Flexible droplet microfluidic devices for tuneable droplet generation

Droplet microfluidics is a promising technology for applications that require precise handling of minute fluid volumes. This technology has broad applications in the pharmaceutical industry, food and beverage, and material synthesis. Droplet size and frequency are the two key parameters in these applications. Current droplet microfluidic devices are rigid platforms where the geometry and dimensions of microchannels are fixed after the device fabrication. This poses a significant limitation when adjusting the droplet generation characteristics. Repetitive design, fabrication, and testing are often needed to achieve the optimal microchannel dimensions. To overcome this bottleneck, we develop a proof-of-concept stretchable microfluidic device that can control droplet size and generation frequency by precisely controlling the microchannel dimensions in real-time. Theoretical analysis, numerical modelling, and experimental characterisation were conducted to study the influence of device lateral stretching on these characteristics. We found that the lateral stretching of the device increased the droplet diameter and spacing but reduced the droplet generation frequency. Droplet diameter and spacing increased by ∼20 %, and droplet frequency decreased by ∼45 % when the device was strained up to 25 %. We believe this innovative, flexible droplet microfluidic platform will provide an alternative way to precisely control the droplet formation by modifying the channel dimensions on-site and in real-time. This technical paper provides proof of concept for fully flexible and stretchable microfluidic technology for tuneable droplet generation. The phenomenon is justified through theoretical, numerical and experimental studies. • On-demand microdroplet generation using micro elastofluidic devices. • Tuneable droplet characteristics by stretching the device without changing the discrete and continuous fluid flow rates. • Droplet size increases by 20 %, and frequency decreases by 45 % for 25 % device strain at fixed flow rate ratios. • Minimise the limitations caused by fixed channel geometries for tunable microdroplet formation in microfluidics.