Closed-loop feedback control of microbubble diameter from a flow-focusing microfluidic device.

Real-time observation and control of particle size and production rate in microfluidic devices are important capabilities for a number of applications, including the production, sorting, and manipulation of microbubbles and droplets. The production of microbubbles from flow-focusing microfluidic devices had been investigated in multiple studies, but each lacked an approach for on-chip measurement and control of microbubble diameter in real time. In this work, we implement a closed-loop feedback control system in a flow-focusing microfluidic device with integrated on-chip electrodes. Using our system, we measure and count microbubbles between 13 and 28 µ m in diameter and control their diameter using a proportional-integral controller. We validate our measurements against an optical benchmark with R 2 = 0.98 and achieve a maximum production rate of 1.4 × 10 5 /s. Using the feedback control system, the device enabled control in microbubble diameter over the range of 14-24 µ m.

Correction: A flow focusing microfluidic device with an integrated Coulter particle counter for production, counting and size characterization of monodisperse microbubbles.

Correction for 'A flow focusing microfluidic device with an integrated Coulter particle counter for production, counting and size characterization of monodisperse microbubbles' by J. M. Robert Rickel et al., Lab Chip, 2018, 18, 2653-2664.

A flow focusing microfluidic device with an integrated Coulter particle counter for production, counting and size characterization of monodisperse microbubbles.

Flow focusing microfluidic devices (FFMDs) have been investigated for the production of monodisperse populations of microbubbles for chemical, biomedical and mechanical engineering applications. High-speed optical microscopy is commonly used to monitor FFMD microbubble production parameters, such as diameter and production rate, but this limits the scalability and portability of the approach. In this work, a novel FFMD design featuring integrated electronics for measuring microbubble diameters and production rates is presented. A micro Coulter particle counter (µCPC), using electrodes integrated within the expanding nozzle of an FFMD (FFMD-µCPC), was designed, fabricated and tested. Finite element analysis (FEA) of optimal electrode geometry was performed and validated with experimental data. Electrical data was collected for 8-20 µm diameter microbubbles at production rates up to 3.25 × 105 MB s-1 and compared to both high-speed microscopy data and FEA simulations. Within a valid operating regime, Coulter counts of microbubble production rates matched optical reference values. The Coulter method agreed with the optical reference method in evaluating the microbubble diameter to a coefficient of determination of R2 = 0.91.