Untethered miniature soft robots have significant application potentials in biomedical and industrial fields due to their space accessibility and safe human interaction. However, the lack of selective and forceful actuation is still challenging in revolutionizing and unleashing their versatility. Here, we propose a focused ultrasound-controlled phase transition strategy for achieving millimeter-level spatially selective actuation and Newton-level force of soft robots, which harnesses ultrasound-induced heating to trigger the phase transition inside the robot, enabling powerful actuation through inflation. The millimeter-level spatial resolution empowers single robot to perform multiple tasks according to specific requirements. As a concept-of-demonstration, we designed soft robot for liquid cargo delivery and biopsy robot for tissue acquisition and patching. Additionally, an autonomous control system is integrated with ultrasound imaging to enable automatic acoustic field alignment and control. The proposed method advances the spatiotemporal response capability of untethered miniature soft robots, holding promise for broadening their versatility and adaptability. Spatially selective actuation and large output force enables versatile task performance in soft robotics. Here, the authors report a method for actuating untethered soft robots using focused ultrasound waves to perform liquid cargo delivery and biopsy.

Untethered microrobots possess a promising perspective for micromanipulation applications. With specifically designed morphologies and structures, microrobots are able to perform controllable delivery of target objects. However, the manipulation process still lacks autonomy, to achieve which the mechanism of picking, transporting, and releasing behaviors needs further investigation. In this article, we propose to achieve automated microrobotic manipulation using magnetic microswarms with multimodal morphology. The microswarm is composed of around 11-21 million Fe(3)O(4 )nanoparticles (1.0 -1.8 mu L particle suspension). When exposed to different dynamic magnetic fields, the swarm could exhibit corresponding forms. We realize precise and controllable cargo picking and releasing by exploiting the fluid fields of different swarm forms. In order to quantitatively describe these behaviors, we design a finite-state machine. A super-twisting sliding-mode controller has been formulated for the motion control of swarms. The disturbances are compensated via a disturbance observer. To enable automated micromanipulation in obstructed scenarios, a path planner inspired by rapidly exploring random tree algorithm is designed for path planning when obstacles exist. We also propose an enhanced-genetic algorithm to optimally transport multiple objects to the target position. Experiments demonstrate that our method could effectively transport micro-objects with different sizes and shapes. The precise selectivity of the method is validated when multiple objects exist in the working environment. Finally, the long-distance delivery ability and adaptivity to various friction situations of our strategy are demonstrated. This work explores a concise, untethered, and automated micromanipulation strategy, provides a new automatic tool for micromanipulation tasks, and extends the application potential of swarm microrobotics.

Precise trajectory control is imperative to ensure the safety and efficacy of in vivo therapy employing the magnetic helical millirobots. However, achieving accurate 3-D path following of helical millirobots under fluid flow conditions remains challenging due to the presence of the lumped disturbances, encompassing complex fluid dynamics and input frequency saturation. This study proposes a robust 3-D path following control framework that combines a disturbance observer for perturbation estimation with an adaptive finite-time sliding mode controller for autonomous navigation along the reference trajectories. First, a magnetic helical millirobot’s kinematic model based on the 3-D hand position approach is established. Subsequently, a robust smooth differentiator is implemented as an observer to estimate disturbances within a finite time. We then investigate an adaptive finite-time sliding mode controller incorporating an auxiliary system to mitigate the estimated disturbance and achieve precise 3-D path tracking while respecting the input constraints. The adaptive mechanism of this controller ensures fast convergence of the system while alleviating the chattering effects. Finally, we provide a rigorous theoretical analysis of the finite-time stability of the closed-loop system based on the Lyapunov functions. Utilizing a robotically-actuated magnetic manipulation system, experimental results demonstrate the efficacy of the proposed approach in terms of the control accuracy and convergence time.

Robotic tasks that require robust propulsion abilities such as jumping, ejecting or catapulting require power-amplification strategies where kinetic energy is generated from pre-stored energy. Here we report an engineered accumulated strain energy-fracture power-amplification method that is inspired by the pressurized fluidic squirting mechanism of Ecballium elaterium (squirting cucumber plants). We realize a light-driven hydrogel launcher that harnesses fast liquid vapourization triggered by the photothermal response of an embedded graphene suspension. This vapourization leads to appreciable elastic energy storage within the surrounding hydrogel network, followed by rapid elastic energy release within 0.3 ms. These soft hydrogel robots achieve controlled launching at high velocity with a predictable trajectory. The accumulated strain energy-fracture method was used to create an artificial squirting cucumber that disperses artificial seeds over metres, which can further achieve smart seeding through an integrated radio-frequency identification chip. This power-amplification strategy provides a basis for propulsive motion to advance the capabilities of miniaturized soft robotic systems. Propulsive motion in soft robotic systems requires the power amplification of stored energy. An accumulated strain energy-fracture power-amplification method is used to create light-driven soft robotic systems with a controlled launching ability.

Bacterial biofilms are widely found in nature, and they can be a major factor in many local chronic infections inside the human body. To date, effective elimination of biofilms is intractable for conventional antibiotic therapies due to the existence of bacteria‐protecting extracellular polymeric substances. For biofilm eradication in tiny tubular structures, magnetic hydrogel micromachines (MHM) are designed that are capable of performing mechanical disruption of biofilms while releasing antibacterial agents in a controllable fashion. Two modes of motion controlled by external magnetic fields, namely planar rotation and wobbling modes, have been investigated to drive the micromachines to interact and destruct biofilms. In addition, the presented micromachines are composed of thermosensitive PNIPAm hydrogel that can load with the antibacterial agent (H 2 O 2 ) and release them upon heating. The Fe 3 O 4 nanoparticles embedded in the hydrogel matrix act as catalysts for the Fenton reaction, generating bacteria‐killing free radicals. The synergetic biofilm elimination effect has been experimentally demonstrated in well plates and small tubes. The presented MHMs may provide a new design to treat biofilm‐related infections in narrow and confined spaces.

Multimodal and controllable locomotion in complex terrain is of great importance for practical applications of insect-scale robots. Robust locomotion plays a particularly critical role. In this study, a locomotion mechanism for magnetic robots based on asymmetrical friction effect induced by magnetic torque is revealed and defined. The defined mechanism overcomes the design constraints imposed by both robot and substrate structures, enabling the realization of multimodal locomotion on complex terrains. Drawing inspiration from human walking and running locomotion, a biped robot based on the mechanism is proposed, which not only exhibits rapid locomotion across substrates with varying friction coefficients but also achieves precise locomotion along patterned trajectories through programmed controlling. Furthermore, apart from its exceptional locomotive capabilities, the biped robot demonstrates remarkable robustness in terms of load-carrying and weight-bearing performance. The presented locomotion and mechanism herein introduce a novel concept for designing magnetic robots while offering extensive possibilities for practical applications in insect-scale robotics.

Magnetic continuum robots (MCRs), which are free of complicated structural designs for transmission, can be miniaturized and are therefore widely used in the medical field. However, the deformation shapes of different segments, including deflection directions and curvatures, are difficult to control simultaneously under an external programmable magnetic field. This is because the latest MCRs have designs with an invariable magnetic moment combination or profile of one or more actuating units. Therefore, the limited dexterity of the deformation shape causes the existing MCRs to collide readily with their surroundings or makes them unable to approach difficult-to-reach regions. These prolonged collisions are unnecessary or even hazardous, especially for catheters or similar medical devices. In this study, a novel magnetic moment intraoperatively programmable continuum robot (MMPCR) is introduced. By applying the proposed magnetic moment programming method, the MMPCR can deform under three modalities, that is, J, C, and S shapes. Additionally, the deflection directions and curvatures of different segments in the MMPCR can be modulated as desired. Furthermore, the magnetic moment programming and MMPCR kinematics are modeled, numerically simulated, and experimentally validated. The experimental results exhibit a mean deflection angle error of 3.3° and correspond well with simulation results. Comparisons between navigation capacities of the MMPCR and MCR demonstrate that the MMPCR has a higher capacity for dexterous deformation.

Electrical stimulation is a promising method to modulate gastrointestinal disorders. However, conventional stimulators need invasive implantation and removal surgeries associated with risks of infection and secondary injuries. Here, we report a battery-free and deformable electronic esophageal stent for wireless stimulation of the lower esophageal sphincter in a noninvasive fashion. The stent consists of an elastic receiver antenna infilled with liquid metal (eutectic gallium-indium), a superelastic nitinol stent skeleton, and a stretchable pulse generator that jointly enables 150% axial elongation and 50% radial compression for transoral delivery through the narrow esophagus. The compliant stent adaptive to the dynamic environment of the esophagus can wirelessly harvest energy through deep tissue. Continuous electrical stimulations delivered by the stent in vivo using pig models significantly increase the pressure of the lower esophageal sphincter. The electronic stent provides a noninvasive platform for bioelectronic therapies in the gastrointestinal tract without the need for open surgery.

Miniature magnetic soft machines could significantly impact minimally invasive robotics and biomedical applications. However, most soft machines are limited to solid magnetic materials, whereas further progress also relies on fluidic constructs obtained by reconfiguring liquid magnetic materials, such as ferrofluid. Here we show how harnessing the wettability of ferrofluids allows for controlled reconfigurability and the ability to create versatile soft machines. The ferrofluid droplet exhibits multimodal motions, and a single droplet can be controlled to split into multiple sub-droplets and then re-fuse back on demand. The soft droplet machine can negotiate changing terrains in unstructured environments. In addition, the ferrofluid droplets can be configured as a liquid capsule, enabling cargo delivery; a wireless omnidirectional liquid cilia matrix capable of pumping biofluids; and a wireless liquid skin, allowing multiple types of miniature soft machine construction. This work improves small magnetic soft machines' achievable complexity and boosts their future biomedical applications capabilities.

In nature, many microorganisms (such as volvox) normally rotate in situ and exhibit the phototactic motion when they sense the changes of the light signal. However, it is still challenging for the artificial micro/nanomotor counterpart to achieve such switchable motion behavior. Herein, we report a biomimetic visible light driven micro/nanomotor (MNM) with motion behavior similar to that of the volvox. The MNM, which consists of Ag nanoparticle decorated WO3 microrod (with a size of-5 mu m), exhibits the in-situ rotation with an angular speed of -4.67 rad/s (under vertical light irradiation with an intensity of 600 mW/cm2) and shows the negative phototaxis when the irradiation condition is changed to the tilted one (e.g. 45 degrees incident angle) with the angular and linear velocities of -4.59 rad/s and -1.47 mu m/s, respectively. The biomimetic motion behavior relies on the interaction between the two underlying mechanisms, i.e. self-electrophoresis and self-diffusiophoresis. More interestingly, the MNM exhibits the controlled in situ clockwise/counterclockwise rotation with designated angles (e.g. 90 degrees, 180 degrees). The results in the current study may further boost the development of light-driven MNMs with biomimetic features for a wide range of microfluidics, microrobotics, and cargo transportation applications.

Magnetic miniature soft‐bodied robots allow non‐invasive access to restricted spaces and provide ideal solutions for minimally invasive surgery, micromanipulation, and targeted drug delivery. However, the existing elastomer‐based (silicone) and fluid‐based (ferrofluid or liquid metal) magnetically actuated miniature soft robots have limitations. Owing to its limited deformability, the elastomer‐based small‐scale soft robot cannot navigate through a highly restricted environment. In contrast, although fluid‐based soft robots are more capable of deformation, they are also limited by the unstable shape of the fluid itself, and are therefore poorly adapted to the environment. In this study, non‐Newtonian fluid‐based magnetically actuated slime robots with both the adaptability of elastomer‐based robots and reconfigurable significant deformation capabilities of fluid‐based robots are demonstrated. The robots can negotiate through narrow channels with a diameter of 1.5 mm and maneuver on multiple substrates in complex environments. The proposed slime robot implements various functions, including grasping solid objects, swallowing and transporting harmful things, human motion monitoring, and circuit switching and repair. This study proposes the design of novel soft‐bodied robots and enhances their future applications in biomedical, electronic, and other fields.