Syringe pumps are widely used biomedical equipment which offer low-cost solutions to drive and control flow through microfluidic chips. However, they have been shown to transmit mechanical oscillations resulting from their stepper motors, into the flow, perturbing device performance. In this work, unlike previous studies at lower flow rates, we have uncovered that the relative pressure fluctuation plateau from 5mL/h onwards to approximately 2% of the average pressure. Furthermore, we find that absolute pressure fluctuations increase as a non-linear monotonic function of kinematic viscosity at flow rates in the 5-25 mL/h range, while the relative pressure fluctuations peak at 1.25 cSt. Using a novel low-cost coded compressive rotating mirror (CCRM) camera, we investigated the effect of fluctuations in a hydrodynamic microfluidic separation device based on a cell-free layer concept. Using this high-speed imaging set-up, we quantified the cell-free zone width fluctuations at bifurcations. We demonstrated that these fluctuations have the same frequency and amplitude than the syringe pump induced pressure oscillations. Finally, to illustrate that pressure fluctuations degrade the separation efficiency in such devices, we demonstrate using milk samples, instances of particles diverted to undesired outlets. This work provides an insight into the effect of syringe pump fluctuations on microfluidic separation, which will inform the design of microfluidic systems and improve their resilience to pulsating or fluctuating flow conditions.
Blood plasma separation is a prerequisite in numerous biomedical assays involving low abundance plasma-borne biomarkers and thus is the fundamental step before many bioanalytical steps. Conventionally, plasma separation is performed using high-capacity refrigerated centrifuges which have the advantage of handling large volume blood samples. These centrifuges are bulky, and prohibitively expensive for low-resource settings, with prices starting from $1,500. Although commercial and existing open-source micro-centrifuges are relatively low-cost, they cannot handle large volume blood samples. Microfluidic blood plasma separation also has been adopted by many researchers to enable low-cost plasma separation, however, these systems still present yield and purity issues for extremely low abundance biomarker detection such as the detection of various fractions of circulating cell-free DNA. To overcome this, we customised the rotor of a commercially available micro-centrifuge ∼$125) using fused filament fabrication to enable centrifugation of large clinical blood samples in resource poor-settings. Our designed adaptor ($15) can hold two 9 mL S-Monovette tubes and maintain the same separation performance (yield, cell count, hemolysis, albumin levels) as the control benchtop refrigerated centrifuge. This low-cost open-source centrifugation system capable of processing clinical blood tubes could be valuable to low-funded laboratories or low-resource settings where centrifugation is required immediately after blood withdrawal for further testing.
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