Rotational multimaterial printing of filaments with subvoxel control.

Helical structures are ubiquitous in nature and impart unique mechanical properties and multifunctionality1. So far, synthetic architectures that mimic these natural systems have been fabricated by winding, twisting and braiding of individual filaments1-7, microfluidics8,9, self-shaping1,10-13 and printing methods14-17. However, those fabrication methods are unable to simultaneously create and pattern multimaterial, helically architected filaments with subvoxel control in arbitrary two-dimensional (2D) and three-dimensional (3D) motifs from a broad range of materials. Towards this goal, both multimaterial18-23 and rotational24 3D printing of architected filaments have recently been reported; however, the integration of these two capabilities has yet to be realized. Here we report a rotational multimaterial 3D printing (RM-3DP) platform that enables subvoxel control over the local orientation of azimuthally heterogeneous architected filaments. By continuously rotating a multimaterial nozzle with a controlled ratio of angular-to-translational velocity, we have created helical filaments with programmable helix angle, layer thickness and interfacial area between several materials within a given cylindrical voxel. Using this integrated method, we have fabricated functional artificial muscles composed of helical dielectric elastomer actuators with high fidelity and individually addressable conductive helical channels embedded within a dielectric elastomer matrix. We have also fabricated hierarchical lattices comprising architected helical struts containing stiff springs within a compliant matrix. Our additive-manufacturing platform opens new avenues to generating multifunctional architected matter in bioinspired motifs.

Optically addressable dielectric elastomer actuator arrays using embedded percolative networks of zinc oxide nanowires.

Dielectric elastomer actuators (DEAs) are electrically driven soft actuators that generate fast and reversible deformations, enabling lightweight actuation of many novel soft robots and haptic devices. However, the high-voltage operation of DEAs combined with the paucity of soft, small high-voltage microelectronics has limited the number of discrete DEAs that can be incorporated into soft robots. This has hindered the versatility as well as complexity of the tasks that they can perform which, in practice, depends on the number of independently addressable actuating elements. This paper presents a new class of optically addressable dielectric elastomer actuators that utilize the photoconductivity of semiconducting zinc oxide nanowires to create optically switchable and stretchable electrical channels. This enables non-contact, optical control of local actuation. To illustrate the versatility of the new capabilities of this integration, we describe the response of dielectric elastomer actuators with integrated photoconductive channels, formed from thin films of percolating semiconducting nanoparticles. By using a switchable array of small light emitting diodes to optically address the actuator array, its actuation can be controlled both spatially and temporally.

A novel method for identifying coded tags recorded on aquatic acoustic monitoring systems.

Aquatic biotelemetry increasingly relies on using acoustic transmitters ('tags') that enable passive detection of tagged animals using fixed or mobile receivers. Both tracking methods are resource-limited, restricting the spatial area in which movements of highly mobile animals can be measured using proprietary detection systems. Transmissions from tags are recorded by underwater noise monitoring systems designed for other purposes, such as cetacean monitoring devices, which have been widely deployed in the marine environment; however, no tools currently exist to decode these detections, and thus valuable additional information on animal movements may be missed. Here, we describe simple hybrid methods, with potentially wide application, for obtaining information from otherwise unused data sources. The methods were developed using data from moored, acoustic cetacean detectors (C-PODs) and towed passive receiver arrays, often deployed to monitor the vocalisations of cetaceans, but any similarly formatted data source could be used. The method was applied to decode tag detections that were found to have come from two highly mobile fish species, bass (Dicentrarchus labrax) and Twaite shad (Alosa fallax), that had been tagged in other studies. Decoding results were validated using test tags; range testing data were used to demonstrate the relative efficiency of these receiver methods in detecting tags. This approach broadens the range of equipment from which acoustic tag detections can be decoded. Novel detections derived from the method could add significant value to past and present tracking studies at little additional cost, by providing new insights into the movement of mobile animals at sea.

A Wearable Textile-Embedded Dielectric Elastomer Actuator Haptic Display.

With advances in mobile computing and virtual/augmented reality technologies, communicating through touch using wearable haptic devices is poised to enrich and augment current information delivery channels that typically rely on sight and hearing. To realize a wearable haptic device capable of effective data communication, both ergonomics and haptic performance (i.e., array size, bandwidth, and perception accuracy) are essential considerations. However, these goals often involve challenging and conflicting requirements. We present an integrated approach to address these conflicts, which includes incorporating multilayered dielectric elastomer actuators, a lumped-parameter model of the skin, and a wearable frame in the design loop. An antagonistic arrangement-consisting of an actuator deforming the skin-was used to achieve effective force transmission while maintaining a low profile, and the effect of the wearable frame and structure was investigated through lumped-model analysis and human perception studies.

Programmed shape-morphing into complex target shapes using architected dielectric elastomer actuators.

Dielectric elastomer actuators (DEAs) are among the fastest and most energy-efficient, shape-morphing materials. To date, their shapes have been controlled using patterned electrodes or stiffening elements. While their actuated shapes can be analyzed for prescribed configurations of electrodes or stiffening elements (the forward problem), the design of DEAs that morph into target shapes (the inverse problem) has not been fully addressed. Here, we report a simple analytical solution for the inverse design and fabrication of programmable shape-morphing DEAs. To realize the target shape, two mechanisms are combined to locally control the actuation magnitude and direction by patterning the number of local active layers and stiff rings of varying shapes, respectively. Our combined design and fabrication strategy enables the creation of complex DEA architectures that shape-morph into simple target shapes, for instance, those with zero, positive, and negative Gaussian curvatures as well as complex shapes, such as a face.

Voltage-tunable elastomer composites that use shape instabilities for rapid structural color changes.

Structurally colored materials can switch colors in response to external stimuli, which makes them potentially useful as colorimetric sensors, dynamic displays, and camouflage. However, their applications are limited by the angular dependence, slow response, and absence of synchronous control in time and space. In addition, out-of-plane deformation from shape instability easily occurs in photonic films, leading to inhomogeneous colors in photonic-crystal materials. To address these challenges, we combine structurally colored photonic glasses and dielectric elastomer actuators. We use an external voltage signal to tune color changes quickly (much less than 0.1 s). The photonic glassses produce colors with low angular dependence, so that their colors are homogeneous even when they become curved due to voltage-triggered instabilities (buckling or wrinkling). As proof of concept, we present a pixelated display in which segments can be independently and rapidly turned on and off. This wide-angle, instability-tolerant, color-changing platform could be used in next-generation soft and curved color displays, camouflage with both shape and color changes, and multifunctional sensors.

Photoswitchable Covalent Adaptive Networks Based on Thiol-Ene Elastomers.

Covalent adaptive networks combine the advantages of cross-linked elastomers and dynamic bonding in a single system. In this work, we demonstrate a simple one-pot method to prepare thiol-ene elastomers that exhibit reversible photoinduced switching from an elastomeric gel to fluid state. This behavior can be generalized to thiol-ene cross-linked elastomers composed of different backbone chemistries (e.g., polydimethylsiloxane, polyethylene glycol, and polyurethane) and vinyl groups (e.g., allyl, vinyl ether, and acrylate). Photoswitching from the gel to fluid state occurs in seconds upon exposure to UV light and can be repeated over at least 180 cycles. These thiol-ene elastomers also exhibit the ability to heal, remold, and serve as reversible adhesives.

A Wearable Soft Haptic Communicator Based on Dielectric Elastomer Actuators.

Dielectric elastomer actuators exhibit an unusual combination of large displacements, moderate bandwidth, low power consumption, and mechanical impedance comparable with human skin, making them attractive for haptic devices. In this article, we propose a wearable haptic communication device based on a two-by-two array of dielectric elastomer linear actuators. We briefly describe the architecture of the actuators and their mechanical and electrical integration into a wearable armband. We then characterize the actuators' force, displacement, and thermal properties in a bench-top configuration. We also report on the power and drive circuit design. Finally, we perform a set of preliminary perception evaluations on participants using our haptic device, including detection threshold tests and identification tests for locations and directions on the forearm. Human testing with individual actuators demonstrates that the broadband actuation can be easily perceived on the forearm, providing the basis for both the development of a wearable actuator array and its use in more extensive perception evaluation as described herein.

Controlled flight of a microrobot powered by soft artificial muscles.

Flying insects capable of navigating in highly cluttered natural environments can withstand in-flight collisions because of the combination of their low inertia1 and the resilience of their wings2, exoskeletons1 and muscles. Current insect-scale (less than ten centimetres long and weighing less than five grams) aerial robots3-6 use rigid microscale actuators, which are typically fragile under external impact. Biomimetic artificial muscles7-10 that are capable of large deformation offer a promising alternative for actuation because they can endure the stresses caused by such impacts. However, existing soft actuators11-13 have not yet demonstrated sufficient power density to achieve lift-off, and their actuation nonlinearity and limited bandwidth create further challenges for achieving closed-loop (driven by an input control signal that is adjusted based on sensory feedback) flight control. Here we develop heavier-than-air aerial robots powered by soft artificial muscles that demonstrate open-loop (driven by a predetermined signal without feedback), passively stable (upright during flight) ascending flight as well as closed-loop, hovering flight. The robots are driven by multi-layered dielectric elastomer actuators that weigh 100 milligrams each and have a resonance frequency of 500 hertz and power density of 600 watts per kilogram. To increase the mechanical power output of the actuator and to demonstrate flight control, we present ways to overcome challenges unique to soft actuators, such as nonlinear transduction and dynamic buckling. These robots can sense and withstand collisions with surrounding obstacles and can recover from in-flight collisions by exploiting material robustness and vehicle passive stability. We also fly two micro-aerial vehicles simultaneously in a cluttered environment. They collide with the wall and each other without suffering damage. These robots rely on offboard amplifiers and an external motion-capture system to provide power to the dielectric elastomer actuators and to control their flight. Our work demonstrates how soft actuators can achieve sufficient power density and bandwidth to enable controlled flight, illustrating the potential of developing next-generation agile soft robots.

Ten Years of Data Verification: The Society of Thoracic Surgeons Congenital Heart Surgery Database Audits.

BACKGROUND: The completeness and accuracy of data contained within clinical databases and registries is critical to the reliability of reports emanating from these platforms. Therefore, vigorous data verification processes are a core competency of any mature database or registry. The Society of Thoracic Surgeons Congenital Heart Surgery Database (STS CHSD) has conducted audits of participant data for just over ten years. This report documents the validity of data elements within the STS CHSD. METHODS: We review the various elements of a robust audit process, detail the STS CHSD audit methodology, and report completeness and agreement rates for all adjudicated fields in the most recently completed audit. RESULTS: The rate of completeness for general data elements was 97.6% and the rate of agreement was 97.4%. The rate of completeness for variables in the mortality review was 100% and the rate of agreement was 99.3%. CONCLUSIONS: The STS CHSD audit is a highly structured and reproducible process. The most recently completed audit documents a very high level of completeness and accuracy of data variables, particularly those most germane to outcomes measurement.

Realizing the potential of dielectric elastomer artificial muscles.

Soft robotics represents a new set of technologies aimed at operating in natural environments and near the human body. To interact with their environment, soft robots require artificial muscles to actuate movement. These artificial muscles need to be as strong, fast, and robust as their natural counterparts. Dielectric elastomer actuators (DEAs) are promising soft transducers, but typically exhibit low output forces and low energy densities when used without rigid supports. Here, we report a soft composite DEA made of strain-stiffening elastomers and carbon nanotube electrodes, which demonstrates a peak energy density of 19.8 J/kg. The result is close to the upper limit for natural muscle (0.4-40 J/kg), making these DEAs the highest-performance electrically driven soft artificial muscles demonstrated to date. To obtain high forces and displacements, we used low-density, ultrathin carbon nanotube electrodes which can sustain applied electric fields upward of 100 V/µm without suffering from dielectric breakdown. Potential applications include prosthetics, surgical robots, and wearable devices, as well as soft robots capable of locomotion and manipulation in natural or human-centric environments.

Reconfigurable shape-morphing dielectric elastomers using spatially varying electric fields.

Exceptionally large strains can be produced in soft elastomers by the application of an electric field and the strains can be exploited for a variety of novel actuators, such as tunable lenses and tactile actuators. However, shape morphing with dielectric elastomers has not been possible since no generalizable method for changing their Gaussian curvature has been devised. Here it is shown that this fundamental limitation can be lifted by introducing internal, spatially varying electric fields through a layer-by-layer fabrication method incorporating shaped, carbon-nanotubes-based electrodes between thin elastomer sheets. To illustrate the potential of the method, voltage-tunable negative and positive Gaussian curvatures shapes are produced. Furthermore, by applying voltages to different sets of internal electrodes, the shapes can be re-configured. All the shape changes are reversible when the voltage is removed.

Adaptive metalenses with simultaneous electrical control of focal length, astigmatism, and shift.

Focal adjustment and zooming are universal features of cameras and advanced optical systems. Such tuning is usually performed longitudinally along the optical axis by mechanical or electrical control of focal length. However, the recent advent of ultrathin planar lenses based on metasurfaces (metalenses), which opens the door to future drastic miniaturization of mobile devices such as cell phones and wearable displays, mandates fundamentally different forms of tuning based on lateral motion rather than longitudinal motion. Theory shows that the strain field of a metalens substrate can be directly mapped into the outgoing optical wavefront to achieve large diffraction-limited focal length tuning and control of aberrations. We demonstrate electrically tunable large-area metalenses controlled by artificial muscles capable of simultaneously performing focal length tuning (>100%) as well as on-the-fly astigmatism and image shift corrections, which until now were only possible in electron optics. The device thickness is only 30 µm. Our results demonstrate the possibility of future optical microscopes that fully operate electronically, as well as compact optical systems that use the principles of adaptive optics to correct many orders of aberrations simultaneously.

Large area metalenses: design, characterization, and mass manufacturing.

Optical components, such as lenses, have traditionally been made in the bulk form by shaping glass or other transparent materials. Recent advances in metasurfaces provide a new basis for recasting optical components into thin, planar elements, having similar or better performance using arrays of subwavelength-spaced optical phase-shifters. The technology required to mass produce them dates back to the mid-1990s, when the feature sizes of semiconductor manufacturing became considerably denser than the wavelength of light, advancing in stride with Moore's law. This provides the possibility of unifying two industries: semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips is used to make optical components, such as lenses, based on metasurfaces. Using a scalable metasurface layout compression algorithm that exponentially reduces design file sizes (by 3 orders of magnitude for a centimeter diameter lens) and stepper photolithography, we show the design and fabrication of metasurface lenses (metalenses) with extremely large areas, up to centimeters in diameter and beyond. Using a single two-centimeter diameter near-infrared metalens less than a micron thick fabricated in this way, we experimentally implement the ideal thin lens equation, while demonstrating high-quality imaging and diffraction-limited focusing.

Multilayer Dielectric Elastomers for Fast, Programmable Actuation without Prestretch.

A novel method for the fabrication of dielectric elastomer actuators (DEAs) combines acrylic polymers and single wall carbon nanotube network electrodes. DEAs made using this technique do not require prestretching, have extremely thin electrodes, and can be actuated at low voltage. The method is applied to create a multimorph device with nine actuation modes based on just four inputs.

Pattern formation in plastic liquid films on elastomers by ratcheting.

Plastic liquids, also known as Bingham liquids, retain their shape when loads are small, but flow when loads exceed a threshold. We discovered that plastic liquid films coated on elastomers develop wavy patterns under cyclic loads. As the number of cycles increases, the wavelength of the patterns remains unchanged, but the amplitude of the patterns increases and then saturates. Because the patterns develop progressively under cyclic loads, we call this phenomenon as "patterning by ratcheting". We observe the phenomenon in plastic liquids of several kinds, and studied the effects of thickness, the cyclic frequency of the stretch, and the range of the stretch. Finite element simulations show that the ratcheting phenomenon can occur in materials described by a commonly used model of elastic-plastic deformation.

Electrically-tunable surface deformation of a soft elastomer.

The flat surface of a thin elastomer on a conducting substrate can be deformed by applying an electric field to a percolating network of metallic nanowires randomly dispersed over the surface. The magnitude of the field-induced surface undulations increases with the applied field and can locally be several times the diameter of the nanowires. Optical imaging indicates that the effect is reversible and the surface flatness is recovered when the electric field is removed. It is found that it is the field-induced changes in the surface morphology rather than the nanowires themselves that strongly scatter light. The optical effects could be exploited in functional devices including tunable privacy windows, displays, and camouflage. There is also the potential for tuning the adhesion of elastomers to other materials.

Electrically tunable window device.

A device for controlling the transmittance of light over large areas, such as windows, is described. It is based on electrostatically induced surface deformation of soft dielectric elastomer sheets produced when a voltage is applied between two networks of electrically conducting nanowires on either side of the elastomer. Variations in the surface curvature are produced by the applied voltage refract light, decreasing the optical transmittance at all wavelengths. As the device relies on changes in the geometric propagation of light, rather than on chemical changes, it is color neutral.

Dielectric Elastomer Based "Grippers" for Soft Robotics.

The use of few stiff fibers to control the deformation of dielectric elastomer actuators, in particular to break the symmetry of equi-biaxial lateral strain in the absence of prestretch, is demonstrated. Actuators with patterned fibers are shown to evolve into unique shapes upon electrical actuation, enabling novel designs of gripping actuators for soft robotics.