Microfluidic hydraulic oscillators: A comprehensive review of emerging biochemical and biomedical applications

Microfluidics provides microenvironments for drug delivery, transport, mixing, chemical reaction, cell culture, and tissue engineering. Developing microfluidic circuit networks comparable to electronic circuits is beneficial because they can significantly reduce the need for dynamic off-chip controllers and reagent volume. A microfluidic hydraulic oscillator (MHO) is a fluidic circuit network analogous to a hydraulic-electric system that converts constant input into a pulsatile output. The challenge lies in integrating the MHO with an on-chip controller for biochemical applications and precise fluid control. Herein, we present fundamental working principles and components of multiple types of MHO to produce pulsatile pressure and review the current biochemical applications of MHO. First, we present fundamental working principles of multiple types of MHO and components to build the MHO to produce pulsatile pressure. The coupling of the MHO with various on-chip controllers, such as a diode pump, reset valve, droplet generator, filter, etc., will then be explored. Next, current applications are discussed, including their employment in chemistry for mixing, crystallization, coating, biomedical for cellular biology, filtration, staining, and amplification of targets. Finally, we explore the potential future application of MHO to show its versatility. The adaptive nature of MHO highlights their potential to transform biochemical and biomedical applications, from precise fluid control in point-of-care (POC) and lab-on-chip devices to innovative diagnostic and therapeutic solutions.