Study of blood flow behaviour in microchannels
Marson S., Benade M., Attia UM., Allen DM., Kersaudy Kerhoas M., Hedge J., Morgan S., Larcombe L., Alcock JR.
Microfluidic (also known as lab-on-a-chip) devices offer the capability of manipulating very low volumes of fluids (of the order of micro litres) for several applications including medical diagnostics. This property makes microfluidic devices very attractive when the fluid, such as blood, has a limited supply because the patients cannot easily and frequently provide a large sample. This is typically the case for aged, diseased patients that do require frequent sampling during acute care or of older people that have the option of being treated and cared for at home . Prototype lab-on-a-chip devices for medical diagnostics comprise a number of elements which separately perform different functions within the system. Activity within the research community is focusing on the better integration of device functionalities with the long term goal of creating fully integrated, portable, affordable clinical devices. However, engineering these solutions for the large volume production of lab-on-a-chip devices requires design rules which are not yet entirely available. This paper describes the results obtained from a set of experiments run to draw generic design rules for the manufacture of a cells/plasma micro separator  . The cells/plasma micro separator was selected for investigation because it is a strategic element required in the preparation of blood samples for many different analytical devices. The experiments focused on the study of the behaviour of whole blood passing through micro constrictions which are required for enhancing the separation effect . The test microfluidic device was an aluminium specimen designed and manufactured to incorporate micro constrictions of different width and length. The metallic aluminium test device was designed for manufacturing by micromilling and diamond cutting processes in view of applying these techniques to the manufacture of micro-moulds for the high-volume production of plastic microfluidic devices via micro-injection moulding. The widths of the constrictions were 23, 53 and 93um and the lengths were 300 and 700um. The blood flow pattern and the level of haemolysis generated in the whole blood were determined for flow rates between 0.2 and 1 ml/min. Initial results suggested that the above conditions generate a stable flow and do not cause blood haemolysis following passage through the narrow constrictions. This result implies that constrictions as narrow as 23 um and as long as 700um can be safely used in blood microfluidic devices under appropriate flow conditions without the risk of damaging the blood components.