Pulsatile Flow in Microfluidic Systems

Abstract

This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.

Optimizing pressure-driven pulsatile flows in microfluidic devices

“…For the particular system considered here, the output pressure p(t) must be identical to the set pressure p set (t) in the limit of very slow variation of the set signal. This low-frequency limit corresponds to the elimination of the time derivative in eqn (2). Therefore, the two systemdependent constants ζ and ω 0 completely characterize the linear response of the systems, in contrast to the three constants for a general PID controlled system.…”

“…In microfluidic devices, pulsatile or oscillatory driving of the flow enhances a broad range of operations and is also used for biomimicry in physiological studies. 1,2 The inherent timedependency of velocity, shear stress, and pressure in such flows plays a pivotal advantage in a variety of microfluidic applications, such as mixing, [3][4][5] droplet generation, [6][7][8] clog mitigation, and filtration of circulating tumor cells from whole blood, 9 in bioassays, 10 and for particle manipulation. [11][12][13] Additionally, due to their potential to improve the growth and viability of mechanosensitive cells, pulsatile flows are used in bioreactors for regenerative tissue engineering and to enhance microfluidic cell culture efficacy.…”

“…To drive a pulsatile flow in microfluidic channels, different generation mechanisms exist, including active, passive, external, and onchip strategies. 1,2 Sophisticated microfluidic setups with surface acoustic wave-driven flow chambers 18 or complex cardiac-like flow generators 19 have been used to examine the response of cells in pulsatile microscale flows. However, to generate pulsatile or oscillatory flows in microfluidic systems, most studies rely on commercially available pumps or pressure controllers.…”

Tunable Harmonic Flow Patterns in Microfluidic Systems through Simple Tube Oscillation

“…This includes studying mechanical and rheological properties of complex fluids and soft materials such as polymers, emulsions, colloids, liquid crystals, and their biological counterparts, [5][6][7][8][9][10] chemical synthesis of hazardous chemical compounds, pharmaceutical agents, and micro/nanomaterials, [11][12][13][14] and mimicking harmonic/disturbed flows occurring in the natural systems, such as the human circulatory system, where they may cause dysfunction or disease. [15][16][17][18][19] Passive and active mechanisms have been used to generate disturbed flow patterns in microfluidic systems. [20] The passive mechanisms take advantage of asymmetric geometries or sudden changes in the geometry to generate secondary flows.…”

“…This includes studying mechanical and rheological properties of complex fluids and soft materials such as polymers, emulsions, colloids, liquid crystals, and their biological counterparts, [ 5–10 ] chemical synthesis of hazardous chemical compounds, pharmaceutical agents, and micro/nanomaterials, [ 11–14 ] and mimicking harmonic/disturbed flows occurring in the natural systems, such as the human circulatory system, where they may cause dysfunction or disease. [ 15–19 ]…”