Dimension effect on the performance of carbon nanotube nanobolometers.

Carbon nanotube (CNT) film nanobolometers take advantages of high infrared absorption of CNTs, proving a promising alternative for low-cost, uncooled infrared detection. The performance of the CNT nanobolometers is determined by the optoelectronic process on CNTs at a microscopic scale, which links intimately to the diameter of the CNT-a critical parameter that intrinsically affects the band gap and hence infrared absorption, as well as extrinsically affects the surface oxygen adsorption effect and thermal-link of the CNT detector element to the environment. Both the intrinsic and extrinsic factors play important roles in the photoresponse, noise spectrum and the figure-of-merit detectivity D* of the CNT nanobolometers and their interplay determines the device's ultimate performance. In this work, we present a systematic study of the effect of CNT diameter in the range of 1-50 nm on the physical properties relevant to CNT nanobolometers. The optimal CNT diameter was found to be in the range of 2-12 nm with the D* up to 3.3 × 10(7) cm(Hz)(1/2) W(-1), which represents an order of magnitude improvement over the best D* reported previously on CNT film nanobolometers.

Extraordinary photocurrent harvesting at type-II heterojunction interfaces: toward high detectivity carbon nanotube infrared detectors.

Despite the potentials and the efforts put in the development of uncooled carbon nanotube infrared detectors during the past two decades, their figure-of-merit detectivity remains orders of magnitude lower than that of conventional semiconductor counterparts due to the lack of efficient exciton dissociation schemes. In this paper, we report an extraordinary photocurrent harvesting configuration at a semiconducting single-walled carbon nanotube (s-SWCNT)/polymer type-II heterojunction interface, which provides highly efficient exciton dissociation through the intrinsic energy offset by designing the s-SWCNT/polymer interface band alignment. This results in significantly enhanced near-infrared detectivity of 2.3 × 10(8) cm·Hz(1/2)/W, comparable to that of the many conventional uncooled infrared detectors. With further optimization, the s-SWCNT/polymer nanohybrid uncooled infrared detectors could be highly competitive for practical applications.

Cephalopod-inspired robot capable of cyclic jet propulsion through shape change.

The compliance and conformability of soft robots provide inherent advantages when working around delicate objects or in unstructured environments. However, rapid locomotion in soft robotics is challenging due to the slow propagation of motion in compliant structures, particularly underwater. Cephalopods overcome this challenge using jet propulsion and the added mass effect to achieve rapid, efficient propulsion underwater without a skeleton. Taking inspiration from cephalopods, here we present an underwater robot with a compliant body that can achieve repeatable jet propulsion by changing its internal volume and cross-sectional area to take advantage of jet propulsion as well as the added mass effect. The robot achieves a maximum average thrust of 0.19 N and maximum average and peak swimming speeds of 18.4 cm/s (0.54 body lengths/s) and 32.1 cm/s (0.94 BL/s), respectively. We also demonstrate the use of an onboard camera as a sensor for ocean discovery and environmental monitoring applications.

Design Considerations for 3D Printed, Soft, Multimaterial Resistive Sensors for Soft Robotics.

Sensor design for soft robots is a challenging problem because of the wide range of design parameters (e.g., geometry, material, actuation type, etc.) critical to their function. While conventional rigid sensors work effectively for soft robotics in specific situations, sensors that are directly integrated into the bodies of soft robots could help improve both their exteroceptive and interoceptive capabilities. To address this challenge, we designed sensors that can be co-fabricated with soft robot bodies using commercial 3D printers, without additional modification. We describe an approach to the design and fabrication of compliant, resistive soft sensors using a Connex3 Objet350 multimaterial printer and investigated an analytical comparison to sensors of similar geometries. The sensors consist of layers of commercial photopolymers with varying conductivities. We characterized the conductivity of TangoPlus, TangoBlackPlus, VeroClear, and Support705 materials under various conditions and demonstrate applications in which we can take advantage of these embedded sensors.

Jellyfish-Inspired Soft Robot Driven by Fluid Electrode Dielectric Organic Robotic Actuators.

Robots for underwater exploration are typically comprised of rigid materials and driven by propellers or jet thrusters, which consume a significant amount of power. Large power consumption necessitates a sizeable battery, which limits the ability to design a small robot. Propellers and jet thrusters generate considerable noise and vibration, which is counterproductive when studying acoustic signals or studying timid species. Bioinspired soft robots provide an approach for underwater exploration in which the robots are comprised of compliant materials that can better adapt to uncertain environments and take advantage of design elements that have been optimized in nature. In previous work, we demonstrated that frameless DEAs could use fluid electrodes to apply a voltage to the film and that effective locomotion in an eel-inspired robot could be achieved without the need for a rigid frame. However, the robot required an off-board power supply and a non-trivial control signal to achieve propulsion. To develop an untethered soft swimming robot powered by DEAs, we drew inspiration from the jellyfish and attached a ring of frameless DEAs to an inextensible layer to generate a unimorph structure that curves toward the passive side to generate power stroke, and efficiently recovers the original configuration as the robot coasts. This swimming strategy simplified the control system and allowed us to develop a soft robot capable of untethered swimming at an average speed of 3.2 mm/s and a cost of transport of 35. This work demonstrates the feasibility of using DEAs with fluid electrodes for low power, silent operation in underwater environments.

Translucent soft robots driven by frameless fluid electrode dielectric elastomer actuators.

Dielectric elastomer actuators (DEAs) are a promising enabling technology for a wide range of emerging applications, including robotics, artificial muscles, and microfluidics. This is due to their large actuation strains, rapid response rate, low cost and low noise, high energy density, and high efficiency when compared with alternative actuators. These properties make DEAs ideal for the actuation of soft submersible devices, although their use has been limited because of three main challenges: (i) developing suitable, compliant electrode materials; (ii) the need to effectively insulate the actuator electrodes from the surrounding fluid; and (iii) the rigid frames typically required to prestrain the dielectric layers. We explored the use of a frameless, submersible DEA design that uses an internal chamber filled with liquid as one of the electrodes and the surrounding environmental liquid as the second electrode, thus simplifying the implementation of soft, actuated submersible devices. We demonstrated the feasibility of this approach with a prototype swimming robot composed of transparent bimorph actuator segments and inspired by transparent eel larvae, leptocephali. This design achieved undulatory swimming with a maximum forward swimming speed of 1.9 millimeters per second and a Froude efficiency of 52%. We also demonstrated the capability for camouflage and display through the body of the robot, which has an average transmittance of 94% across the visible spectrum, similar to a leptocephalus. These results suggest a potential for DEAs with fluid electrodes to serve as artificial muscles for quiet, translucent, swimming soft robots for applications including surveillance and the unobtrusive study of marine life.

A Biologically Inspired, Functionally Graded End Effector for Soft Robotics Applications.

Soft robotic actuators offer many advantages over their rigid counterparts, but they often are unable to apply highly localized point loads. In contrast, many invertebrates have not only evolved extremely strong "hybrid appendages" that are composed of rigid ends that can grasp, puncture, and anchor into solid substrates, but they also are compliant and resilient, owing to the functionally graded architecture that integrates rigid termini with their flexible and highly extensible soft musculatures. Inspired by the design principles of these natural hybrid appendages, we demonstrate a synthetic hybrid end effector for soft-bodied robots that exhibits excellent piercing abilities. Through the incorporation of functionally graded interfaces, this design strategy minimizes stress concentrations at the junctions adjoining the fully rigid and soft components and optimizes the bending stiffness to effectively penetrate objects without interfacial failure under shear and compressive loading regimes. In this composite architecture, the radially aligned tooth-like elements apply balanced loads to maximize puncturing ability, resulting in the coordinated fracture of an object of interest.

RBC micromotors carrying multiple cargos towards potential theranostic applications.

Red blood cell (RBC)-based micromotors containing both therapeutic and diagnostic modalities are described as a means for potential theranostic applications. In this natural RBC-based multicargo-loaded micromotor system, quantum dots (QDs), anti-cancer drug doxorubicin (DOX), and magnetic nanoparticles (MNPs), were co-encapsulated into RBC micromotors. The fluorescent emission of both QDs and DOX provides direct visualization of their loading inside the RBC motors at two distinct wavelengths. The presence of MNPs within the RBCs allows for efficient magnetic guidance under ultrasound propulsion along with providing the potential for magnetic resonance imaging. The simultaneous encapsulation of the imaging nanoparticles and therapeutic payloads within the same RBC micromotor has a minimal effect upon its propulsion behavior. The ability of the RBC micromotors to transport imaging and therapeutic agents at high speed and spatial precision through a complex microchannel network is also demonstrated. Such ability to load and transport diagnostic imaging agents and therapeutic drugs within a single cell-based motor, in addition to a lower toxicity observed once the drug is encapsulated within the multicargo RBC motor, opens the door to the development of theranostic micromotors that may simultaneously treat and monitor diseases.

Vapor-Driven Propulsion of Catalytic Micromotors.

Chemically-powered micromotors offer exciting opportunities in diverse fields, including therapeutic delivery, environmental remediation, and nanoscale manufacturing. However, these nanovehicles require direct addition of high concentration of chemical fuel to the motor solution for their propulsion. We report the efficient vapor-powered propulsion of catalytic micromotors without direct addition of fuel to the micromotor solution. Diffusion of hydrazine vapor from the surrounding atmosphere into the sample solution is instead used to trigger rapid movement of iridium-gold Janus microsphere motors. Such operation creates a new type of remotely-triggered and powered catalytic micro/nanomotors that are responsive to their surrounding environment. This new propulsion mechanism is accompanied by unique phenomena, such as the distinct off-on response to the presence of fuel in the surrounding atmosphere, and spatio-temporal dependence of the motor speed borne out of the concentration gradient evolution within the motor solution. The relationship between the motor speed and the variables affecting the fuel concentration distribution is examined using a theoretical model for hydrazine transport, which is in turn used to explain the observed phenomena. The vapor-powered catalytic micro/nanomotors offer new opportunities in gas sensing, threat detection, and environmental monitoring, and open the door for a new class of environmentally-triggered micromotors.

Turning erythrocytes into functional micromotors.

Attempts to apply artificial nano/micromotors for diverse biomedical applications have inspired a variety of strategies for designing motors with diverse propulsion mechanisms and functions. However, existing artificial motors are made exclusively of synthetic materials, which are subject to serious immune attack and clearance upon entering the bloodstream. Herein we report an elegant approach that turns natural red blood cells (RBCs) into functional micromotors with the aid of ultrasound propulsion and magnetic guidance. Iron oxide nanoparticles are loaded into the RBCs, where their asymmetric distribution within the cells results in a net magnetization, thus enabling magnetic alignment and guidance under acoustic propulsion. The RBC motors display efficient guided and prolonged propulsion in various biological fluids, including undiluted whole blood. The stability and functionality of the RBC motors, as well as the tolerability of regular RBCs to the ultrasound operation, are carefully examined. Since the RBC motors preserve the biological and structural features of regular RBCs, these motors possess a wide range of antigenic, transport, and mechanical properties that common synthetic motors cannot achieve and thus hold considerable promise for a number of practical biomedical uses.

High photoresponse in hybrid graphene-carbon nanotube infrared detectors.

Efficient exciton dissociation is crucial to obtaining high photonic response in photodetectors. This work explores implementation of a novel exciton dissociation mechanism through heterojunctions self-assembled at the graphene/MWCNT (multiwall carbon nanotube) interfaces in graphene/MWCNT nanohybrids. Significantly enhanced near-infrared photoresponsivity by nearly an order of magnitude has been achieved on the graphene/MWCNT nanohybrids as compared to the best achieved so far on carbon nanotube (CNT) only infrared (IR) detectors. This leads to a high detectivity up to 1.5 × 10(7) cm·Hz(1/2)·W(-1) in the graphene/MWCNT nanohybrid, which represents a 500% improvement over the best D* achieved on MWCNT film IR detectors and may be further improved with optimization on the interfacial heterojunctions. This approach of the self-assembly of graphene/CNT nanohybrids provides a pathway toward high-performance and low-cost carbon nanostructure IR detectors.