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Simultaneous monitoring of critical parameters (e.g., pressure, shear, and temperature) at bony prominences is essential for the prevention of pressure injuries in a systematic manner. However, the development of wireless sensor array for accurate mapping of risk factors has been limited due to the challenges in the convergence of wireless technologies and wearable sensor arrays with a thin and small form factor. Herein, a battery-free, wireless, miniaturized multi-modal sensor array is introduced for continuous mapping of pressure, shear, and temperature at skin interfaces. The sensor array includes an integrated pressure and shear sensor consisting of 3D strain gauges and micromachined components. The mechanically decoupled design of the integrated sensor enables reliable data acquisition of pressure and shear at skin interfaces without the need for additional data processing. The sensor platform enables the analysis of interplay among localized pressure, shear, and temperature in response to changes in the patient's movement, posture, and bed inclination. The validation trials using a novel combination of wireless sensor arrays and customized pneumatic actuator demonstrate the efficacy of the platform in continuous monitoring and efficient redistribution of pressure and shear without repositioning, thereby improving the patient's quality of life.
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Contact lenses have been instrumental in vision correction and are expected to be utilized in augmented reality (AR) displays through the integration of electronic and optical components. In optics, metasurfaces, an array of sub-wavelength nanostructures, have offered optical multifunctionality in an ultra-compact form factor, facilitating integration into various imaging, and display systems. However, transferring metasurfaces onto contact lenses remains challenging due to the non-biocompatible materials of extant imprinting methods and the structural instability caused by the swelling and shrinking of the wetted surface. Here, a biocompatible method is presented to transfer metasurfaces onto contact lenses using hyaluronic acid (HA) as a soft mold and to allow for holographic light projection. A high-efficiency metahologram is obtained with an all-metallic 3D meta-atom enhanced by the anisotropy of a rectangular structure, and a reflective background metal layer. A corrugated metal layer on the HA mold is supported with a SiO2 capping layer, to avoid unwanted wrinkles and to ensure structural stability when transferred to the surface of pliable and wettable contact lenses. Biocompatible method of transferring metasurfaces onto contact lenses promises the integration of diverse optical components, including holograms, lenses, gratings and more, to advance the visual experience for AR displays and human-computer interfaces.
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Nanomaterial-based yarns have been actively developed owing to their advantageous features, namely, high surface-area-to-volume ratios, flexibility, and unusual material characteristics such as anisotropy in electrical/thermal conductivity. The superior properties of the nanomaterials can be directly imparted and scaled-up to macro-sized structures. However, most nanomaterial-based yarns have thus far, been fabricated with only organic materials such as polymers, graphene, and carbon nanotubes. This paper presents a novel fabrication method for fully inorganic nanoribbon yarn, expanding its applicability by bundling highly aligned and suspended nanoribbons made from various inorganic materials (e.g., Au, Pd, Ni, Al, Pt, WO3, SnO2, NiO, In2O3, and CuO). The process involves depositing the target inorganic material on a nanoline mold, followed by suspension through plasma etching of the nanoline mold, and twisting using a custom-built yarning machine. Nanoribbon yarn structures of various functional inorganic materials are utilized for chemical sensors (Pd-based H2 and metal oxides (MOx)-based green gas sensors) and green energy transducers (water splitting electrodes/triboelectric nanogenerators). This method is expected to provide a comprehensive fabrication strategy for versatile inorganic nanomaterials-based yarns.
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Soft pressure sensors based on 3D microstructures exhibit high sensitivity in the low-pressure range, which is crucial for various wearable and soft touch applications. However, it is still a challenge to manufacture soft pressure sensors with sufficient sensitivity under small mechanical stimuli for wearable applications. This work presents a novel strategy for extremely sensitive pressure sensors based on the composite film with local changes in curved 3D carbon nanotube (CNT) structure via expandable microspheres. The sensitivity is significantly enhanced by the synergetic effects of heterogeneous contact of the microdome structure and changes of percolation network within the curved 3D CNT structure. The finite-element method simulation is used to comprehend the relationships between the sensitivity and mechanical/electrical behavior of microdome structure under the applied pressure. The sensor shows an excellent sensitivity (571.64 kPa-1 ) with fast response time (85 ms), great repeatability, and long-term stability. Using the developed sensor, a wireless wearable health monitoring system to avoid carpel tunnel syndrome is built, and a multi-array pressure sensor for realizing a variety of movements in real-time is demonstrated.
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The high demand for micro-/nanohierarchical structures as components of functional substrates, bioinspired devices, energy-related electronics, and chemical/physical transducers has inspired their in-depth studies and active development of the related fabrication techniques. In particular, significant progress has been achieved in hierarchical structures physically engineered on surfaces, which offer the advantages of wide-range material compatibility, design diversity, and mechanical stability, and numerous unique structures with important niche applications have been developed. This review categorizes the basic components of hierarchical structures physically engineered on surfaces according to function/shape and comprehensively summarizes the related advances, focusing on the fabrication strategies, ways of combining basic components, potential applications, and future research directions. Moreover, the physicochemical properties of hierarchical structures physically engineered on surfaces are compared based on the function of their basic components, which may help to avoid the bottlenecks of conventional single-scale functional substrates. Thus, the present work is expected to provide a useful reference for scientists working on multicomponent functional substrates and inspire further research in this field.
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Correction for 'A wearable colorimetric sweat pH sensor-based smart textile for health state diagnosis' by Ji-Hwan Ha et al., Mater. Horiz., 2023, 10, 4163-4171, https://doi.org/10.1039/d3mh00340j.
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The growing demand for soft intelligent systems, which have the potential to be used in a variety of fields such as wearable technology and human-robot interaction systems, has spurred the development of advanced soft transducers. Among soft systems, sensor-actuator hybrid systems are considered the most promising due to their effective and efficient performance, resulting from the synergistic and complementary interaction between their sensor and actuator components. Recent research on integrated sensor and actuator systems has resulted in a range of conceptual and practical soft systems. This review article provides a comprehensive analysis of recent advances in sensor and actuator integrated systems, which are grouped into three categories based on their primary functions: i) actuator-assisted sensors for intelligent detection, ii) sensor-assisted actuators for intelligent movement, and iii) sensor-actuator interactive devices for a hybrid of intelligent detection and movement. In addition, several bottlenecks in current studies are discussed, and prospective outlooks, including potential applications, are presented. This categorization and analysis will pave the way for the advancement and commercialization of sensor and actuator-integrated systems.
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Sweat pH is an important indicator for diagnosing disease states, such as cystic fibrosis. However, conventional pH sensors are composed of large brittle mechanical parts and need additional instruments to read signals. These pH sensors have limitations for practical wearable applications. In this study, we propose wearable colorimetric sweat pH sensors based on curcumin and thermoplastic-polyurethane (C-TPU) electrospun-fibers to diagnose disease states by sweat pH monitoring. This sensor aids in pH monitoring by changing color in response to chemical structure variation from enol to di-keto form via H-atom separation. Its chemical structure variation changes the visible color due to light absorbance and reflectance changes. Furthermore, it can rapidly and sensitively detect sweat pH due to its superior permeability and wettability. By O2 plasma activation and thermal pressing, this colorimetric pH sensor can be easily attached to various fabric substrates such as swaddling and patient clothing via surface modification and mechanical interlocking of C-TPU. Furthermore, the diagnosable clothing is durable and reusable enough to neutral washing conditions due to the reversible pH colorimetric sensing performance by restoring the enol form of curcumin. This study contributes to the development of smart diagnostic clothing for cystic fibrosis patients who require continuous sweat pH monitoring.
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Curcumina , Fibrosis Quística , Dispositivos Electrónicos Vestibles , Humanos , Sudor/química , Fibrosis Quística/diagnóstico , Colorimetría , Curcumina/análisis , Textiles , Concentración de Iones de HidrógenoRESUMEN
The growing demand for nanophotonic devices has driven the advancement of nanotransfer printing (nTP) technology. Currently, the scope of nTP is limited to certain materials and substrates owing to the temperature, pressure, and chemical bonding requirements. In this study, we developed a universal nTP technique utilizing covalent bonding-based adhesives to improve the adhesion between the target material and substrate. Additionally, the technique employed plasma-based selective etching to weaken the adhesion between the mold and target material, thereby enabling the reliable modulation of the relative adhesion forces, regardless of the material or substrate. The technique was evaluated by printing four optical materials on nine substrates, including rigid, flexible, and stretchable substrates. Finally, its applicability was demonstrated by fabricating a ring hologram, a flexible plasmonic color filter, and extraordinary optical transmission-based strain sensors. The high accuracy and reliability of the proposed nTP method were verified by the performance of nanophotonic devices that closely matched numerical simulation results.
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The growing demand for complex three-dimensional (3D) micro-/nanostructures has inspired the development of the corresponding manufacturing techniques. Among these techniques, 3D fabrication based on mechanically guided assembly offers the advantages of broad material compatibility, high designability, and structural reversibility under strain but is not applicable for nanoscale device printing because of the bottleneck at nanofabrication and design technique. Herein, a configuration-designable nanoscale 3D fabrication is suggested through a robust nanotransfer methodology and design of substrate's mechanical characteristics. Covalent bonding-based two-dimensional nanotransfer allowing for nanostructure printing on elastomer substrates is used to address fabrication problems, while the feasibility of configuration design through the modulation of substrate's mechanical characteristics is examined using analytical calculations and numerical simulations, allowing printing of various 3D nanostructures. The printed nanostructures exhibit strain-independent electrical properties and are therefore used to fabricate stretchable H2 and NO2 sensors with high performances stable under external strains of 30%.
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Repositioning is a common guideline for the prevention of pressure injuries of bedridden or wheelchair patients. However, frequent repositioning could deteriorate the quality of patient's life and induce secondary injuries. This paper introduces a method for continuous multi-site monitoring of pressure and temperature distribution from strategically deployed sensor arrays at skin interfaces via battery-free, wireless ionic liquid pressure sensors. The wirelessly delivered power enables stable operation of the ionic liquid pressure sensor, which shows enhanced sensitivity, negligible hysteresis, high linearity and cyclic stability over relevant pressure range. The experimental investigations of the wireless devices, verified by numerical simulation of the key responses, support capabilities for real-time, continuous, long-term monitoring of the pressure and temperature distribution from multiple sensor arrays. Clinical trials on two hemiplegic patients confined on bed or wheelchair integrated with the system demonstrate the feasibility of sensor arrays for a decrease in pressure and temperature distribution under minimal repositioning.
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Líquidos Iónicos , Silla de Ruedas , Humanos , Temperatura , Tecnología Inalámbrica , PielRESUMEN
Three-dimensional (3D) hierarchical structures have been explored for various applications owing to the synergistic effects of micro- and nanostructures. However, the development of spherical micro/nano hierarchical structures (S-HSs), which can be used as energy/water harvesting systems and sensing devices, remains challenging owing to the trade-off between structural complexity and fabrication difficulty. This paper presents a new strategy for facile, scalable S-HS fabrication using a thermal expansion of microspheres and nanopatterned structures. When a specific temperature is applied to a composite film of microspheres and elastomers with nanopatterned surfaces, microspheres are expanded and 3D spherical microstructures are generated. Various nanopatterns and densities of spherical microstructures can thereby be quantitatively controlled. The fabricated S-HSs have been used in renewable electrical energy harvesting and sustainable water management applications. Compared to a triboelectric nanogenerator (TENG) with bare film, the S-HS-based TENG exhibited 4.48 times higher triboelectric performance with high mechanical durability. Furthermore, an S-HS is used as a water harvesting device to capture water in a fog environment. The water collection rate is dramatically enhanced by the increased surface area and locally concentrated vapor diffusion flux due to the spherical microstructures.
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Many conventional micropatterning and nanopatterning techniques employ toxic chemicals, rendering them nonbiocompatible and unsuited for biodevice production. Herein the formation of water bridges on the surface of hyaluronic acid (HA) films is exploited to develop a transfer-based nanopatterning method applicable to diverse structures and materials. The HA film surface, made deformable via water bridge generation, is brought into contact with a functional material and subjected to thermal treatment, which results in film shrinkage, allowing a robust pattern transfer. The proposed biocompatible method, which avoids the use of extra chemicals, enables the transfer of nanoscale, microscale, and thin-film structures as well as functional materials such as metals and metal oxides. A nanopatterned HA film is transferred onto a moisture-containing contact lens to fabricate smart contact lenses with unique optical characteristics of rationally designed optical nanopatterns. These lenses demonstrated binocular parallax-induced stereoscopy via nanoline array polarization and acted as cutoff filters, with nanodot arrays, capable of treating Irlen syndrome.
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Materiales Biocompatibles/química , Lentes de Contacto , Ácido Hialurónico/química , Impresión , Materiales Inteligentes/química , Agua/química , Percepción de Profundidad , Nanoestructuras/química , Poliuretanos/química , Plata/químicaRESUMEN
In the aviation industry, the process of de-icing is critical for stable flying because of the occurrence of airplane icing. To solve the icing problem, an electrical heating system is applied for airplane de-icing. Among the materials used in the electrical heating system, carbon-nanotube polymer composites are appropriate for an ice-prevention system owing to their rapid heating properties and flexibility. In this study, we fabricated a flexible carbon-nanotube/polydimethylsiloxane composite with a high content of carbon nanotube (20 wt%) for airplane de-icing. The high-load carbon nanotube composite was fabricated using a three-roll milling method, resulting in uniform dispersion of carbon nanotubes in the polymer matrix. The carbon nanotube/polydimethylsiloxane composites exhibited uniform and stable heating performance (from room temperature to 100 °C for 25 s without thermal aggregation). In addition, the carbon nanotube/polydimethylsiloxane composite is suitable for application to the curved surface of airfoils. For the de-icing experiments, a small airplane wing consisting of carbon nanotube/polydimethylsiloxane composite as a heating unit was fabricated with a scale ratio of 15:1. We conducted electrical heating and de-icing experiments using the developed airplane-wing system for actual anti-icing/de-icing applications.
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Heating elements need a rapid heating property and long-term cycle stability when subjected to extreme temperatures. Carbon nanotube-based films can be used as ideal heating units owing to their superior electrical and thermal properties. However, carbon nanotube polymer composites are not appropriate for extreme conditions such as high temperatures (300 °C) due to the poor thermal stability of the polymer matrix. In this study, we fabricated a carbon nanotube web film, comprising heating elements consisting of pure carbon nanotubes, through the direct spinning method. The carbon nanotube web film has a microscale thickness. The carbon nanotube web film showed flexibility at high temperatures, while a fracture occurred in the case of the carbon nanotube polymer composite. We conducted electrical heating experiments on the curved carbon nanotube web film to observe the heating uniformity and flexibility. The heating test is conducted on various curved form heaters. The carbon nanotube web film showed rapid heating properties and a uniform heat distribution (temperature departure of less than 3%) without thermal aggregation. The curved heating units can be utilized in various applications such as functional clothes and de-icing systems having curved surfaces.
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For filler composite systems used in strain sensor applications, piezoresistive effect, strain hysteresis, and repeatability are critical factors, which have to be clearly evaluated and understood. To investigate the effects of the aspect ratio and content of a multiwalled carbon nanotube (MWCNT) on the strain sensor properties of the composite, MWCNT/Polydimethylsiloxane (PDMS) composites with varying filler contents and aspect ratios were fabricated. In order to uniformly disperse MWCNTs on the polymer matrix, we used a threeroll milling method to generate high shear force for debundling MWCNTs. Mechanical and electrical properties of the MWCNT composites were evaluated for each case. In addition, through the cyclic stretching test, we optimized the strainsensing properties of the MWCNT composites by considering their piezoresistive effects and strain hysteresis.
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We developed a multi-functional graphene composite with electromagnetic interference (EMI) shielding and de-icing properties. Two-dimensional graphene fillers were homogeneously dispersed in a polymer by three-roll milling. The electrical properties and percolation threshold of the graphene composites were measured with various graphene contents. The variation in the EMI shielding properties of the graphene composites with respect to the filler content was measured. The shielding efficiency improved with increasing graphene filler content. Furthermore, we conducted electrical heating tests on the graphene composites. The composites could be heated rapidly to 200 °C by electrical Joule heating with low electric power because of the high electrical conductivity of the composite. Moreover, the composite film was suitable for application in a de-icing unit because of its rapid and homogenous heating performance.
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For practical use of carbon nanotube (CNT) composites, especially in electronic applications, uniform dispersion of a high concentration of CNTs in a polymer matrix is a critical challenge. Three-roll milling is one of most reliable dispersion techniques. We investigate the effect of three-roll milling time on CNT length and the electrical properties of a CNT/polydimethylsiloxane composite film with 10 wt% CNTs. During the milling process, the CNT length is decreased from 10 to 1-4 µm by mechanical shear forces. The electrical conductivity increases after 1.5 min of milling owing to dispersion of the CNTs but decreases with increasing milling time owing to the decrease in the CNT length. Considering the changes in the electrical conductivity of the CNT composite and CNT length, we determined how to optimize the three-roll milling time to obtain a suitable dispersion state.
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Hybrid carbon nanotube composites with two different types of fillers have attracted considerable attention for various advantages. The incorporation of micro-scale secondary fillers creates an excluded volume that leads to the increase in the electrical conductivity. By contrast, nano-scale secondary fillers shows a conflicting behavior of the decreased electrical conductivity with micro-scale secondary fillers. Although several attempts have been made in theoretical modeling of secondary-filler composites, the knowledge about how the electrical conductivity depends on the dimension of secondary fillers was not fully understood. This work aims at comprehensive understanding of the size effect of secondary particulate fillers on the electrical conductivity, via the combination of Voronoi geometry induced from Swiss cheese models and the underlying percolation theory. This indicates a transition in the impact of the excluded volume, i.e., the adjustment of the electrical conductivity was measured in cooperation with loading of second fillers with different sizes.
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We report the enhanced electromagnetic interference (EMI) shielding properties of hybrid carbon nanotube (CNT) composites consisting of more than two kinds of fillers through the use of segregate conducting networks. An excluded volume was created by micro-sized silica particles that concentrate the CNT network, resulting in improved electrical conductivity and microwave properties. To achieve the optimal dispersion of CNTs and silica particles, high shear force was applied to the pre-cured composite mixture via three-roll milling. Depending on the micro-silica content ratio, we observed improved electrical conductivity and EMI shielding properties. For a quantitative comparison to observe the excluded-volume effects, a CNT composite without micro-silica was measured in parallel with the other sample.