Hydro-elasto-capillary interactions for programmable microfluidics*

Soft microfibers can be strongly bent by capillary forces and can even be reversibly coiled inside fluid cavities. If present, hydrodynamic forces may compete with capillary forces, uncoil the microfiber and induce its deployment from its original coiled state.
Here we fabricate a microfiber coiled within a droplet that is attached on the wall of a microfluidic channel. This is done by photocuring a liquid microjet of hydrogel (PEG-DA) and transporting the resulting soft microfibre to the carefully prepared droplet for adequate coiling. The mechanical response of the hybrid system is then investigated under increasing flow rates.
The present results open opportunities to form the building blocks of microfluidic elements with high on-off ratio that may be useful for the design of on-chip tunable circuits for bioengineering applications.