Skin-integrated wireless haptic interfaces for virtual and augmented reality.

Traditional technologies for virtual reality (VR) and augmented reality (AR) create human experiences through visual and auditory stimuli that replicate sensations associated with the physical world. The most widespread VR and AR systems use head-mounted displays, accelerometers and loudspeakers as the basis for three-dimensional, computer-generated environments that can exist in isolation or as overlays on actual scenery. In comparison to the eyes and the ears, the skin is a relatively underexplored sensory interface for VR and AR technology that could, nevertheless, greatly enhance experiences at a qualitative level, with direct relevance in areas such as communications, entertainment and medicine1,2. Here we present a wireless, battery-free platform of electronic systems and haptic (that is, touch-based) interfaces capable of softly laminating onto the curved surfaces of the skin to communicate information via spatio-temporally programmable patterns of localized mechanical vibrations. We describe the materials, device structures, power delivery strategies and communication schemes that serve as the foundations for such platforms. The resulting technology creates many opportunities for use where the skin provides an electronically programmable communication and sensory input channel to the body, as demonstrated through applications in social media and personal engagement, prosthetic control and feedback, and gaming and entertainment.

Silicon-based transient electronics: principles, devices and applications.

Recent advances in materials science, device designs and advanced fabrication technologies have enabled the rapid development of transient electronics, which represents a class of devices or systems that their functionalities and constitutions can be partially/completely degraded via chemical reaction or physical disintegration over a stable operation. Therefore, numerous potentials, including zero/reduced waste electronics, bioresorbable electronic implants, hardware security, and others, are expected. In particular, transient electronics with biocompatible and bioresorbable properties could completely eliminate the secondary retrieval surgical procedure after their in-body operation, thus offering significant potentials for biomedical applications. In terms of material strategies for the manufacturing of transient electronics, silicon nanomembranes (SiNMs) are of great interest because of their good physical/chemical properties, modest mechanical flexibility (depending on their dimensions), robust and outstanding device performances, and state-of-the-art manufacturing technologies. As a result, continuous efforts have been made to develop silicon-based transient electronics, mainly focusing on designing manufacturing strategies, fabricating various devices with different functionalities, investigating degradation or failure mechanisms, and exploring their applications. In this review, we will summarize the recent progresses of silicon-based transient electronics, with an emphasis on the manufacturing of SiNMs, devices, as well as their applications. After a brief introduction, strategies and basics for utilizing SiNMs for transient electronics will be discussed. Then, various silicon-based transient electronic devices with different functionalities are described. After that, several examples regarding on the applications, with an emphasis on the biomedical engineering, of silicon-based transient electronics are presented. Finally, summary and perspectives on transient electronics are exhibited.

Transient, Implantable, Ultrathin Biofuel Cells Enabled by Laser-Induced Graphene and Gold Nanoparticles Composite.

Transient power sources with excellent biocompatibility and bioresorablility have attracted significant attention. Here, we report high-performance, transient glucose enzymatic biofuel cells (TEBFCs) based on the laser-induced graphene (LIG)/gold nanoparticles (Au NPs) composite electrodes. Such LIG electrodes can be easily fabricated from polyimide (PI) with an infrared CO2 laser and exhibit a low impedance (16 Ω). The resulted TEBFC yields a high open circuit potential (OCP) of 0.77 V and a maximum power density of 483.1 µW/cm2. The TEBFC not only exhibits a quick response time that enables reaching the maximum OCP within 1 min but also owns a long lifetime over 28 days in vitro. The excellent biocompatibility and transient performance from in vitro and in vivo tests allow long-term implantation of TEBFCs in rats for energy harvesting. The TEBFCs with advanced processing methods provide a promising power solution for transient electronics.

Flexible Liquid Crystal Polymer Technologies from Microwave to Terahertz Frequencies.

With the emergence of fifth-generation (5G) cellular networks, millimeter-wave (mmW) and terahertz (THz) frequencies have attracted ever-growing interest for advanced wireless applications. The traditional printed circuit board materials have become uncompetitive at such high frequencies due to their high dielectric loss and large water absorption rates. As a promising high-frequency alternative, liquid crystal polymers (LCPs) have been widely investigated for use in circuit devices, chip integration, and module packaging over the last decade due to their low loss tangent up to 1.8 THz and good hermeticity. The previous review articles have summarized the chemical properties of LCP films, flexible LCP antennas, and LCP-based antenna-in-package and system-in-package technologies for 5G applications, although these articles did not discuss synthetic LCP technologies. In addition to wireless applications, the attractive mechanical, chemical, and thermal properties of LCP films enable interesting applications in micro-electro-mechanical systems (MEMS), biomedical electronics, and microfluidics, which have not been summarized to date. Here, a comprehensive review of flexible LCP technologies covering electric circuits, antennas, integration and packaging technologies, front-end modules, MEMS, biomedical devices, and microfluidics from microwave to THz frequencies is presented for the first time, which gives a broad introduction for those outside or just entering the field and provides perspective and breadth for those who are well established in the field.

PVDF-triggered multicolor fluorine-doped graphene quantum dots for water detection and anti-counterfeiting.

Fluorescent fluorine-doped graphene quantum dots (F-GQDs) have been synthesized via the hydrothermal method using long-chain polymer polyvinylidene fluoride (PVDF) as the precursor. Due to the unique molecular structure of PVDF, a possible synthesis process of F-GQDs has been put forward. F-GQDs have adjustable emission wavelength by simply adjusting the concentration of the solution. As the concentration increases, the emission wavelength of F-GQDs gradually red shifts from 455 nm (blue) to 551 nm (yellow-green). In addition, F-GQDs also exhibit a sensitive fluorescence response to water content in organic solvents, and the ultralow detections limit are 0.056% in ethanol and 0.124% in DMF. Besides, due to strong UV absorption capacity, a photothermal film is fabricated by embedding F-GQDs in PDMS. The temperature of F-GQDs/PDMS polymer film can reach 33.4 oC under simulated sunlight, while the maximum temperature of blank PDMS film only reach 29.4 oC. Based on this phenomenon, a new type of anti-counterfeiting device is designed by combining F-GQDs/PDMS film with temperature change ink.

Promising Fast Energy Transfer System Between Graphene Quantum Dots and the Application in Fluorescent Bioimaging.

Tunable photoluminescence performance of graphene quantum dots (GQDs) is one of the most important topics for the development of GQDs. In this paper, we report lattice-doped GQDs (boron-doped GQDs (B-GQDs) and phosphorus-doped GQDs (P-GQDs)). Because of the matched band structure, the fast energy transfer between blue-emitted B-GQDs (emission wavelength: 460 nm) and orange-emitted P-GQDs (emission wavelength: 630 nm) can induce an efficient fluorescence emission in P-GQDs once B-GQDs are excited under the optimal excitation wavelength of 460 nm. Moreover, with the effective energy transfer, the quantum yield of P-GQDs increased to 0.48, which is much higher than that of pure P-GQDs. We also demonstrated the potentials of this system for fluorescent bioimaging in vitro.

Flexible Transient Phototransistors by Use of Wafer-Compatible Transferred Silicon Nanomembranes.

Flexible transient photodetectors, a form of optoelectronic sensors that can be physically self-destroyed in a controllable manner, could be one of the important components for future transient electronic systems. In this work, a scalable, device-first, and bottom-up thinning process enables the fabrication of a flexible transient phototransistor on a wafer-compatible transferred silicon nanomembrane. A gate modulation significantly restrains the dark current to 10-12 A. With full exposure of the light-sensitive channel, such a device yields an ultrahigh photo-to-dark current ratio of 107 with a responsivity of 1.34 A W-1 (λ = 405 nm). The use of a high-temperature degradable polymer transient interlayer realizes on-demand self-destruction of the fabricated phototransistors, which offers a solution to the technical security issue of advanced flexible electronics. Such demonstration paves a new way for designing transient optoelectronic devices with a wafer-compatible process.

Size-dependent Young's modulus in ZnO nanowires with strong surface atomic bonds.

The mechanical properties of size-dependent nanowires are important in nano-electro-mechanical systems (NEMSs), and have attracted much research interest. Characterization of the size effect of nanowires in atmosphere directly to broaden their practical application instead of just in high vacuum situations, as reported previously, is desperately needed. In this study, we systematically studied the Young's modulus of vertical ZnO nanowires in atmosphere. The diameters ranged from 48 nm to 239 nm with a resonance method using non-contact atomic force microscopy. The values of Young's modulus in atmosphere present extremely strong increasing tendency with decreasing diameter of nanowire due to stronger surface atomic bonds compared with that in vacuum. A core-shell model for nanowires is proposed to explore the Young's modulus enhancement in atmosphere, which is correlated with atoms of oxygen occurring near the nanowire surface. The modified model is more accurate for analyzing the mechanical behavior of nanowires in atmosphere compared with the model in vacuum. Furthermore, it is possible to use this characterization method to measure the size-related elastic properties of similar wire-sharp nanomaterials in atmosphere and estimate the corresponding mechanical behavior. The study of the size-dependent Young's modulus in ZnO nanowires in atmosphere will improve the understanding of the mechanical properties of nanomaterials as well as providing guidance for applications in NEMSs, nanogenerators, biosensors and other related areas.

Deterministic Assembly of Flexible Si/Ge Nanoribbons via Edge-Cutting Transfer and Printing for van der Waals Heterojunctions.

As the promising building blocks for flexible electronics and photonics, inorganic semiconductor nanomembranes have attracted considerable attention owing to their excellent mechanical flexibility and electrical/optical properties. To functionalize these building blocks with complex components, transfer and printing methods in a convenient and precise way are urgently demanded. A combined and controllable approach called edge-cutting transfer method to assemble semiconductor nanoribbons with defined width (down to submicrometer) and length (up to millimeter) is proposed. The transfer efficiency can be comprehended by a classical cantilever model, in which the difference of stress distributions between forth and back edges is investigated using finite element method. In addition, the vertical van der Waals PN (p-Si/n-Ge) junction constructed by a two-round process presents a typical rectifying behavior. The proposed technology may provide a practical, reliable, and cost-efficient strategy for transfer and printing routines, and thus expediting its potential applications for roll-to-roll productions for flexible devices.

Bioinspired Artificial Visual-Respiratory Synapse as Multimodal Scene Recognition System with Oxidized-Vacancies MXene.

In the pursuit of artificial neural systems, the integration of multimodal plasticity, memory retention, and perceptual functions stands as a paramount objective in achieving neuromorphic perceptual components inspired by the human brain, to emulating the neurological excitability tuning observed in human visual and respiratory collaborations. Here, an artificial visual-respiratory synapse is presented with monolayer oxidized MXene (VRSOM) exhibiting synergistic light and atmospheric plasticity. The VRSOM enables to realize facile modulation of synaptic behaviors, encompassing postsynaptic current, sustained photoconductivity, stable facilitation/depression properties, and "learning-experience" behavior. These performances rely on the privileged photocarrier trapping characteristics and the hydroxyl-preferential selectivity inherent of oxidized vacancies. Moreover, environment recognitions and multimodal neural network image identifications are achieved through multisensory integration, underscoring the potential of the VRSOM in reproducing human-like perceptual attributes. The VRSOM platform holds significant promise for hardware output of human-like mixed-modal interactions and paves the way for perceiving multisensory neural behaviors in artificial interactive devices.

Synthesis, Characterization, and in vitro Anti-Inflammatory Activity of Novel Ferrocenyl(Piperazine-1-Yl)Methanone-based Derivatives.

BACKGROUND: Inflammation is closely related to the occurrence and development of various diseases in the clinical scope. Finding effective anti-inflammatory agents is of great significance for clinical treatment. A series of novel ferrocenyl(piperazine-1-yl)methanone-based sulfamides and carboxamides were synthesized to discover potent anti-inflammatory agents. METHODS: The compounds were characterized by 1H NMR, 13C NMR, and MS spectra. Compound 5h was further determined by single crystal X-ray diffraction. All the target compounds were screened for anti-inflammatory activity by evaluating the inhibition effect of LPS-induced NO production in RAW264.7 macrophages. The novel compound (4i) is the preliminary anti-inflammatory mechanism detected by western blot. RESULTS: In a multi-stage screening campaign, compound 4i was shortlisted, which exhibited physicochemical properties suitable for human administration. Among them, compound 4i was found to be most potent in inhibiting NO production (IC50 = 7.65 µM) with low toxicity. This compound also exhibited significant inhibition of the production of iNOS and COX-2. Preliminary mechanism studies indicated that compound 4i could inhibit the activation of the LPS-induced TLR4/NF-κB signaling pathway. CONCLUSION: The promising anti-inflammatory activity of compound 4i compared with the reference drug suggests that this compound may contribute as a lead compound in the search for new potential anti-inflammatory agents.

Wearable, Biodegradable, and Antibacterial Multifunctional Ti3C2Tx MXene/Cellulose Paper for Electromagnetic Interference Shielding and Passive and Active Dual-Thermal Management.

An energy-saving scheme that can simultaneously realize electromagnetic interference (EMI) shielding, passive solar radiative heating, and active Joule heating in a single wearable device is still a huge challenge. Here, by combining the unique properties of Ti3C2Tx MXene and biocompatible cellulose nanofibers (CNFs), a flexible, degradable, and antibacterial multifunctional Ti3C2Tx/CNF paper (∼0.6 Ω/sq) is constructed through a facile vacuum filtration strategy. The resultant device not only exhibits an admirable EMI shielding effectiveness of ∼48.5 dB at the X-band and a superior heating property including dual-driven electrothermal and photothermal conversion without energy but also possesses wide temperature range regulation and long-time stability. More impressively, both high antibacterial efficiency (toward both gram-positive and gram-negative bacteria) and good degradability with low-concentration hydrogen peroxide solution can also be achieved in Ti3C2Tx/CNF papers. This study provides a promising platform for practical applications of multifunctional Ti3C2Tx/CNFs in EMI shielding, thermotherapy, heat preservation, and antibacterial protection in harsh environments, satisfying the demands for energy-saving, environmentally friendly, and sustainable development.

Soft, miniaturized, wireless olfactory interface for virtual reality.

Recent advances in virtual reality (VR) technologies accelerate the creation of a flawless 3D virtual world to provide frontier social platform for human. Equally important to traditional visual, auditory and tactile sensations, olfaction exerts both physiological and psychological influences on humans. Here, we report a concept of skin-interfaced olfactory feedback systems with wirelessly, programmable capabilities based on arrays of flexible and miniaturized odor generators (OGs) for olfactory VR applications. By optimizing the materials selection, design layout, and power management, the OGs exhibit outstanding device performance in various aspects, from response rate, to odor concentration control, to long-term continuous operation, to high mechanical/electrical stability and to low power consumption. Representative demonstrations in 4D movie watching, smell message delivery, medical treatment, human emotion control and VR/AR based online teaching prove the great potential of the soft olfaction interface in various practical applications, including entertainment, education, human machine interfaces and so on.

Accelerable Self-Sintering of Solvent-Free Molybdenum/Wax Biodegradable Composites for Multimodally Transient Electronics.

Biodegradable conductive composites are key materials or components for printable transient electronics that can be fabricated in a low-cost and high-efficiency manner, thereby boosting their wide applications in biomedical engineering, hardware security, and environmental-friendly electronics. Continuous efforts in this area still lie in the development of strategies for highly conductive, safe, and reliable biodegradable conductive composite materials and devices. This paper introduces molybdenum/wax composites for multimodally printable transient electronics in which multiple transience modes including dissolution-induced degradation and thermally triggered degradation are available. Systematic experiments demonstrate several advantages and unique properties of this material system, including solvent-free fabrication, self-sintering behavior, and long-term and high conductivity via accelerable self-sintering treatment and rehealing capabilities. Notably, the immersion of molybdenum/wax composites in phosphate buffer solution can provide both positive effects (accelerated self-sintering-dominated) and negative effects (degradation-dominated) on their electrical conductivities. Mechanism analyses reveal the basis for balancing the degradation and accelerated self-sintering processes. The presented demonstrations foreshadow opportunities of the developed molybdenum/wax composites in rehealable electronics, on-demand smart transient electronics with multiple transience modes, and many other related unusual applications.

Promising energy transfer system between fuorine and nitrogen Co-doped graphene quantum dots and Rhodamine B for ratiometric and visual detection of doxycycline in food.

A novel sensor based on dual emissive fluorescent graphene quantum dots is developed for a rapid, selective, sensitive and visual detection of doxycycline (DOX). The ratiometric fluorescent probe is designed by grafting fluorescent group (Rhodamine B, RhB) on F, N-doped graphene quantum dots (FNGQDs). In the presence of DOX, the fluorescence at 466 nm is remarkably quenched due to inner filter effect and fluorescence resonance energy transfer, whereas the peak at 592 nm is attenuated slightly due to the energy transfer in the emission peaks of FNGQDs and RhB functional group. The sensor shows good linear relationship from 0.04 to 100 µM with a low detection limit of 40 nM. Furthermore, the flexible solid-state fluorescent sensing platform is used for detecting DOX in milk, pork and water samples. Therefore, this dual-emission FGQD-RhB can be used as a high-performance fluorescent and visual sensor for food safety and environmental monitoring.

A Review of the Biological Activities of Heterocyclic Compounds Comprising Oxadiazole Moieties.

The oxadiazole core is considered a privileged moiety in many medicinal chemistry applications. The oxadiazole class includes 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,3,4-oxadiazole, and 1,2,5-oxadiazole. Compounds bearing an oxadiazole ring show a wide range of biological activities, such as anticancer, antibacterial, anti-inflammatory, anti-malarial, and insecticidal properties. Among oxadiazoles, the 1,3,4-oxadiazole has been the most widely explored moiety in medicinal chemistry research. This review is primarily focused on the anticancer, antibacterial, and anti-inflammatory activities of compounds containing 1,2,4-oxadiazole, 1,3,4-oxadiazole and 1,2,5-oxadiazole reported in the last five years.

Monolayer MXene Nanoelectromechanical Piezo-Resonators with 0.2 Zeptogram Mass Resolution.

2D materials-based nanoelectromechanical resonant systems with high sensitivity can precisely trace quantities of ultra-small mass molecules and therefore are broadly applied in biological analysis, chemical sensing, and physical detection. However, conventional optical and capacitive transconductance schemes struggle to measure high-order mode resonant effectively, which is the scientific key to further achieving higher accuracy and lower noise. In the present study, the different vibrations of monolayer Ti3 C2 Tx MXene piezo-resonators are investigated, and achieve a high-order f2,3 resonant mode with a ≈234.59 ± 0.05 MHz characteristic peak due to the special piezoelectrical structure of the Ti3 C2 Tx MXene layer. The effective measurements of signals have a low thermomechanical motion spectral density (9.66 ± 0.01  fmHz$\frac{{fm}}{{\sqrt {Hz} }}$ ) and an extensive dynamic range (118.49 ± 0.42 dB) with sub-zeptograms resolution (0.22 ± 0.01 zg) at 300 K temperature and 1 atm. Furthermore, the functional groups of the Ti3 C2 Tx MXene with unique adsorption properties enable a high working range ratio of ≈3100 and excellent repeatability. This Ti3 C2 Tx MXene device demonstrates encouraging performance advancements over other nano-resonators and will lead the related engineering applications including high-sensitivity mass detectors.

Recent Progress on Bioresorbable Passive Electronic Devices and Systems.

Bioresorbable electronic devices and/or systems are of great appeal in the field of biomedical engineering due to their unique characteristics that can be dissolved and resorbed after a predefined period, thus eliminating the costs and risks associated with the secondary surgery for retrieval. Among them, passive electronic components or systems are attractive for the clear structure design, simple fabrication process, and ease of data extraction. This work reviews the recent progress on bioresorbable passive electronic devices and systems, with an emphasis on their applications in biomedical engineering. Materials strategies, device architectures, integration approaches, and applications of bioresorbable passive devices are discussed. Furthermore, this work also overviews wireless passive systems fabricated with the combination of various passive components for vital sign monitoring, drug delivering, and nerve regeneration. Finally, we conclude with some perspectives on future fundamental studies, application opportunities, and remaining challenges of bioresorbable passive electronics.

High-Performance and Reliable Silver Nanotube Networks for Efficient and Large-Scale Transparent Electromagnetic Interference Shielding.

The development of flexible and transparent electromagnetic interference (EMI) shielding materials with excellent comprehensive properties is urgently demanded as visual windows and display devices in aeronautic, industry, medical, and research facilities. However, the method of how to obtain highly efficient and reliable transparent EMI shielding devices is still facing lots of obstacles. Here, a high-performance silver nanotube (AgNT) network with stable and integrated interconnects is prepared by physical depositing technology, based on a uniform and large-scale nanofiber skeleton. This unique structure enables the AgNT network to achieve one order higher conductivity (∼1.0 Ω/sq at >90% transmittance) than previous research studies and keeps <10% variation with random deformations (>5000 times). Moreover, the manufactured AgNT shielding film with a thickness of less than 1 mm can be easily transferred to arbitrary surfaces as a transparent and flexible EMI shielding film at commercial ∼35 dB EMI shielding effectiveness, with large-scale, low-cost, and simple preparation processes. These excellent properties endow the AgNT shielding film to achieve great potential for future flexible and transparent scenarios.

Synthesis of multi-color fluorine and nitrogen co-doped graphene quantum dots for use in tetracycline detection, colorful solid fluorescent ink, and film.

Fluorine-doped graphene quantum dots have unique chemical bonds and charge distribution, which can bring unexpected properties compared to other common atom-doped graphene quantum dots. In the present work, fluorine and nitrogen co-doped graphene quantum dots (F, N-GQDs) are synthesized from levofloxacin via a simple hydrothermal method. Systematic studies demonstrate that F, N-GQDs can emit various fluorescence with the wavelength ranging from blue to green by dispersing F, N-GQDs into different solvents. Moreover, multi-color fluorescence is available by simply changing the concentration of F, N-GQDs. In addition to these unique characteristics, F, N-GQDs also exhibit a sensitive fluorescence response to tetracycline with an ultralow detection limit of 77 nM in water. Because of high photostability and high quantum yield, the F, N-GQDs are exploited as a unique invisible ink, which is printable and writable on paper. Meanwhile, based on the solvatochromism of F, N-GQDs, we realized the color adjustable fluorescent ink. Finally, large-area flexible multi-color fluorescent films are realized. Our synthesized F, N-GQDs, with tunable fluorescence in wavelength and intensity, have numerous opportunities for optical molecular sensors, information security, flexible optics, and others.