Effects of syringe pump fluctuations on cell-free layer in hydrodynamic separation microfluidic devices

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. These detrimental effects have mostly been reported on microdroplet production, but have never been reported on hydrodynamic two-phase separation, such as in microdevices making use of cell-free layer phenomena. While various mechanisms can be used to circumvent syringe pump oscillations, it is of interest to study the oscillation effects in naive systems, which are common in research settings. Previous fluctuation studies focused on relatively low flow rates, typically below 5ml/h, and showed a linear decay of the relative pressure fluctuations as a function of the flow rate. In this work, we have uncovered that the relative pressure fluctuations reach a plateau at higher flow rates, typically above 5ml/h. Using a novel low-cost coded compressive rotating mirror camera, we investigated the effect of fluctuations in a hydrodynamic microfluidic separation device based on a cell-free layer concept. We demonstrated that cell-free zone width fluctuations have the same frequency and amplitude than the syringe pump-induced pressure oscillations and illustrated the subsequent degradation of particle separation. 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 without the use of ancillary equipment.

Automated summary

The study reveals that syringe pump fluctuations can have a negative impact on microfluidic separation, especially in devices based on the cell-free layer concept. It was found that pressure fluctuations tend to stabilize at higher flow rates. This work provides insights for the design and improvement of microfluidic systems in resisting pulsating or fluctuating flow conditions.