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

Abstract

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 µm-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.

Fully 3D-printed soft robots with integrated fluidic circuitry

“…Although all of the fluidic circuit elements and soft robots were designed and fabricated as multimaterial entities, for applications that require entirely soft robots, the rigid materials could be replaced with compliant materials as desired. Similarly, the presented approach is not exclusively limited to PolyJet 3D printing and could be adapted for alternative additive technologies, such as using direct laser writing-based fluidic circuit elements (53)(54)(55) for soft microrobots or stereolithography-compatible soft materials (56) for meso-/macroscale systems. Nonetheless, the PolyJet-based strategy presented here offers distinctive promise to enhance accessibility within the field of soft robotics while supporting a level of reproducibility and design versatility (e.g., for the fluidic operators, integrated fluidic circuits, and the overall architectures of unified soft robotic systems) that has not been reported for alternative methodologies.…”

3D printed microfluidics: advances in strategies, integration, and applications

“…10c), where the entire soft robotic entity was fabricated inside the microfluidic channel (40 μm in height and 60 μm in width) via the is DLW technique. 17 The microfluidic channels connected the hydraulic pressure source and the microfluidic controller. The bellow-structured controller acted as a normally closed transistor, in which a certain gate pressure was required to expand the bellow to displace the disk such that the flow can travel through the structure (from left to right) to inflate the bellow actuator (Fig.…”

“…Beyond the interconnecting networks, a few recent studies have developed methods to integrate 3D printed microfluidics or millifluidics into the fluidic controller networks within soft robots. 17,75,166 For instance, a microfluidic controller consisting of a 3D printed hydraulic valve was recently demonstrated (Fig. 10b-i and ii).…”

Advanced medical micro-robotics for early diagnosis and therapeutic interventions

“…It also has the potential for deployment in minimally invasive microsurgical tasks or biopsy. A fluid-pressure actuated micro-gripper has been fabricated using an in situ DLW (isDLW) technique, using IP-L 780 material ( Alsharhan et al., 2021 ). When pressure was not present, the micro-grippers remained open.…”

“…The inward movement of micro-grippers was triggered by the input pressure. With different pressure inputs, the flow modes inside these microfluidic devices could be altered ( Alsharhan et al., 2021 ).…”