Simple Synthesis of Elastomeric Photomechanical Switches That Self-Heal.

This article introduces a simple two-stage method to synthesize and program a photomechanical elastomer (PME) for light-driven artificial muscle-like actuations in soft robotics. First, photochromic azobenzene molecules are covalently attached to a polyurethane backbone via a two-part step-growth polymerization. Next, mechanical alignment is applied to induce anisotropic deformations in the PME-actuating films. Cross-linked through dynamic hydrogen bonds, the PMEs also possess autonomic self-healing properties without external energy input. This self-healing allows for a single alignment step of the PME film and subsequent "cut and paste" assembly for multi-axis actuation of a self-folded soft-robotic gripper from a single degree of freedom optical input.

Bio-inspired Design and Additive Manufacturing of Soft Materials, Machines, Robots, and Haptic Interfaces.

Soft materials possess several distinctive characteristics, such as controllable deformation, infinite degrees of freedom, and self-assembly, which make them promising candidates for building soft machines, robots, and haptic interfaces. In this Review, we give an overview of recent advances in these areas, with an emphasis on two specific topics: bio-inspired design and additive manufacturing. Biology is an abundant source of inspiration for functional materials and systems that mimic the function or mechanism of biological tissues, agents, and behaviors. Additive manufacturing has enabled the fabrication of materials and structures prevalent in biology, thereby leading to more-capable soft robots and machines. We believe that bio-inspired design and additive manufacturing have been, and will continue to be, important tools for the design of soft robots.

Bioresorbable, wireless, passive sensors for continuous pH measurements and early detection of gastric leakage.

Continuous monitoring of biomarkers at locations adjacent to targeted internal organs can provide actionable information about postoperative status beyond conventional diagnostic methods. As an example, changes in pH in the intra-abdominal space after gastric surgeries can serve as direct indicators of potentially life-threatening leakage events, in contrast to symptomatic reactions that may delay treatment. Here, we report a bioresorbable, wireless, passive sensor that addresses this clinical need, designed to locally monitor pH for early detection of gastric leakage. A pH-responsive hydrogel serves as a transducer that couples to a mechanically optimized inductor-capacitor circuit for wireless readout. This platform enables real-time monitoring of pH with fast response time (within 1 hour) over a clinically relevant period (up to 7 days) and timely detection of simulated gastric leaks in animal models. These concepts have broad potential applications for temporary sensing of relevant biomarkers during critical risk periods following diverse types of surgeries.

A wireless and battery-less implant for multimodal closed-loop neuromodulation in small animals.

Fully implantable wireless systems for the recording and modulation of neural circuits that do not require physical tethers or batteries allow for studies that demand the use of unconstrained and freely behaving animals in isolation or in social groups. Moreover, feedback-control algorithms that can be executed within such devices without the need for remote computing eliminate virtual tethers and any associated latencies. Here we report a wireless and battery-less technology of this type, implanted subdermally along the back of freely moving small animals, for the autonomous recording of electroencephalograms, electromyograms and body temperature, and for closed-loop neuromodulation via optogenetics and pharmacology. The device incorporates a system-on-a-chip with Bluetooth Low Energy for data transmission and a compressed deep-learning module for autonomous operation, that offers neurorecording capabilities matching those of gold-standard wired systems. We also show the use of the implant in studies of sleep-wake regulation and for the programmable closed-loop pharmacological suppression of epileptic seizures via feedback from electroencephalography. The technology can support a broader range of applications in neuroscience and in biomedical research with small animals.

Autonomous self-healing optical sensors for damage intelligent soft-bodied systems.

We introduce damage intelligent soft-bodied systems via a network of self-healing light guides for dynamic sensing (SHeaLDS). Exploiting the intrinsic damage resilience of light propagation in an optical waveguide, in combination with a tough, transparent, and autonomously self-healing polyurethane urea elastomer, SHeaLDS enables damage resilient and intelligent robots by self-healing cuts as well as detecting this damage and controlling the robot's actions accordingly. With optimized material and structural design for hyperelastic deformation of the robot and autonomous self-healing capacity, SHeaLDS provides reliable dynamic sensing at large strains (ε = 140%) with no drift or hysteresis, is resistant to punctures, and self-heals from cuts at room temperature with no external intervention. As a demonstration of utility, a soft quadruped protected by SHeaLDS detects and self-heals from extreme damage (e.g., six cuts on one leg) in 1 min and monitors and adapts its gait based on the damage condition autonomously through feedback control.

Reducing Metabolic Cost During Planetary Ambulation Using Robotic Actuation.

INTRODUCTION: Current spacesuits are cumbersome and metabolically expensive. The use of robotic actuators could improve extravehicular activity performance. We propose a novel method to quantify the benefit of robotic actuators during planetary ambulation.METHODS: Using the OpenSim framework, we completed a biomechanical analysis of three walking conditions: unsuited, suited with the extravehicular mobility unit (EMU) spacesuit (represented as external joint torques applied to human joints), and suited with the EMU and assisted by robotic actuators capable of producing up to 10 Nm of torque. For each scenario, we calculated the inverse kinematics and inverse dynamics of the lower body joints (hip, knee, and ankle). We also determined the activation of muscles and robotic actuators (when present). Finally, from inverse dynamics and muscle activation results, the metabolic cost of one gait cycle was calculated in all three conditions.RESULTS: The moments of lower body joints increased due to the increased resistance to movement from the spacesuit. The additional torque increased the overall metabolic cost by 85 compared to the unsuited condition. The assistive robotic actuators were able to reduce the metabolic cost induced by EMU resistance by 15.DISCUSSION: Our model indicates that the majority of metabolic cost reduction can be attributed to the actuators located at the hip. The robotic actuators reduced metabolic cost similar to that of modern-day actuators used to improve walking. During a Mars mission, the actuators could save one crewmember up to 100,000 kilocal on one 539-d planetary expedition.Kluis L, Keller N, Bai H, Iyengar N, Shepherd R, Diaz-Artiles A. Reducing metabolic cost during planetary ambulation using robotic actuation. Aerosp Med Hum Perform. 2021; 92(7):570578.

Digital light processing of liquid crystal elastomers for self-sensing artificial muscles.

Artificial muscles based on stimuli-responsive polymers usually exhibit mechanical compliance, versatility, and high power-to-weight ratio, showing great promise to potentially replace conventional rigid motors for next-generation soft robots, wearable electronics, and biomedical devices. In particular, thermomechanical liquid crystal elastomers (LCEs) constitute artificial muscle-like actuators that can be remotely triggered for large stroke, fast response, and highly repeatable actuations. Here, we introduce a digital light processing (DLP)-based additive manufacturing approach that automatically shear aligns mesogenic oligomers, layer-by-layer, to achieve high orientational order in the photocrosslinked structures; this ordering yields high specific work capacity (63 J kg-1) and energy density (0.18 MJ m-3). We demonstrate actuators composed of these DLP printed LCEs' applications in soft robotics, such as reversible grasping, untethered crawling, and weightlifting. Furthermore, we present an LCE self-sensing system that exploits thermally induced optical transition as an intrinsic option toward feedback control.

Stretchable distributed fiber-optic sensors.

Silica-based distributed fiber-optic sensor (DFOS) systems have been a powerful tool for sensing strain, pressure, vibration, acceleration, temperature, and humidity in inextensible structures. DFOS systems, however, are incompatible with the large strains associated with soft robotics and stretchable electronics. We develop a sensor composed of parallel assemblies of elastomeric lightguides that incorporate continuum or discrete chromatic patterns. By exploiting a combination of frustrated total internal reflection and absorption, stretchable DFOSs can distinguish and measure the locations, magnitudes, and modes (stretch, bend, or press) of mechanical deformation. We further demonstrate multilocation decoupling and multimodal deformation decoupling through a stretchable DFOS-integrated wireless glove that can reconfigure all types of finger joint movements and external presses simultaneously, with only a single sensor in real time.