Spider-Inspired, Fully 3D-Printed Micro-Hydraulics for Tiny, Soft Robotics

Many arachnids use internal hemolymph pressure to actuate extension in their leg joints. The inherent large foot displacement-to-body length ratio that arachnids can achieve through hydraulics relative to muscle-based actuators is both energy and volumetrically efficient. Until recent advances in nano/microscale 3D printing with two-photon polymerization (2PP), the physical realization of synthetic complex 'soft' joints would have been impossible to replicate and fill with a hydraulic fluid into a sealed sub-millimeter system. Inspired by nature, the smallest scale 3D-printed hydraulic actuator (4.9 x 10(-4) mm(3)) by more than an order of magnitude is demonstrated. The use of stiff 2PP polymers with micron-scale dimensions enable compliant membranes similar to exoskeletons seen in nature without the requirement for low-modulus materials. The bio-inspired system is designed to mimic similar hydraulic pressure-activated mechanisms in arachnid joints utilized for large displacement motions relative to body length. Using variations on this actuator design, the ability to transmit forces with relatively large magnitudes (milliNewtons) in 3D space is demonstrated, as well as the ability to direct motion that is useful towards microrobotics and medical applications. Microscale hydraulic actuation provides a promising approach toward the transmission of large forces and 3D motions at small scales, previously unattainable in wafer-level 2D microelecromechanical systems (MEMS).