Embedded Three-Dimensional Printing of Autonomous and Somatosensitive Soft Robots

Abstract

Soft robots possess attributes that are difficult, if not impossible, to achieve with traditional robots. However, soft robots remain dependent on rigid hardware components, inhibiting the full benefits of being soft. New fabrication methods that enable the assembly of soft matter with multifunctional properties are needed to realize soft robots’ full potential. This dissertation focuses on new material and manufacturing strategies for creating soft robots that possess soft analogues of power, control, and sensory components. Central to this research is a technique called embedded three-dimensional (EMB3D) printing, in which functional inks are extruded through nozzles that translate omnidirectionally within viscoplastic matrix materials. For this work, several functional inks and elastomeric matrices that cure after printing were designed for printing soft robots with pneumatic/fluidic, catalytic, and sensory elements. We first investigate how matrix rheology, various printing parameters, and print path influence printing results. We find that maximizing the Oldroyd number associated with EMB3D printing conditions improves print fidelity. Next, we use EMB3D printing to assemble the “Octobot,” the first entirely soft, autonomous robot capable of untethered operation. Octobots are controlled by microfluidic logic-based devices that autonomously regulate the catalytic decomposition of an on-board monopropellant fuel supply. Gas generated from fuel decomposition inflates networks of fluidic actuators. The Octobot’s body and microfluidic logic are fabricated using molding and soft lithography, respectively, while all mesofluidic and catalytic features are EMB3D printed. The fluidic and elastomeric architectures required for Octobot operation are straightforwardly achieved with EMB3D printing. Lastly, we EMB3D print soft, somatosensitive actuators (SSAs) that are innervated with conductive features that enable bioinspired haptic, proprioceptive, and thermoceptive sensing. Each sensor is printed with our ionogel-based sensor ink and exhibits long-term stability and hysteresis-free conduction. For a simple demonstration, SSAs were assembled into soft robotic grippers, and their somatosensory feedback during handling of spherical objects of varying stiffness, textures, and temperature was characterized. With EMB3D printing, we have created soft robots with novel attributes. Our manufacturing platform can be adopted to design other soft robots that are entirely soft, require somatosensory feedback for improved control, or cannot be made with other manufacturing methods.