Self-powered soft robot in the Mariana Trench.

The deep sea remains the largest unknown territory on Earth because it is so difficult to explore1-4. Owing to the extremely high pressure in the deep sea, rigid vessels5-7 and pressure-compensation systems8-10 are typically required to protect mechatronic systems. However, deep-sea creatures that lack bulky or heavy pressure-tolerant systems can thrive at extreme depths11-17. Here, inspired by the structure of a deep-sea snailfish15, we develop an untethered soft robot for deep-sea exploration, with onboard power, control and actuation protected from pressure by integrating electronics in a silicone matrix. This self-powered robot eliminates the requirement for any rigid vessel. To reduce shear stress at the interfaces between electronic components, we decentralize the electronics by increasing the distance between components or separating them from the printed circuit board. Careful design of the dielectric elastomer material used for the robot's flapping fins allowed the robot to be actuated successfully in a field test in the Mariana Trench down to a depth of 10,900 metres and to swim freely in the South China Sea at a depth of 3,224 metres. We validate the pressure resilience of the electronic components and soft actuators through systematic experiments and theoretical analyses. Our work highlights the potential of designing soft, lightweight devices for use in extreme conditions.

Composite elastomers with on-demand convertible phase separations achieve large and healable electro-actuation.

Phase separation has been widely exploited for fabricating structured functional materials. Generally, after being fabricated, the phase structure in a hybrid material system has been set at a specific length scale and remains unchanged during the lifespan of the material. Herein, we report a strategy to construct on-demand and reversible phase switches among homogenous, nano- and macro-phase separation states in a composite elastomer during its lifespan. We trigger the nanophase separation by super-saturating an elastomer matrix with a carefully selected small-molecule organic compound (SMOC). The nanoparticles of SMOC that precipitate out upon quenching will stretch the elastomer network, yet remain stably arrested in the elastomer matrix at low temperatures for a long time. However, at elevated temperatures, the nano-phase separation will transform into the macro-one. The elastic recovery will drive the SMOC onto the elastomer surface. The phase-separated structures can be reconfigured through the homogeneous solution state at a further elevated temperature. Taking advantage of the reversible phase switches leads to a novel strategy for designing high-performance dielectric elastomers. The in situ formed nanoparticles can boost the electro-actuation performance by eliminating electro-mechanical instability and lead to a very large actuation strain (∼146%). Once the actuator broke down, SMOC could on-demand be driven to the breakdown holes and heal the actuator.

Adaptively reconstructing network of soft elastomers to increase strand rigidity: towards free-standing electro-actuation strain over 100.

Soft biological tissues and muscles composed of semiflexible networks exhibit rapid strain-hardening behaviors to protect them from accidental rupture. In contrast, synthetic soft elastomers, usually featuring flexible networks, lack such behaviors, leading to a notorious issue when applying them to a promising artificial muscle technology (dielectric elastomer, DE), that is electromechanical instability (EMI) induced premature breakdown. We report that a facile thermomechanical training method can adaptively reconstruct the network of a soft triblock copolymer elastomer to transform its flexible network strands into semiflexible ones without extra chemical modifications and additives so that the electro-actuation performance is significantly enhanced by avoiding EMI. The free-standing actuators of trained elastomers exhibit a large stable electro-actuation strain and a high theoretical energy density (133%, 307 kJ m-3 at 158.1 V µm-1), and the capacity of actuating at low-temperature environments (-15 °C).

Anisotropic electroactive elastomer for highly maneuverable soft robotics.

Dielectric elastomers (DEs) are promising electroactive artificial muscles for use in soft machines. However, achieving anisotropy and sub-kV actuation voltage remains a great challenge for DE actuators. Herein, we report a facile method to fabricate ultrathin anisotropic DE films of an amorphous triblock copolymer poly(styrene-b-butyl acrylate-b-styrene) (SBAS) for soft actuators. The modulus of anisotropic SBAS in one direction can be modulated from 0.3 MPa to 10.5 MPa, and the modulus in the orthogonal direction remains the same as that of the pristine film (0.3 MPa). The anisotropy endows soft DE actuators with the directional-preferred response to an applied electric field and programmable multiple actuation morphs. These anisotropic SBAS films allowed us to fabricate compact soft robotics with high maneuverability, including soft grippers for object manipulation and crawling robots with reversible moving ability under an actuation voltage around 800 V.

Highly conductive porous graphene/sulfur composite ribbon electrodes for flexible lithium-sulfur batteries.

Flexible batteries have become an indispensable component of emerging devices, such as wearable, foldable electronics and sensors. Although various flexible batteries have been explored based on one-dimensional and two-dimensional platforms, developing a high energy density electrode with high structural integrity remains challenging. Herein, a scalable, one-pot wet spinning strategy is used to synthesize a flexible porous cathode for lithium-sulfur batteries (LSBs) for the first time, which consists of reduced graphene oxide (rGO), graphene crumples (GCs) and sulfur powders. The electrode structures are tailored using GCs with different dimensions and functional features that are critical to its robustness under mechanical deformation and electrolyte penetration into the battery components. The optimized rGO/GC/S composite ribbon cathodes deliver a high capacity of 524 mA h g-1 after 100 cycles at a current rate of 0.2 C. A shape-conformable battery prototype comprising an rGO/GC/S cathode and a lithium anode demonstrates a stable discharge characteristic under repeated bending/flattening cycles. The LSB prototype supported by an elastomer presents stable discharge behavior with high mechanical robustness against an extension of up to 50%. The above-mentioned findings shed new light on developing sulfur cathodes for flexible, high performance LSBs based on the rational design of graphene structures.

A soft artificial muscle driven robot with reinforcement learning.

Soft robots driven by stimuli-responsive materials have their own unique advantages over traditional rigid robots such as large actuation, light weight, good flexibility and biocompatibility. However, the large actuation of soft robots inherently co-exists with difficulty in control with high precision. This article presents a soft artificial muscle driven robot mimicking cuttlefish with a fully integrated on-board system including power supply and wireless communication system. Without any motors, the movements of the cuttlefish robot are solely actuated by dielectric elastomer which exhibits muscle-like properties including large deformation and high energy density. Reinforcement learning is used to optimize the control strategy of the cuttlefish robot instead of manual adjustment. From scratch, the swimming speed of the robot is enhanced by 91% with reinforcement learning, reaching to 21 mm/s (0.38 body length per second). The design principle behind the structure and the control of the robot can be potentially useful in guiding device designs for demanding applications such as flexible devices and soft robots.

Highly stretchable carbon aerogels.

Carbon aerogels demonstrate wide applications for their ultralow density, rich porosity, and multifunctionalities. Their compressive elasticity has been achieved by different carbons. However, reversibly high stretchability of neat carbon aerogels is still a great challenge owing to their extremely dilute brittle interconnections and poorly ductile cells. Here we report highly stretchable neat carbon aerogels with a retractable 200% elongation through hierarchical synergistic assembly. The hierarchical buckled structures and synergistic reinforcement between graphene and carbon nanotubes enable a temperature-invariable, recoverable stretching elasticity with small energy dissipation (~0.1, 100% strain) and high fatigue resistance more than 106 cycles. The ultralight carbon aerogels with both stretchability and compressibility were designed as strain sensors for logic identification of sophisticated shape conversions. Our methodology paves the way to highly stretchable carbon and neat inorganic materials with extensive applications in aerospace, smart robots, and wearable devices.

Sheet Collapsing Approach for Rubber-like Graphene Papers.

Understanding and modulating the conformation of graphene are pivotal in designing graphene macroscopic materials. Here, we revealed the sheet collapsing behavior of graphene oxide (GO) sheets by poor solvents in an analogy with linear macromolecules. Triggered by poor solvents, extended GO sheets in good solvents can collapse to hierarchically wrinkled conformations. The collapsing behavior of GO enabled the fabrication of amorphous self-standing GO and graphene papers with rich hierarchical wrinkles and folds over mutliple size scales. The collapsed GO and graphene papers had a rubber-like mechanical behavior with viscoelasticity. By our collapsing method, GO and graphene self-standing papers were designed to be stiff with high modulus or to become soft with low modulus of 100 MPa at a remarkably large breakage elongation up to 23%. Our philosophy of treating graphene as a 2D polymer enables the efficient control of molecular conformations of graphene and other 2D polymers and the design of macroscopic materials of 2D nanomaterials as in the polymer industry.