Flow rate-controlled pipetting for microfluidics: second-generation flexible hydraulic reservoir (FHRv2)

A critical component of microfluidic technology is the fluid pumping mechanism. Syringe and pressure pumps are typically used in the lab environment; however, their operations generate considerable dead volume that is often larger than the volume of the chip itself, leading to considerable waste of precious sample. As an alternative, pipetting allows for precise liquid dispensing with zero dead volume; however, it has a limited flow control. Recently, we have introduced a low-cost sample loading interface with zero dead-volume named flexible hydraulic reservoir (FHR). In this study, we present a second-generation FHRv2 that combines continuous pumping, zero-dead volume and the versatility of pipetting. The performance of FHRv2 is tested against a syringe pump at flow rates ranging between 20 and 60 mu L/min. It demonstrated smoother operation and identical transient time to reach steady flow rate as confirmed by a mathematical model developed for the occasion. Importantly, we also demonstrate that the FHRv2 prevents sedimentation-induced artifacts typically encountered in typical syringe pumps when dispensing particles. Finally, we demonstrate the fabrication of the FHRv2 concept with injection molding using a 3D-printed mold. Overall, our FHRv2 offers a low-cost and versatile solution for zero-volume liquid handling in microfluidic devices.