Integrated 3D printed microfluidic circuitry and soft microrobotic actuators via in situ direct laser writing

Over the past two decades, researchers have advanced and employed integrated microfluidic circuitry to enable a wide range of chemical and biological 'lab-on-a-chip' capabilities. Yet in recent years, a wholly different field, soft robotics, has begun harnessing microfluidic circuitry as a promising means to enhance soft robot autonomy. Unfortunately, key challenges associated with not only the fabrication of microfluidic circuitry, but also its integration with soft robotic systems represent critical barriers to progress. To overcome such issues, here we present a strategy that leverages 'in situ direct laser writing (isDLW)'-a submicron-scale additive manufacturing (or 'three-dimensional (3D) printing') approach developed previously by our group-to fabricate microfluidic circuit elements and soft microrobotic actuators directly inside of enclosed microchannels. In addition, we introduce 'normally closed' microfluidic transistors that comprise free-floating sealing discs designed to block source-to-drain fluid flow until the application of a target gate pressure. As an exemplar, we printed microfluidic transistors with distinct gate activation properties as well as identical soft microgrippers downstream of each drain within 40 mu m-tall microchannels. Experimental results for a source pressure of 100 kPa revealed that microgripper deformation was prevented in the absence of a gate input; however, increasing the gate pressure to 300 kPa induced actuation of one set of microgrippers, while a further increase to 400 kPa led to both sets of microgrippers actuating successfully. These results suggest that the presented isDLW-based strategy for manufacturing and integrating 3D microfluidic circuit elements and microrobotic end effectors could offer unique potential for emerging soft robotic applications.