Towards an AI-driven soft toy for automatically detecting and classifying infant-toy interactions using optical force sensors

Introduction: It is crucial to identify neurodevelopmental disorders in infants early on for timely intervention to improve their long-term outcomes. Combining natural play with quantitative measurements of developmental milestones can be an effective way to swiftly and efficiently detect infants who are at risk of neurodevelopmental delays. Clinical studies have established differences in toy interaction behaviors between full-term infants and pre-term infants who are at risk for cerebral palsy and other developmental disorders. Methods: The proposed toy aims to improve the quantitative assessment of infant-toy interactions and fully automate the process of detecting those infants at risk of developing motor delays. This paper describes the design and development of a toy that uniquely utilizes a collection of soft lossy force sensors which are developed using optical fibers to gather play interaction data from infants laying supine in a gym. An example interaction database was created by having 15 adults complete a total of 2480 interactions with the toy consisting of 620 touches, 620 punches-"kick substitute," 620 weak grasps and 620 strong grasps. Results: The data is analyzed for patterns of interaction with the toy face using a machine learning model developed to classify the four interactions present in the database. Results indicate that the configuration of 6 soft force sensors on the face created unique activation patterns. Discussion: The machine learning algorithm was able to identify the distinct action types from the data, suggesting the potential usability of the toy. Next steps involve sensorizing the entire toy and testing with infants.

A Low-Voltage, High-Force Capacity Electroadhesive Clutch Based on Ionoelastomer Heterojunctions

Electroadhesive devices with dielectric films can electrically program changes in stiffness and adhesion, but require hundreds of volts and are subject to failure by dielectric breakdown. Recent work on ionoelastomer heterojunctions has enabled reversible electroadhesion with low voltages, but these materials exhibit limited force capacities and high detachment forces. It is a grand challenge to engineer electroadhesives with large force capacities and programmable detachment at low voltages (<10 V). In this work, tough ionoelastomer/metal mesh composites with low surface energies are synthesized and surface roughness is controlled to realize sub-ten-volt clutches that are small, strong, and easily detachable. Models based on fracture and contact mechanics explain how clutch compliance and surface texture affect force capacity and contact area, which is validated over different geometries and voltages. These ionoelastomer clutches outperform the best existing electroadhesive clutches by fivefold in force capacity per unit area (102 N cm-2 ), with a 40-fold reduction in operating voltage (± 7.5 V). Finally, the ability of the ionoelastomer clutches to resist bending moments in a finger wearable and as a reversible adhesive in an adjustable phone mount is demonstrated.

Electrochemical Healing of Fractured Metals

Repairing fractured metals to extend their useful lifetimes advances sustainability and mitigates carbon emissions from metal mining and processing. While high-temperature techniques are being used to repair metals, the increasing ubiquity of digital manufacturing and "unweldable" alloys, as well as the integration of metals with polymers and electronics, call for radically different repair approaches. Herein, a framework for effective room-temperature repair of fractured metals using an area-selective nickel electrodeposition process refered to as electrochemical healing is presented. Based on a model that links geometric, mechanical, and electrochemical parameters to the recovery of tensile strength, this framework enables 100% recovery of tensile strength in nickel, low-carbon steel, two "unweldable" aluminum alloys, and a 3D-printed difficult-to-weld shellular structure using a single common electrolyte. Through a distinct energy-dissipation mechanism, this framework also enables up to 136% recovery of toughness in an aluminum alloy. To facilitate practical adoption, this work reveals scaling laws for the energetic, financial, and time costs of healing, and demonstrates the restoration of a functional level of strength in a fractured standard steel wrench. Empowered with this framework, room-temperature electrochemical healing can open exciting possibilities for the effective, scalable repair of metals in diverse applications.

High-Energy-Density Zinc-Air Microbatteries with Lean PVA-KOH-K2CO3 Gel Electrolytes

Small-scale, primary electrochemical energy storage devices ("microbatteries") are critical power sources for microelectromechanical system (MEMS)-based sensors and actuators. However, the achievable volumetric and gravimetric energy densities of microbatteries are typically insufficient for intermediate-term applications of MEMS-enabled distributed internet-connected devices. Further, in the increasing subset of Internet of Things (IoT) nodes, where actuation is desired, the peak power density of the microbattery must be simultaneously considered. Metal-air approaches to achieving microbatteries are attractive, as the anode and cathode are amenable to miniaturization; however, further improvements in energy density can be obtained by minimizing the electrolyte volume. To investigate these potential improvements, this work studied very lean hydrogel electrolytes based on poly(vinyl alcohol) (PVA). Integration of high potassium hydroxide (KOH) loading into the PVA hydrogel improved electrolyte performance. The addition of potassium carbonate (K₂CO₃) to the KOH-PVA gel decreased the carbonation consumption rate of KOH in the gel electrolyte by 23.8% compared to PVA-KOH gel alone. To assess gel performance, a microbattery was formed from a zinc (Zn) anode layer, a gel electrolyte layer, and a carbon-platinum (C-Pt) air cathode layer. Volumetric energy densities of approximately 1400 Wh L^-1 and areal peak power densities of 139 mW cm^-2 were achieved with a PVA-KOH-K₂CO₃ electrolyte. Further structural optimization, including using multilayer gel electrolytes and thinning the air cathode, resulted in volumetric and gravimetric energy densities of 1576 Wh L^-1 and 420 Wh kg^-1, respectively. The batteries described in this work are manufactured in an open environment and fabricated using a straightforward layer-by-layer method, enabling the potential for high fabrication throughput in a MEMS-compatible fashion.

A mechanics-based approach to realize high–force capacity electroadhesives for robots

Materials with electroprogrammable stiffness and adhesion can enhance the performance of robotic systems, but achieving large changes in stiffness and adhesive forces in real time is an ongoing challenge. Electroadhesive clutches can rapidly adhere high stiffness elements, although their low force capacities and high activation voltages have limited their applications. A major challenge in realizing stronger electroadhesive clutches is that current parallel plate models poorly predict clutch force capacity and cannot be used to design better devices. Here, we use a fracture mechanics framework to understand the relationship between clutch design and force capacity. We demonstrate and verify a mechanics-based model that predicts clutch performance across multiple geometries and applied voltages. On the basis of this approach, we build a clutch with 63 times the force capacity per unit electrostatic force of state-of-the-art electroadhesive clutches. Last, we demonstrate the ability of our electroadhesives to increase the load capacity of a soft, pneumatic finger by a factor of 27 times compared with a finger without an electroadhesive.

Centimetre-scale crack-free self-assembly for ultra-high tensile strength metallic nanolattices

Nanolattices exhibit attractive mechanical, energy conversion and optical properties, but it is challenging to fabricate large nanolattices while maintaining the dense regular nanometre features that enable their properties. Here we report a crack-free self-assembly approach for fabricating centimetre-scale nickel nanolattices with much larger crack-free areas than prior self-assembled nanolattices and many more unit cells than three-dimensionally printed nanolattices. These nickel nanolattices have a feature size of 100 nm, a grain size of 30 nm and a tensile strength of 260 MPa, which approaches the theoretical strength limit for porous nickel. The self-assembly method and porous metal mechanics reported in this work may advance the fabrication and applications of high-strength multifunctional porous materials.

Materials with Electroprogrammable Stiffness

Stiffness is a mechanical property of vital importance to any material system and is typically considered a static quantity. Recent work, however, has shown that novel materials with programmable stiffness can enhance the performance and simplify the design of engineered systems, such as morphing wings, robotic grippers, and wearable exoskeletons. For many of these applications, the ability to program stiffness with electrical activation is advantageous because of the natural compatibility with electrical sensing, control, and power networks ubiquitous in autonomous machines and robots. The numerous applications for materials with electrically driven stiffness modulation has driven a rapid increase in the number of publications in this field. Here, a comprehensive review of the available materials that realize electroprogrammable stiffness is provided, showing that all current approaches can be categorized as using electrostatics or electrically activated phase changes, and summarizing the advantages, limitations, and applications of these materials. Finally, a perspective identifies state-of-the-art trends and an outlook of future opportunities for the development and use of materials with electroprogrammable stiffness.

A Nearly Packaging-Free Design Paradigm for Light, Powerful, and Energy-Dense Primary Microbatteries

Billions of internet connected devices used for medicine, wearables, and robotics require microbattery power sources, but the conflicting scaling laws between electronics and energy storage have led to inadequate power sources that severely limit the performance of these physically small devices. Reported here is a new design paradigm for primary microbatteries that drastically improves energy and power density by eliminating the vast majority of the packaging and through the use of high-energy-density anode and cathode materials. These light (50-80 mg) and small (20-40 µL) microbatteries are enabled though the electroplating of 130 µm-thick 94% dense additive-free and crystallographically oriented LiCoO₂ onto thin metal foils, which also act as the encapsulation layer. These devices have 430 Wh kg^-1 and 1050 Wh L^-1 energy densities, 4 times the energy density of previous similarly sized microbatteries, opening up the potential to power otherwise unpowerable microdevices.

Surface Facet Engineering in Nanoporous Gold for Low-Loading Catalysts in Aluminum-Air Batteries

The performance of metal-air batteries and fuel cells depends on the speed and efficiency of electrochemical oxygen reduction reactions at the cathode, which can be improved by engineering the atomic arrangement of cathode catalysts. It is, however, difficult to improve upon the performance of platinum nanoparticles in alkaline electrolytes with low-loading catalysts that can be manufactured at scale. Here, the authors synthesized nanoporous gold catalysts with increased (100) surface facets using electrochemical dealloying in sodium citrate surfactant electrolytes. These modified nanoporous gold catalysts achieved an 8% higher operating voltage and 30% greater power density in aluminum-air batteries over traditionally prepared nanoporous gold, and their performance was superior to commercial platinum nanoparticle electrodes at a 10 times lower mass loading. The authors used rotation disc electrode studies, backscattering of electrons, and underpotential deposition to show that the increased (100) facets improved the catalytic activity of citrate dealloyed nanoporous gold compared to conventional nanoporous gold. The citrate dealloyed samples also had the highest stability and least concentration of steps and kinks. The developed synthesis and characterization techniques will enable the design and synthesis of metal nanostructured catalysts with controlled facets for low-cost and mass production of metal-air battery cathodes.

First ptychographic X-ray computed tomography experiment on the NanoMAX beamline

Documentation is presented for the first ptychographic X-ray computed tomography experiment on the NanoMAX beamline, along with a quantitative analysis of the reconstruction quality and a discussion of possibilities for future improvements.

Ptychographic X-ray computed tomography is a quantitative three-dimensional imaging technique offered to users of multiple synchrotron radiation sources. Its dependence on the coherent fraction of the available X-ray beam makes it perfectly suited to diffraction-limited storage rings. Although MAX IV is the first, and so far only, operating fourth-generation synchrotron light source, none of its experimental stations is currently set up to offer this technique to its users. The first ptychographic X-ray computed tomography experiment has therefore been performed on the NanoMAX beamline. From the results, information was gained about the current limitations of the experimental setup and where attention should be focused for improvement. The extracted parameters in terms of scanning speed, size of the imaged volume and achieved resolutions should provide a baseline for future users designing nano-tomography experiments on the NanoMAX beamline.

Thick Free-Standing Metallic Inverse Opals Enabled by New Insights into the Fracture of Drying Particle Films

Metallic inverse opals are porous materials with enhanced mechanical, chemical, thermal, and photonic properties used to improve the performance of many technologies, such as battery electrodes, photonic devices, and heat exchangers. Cracking in the drying opal templates used to fabricate inverse opals, however, is a major hindrance to the use of these materials for practical and fundamental studies. In this work, we conduct desiccation experiments on polystyrene particle opals self-assembled on indium-tin oxide coated substrates to study their fracture mechanisms, which we describe using an energy-conservation fracture model. The model incorporates film yielding, particle order, and interfacial friction to explain several experimental observations, including thickness-dependent crack spacings, cracking stresses, and order-dependent crack behavior. Guided by this model, we are the first to fabricate 120 μm thick free-standing metallic inverse opals, which are 4 times thicker than previously reported non-free-standing metallic inverse opals. Moreover, by controlling cracks, we achieve a crack-free single-crystal domain up to 1.35 mm², the largest ever reported in metallic inverse opals. This work improves our understanding of fracture mechanics in drying particle films, provides guidelines to reduce crack formation in opal templates, and enables the fabrication of free-standing large-area single-crystal inverse opals.

Fiber Embroidery of Self-Sensing Soft Actuators

Natural organisms use a combination of contracting muscles and inextensible fibers to transform into controllable shapes, camouflage into their surrounding environment, and catch prey. Replicating these capabilities with engineered materials is challenging because of the difficulty in manufacturing and controlling soft material actuators with embedded fibers. In addition, while linear and bending motions are common in soft actuators, rotary motions require three-dimensional fiber wrapping or multiple bending or linear elements working in coordination that are challenging to design and fabricate. In this work, an automatic embroidery machine patterned Kevlar™ fibers and stretchable optical fibers into inflatable silicone membranes to control their inflated shape and enable sensing. This embroidery-based fabrication technique is simple, low cost, and allows for precise and custom patterning of fibers in elastomers. Using this technique, we developed inflatable elastomeric actuators embedded with a planar spiral pattern of high-strength Kevlar™ fibers that inflate into radially symmetric shapes and achieve nearly 180° angular rotation and 10 cm linear displacement.

Click chemistry stereolithography for soft robots that self-heal

Although soft robotics promises a new generation of robust, versatile machines capable of complex functions and seamless integration with biology, the fabrication of such soft, three dimensional (3D) hierarchical structures remains a significant challenge. Stereolithography (SLA) is an additive manufacturing technique that can rapidly fabricate the complex device architectures required for the next generation of these systems. Current SLA materials and processes are prohibitively expensive, display little elastic deformation at room temperature, or exhibit Young's moduli exceeding most natural tissues, all of which limit use in soft robotics. Herein, we report a low-cost build window substrate that enables the rapid fabrication of high resolution (∼50 μm) silicone (polydimethylsiloxane) based elastomeric devices using an open source SLA printer. Our thiol-ene click chemistry permits photopolymerization using low energy (H_e < 20 mJ cm^-2) optical wavelengths (405 nm < λ < 1 mm) available on many low-cost SLA machines. This chemistry is easily tuned to achieve storage moduli, 6 < E < 283 kPa at engineering strains, γ = 0.02; similarly, a large range of ultimate strains, 0.5 < γ_ult < 4 is achievable through appropriate selection of the two primary chemical constituents (mercaptosiloxane, M.S., and vinylsiloxane, V.S.). Using this chemo-mechanical system, we directly fabricated compliant machines, including an antagonistic pair of fluidic elastomer actuators (a primary component in most soft robots). During printing, we retained unreacted pockets of M.S. and V.S. that permit autonomic self-healing, via sunlight, upon puncture of the elastomeric membranes of the soft actuators.

Hydrothermal fabrication of three-dimensional secondary battery anodes

A generalized hydrothermal strategy for fabricating three-dimensional (3D) battery electrodes is presented. The hydrothermal growth deposits electrochemically active nanomaterials uniformly throughout the complex 3D mesostructure of the scaffold. Ni inverse opals coated with SnO2 nanoparticles or Co3O4 nanoplatelets, and SiO2 inverse opals coated with Fe3O4 are fabricated, all of which show attractive properties including good capacity retention and C-rate performances.