Microfluidic pulse oscillator enabled by a shapeshifting liquid metal capacitor

Analogous to an inductor-capacitor oscillator circuit, the microfluidic oscillator employs a logic fluidic network to generate cascading and oscillatory flows, bringing the advanced function of flow control to the lab-on-chip platform. Despite notable advancements, current microfluidic oscillators are predominantly limited to fixed multilayer structures and cannot satisfy the requirements for flexibility, reconfigurability, and rapid-response characteristics. Herein, we developed a monolayer microfluidic pulse oscillator with a shapeshifting liquid metal (LM) capacitor for real-time control of oscillatory flows. This fluidic pulse oscillator exploits the interplay between LM capacitive energy storage and the surrounding Marangoni flow to convert stored interfacial energy into fluidic pulsed motion and realize fluid oscillation in alternating current fields. A theoretical model considering fluidic resistance, capacitance, and inductance is developed to decipher the fluid flow behavior. Furthermore, we employed both particle tracing to track transient flow field changes and numerical simulations to characterize the flow dynamics. The results reveal that vortex flow emerges in the near-field region adjacent to the LM capacitor, while pulse oscillatory flow prevails in the far-field region distant from the LM capacitor and occupies most of the microchannel. Axial oscillation and lateral lift-induced cumulative displacement are employed by oscillatory flow for frequency-tunable particle focusing and separation. By leveraging the principles of electronic circuits, the microfluidic pulse oscillator enables the advanced control of liquids and suspended particles for more lab-on-a-chip applications.