A 3D Nanoprinted Normally Closed Microfluidic Transistor

Abstract

Emerging applications in areas such as soft micro-robotics and biofluidic microsystems demand microfluidic circuitry at smaller scales. State-of-the-art additive manufacturing (or colloquially, “three-dimensional (3D) printing”) technologies are uniquely suited to enable such capabilities; however, current 3D printed microfluidic transistors are all based on “normally open” operations (i.e., fluid flow persists until a control pressure is applied to stop the flow). As both p-channel and n-channel transistors offer distinct benefits in varying electronics scenarios, we seek to provide such alternatives for microfluidics. Here we present the first 3D printed “normally closed” microfluidic transistor - fabricated in a 30-μm-tall channel via two-photon direct laser writing (DLW) - which comprises a “free-floating” sealing element that can be actively displaced to permit source-to-drain fluid flow ( QSD). Theoretical and experimental results revealed that the sealing disc effectively blocked QSD through the 3D microfluidic transistor until a gate pressure ( PG) of sufficient magnitude led to displacement of the sealing disc, and in turn, unobstructed QSD. These results suggest that the presented normally closed microfluidic transistor - the smallest reported to our knowledge - offers unique promise for fluidic processing applications in diverse chemical, biomedical, and soft robotics fields.