Vacuum-induced droplet generation and transport in parallel microchannels

Abstract

Despite the widespread use of droplet microfluidics, achieving simultaneous, uniform, and controllable droplet generation across multiple channels remains a challenge, especially without relying on complex pressure controllers or individual channel actuation. This study introduces a simplified yet powerful multichannel vacuum-driven droplet microfluidic platform that enables synchronised droplet production using a single shared vacuum source. Through experiments, we demonstrated robust control over droplet size and generation frequency by tuning the hydrostatic head of the continuous phase and the outlet vacuum strength. Parallel droplet formation is investigated in 3, 5, and 7-channel chips, revealing excellent inter-channel uniformity over a wide pressure range. Additionally, a novel strategy for generating distinct droplet sizes simultaneously within the same chip by modulating the channel hydraulic resistance is introduced, enabling multiplexed operations without added complexity. To further enhance scalability, a 3D chip design featuring a common-inlet architecture for the dispersed and continuous phases is introduced and analyzed for droplet generation in parallel microchannels, enabling the splitting of a single sample into multiple droplets across parallel channels. This work establishes vacuum-driven multichannel droplet systems as a compact, cost-effective, and scalable solution for high-throughput lab-on-a-chip applications, including multiplexed diagnostics and parallelized chemical or biological assays, particularly in resource-limited settings.