Self-Sensing, Optoelectronic Artificial Muscle Tissues for Energy Efficient Locomotion in Soft Machines

This research program will develop soft artificial muscle tissues capable of high power density, energy-efficient actuation for untethered locomotion in soft, bioinspired machines. The 3D printable, artificial muscle tissues proposed here involve the design and fabrication of optoelectronically-stimulated, liquid crystal elastomer and ionogel composite fibers. Bundles of individually-addressable artificial muscle fibers are readily organized into large-scale artificial muscle tissues with distributed actuation and proprioceptive capabilities. The proposed artificial muscle tissues will provide high force, high strain, and truly contractile actuation in a high power density, energy-efficient design. We will fill three key technological gaps for designing self-sensing artificial muscles for robust, reliable, and bioinspired locomotion in untethered soft robots. First, most soft matter actuators suffer from key performance and hardware trade-offs. Soft actuators – including hydraulic, electrostatic and thermomechanical actuators – typically exhibit low actuation frequency and low energy efficiency compared to traditional robot actuators and motors. Liquid crystal elastomer actuators (LCEAs) are a popular soft actuator for driving high strain, high force actuation. However, current varieties do not offer energy efficient performance. Phototropic LCEAs can theoretically offer a more energy efficient design than thermotropic varieties, but requirements for remote light sources and short penetration depths of incident optical stimuli are major barriers to their practical adoption. We will develop photoactuated LCEA fibers with internal cores of deformable ionogel waveguides. The waveguides will facilitate propagation of light along the length of the fiber to achieve a more energy-efficient, high work capacity LCEA design. We will develop new 3D printing methods and materials to fabricate the LCEA fibers with internal waveguide cores. Second, current LCEAs exhibit low actuation bandwidths, which limit their ability to facilitate practical locomotion speeds in untethered soft robots. We will demonstrate an energy-efficient approach to improve actuation bandwidth in the artificial muscle fibers using electrostatically driven isotropic-nematic transitions. We will design new materials and testbeds to demonstrate our novel approach for simplifying LCEA relaxation and increasing LCEA actuation frequency. Finally, we will use multimaterial printing methods to fabricate artificial muscle tissues and untethered soft robots capable of terrestrial and underwater locomotion. Overall, this proposal will achieve three key innovations: (1) 3D print photoactuatable, core-shell liquid crystal elastomer fibers with internal ionogel waveguides; (2) electrostatically control cis-to-trans isomerization in azobenzene-functionalized liquid crystal elastomers for rapid reversibility; and (3) 3D print soft robotic muscle tissue with distributed sensorimotor capabilities for untethered terrestrial and underwater locomotion. This proposal introduces new materials and manufacturing methods to 3D print artificial muscle tissues and novel soft robot embodiments. The materials, 3D printing methods, and actuators developed by this program will pioneer novel capabilities in applications of broad naval interest, spanning, robotics, wearable technologies, bioinspired materials, and more.