Safer human–robot interactions mandate the adoption of proprioceptive actuation. Strain sensors can detect the deformation of tools and devices in unstructured and capricious environments. However, such sensor integration in surgical/clinical settings is challenging due to confined spaces, structural complexity, and performance losses of tools and devices. Herein, we report a highly stretchable skin-like strain sensor based on a silver nanowire (AgNW) layer and hydrogel substrate. Our facile fabrication method utilizes thermal annealing to modulate the gauge factor (GF) by forming multidimensional wrinkles and a layered conductive network. The developed AgNW-hydrogel (AGel) sensors sustain and exhibit a strain-sensitive profile (max. GF = ∼70) with high stretchability (200%). Due to its conformability, the sensor demonstrates efficacy in integration and motion monitoring with minimal mechanical constraints. We provide contextual cognizance of tooltip during a transoral procedure by incorporating AGel sensors and showing the fabrication methodology’s versatility by developing a hybrid self-sensing actuator with real-time performance feedback.
Shape-memory Nitinol holds burgeoning promise as smart actuators due to its effective resilience, high energy density, and scalability for a myriad of mesoscale machines and robotic applications. However, the higher actuation temperature and prolonged cooling time for a cyclic response make Nitinol precarious and less appealing for commercial use. On the contrary, hydrogels belong to the three dimensional (3D) polymer family where the bulk of the matrix encapsulates water (z80-90 wt%) constituting a compelling heat-trapping medium. In this paper, we demonstrate a novel self-cooling mechanism comprising a Hydrogel-matrix Encapsulated Nitinol Actuator (HENA) where the heat emitted due to the high temperature (200-400 C) of Nitinol is trapped in the hydrogel-matrix, maintaining a surface temperature of 20-22 C. For quantitative analysis, we performed control tests with the stateof-the-art Silicone Elastomer Nitinol Actuator (SENA) which maintained a three times or higher temperature profile (65-90 C) than its HENA counterpart. HENA is able to entrap 85% heat for actuation of 200 cycles while SENA dissipates the same amount in the first cycle. For impending biomedical applications, HENA with a single Nitinol wire shows a bending displacement up to 45% of its length for trans-oral navigation purposes. A HENA soft robotic gripper with two Nitinol wires can carry delicate, low-melting-point food items (e.g. cheese, chocolate, tofu etc.) with different morphologies that weigh up to 450% of its own weight.
Flame-retardant coatings are crucial for intelligent systems operating in high-temperature (300-800°C) scenarios, which typically involve multi-joint discrete or continuous kinematic systems. These multi-segment motion generation systems call for conformable yet resilient skin for dexterous work, including firefighting, packaging inflammable substances, encapsulating energy storage devices, and preventing from burning. In fire scenes, a flameretardant soft robot shall protect integrated electronic components safely and work for navigation and surveillance effectively. Here, we establish fire-resistant robotic mechanisms with montmorillonite (MMT)-biocompatible hydrogel skin, offering effective flame retardancy (*78°C surface temperature after 3 min in fire) and high postfire stretchability (*360% uniaxial tensile strain). Fatigue test results in the MMT-hydrogel polymer matrix to portray a change in post-fire energy consumption of *21% (between the first cycle and the 200th cycle), further indicating robustness. MMT-hydrogel synthetic skin medium is then applied to everyday household items and electronics, offering appealing protections in fire scenes (£10% capacitance loss after 3 min and £14% diode lightintensity loss after 1 min in fire). We deploy shape memory alloy (SMA) actuated inchworm-, starfish-, and snaillike locomotion (average velocity *12 mm$min -1 ) for translating inside fire applications. With the stretchable and flame-retardant translucent barriers, the MMT-hydrogel skinned soft robots demonstrate stable compression/ relaxation cycles (25 cycles) within flames (4 min 10 s) while protecting the electronic components inside in fire scene. We solve the agility vs. endurance conundrum in this article with SMA actuation independently via Joule heating without a cross-talk from the surrounding high-temperature arena.
Nature's pumping systems allow for a more even stress distribution throughout the circuit than human-made devices. [1,2] Squid and jellyfish locomotion involves active fluid movement by soft tubular membranes. This also pertains to the transport of fluids within vessel invertebrates and the associated biofluid dynamics. To limit the damage to tissues (e.g., cardiac tissues), it is imperative to bound the problem of local stress maxima. Assistive devices with more muscle-like behavior are now required and soft actuators lend themselves for this purpose. [3,4] Human-made examples of valveless chamber pumps include bellows and diaphragms, with natural analogies of these found in urethral pumps, jellyfish jet propulsion, dragonfly nymphs' anal jets, snakes, spiders with venom injection, and insects blood-and-nectar sucking. [2] Attempts have been made to model the squid and jellyfish with dielectric elastomers (DEs), with limited performance. [5] Translatory or peristaltic pumping corresponding to valveless moving chambers is found in intestines, mammalian esophagus, annelid hearts, and those of holothurians and arthropods, as well as burrowing worms. [2] In this spirit, biorobotics aims to emulate natural system performance to study the underlying fundamental mechanisms of complex behaviors such as locomotion [6,7] in fluids which can involve pumping action. [8] However, the substantial utilization of soft materials poses an essential discrepancy between animals and conventional robots, [9] due to its high-impact dissipation energy, damping oscillations, and the smoothing out of irregular movements and forces. Soft active materials are therefore now required to develop compliant, intelligent systems to develop more life-like capabilities with less impedance mismatch vis-a-vis natural systems. [10,11] When it comes to soft actuators inspired by muscle-like behavior, a variety of solutions have been proposed, each of which with its limitations. For example, fluidic soft actuators [12] have been used in a multitude of applications, [13,14] though the speed of operation and efficiency still pose major limitations. Likewise, thermally actuated fiber-reinforced polymer-based artificial actuators generate large actuation forces, though these solutions are
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