A hydrostatic pressure-driven passive micropump enhanced with siphon-based autofill function

Abstract

Autonomous and self-powered micropumps are in critical demand for versatile cell- and tissue-based applications as well as for low-cost point-of-care testing (POCT) in microfluidics fields. The hydrostatic pressure-driven passive micropumps are simple and widely used, but they cannot maintain steady and continuous flow for long periods of time. Here, we propose a hydrostatic pressure-driven passive micropump enhanced with siphon-based autofill function, which can realize the autonomous and continuous perfusion with well-controlled steady flow over an extended time without electric power consumption. The characterization results reveal that both the cycle number in one refilling loop and the siphon diameter will affect the refilling time. Furthermore, this micropump also enables multiplexed medium delivery under either the same or different flow conditions with high flexibility. The system was validated using an in vitro vasculogenesis model over the course of several days. Most importantly, the device can consistently provide steady medium perfusion for up to 5 days at a predefined hydrostatic pressure drop without the need for supplemental medium changes. We believe that this hydrostatic pressure-driven passive micropump will become a critical module for a broad range of sophisticated microfluidic operations and applications.

Fig. 1

Schematic diagram showing the platform setup of the hydrostatic pressure-driven passive micropump enhanced with siphon-based autofill function.

Fig. 2

Schematic diagram showing the working principle of siphon-based autofill function. (a) Liquid from both siphons during the initial filling process. (b) No liquid inside the high siphon due to the decreased pressure inside the MSC. (c) Cavitation inside the high siphon and air bubbles appearing inside the MSC. (d) No liquid inside both siphons and no air bubble appearing inside the MSC when the liquid level inside the IMR reached to the DPHS. (e) Activation of refilling process when liquid level inside the IMR dropping below the DPHS. (f) Autonomous repetition of refilling process.

Fig. 3

Electric-fluidic circuit analogy of siphon-based autofill function. (a) Electric circuit of variable capacitor charging process to simulate the air supplementation inside the MSC during the refilling process. (b) Electric circuit of fixed capacitor charging process to simulate the liquid filling inside the IMR during the auto-filling process.

Fig. 4

Schematic diagram showing the sensitivity analysis of autofill function. (a) Liquid column formation inside the high siphon to block the air supplementation into the MSC. (b) Low sensitivity of liquid level drop inside the IMR through a certain distance to reactivate the autofill function.

Fig. 5

Schematic diagram showing the LBC design and operation optimization. (a) Schematic view of the LBC configuration with PDMS and gas permeable/liquid impermeable film, and its integration at the DPHS to prevent liquid column formation during the refilling process. (b) Lift up the high siphon when its top end is immersed into liquid inside MSC to eliminate liquid column formation during the initial filling process. (c) No liquid column formation during initial filling process if the top end of the high siphon is immersed into air inside the MSC.

Fig. 6

Comparison experiment to test the effectiveness of the enhanced micropump with siphon-based autofill function. (a) Decreased hydrostatic pressure drop for conventional micropump without autofill function. (b) Constant hydrostatic pressure drop for enhanced micropump with siphon-based autofill function. (c) Quantitative analysis of flow rate obtained from hydrostatic pressure-driven passive micropump with and without autofill function over time.

Fig. 7

Quantitative analysis of the characteristics of enhanced micropump with autofill function. (a) Good linear relationship with small error bar range between hydrostatic pressure drop and flow rate. (b) Refilling time in each cycle slightly increased as the cycle number increased in the same refilling loop. (c) The bigger the diameter of the low siphon, the shorter the refilling time (liquid volume:1 mL). (d) The bigger the diameter of the high siphon, the shorter the refilling time (liquid volume:1 mL).

Fig. 8

Multiplexed micropump with the integration of four-way stopcock for selective liquid perfusion into the IMR at the predefined liquid level. (a) Prototype of the multiplexed micropump. (b) Four operation modes controlled by the switch of four-way stopcock with high flexibility.

Fig. 9

Application of the enhanced micropump system for sustaining an in vitro vasculogenesis model. (a) Prototype of system setup for tissue culture inside incubator. (b) Microfluidic chip design and simulation on the interstitial flow profile across tissue chamber for vasculogenesis. (c) Microvascular network formation inside tissue chambers throughout 14 days. Scale bar: 100 μm.