system. [11] Researchers have developed highly stretchable strain sensors made of compliant elastomers and various conductive materials, such as silver nanowire, [12] carbon nanotube (CNT), [13][14][15][16][17][18] carbon grease, [19] graphene, [20] graphite, [21] laser-carbonized polyimide, [22] conductive acrylic elastomer, [10] liquid metal, [23,24] ionic liquid, [25][26][27] and conductive fabric. [28] However, not all of these technologies can be manufactured in large scale at low cost.Here, we propose the use of carbon black (CB)-filled elastomer composites for highly stretchable strain sensors (up to 500%) that can be batch manufactured at low cost. CBs are a type of low-cost conductive nanoparticle, which, when used as a filler in an elastomeric matrix, enhances the mechanical strength, abrasion resistance, UV resistance, and light absorbency of the composite. [29][30][31] The CB-filled elastomer can be printed in large areas by means of a layer-by-layer process, [32] with good wettability and high adhesion to silicone surfaces. Mixing various types of CBs and elastomers [33] gives material designers flexibility to achieve high compliance and stretchability.Our layer-by-layer CB-filled elastomer fabrication process can be used to create resistive or capacitive sensors. [11] Resistive sensing relies on the piezoresistive effect and geometrical changes of electrodes, where mechanical strain causes a change in electrical resistivity. Capacitive sensing exploits changes of the capacitance between a pair of electrodes sandwiching a dielectric layer. Strain expands the area of the electrodes and reduces the thickness of the dielectric layer, leading to an increase of the capacitance. A recent review on strain sensors has pointed that resistive type strain sensors have high sensitivity but hysteresis and nonlinear response, while capacitive type strain sensors display excellent linearity and hysteresis performance but low sensitivity. [11] On the other hand, according to other literature, both resistive and capacitive type strain sensors show good linearity, low hysteresis, and repeatability. [10,13,15,28] Therefore, there is a lack of comprehensive knowledge of highly stretchable strain sensors that clarifies advantages and disadvantages of the two sensing methods. In addition, other characteristics, such as responses to different strain speed and temperature, have not yet been compared. This would result in difficulty when it is required to select an appropriate sensor The advent of soft robotics has led to the development of devices that harness the compliance and natural deformability of media with nonlinear elasticity. This has led to a need of batch-manufacturable soft sensors that can sustain large strains and maintain kinematic compatibility with the systems they track. In this article, an approach to address this challenge is presented with highly stretchable strain sensors that can operate at strains up to 500%. The sensors consist of a carbon black-filled elastomer composite that is batch manufacture...

Soft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated.

Abstract-We present a fully edible pneumatic actuator based on gelatin-glycerol material. The actuator is monolithic, fabricated via a molding process, and measures 90 mm in length, 20 mm in width, and 17 mm in thickness. Thanks to the material mechanical characteristics similar to those of silicone elastomers, the actuator exhibits a bending angle of 170.3• and a blocked force of 0.34 N at the applied pressure of 25 kPa. These values are comparable to elastomer based pneumatic actuators. As a validation example, two actuators are integrated to form a gripper capable of handling various objects, highlighting the high performance and applicability of the edible actuator. These edible actuators, combined with other recent edible materials and electronics, could lay the foundation for a new type of edible robots.

Variable stiffness (VS) is an important feature that significantly enhances the dexterity of magnetic catheters used in minimally invasive surgeries. Existing magnetic catheters with VS consist of sensors, heaters, and tubular structures filled with low melting point alloys, which have a large stiffness change ratio but are toxic to humans. In this paper, a VS magnetic catheter is described for minimally invasive surgery; the catheter is based on a novel variable stiffness thread (VST), which is made of a conductive shape memory polymer (CSMP). The CSMP is nontoxic and simultaneously serves as a heater, a temperature sensor, and a VS substrate. The VST is made through a new scalable fabrication process, which consists of a dipping technique that enables the fabrication of threads with the desired electrical resistance and thickness (with a step size of 70 µm). Selective bending of a multisegmented VST catheter with a diameter of 2.0 mm under an external magnetic field of 20 mT is demonstrated. Compared to existing proof-of-concept VS catheters for cardiac ablation, each integrated VST segment has the lowest wall thickness of 0.75 mm and an outer diameter of 2.0 mm. The segment bends up to 51° and exhibits a stiffness change factor of 21.

The inherent compliance of soft robots often makes it difficult for them to exert forces on surrounding surfaces or withstand mechanical loading. Controlled stiffness is a solution to empower soft robots with the ability to apply large forces on their environments and sustain external loads without deformations. Herein, a compact, soft actuator composed of a shared electrode used for both electrostatic actuation and variable stiffness is described. The device operates as a dielectric elastomer actuator, while variable stiffness is provided by a shared electrode made of gallium. The fabricated actuator, namely variable stiffness dielectric elastomer actuator (VSDEA), has a compact and lightweight structure with a thickness of 930 μm and a mass of 0.7 g. It exhibits a stiffness change of 183×, a bending angle of 31°, and a blocked force of 0.65 mN. Thanks to the lightweight feature, the stiffness change per mass of the actuator (261× g−1) is 2.6 times higher than that of the other type of VSDEA that has no shared electrode.

Electroadhesion is an attractive mechanism to electrically modulate adhesion to surfaces. Electroadhesion arises from the interaction of electric fields with conductive or dielectric materials. Electroadhesion devices consist of in‐plane, interdigitated electrodes that generate out‐of‐plane electric fields, which increase adhesion with target surfaces. To date, these electrodes have predominantly been composed of carbonaceous materials. Here, liquid metal is utilized to create the electrodes in silicone substrates. Liquid metal can be patterned in a variety of unique ways, including microfluidic injection, spray deposition, or printing. These electrodes have nearly unlimited deformation in soft and stretchable substrates while maintaining metallic conductivity. The experimental results show that stretching improves electroadhesion performance due to the changes in geometry of the electrodes and insulation layer, whose behaviors are theoretically predictable. The use of liquid‐filled, sub‐surface microchannels can help to maintain contact between the elastomer and substrate during peeling due to the surface stresses caused by the capillary pressure. This approach to electroadhesion can be implemented in ultra‐stretchable and soft substrates, including those used in soft robotics, due to the inherently compliant and deformable electrical conductivity of the liquid metal electrodes.

Perching in unmanned aerial vehicles (UAVs) offers the possibility of extending the range of aerial robots beyond the limits of their batteries. It has been a topic of intense study for multirotor UAVs. Perching in winged UAVs is harder because a kinetic energy balance has to be struck. Reducing too much energy results in the vehicle stalling and falling. Too much kinetic energy at touchdown could damage the vehicle. Most studies used dangerous pitch‐up maneuvers to manage this balance. This work presents a system that eliminates the pitch‐up maneuver by mechanically capturing and storing kinetic energy at impact. It is validated using a passive mechanical system consisting of a storage mechanism for energy recuperation and a claw for perching on a horizontal rod. The energy stored in the mechanism is then used to unperch. The mathematical model for the recuperation strategy is presented and perching success at various approach attitudes are characterized. The proof‐of‐concept claw recaptures 5% of the kinetic energy during perching. Experiments indicate that the device can successfully perch at a wide range of yaw angles, but requires more precision in roll. We show that our perching mechanism enables the fastest UAV perching to date (7.4 m s−1).

Biodegradable materials decompose and return to nature. This functionality can be applied to derive robotic systems that are environmentally friendly. This study presents a fully biodegradable soft actuator, which is one of the key elements in “green” soft robotics. The working of the actuator is based on an electrohydraulic principle, which is similar to that of hydraulically amplified self‐healing electrostatic actuators. The actuator developed in this study consists of a dielectric film made of polylactic acid (PLA) and polybutylene adipate‐co‐terephthalate (PBAT), with soybean oil as the dielectric liquid and electrodes made from a mixture of gelatin, glycerol, and sodium chloride (NaCl). The synthesized biodegradable electrode material exhibits a Young's modulus of 0.06 MPa and resistivity of 258 Ω·m when the mass fraction of NaCl relative to the amount of gelatin and glycerol is 10 wt%. The softness and resistivity of the electrode material results in actuation strain values of 3.2% (at 1 kV, corresponding to 1.2 kV mm−1) and 18.6% (at 10 kV, corresponding to 9.6 kV mm−1) for the linear‐type and circular‐type actuators, respectively. These values obtained for the biodegradable electrohydraulic soft actuators are comparable to those of nonbiodegradable actuators of the same type, representing the successful implementation of the concept.