Soft Robotics: Sensing, Actuation, and Integration

High pressure and low temperature are the greatest challenges faced by scientists to explore deep oceans, which remain largely unknow to us today. Li et al. review these challenges and give insight into designing soft robots, inspired by deep-sea creatures, that enable resilient operations in harsh conditions.

Microbots have attracted attention due to an ability to reach places and perform tasks which are not possible with conventional techniques in a wide range of applications. Here, the authors review the recent work in the field on the fabrication, application and actuation of 3D printed microbots offering a view of the direction of future microbot research.

Achieving hybrid magnetic actuation, energy transfer and somatosensory actuation functions in soft electromagnetic devices is a challenge. Here, Zhang et. al. present a hybrid core-sheath fiber and use a one-step coaxial printing method to create complex 2D/3D structures with multimodal functionalities.

Developing perceptive and adaptable soft robots without compromising mechanical compliance is a challenge. Here, Choe et. al. developed a soft self-sensing tensile valve with a helical pinching mechanism, enabling integrated sensing and control for soft, untethered, and autonomous robotic systems.

Capacitive soft force sensors require electrical shielding from electromagnetic interference, but this shielding can mess with the effectiveness of the sensing electrodes. Here, Aksoy et al. solve this problem by patterning the central sensing elastomer layer to control its compressibility.

While hydrogels find applications in wearable sensors and electronic skins, they are prone to fatigue fractures upon deformation cycling. Xiong et al. report the synthesis of conductive polymerizable rotaxane hydrogels, exhibiting large fatigue resistance, for 3D printable flexible sensors.

Flexible thermistor epidermal electronics is desired to continuously monitor skin temperature in medical applications. Hao et al. report a nacre mimetic laminated strategy to fabricate thermistors with large mechanical durability for high-fidelity temperature discrimination without signal distortion.

Current wearable solutions for Virtual Reality (VR) have limitations of complicated structures and large driven power. Here, the authors report a highly integrated ring consisting of multimodal sensing and feedback units for augmented interactions in metaverse.

Soft robots are challenging to model and program. Non-specialists face non-negligible obstacles when working with soft robots to perform tasks. Here, the authors propose a method to interactively teach soft robots complex motions through flexible touchless and tactile multimodal sensors.

Designing efficient tactile sensors under high-frequency dynamic stimuli remains a challenge. Here, the authors demonstrate piezoelectric tactile sensor with sensitivity of 346.5 pCN−1, wide bandwidth of 5–600 Hz and a linear force detection range of 0.009–4.3 N using a rigid-soft hybrid force-transmission-layer in combination with a soft bottom substrate.

Conductive materials with tissue-matched softness are needed for ultra-soft electronics. Here, the authors report ultra-soft and conductive bottlebrush elastomer composites and fabricate them into electronics with laser cutting and 3D printing methods.

Electronic visual prostheses, or biomimetic eyes, have shown capability of restoring functional vision through electrical pulses artificially initiating neural responses. Here, authors demonstrate a flexible piezo-array for ultrasound-induced retinal stimulation.

Future robots require compact sensing architectures capable of discerning multiple stimuli. Here, Baines et al., present a multi-modal deformation and temperature sensor which, exploiting the light-to-state mapping, discerns combined stimuli of bending, stretching, compression, and temperature.

In existing soft robotic sensing strategies, additional components and design changes are often required to sense the environment. Zou et al. introduce a retrofit self-sensing strategy for soft pneumatic actuators, utilizing internal pressure variations arising from interactions.

Artificial sensory systems are typically limited by their performance and response to static and dynamic stimuli. Here, Bai et al. propose an iontronic slip-sensor, which responds to both static pressure and high-frequency vibrations up to 400 Hz, achieving high spatiotemporal resolution for texture recognition.

Due to the deformable nature of soft robots, developing robust sensors that can sustain stability and performance is a challenge. Here, the authors report a computational strain sensor design based on a programmed crack array for predictable, tunable, and stable sensing performance.

Shape morphing surfaces demonstrate a wide variety of applications, yet the existing technologies lack high-fidelity, high-speed deformation and embedded state sensing. Johnson et al. integrate soft actuators and soft sensors for high-fidelity shape morphing with self-sensing and high-speed actuation.

Origami-inspired engineering has enabled intelligent materials and structures to react to environments, yet a complete sense-decide-act autonomous loop is still challenging. Yan et al. introduce autonomous origami robots by embedding sensing, computing, and actuating in compliant, conductive materials.

Wireless millirobots are promising as minimally invasive biomedical devices. Here, the authors design a magnetically actuated amphibious millirobot that integrates spinning-enabled locomotion, targeted drug delivery, and cargo transportation by utilizing geometrical features and folding/unfolding capability of the Kresling origami.

Flexible electroluminescent devices are usually arduous to create. Liu et al report a 3D printing strategy to produce flexible and robust electroluminescent devices that can be integrated with soft robots for camouflage applications.

Soft materials are promising candidates for robotics with outstanding performance and functionality. Zhang et al. present an energy harvesting and dissipation mechanism and describe the development of a soft gripper designed for capturing objects with high kinetic energy.

Accessibility into the distal vascular systems to treat various diseases remains challenging using medical catheters. Here, Wang et al. demonstrate that a stent-shaped wireless magnetic soft robot enables adaptive locomotion and medical functions into these distal vascular regions.

Traditional robotic hands are facing several issues due to limitations in structures, principles and transmissions. Here, the authors develop a rigid robotic hand with 4 piezo fingers and 12 DOFs to implement high adaptability multi-DOF motion manipulation from micro to macro, as well as micro grasping operation.

Realizing an artificial camouflage device with a high spatial resolution by adapting to the surrounding environment in real-time is a challenging task, mainly associated with device fabrication and integration with sensor and control circuits. To overcome these limitations, the authors utilize thermochromic liquid crystal ink that reacts to the feedback control system of the vertically stacked silver nanowire heater.

Artificial muscle actuators enabled by responsive functional materials like shape memory alloys are promising candidates for compact e-wearable devices. Here, authors demonstrate augmented reality glasses and two-way communication haptic gloves capable of image depth control and immersive tactile response.

Addressing challenges in voice disorders, the authors present a self-powered, wearable sensor-actuator system based on magnetoelasticity. This innovation enables assisted speaking by capturing laryngeal movements and translating them into voice signals, bypassing the vocal folds.

Current droplet manipulation techniques have limitations such as applying to a large scale of volume or of on-demand droplet release. Here using a magnetic actuated Janus origami robot, Jiang et al. present a strategy to achieve omni-manipulation of micro and nanoliter droplets.

The soft fluidic robots designed so far are lacking intelligent self-protection and present poor fluidic power source. Here, the authors report soft fluidic robots that integrate soft electrohydrodynamic pumps, healing electrofluids, actuators and E-skins endowing them with self-sensing, self-judgment, and self-heating behaviours for rapid self-healing.

Interfacial non-wettability between biocompatible iron oxide and liquid metal caused by the substantial mismatch in surface energy remains an issue. Here, the authors introduce a silver intermediate layer to reduce compositional mismatch and improve the wetting ability between iron oxide and liquid metal.

Concentration polarization electroosmosis (CPEO) has recently been found to produce similar flow patterns around spheres in an AC electric field as induced charge electroosmosis. Katzmeier and Simmel study the flow around the asymmetric particle dimers caused by CPEO and design a microrobot that can be steered with a joystick and facilitates the transport of cargo particles.

Animals use dexterous locomotion to hunt for food or flee from danger. Inspired by this strategy, Wang et al. design a soft robot, containing dielectric elastomer artificial muscles and reconfigurable chiral feet, which enables spontaneous change in movement direction in a controlled and reversible way.

Actuators provide robot locomotion and manipulation, but most are limited by their number of motion types and coupled motions. Here, Zhang et. al. present an origami actuation module based on a modified Kresling pattern with pneumatically-driven pouches, thus enabling seven motion modes in one module.

Song et al. use the weaving principle to overcome load capacity limitations in soft grippers. The woven structure enables exceptional load capacity, supporting up to 100 kg·f with a 130 g·f gripper, while also offering adaptive interactions with objects.

Soft grippers can emulate human hands, but it remains challenging to achieve multiple capability in manipulating various objects in one design. Hong et al. utilize a kirigami gripper with controllable and programmable trajectories to manipulate objects spanning from ultra-soft to ultra-strong with high precision.

A single nanowire morphing strategy has been established to construct ultracompact soft robotic grippers, capable of large amplitude multi-dimensional maneuvering and dexterous manipulation of microscale objects, under swift Lorentz forces driving.

The collective actuation of miniaturized robots is highly desirable for executing cooperative tasks. Won et al. show collective locomotion of ternary-nanocomposite-based magnetic robots that are capable of rectilinear translational and rotational swimming controlled by a pulsed electromagnetic field.

Achieving efficiently reprogrammable actuation and high operational dimensionality for soft robots with a limited number of actuators are challenging. Here, Li et al. use the vector control to manipulate electromagnetic soft robots enabling reprogrammable shape morphing and multimodal locomotion.

Soft robotics holds promise for realizing easy control over complex locomotion and deformation. Lin et al. report an earthworm-inspired untethered magnetic robot that consists one-piece-mold folded diaphragm to achieve large three-dimensional deformation with inside-volume change capability.

Minimally invasive surgeries call for surgical tools that can work at the mesoscale. Here, Gu et al. present a class of magnetic soft robotic chains that can self fold into large assemblies with stable configurations using a combination of elastic and magnetic energies stored in printed chain material.

Inspired by fast running cheetahs, the authors present a class of small-scale soft electromagnetic robots able to reach ultra-high running speeds of 70 BL/s (body lengths per second) as well as the ability to swim, jump, steer and transport cargo.

Low modulus materials that can change shape in response to external stimuli are promising for a wide range of applications. The authors here introduce a shape-reprogrammable construct, based on liquid metal microfluidic networks and electromagnetic actuation, that supports a unique collection of capabilities.

An intracellular antenna that can truly enable probing, modulation or augmentation of biological cells remains an unmet challenge. Here, the authors present the Cell Rover, a magnetostrictive antenna that operates wirelessly inside a living cell and is compatible with 3D biological systems.

Ferrofluids with their extreme deformability are being used as soft machines. Using ferrofluids, Sun et al. show a variety of soft machines by playing with the wetting properties of solid surfaces

Machines capable of magnetically controllable shape morphing and locomotion have diverse promising applications. Here, authors propose a scalable fabrication strategy that transforms 2D magnetic sheets into 3D soft magneto-active machines with customized geometries by incorporating origami folding.

Jumping is an important locomotion function to extend navigation range, overcome obstacles, and adapt to unstructured environments. Here, authors demonstrate legless soft robot capable of rapid, continuous, and steered jumping based on a soft electrohydrostatic bending actuator.

A long puzzle in snake’s locomotion, sidewinding allows them to travel at an angle and reorient in some environments without loss of speed. Here, authors provide a mathematical argument to the evolution of sidewinding gaits and reinforce an analogy between limbless terrestrial locomotion and optics.

Electrically activated soft actuators with large deformability are important for soft robotics but enhancing durability and efficiency of electrochemical actuators is challenging. Here the authors demonstrate that the actuation performance of an ionic two-dimensional covalent-organic framework based electrochemical actuator is improved through the ordered pore structure of opening up efficient ion transport routes

Electroadhesion in soft robotics provides controllable interfacial attraction for robotic functionalities but materials selection is limited. Here, Gao et. al. present an iontronic adhesive to design a soft iontronic gripper with self-healability, tunable adhesion at reduced voltages and rapid release.

Insect-scale untethered micro aerial vehicles such as artificial dandelion devices suffer from high flight randomness and inadequate controllability. Chen et al. design and fabricate an untethered dandelion-inspired microflier, which is spatially and temporally controlled by an ultralight and supersensitive light-driven bimorph soft actuator.

Existing magnetic actuation systems using a single permanent magnet can only achieve 2-DoF orientation manipulation. Wang et al. propose a magnetic actuation method that uses a single anisotropic soft magnet instead of a permanent magnet to enable full 3-DoF orientation manipulation of small, untethered robots.

Handheld robots are limited in controllable degrees of freedom, which can result in lower dexterity for clinical applications. Here, Wang et al. report a handheld time-share driven robot with one motor that powers multiple motion modules for high-dextrous operation.

Traditional McKibben pneumatic artificial muscles are limited by connecting devices, preventing remote control and miniaturization. Here, Ai et all., report a miniaturized McKibben artificial muscle, filled by a low-boiling liquid actuated by light.

Underwater soft robots made of stimuli-responsive shape-changing hydrogels generally present low actuation speed which is limited by the water diffusion between hydrogels and their surrounding environment. Here, the authors develop dynamic hydrogel robots with a fast and switchable actuation based on a thermally driven chain conformation change after mechanical programming.

Inspired by the swift swingable abdomen, conducting canals, and body setae of Stenus comma, the authors present a swift, agile untethered insect-scale soft propulsor, offering new insights into systematically bio-inspired artificial soft robots.

Untethered capsules exhibit clinical promise for diagnosing and treating gastrointestinal diseases. Here, the authors develop small-scale magnetically driven capsules featuring a distinct magnetic soft valve, integrating multiple functional and motion modalities for biomedical applications.

The controllability of deformation height in reconfigurable touch displays currently limits their deliverable information. Hwang et al. present a light-triggered morphable tactile display enabling generation of refreshable, height-adjustable, and latchable 3D topologies with varying textures on a thin film surface.