The real time data processing allows infrastructural investigation of erythrocyte samples by precisely measuring both velocity and a volume index for each erythrocyte.

Video of erythrocytes undergoing controlled high precision deformability studies.

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CFD model mesh of the feed shaft at the centre of the microfluid device.

CFD analysis of erythrocyte flow trajectories within the feed shaft.

Control and handling of real world biological samples has proved to be a significant stumbling block for many microTAS devices and systems. Detailed CFD analysis was performed in order to overcome known problems of bubbles, biological fouling and accurate transport of suspended media. The resulting structures facilitate reliable bubble free priming and cleaning and the suspended erythrocyte samples can be accurately transported and controlled with minimal damage.