A pneumatically actuated microfluidic capacitor for flow stabilization and controlled reagent delivery in cell co-culture systems

Microvalves and pumps provide precise fluid handling in microfluidic devices for biomedical applications, yet achieving flow stability and controlled storage and release of fluid remains a significant challenge due to the pulsatile nature of the actuation. We present the development and characterization of a programmable microfluidic capacitor (PMC) designed for controlled storage and release of fluid in microfluidic systems. The PMC was designed with a resistor–capacitor system consisting of a cell culture chamber that accumulates fluid in response to the pressure-driven actuation of lifting-gate valves, which stabilizes fluid flow. The system's fluidic capacitance (Cf) was determined to be 4.537 nl/kPa, demonstrating a linear volume–pressure relationship. The charging and discharging dynamics were characterized and modeled, yielding a charging actuation time constant of 327.5 ms and a discharging actuation time of 763.94 ms. Additionally, we observed a significant reduction in cell detachment, with only 3% of cells removed during actuation. To validate the PMC's functionality, we performed immunocytochemical staining for microglia and astrocytes under inflammatory conditions. Astrocytes tested complement-C3 positive, while microglia were identified by transmembrane protein 119 (TMEM119). The PMC optimized reagent delivery and stabilized flow around cells, making it a reliable system for automated cell culture and organ-on-a-chip assays.