Closed-loop feedback control for microfluidic systems through automated capacitive fluid height sensing

Abstract

Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (<1 mL) has proven to be an elusive goal, especially if direct fluid-sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to these sensing limitations. Here we present an optimized self-shielded coplanar capacitive sensor design and automated control system to provide submillimeter fluid-height resolution (∼250 μm) and control of small-scale open reservoirs without the need for direct fluid contact. Results from testing and validation of our optimized sensor and system also suggest that accurate fluid height information can be used to robustly characterize, calibrate and dynamically control a range of microfluidic systems with complex pumping mechanisms, even in cell culture conditions. Capacitive sensing technology provides a scalable and cost-effective way to enable continuous monitoring and closed-loop feedback control of fluid volumes in small-scale gravity-dominated wells in a variety of microfluidic applications.

Chips for Biomaterials and Biomaterials for Chips: Recent Advances at the Interface between Microfabrication and Biomaterials Research

“…The transport of cells and liquids within the chip could be controlled automatically by incorporating sensors and actuators in a closed-loop feedback arrangement. [285,286] A range of other workflows important in on-chip biology can be automated through the use of robotic manipulation and dispensing equipment, for example to dispense cell and microsized biomaterial suspensions for the production of cell-biomaterial aggregates or corresponding organoids. [287] Automation has also been applied to the operation and monitoring of organ-on-chip systems, [43] including making fluidic couplings between multiple such chips in a body-on-chip arrangement, [288] though the production of organs on a chip has not yet been automated.…”

“…The transport of cells and liquids within the chip could be controlled automatically by incorporating sensors and actuators in a closed‐loop feedback arrangement. [ 285,286 ]…”

Capacitive Sensor and Alternating Drive Mixing for Microfluidic Applications Using Micro Diaphragm Pumps

“…Another commonly used method is capacitive fluid sensing. This sensing method uses the change in an electric field induced by moving fluids with different relative permittivities [ 15 , 16 , 17 , 18 ]. For example, the sensor system described in [ 19 ] uses the capacitance change induced by air bubbles injected into a fluid stream for continuous flow measurement.…”

Acoustofluidic closed-loop control of microparticles and cells using standing surface acoustic waves

“…To solve this problem, a closed-loop control strategy could be implemented to extract the exact position of the objects and precisely adjust their movement. The closed-loop control strategy has been applied in microfluidic system to control the volume of droplet and fluidheight in open reservoirs over recent years [55][56][57][58]. However, to the best of our knowledge, there is no any previous report for using close-loop control systems for acoustofluidic devices.…”