Circuit-Based Design of Microfluidic Drop Networks

Microfluidic-drop networks consist of several stable drops-interconnected through microfluidic channels-in which organ models can be cultured long-term. Drop networks feature a versatile configuration and an air-liquid interface (ALI). This ALI provides ample oxygenation, rapid liquid turnover, passive degassing, and liquid-phase stability through capillary pressure. Mathematical modeling, e.g., by using computational fluid dynamics (CFD), is a powerful tool to design drop-based microfluidic devices and to optimize their operation. Although CFD is the most rigorous technique to model flow, it falls short in terms of computational efficiency. Alternatively, the hydraulic-electric analogy is an efficient first-pass method to explore the design and operation parameter space of microfluidic-drop networks. However, there are no direct electric analogs to a drop, due to the nonlinear nature of the capillary pressure of the ALI. Here, we present a circuit-based model of hanging- and standing-drop compartments. We show a phase diagram describing the nonlinearity of the capillary pressure of a hanging drop. This diagram explains how to experimentally ensure drop stability. We present a methodology to find flow rates and pressures within drop networks. Finally, we review several applications, where the method, outlined in this paper, was instrumental in optimizing design and operation.

Automated summary

Microfluidic-drop networks, consisting of stable drops connected through microfluidic channels, provide a versatile configuration for long-term organ model culturing. Mathematical modeling, such as computational fluid dynamics (CFD), is useful for designing and optimizing drop-based microfluidic devices, but lacks computational efficiency. Alternatively, the hydraulic-electric analogy is an efficient method to explore design and operation parameters of microfluidic-drop networks. A circuit-based model of hanging- and standing-drop compartments is presented, along with a phase diagram describing the nonlinearity of the capillary pressure of a hanging drop. The methodology for finding flow rates and pressures within drop networks is also discussed. This paper reviews several applications where the method outlined has been instrumental in optimizing design and operation.