Study of blood flow behavior in microchannels

Microfluidic (also known as lab-on-a-chip) devices offer the capability ofmanipulating very low volumes of fluids (of the order of micro litres) for severalapplications including medical diagnostics. This property makes microfluidicdevices very attractive when the fluid, such as blood, has a limited supply becausethe patients cannot easily and frequently provide a large sample. This is typically thecase for aged, diseased patients that do require frequent sampling during acute careor of older people that have the option of being treated and cared for at home [1].Prototype lab-on-a-chip devices for medical diagnostics comprise a number ofelements which separately perform different functions within the system. Activitywithin the research community is focusing on the better integration of devicefunctionalities with the long term goal of creating fully integrated, portable,affordable clinical devices. However, engineering these solutions for the largevolume production of lab-on-a-chip devices requires design rules which are not yetentirely available.This paper describes the results obtained from a set of experiments run to drawgeneric design rules for the manufacture of a cells/plasma micro separator [2]. Thecells/plasma micro separator was selected for investigation because it is a strategicelement required in the preparation of blood samples for many different analyticaldevices. The experiments focused on the study of the behaviour of whole bloodpassing through micro constrictions which are required for enhancing the separationeffect [3].The test microfluidic device was an aluminium specimen designed andmanufactured to incorporate micro constrictions of different width and length. The metallic aluminium test device was designed for manufacturing by micromilling anddiamond cutting processes in view of applying these techniques to the manufactureof micro-moulds for the high-volume production of plastic microfluidic devices viamicro-injection moulding.The widths of the constrictions were 23, 53 and 93µm and the lengths were 300 and700µm. The blood flow pattern and the level of haemolysis generated in the wholeblood were determined for flow rates between 0.2 and 1 ml/min. Initial resultssuggested that the above conditions generate a stable flow and do not cause bloodhaemolysis following passage through the narrow constrictions. This result impliesthat constrictions as narrow as 23 µm and as long as 700µm can be safely used inblood microfluidic devices under appropriate flow conditions without the risk ofdamaging the blood compone