Inertial microfluidics: Recent advances

Abstract

Inertial microfluidics has attracted significant attentions in last decade due to its superior advantages of high throughput, label‐ and external field‐free operation, simplicity, and low cost. A wide variety of channel geometry designs were demonstrated for focusing, concentrating, isolating, or separating of various bioparticles such as blood components, circulating tumor cells, bacteria, and microalgae. In this review, we first briefly introduce the physics of inertial migration and Dean flow for allowing the readers with diverse backgrounds to have a better understanding of the fundamental mechanisms of inertial microfluidics. Then, we present a comprehensive review of the recent advances and applications of inertial microfluidic devices according to different channel geometries ranging from straight channels, curved channels to contraction‐expansion‐array channels. Finally, the challenges and future perspective of inertial microfluidics are discussed. Owing to its superior benefit for particle manipulation, the inertial microfluidics will play a more important role in biology and medicine applications.

Multi-Vortex Regulation for Efficient Fluid and Particle Manipulation in Ultra-Low Aspect Ratio Curved Microchannels

“…The existence of a helical vortex is distinct from vortex flow in the separation zone of the straight channel and dean vortex in the curved channel [ 36 , 37 , 38 ]. The formation of helical vortexes is determined by a number of factors (e.g., the ratio of the contraction area to the expansion area, shape and size of the obstruction, and the flow velocity, as well as the fluid inertia) [ 8 , 9 , 11 ]. Notably, the fluid inertia is largely dependent of the Reynolds number ( Re ).…”

“…As indicated from the mentioned analysis, the qualitative characteristics and magnitude of two vortexes are significantly impacted by channel construction apart from Re , so they act as the vital factors to design the channel structure for preferable fluid and particle applications. To be more specific, the parameters of microchannel construction (e.g., the ratio of D h to R , AR (H/W, H represents the channel’s height and W represents the channel’s width), as well as the various H of the inner and outer wall) significantly impact the distribution and strength of multi-vortex [ 7 , 8 , 9 ]. However, the existing strategy of designing geometry for producing a multi-vortex necessitates a high-AR expansion–contraction channel construction, because of the strengthening of the Dean and helical vortex effect with the increase in height [ 30 , 31 ].…”

“…Thus, by regulating the operation modes, easy-to-operate concentration-gradient constructions in the identical batch of chambers could be achieved from small to large or the opposite. The results showed that the adjustment of the multi-vortex in ultra-low AR curved channels by local confinement has great potential in the controllable mixing and concentration-gradient constructions of fluid manipulation with high throughput (mL/min), which is technologically and functionally comparative to the previous strategy that achieves fluid applications with low throughput (μL/min) [ 7 , 8 , 9 , 34 ]. Further study of the particle manipulation characterization and applications based on the devices are presented in subsequent sections.…”

“…As micro-fabrication equipment is improving, microfluidics has generally been known as a progressive technology for fluid and particle/cell manipulation by applying active and passive principles in micro/nano-scale channels [ 4 , 5 , 6 ]. Inertial microfluidics based on geometry-induced vortexes is recognized as a frequently used passive technology for their prominent merits (e.g., label-and external field-free operating process, high-throughput, increased fluidic controllability, and harmless to cell activity) [ 7 , 8 , 9 ].…”

“…Furthermore, the horizontal helical vortex can be generated in the straight channels with expansion–contraction arrays under a certain flow rate. Such a vortex has been extensively employed in fluid and particle manipulation (e.g., focusing, mixing, trapping and isolation) [ 7 , 9 ]. However, an effective technique and highly easy production method for achieving a vertical Dean vortex and horizontal helical vortex with uncomplicated configuration have remained largely out of reach.…”