Exploring the filtration mechanisms in spiral microchannels: A critical review in inertial microfluidics

A crucial aspect in the design of spiral microchannels is understanding the equilibrium position of particles within them. With a wide array of applications in biomedicine and industry, numerous studies have been carried out to investigate the physical mechanisms influencing particle equilibrium, such as inertial lift and Dean drag forces. Past research, comprising various independent case studies, has highlighted that conventional spiral designs struggle to control lift forces, whereas enhancing the spiral microchannel design can regulate Dean flow intensity effectively. However, there remains a pressing need to delve deeper into and elucidate this phenomenon. This review article systematically concentrates on the factors that influence the shape and intensity of Dean vortices across the cross-section, ultimately determining the particles' equilibrium position within these systems. By synthesizing findings from both experimental and numerical approaches, the study investigates the key factors that govern particle equilibrium positions. Furthermore, the importance of shaping and positioning Dean vortices to effectively manipulate particle trajectories within spiral microchannels is emphasized. Additionally, the advantages and limitations of different cross-sectional shapes (rectangular, trapezoidal, complex) and loop patterns within spiral geometries are deliberated upon to enable more precise particle manipulation strategies.