Micro elastofluidics for tuneable droplet splitting.

Droplet microfluidics is a transformative technology for generating and manipulating droplets in an immiscible carrier fluid. This technology spans many application areas, including biomedicine, food and beverage processing, as well as material synthesis. Droplet splitting is a key task in droplet microfluidics, which is essential for metering fluid samples between multiple assays in lab-on-a-chip applications. Passive droplet splitting with a T-junction is a straightforward and simple method. However, achieving variable droplet sizes typically requires numerous devices with different channel dimensions and complex channel arrangements. To address this limitation, we proposed a fully flexible and stretchable microfluidic technology for tunable droplet splitting. By externally stretching the T-junction, the dimensions of the channel arms can be dynamically altered in real time, allowing precise control over daughter droplet volumes and ratios. We investigated the effects of stretching on channel dimensions, hydraulic resistance, and droplet-splitting behaviour by theoretical analysis, numerical modelling, and experimental evaluations. The results revealed symmetric splitting at zero stretching and a tunable daughter droplet volume ratio up to approximately 4 with up to 4 mm device stretching (∼16% strain). Furthermore, we demonstrated the suitability of this technology for particle sorting, where particle-encapsulating mother droplets were asymmetrically split by adjusting device stretching. Finally, we demonstrated the encapsulation of microalgae within mother droplets and the tuning of microalgae concentration in the daughter droplets with stretching. This innovative approach provides a versatile and straightforward method for tunable droplet splitting, offering real-time control over droplet sizes without complex or multiple microfluidic designs. This advancement in micro elastofluidic technology opens up new possibilities for high-throughput and customisable droplet-based assays.