Hydrophoresis - A Microfluidic Principle for Directed Particle Migration in Flow

Despite the stereotype that secondary flow fields induced by surface grooves are effective for microfluidic mixing and increase the entropy of different fluid flows, many efforts have been made to utilize the grooves for particle separation and focusing, decreasing the entropy of particle distribution. As part of these efforts, hydrophoresis has been proposed to define deterministic particle trajectories in grooved microchannels. Due to the simple, cloggingfree, and high-throughput characteristics, hydrophoresis has become increasingly promising for blood separation in clinical applications and sheathless particle focusing in flow cytometric applications. In this review, I introduce and summarize the basic physics, design parameters, design principles, and applications of hydrophoresis to improve the fundamental understanding of hydrophoresis and expand its use. I also discuss the challenges of hydrophoresis and forecast its future direction.