The reversible capillary field effect transistor: a capillaric element for autonomous flow switching

New flow control elements in capillaric circuits are key to achieving ever more complex lab-on-a-chip functionality while maintaining their autonomous and easy-to-use nature. Capillary field effect transistors valves allow for flow in channels to be restricted and cut off utilising a high pressure triggering channel and occluding air bubble. The reversible capillary field effect transistor presented here provides a new element that can restore fluid flow in closed microchannels <i>via</i> autonomous circuit feedback. This allows new flow switching functionality without the need for direct user input. The valve design utilises new circuitry that draws on competing capillary pressures to withdraw liquid from a reservoir connected to the valve, creating a suction pressure that removes the occluding bubble from the channel to allow flow past the valve. The resulting reopening restores flow to the closed channel and allows for enhanced autonomous control over fluid flows. This new functionality is flexible and has the potential to be applied in a wide variety of situations, as shown here by use in several extended proof of concept arrangements. Firstly, we demonstrate how to reopen one valve while closing another using the same trigger to achieve simultaneous flow switching. We then show how a single trigger can be used for the parallel reopening of multiple valves for simultaneous release of liquids. Finally, we show the reversible capillary field effect transistor used to achieve autonomous transient mixing ratios between multiple liquids utilising a series of triggering events to determine which liquid channels are open or closed as flow progresses. The functionality this valve adds to the capillaric toolbox opens up new possibilities for applications in the creation of fully automatic diagnostic capillaric devices.