Soft Robotics: Sensing, Actuation, and Integration

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.

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.

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.

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.