How flow rate can affect microfluidic cellular assays

The research, published in an early view article in the journal Analytical Chemistry​​, aimed to assess whether microfluidics could be used as a reliable method for high-throughput (HT) screening assays. The work was conducted primarily by Royal Society of Edinburgh Research Fellow Dr Haubing Yin, of the University of Glasgow, in the laboratories of Professor Jon Cooper and in collaboration with researchers from the University of Hull and the GlaxoSmithKline's (GSK's) Technology Department in Harlow. Many cellular assays use intact live cells to gain functional information about cell signalling pathways and kinetic data related to drug absorption, metabolism and toxicity. This trend towards cellular imaging systems has been emphasised by companies such as PerkinElmer​ and GE Healthcare​ paying particular attention to this rapidly evolving market. Recently these assays have been incorporated into microfluidic systems to enable efficient analysis of the responses of cells to potential drugs. The researchers state that previous studies have shown that hydrodynamic forces or shear stresses can have a significant effect within microfluidic systems and can influence the metabolism of hepatocytes and endothelial cells. "Each cell type and assay is different, a lot of people are looking at conducting cell based assays in microfluidic systems, but they are not necessarily considering the effects of the hydrodynamic flow on the cells,"​ said Prof. Cooper. The researchers studied the effects of fluid flow on immobilised Chinese hamster ovary (CHO) cells, which are generally regarded as not sensitive to such mechanical stresses. Changes in the Ca²⁺​ fluxes were observed in the cells even at moderate flow rates that mimic the cells responses to chemical stimuli. These changes are important because Ca²⁺​ is generally regarded as a universal intracellular messenger that regulates a diverse range of processes such as gene transcription, muscle contraction and cell proliferation with localised changes being reported for a range of disease states. If a cell is put into such an environment that causes its function to be altered compared with its normal state, the effects of any drug substance may not accurately mirror those that would be mirrored in the body. "Many cells have mechanically sensitive ion channels and other receptor systems that could be affected by the flow so we have looked at a range of typical flow rates used and found that these calcium channels can be activated under those flow rates,"​ he continued. This calcium channel activation could be avoided by lowering the flow rates in the devices and the researchers advise careful comparisons of new assays using microfluidics with more traditional methods to ensure that results are as accurate as possible. "There has clearly been a lot of interest in moving towards cell systems in microfluidics as there are huge advantages in being able to do assays using smaller numbers of cells and less reagent, but people need to consider the mechanical influence of the fluid flow as well as the chemical stimulation that they will be applying,"​ said Prof. Cooper.