A three-dimensional liquid diode for soft, integrated permeable electronics.

Wearable electronics with great breathability enable a comfortable wearing experience and facilitate continuous biosignal monitoring over extended periods1-3. However, current research on permeable electronics is predominantly at the stage of electrode and substrate development, which is far behind practical applications with comprehensive integration with diverse electronic components (for example, circuitry, electronics, encapsulation)4-8. Achieving permeability and multifunctionality in a singular, integrated wearable electronic system remains a formidable challenge. Here we present a general strategy for integrated moisture-permeable wearable electronics based on three-dimensional liquid diode (3D LD) configurations. By constructing spatially heterogeneous wettability, the 3D LD unidirectionally self-pumps the sweat from the skin to the outlet at a maximum flow rate of 11.6 ml cm-2 min-1, 4,000 times greater than the physiological sweat rate during exercise, presenting exceptional skin-friendliness, user comfort and stable signal-reading behaviour even under sweating conditions. A detachable design incorporating a replaceable vapour/sweat-discharging substrate enables the reuse of soft circuitry/electronics, increasing its sustainability and cost-effectiveness. We demonstrated this fundamental technology in both advanced skin-integrated electronics and textile-integrated electronics, highlighting its potential for scalable, user-friendly wearable devices.

Three-dimensional electronic microfliers inspired by wind-dispersed seeds.

Large, distributed collections of miniaturized, wireless electronic devices1,2 may form the basis of future systems for environmental monitoring3, population surveillance4, disease management5 and other applications that demand coverage over expansive spatial scales. Aerial schemes to distribute the components for such networks are required, and-inspired by wind-dispersed seeds6-we examined passive structures designed for controlled, unpowered flight across natural environments or city settings. Techniques in mechanically guided assembly of three-dimensional (3D) mesostructures7-9 provide access to miniature, 3D fliers optimized for such purposes, in processes that align with the most sophisticated production techniques for electronic, optoelectronic, microfluidic and microelectromechanical technologies. Here we demonstrate a range of 3D macro-, meso- and microscale fliers produced in this manner, including those that incorporate active electronic and colorimetric payloads. Analytical, computational and experimental studies of the aerodynamics of high-performance structures of this type establish a set of fundamental considerations in bio-inspired design, with a focus on 3D fliers that exhibit controlled rotational kinematics and low terminal velocities. An approach that represents these complex 3D structures as discrete numbers of blades captures the essential physics in simple, analytical scaling forms, validated by computational and experimental results. Battery-free, wireless devices and colorimetric sensors for environmental measurements provide simple examples of a wide spectrum of applications of these unusual concepts.

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.

Highly stretchable organic electrochemical transistors with strain-resistant performance.

Realizing fully stretchable electronic materials is central to advancing new types of mechanically agile and skin-integrable optoelectronic device technologies. Here we demonstrate a materials design concept combining an organic semiconductor film with a honeycomb porous structure with biaxially prestretched platform that enables high-performance organic electrochemical transistors with a charge transport stability over 30-140% tensional strain, limited only by metal contact fatigue. The prestretched honeycomb semiconductor channel of donor-acceptor polymer poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-diketo-pyrrolopyrrole-alt-2,5-bis(3-triethyleneglycoloxy-thiophen-2-yl) exhibits high ion uptake and completely stable electrochemical and mechanical properties over 1,500 redox cycles with 104 stretching cycles under 30% strain. Invariant electrocardiogram recording cycles and synapse responses under varying strains, along with mechanical finite element analysis, underscore that the present stretchable organic electrochemical transistor design strategy is suitable for diverse applications requiring stable signal output under deformation with low power dissipation and mechanical robustness.

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.

Implantable Electronic Medicine Enabled by Bioresorbable Microneedles for Wireless Electrotherapy and Drug Delivery.

A combined treatment using medication and electrostimulation increases its effectiveness in comparison with one treatment alone. However, the organic integration of two strategies in one miniaturized system for practical usage has seldom been reported. This article reports an implantable electronic medicine based on bioresorbable microneedle devices that is activated wirelessly for electrostimulation and sustainable delivery of anti-inflammatory drugs. The electronic medicine is composed of a radio frequency wireless power transmission system and a drug-loaded microneedle structure, all fabricated with bioresorbable materials. In a rat skeletal muscle injury model, periodic electrostimulation regulates cell behaviors and tissue regeneration while the anti-inflammatory drugs prevent inflammation, which ultimately enhance the skeletal muscle regeneration. Finally, the electronic medicine is fully bioresorbable, excluding the second surgery for device removal.

[Application of electronic skin in healthcare and virtual reality].

Electronic skin has shown great application potential in many fields such as healthcare monitoring and human-machine interaction due to their excellent sensing performance, mechanical properties and biocompatibility. This paper starts from the materials selection and structures design of electronic skin, and summarizes their different applications in the field of healthcare equipment, especially current development status of wearable sensors with different functions, as well as the application of electronic skin in virtual reality. The challenges of electronic skin in the field of wearable devices and healthcare, as well as our corresponding strategies, are discussed to provide a reference for further advancing the research of electronic skin.

Photocurable bioresorbable adhesives as functional interfaces between flexible bioelectronic devices and soft biological tissues.

Flexible electronic/optoelectronic systems that can intimately integrate onto the surfaces of vital organ systems have the potential to offer revolutionary diagnostic and therapeutic capabilities relevant to a wide spectrum of diseases and disorders. The critical interfaces between such technologies and living tissues must provide soft mechanical coupling and efficient optical/electrical/chemical exchange. Here, we introduce a functional adhesive bioelectronic-tissue interface material, in the forms of mechanically compliant, electrically conductive, and optically transparent encapsulating coatings, interfacial layers or supporting matrices. These materials strongly bond both to the surfaces of the devices and to those of different internal organs, with stable adhesion for several days to months, in chemistries that can be tailored to bioresorb at controlled rates. Experimental demonstrations in live animal models include device applications that range from battery-free optoelectronic systems for deep-brain optogenetics and subdermal phototherapy to wireless millimetre-scale pacemakers and flexible multielectrode epicardial arrays. These advances have immediate applicability across nearly all types of bioelectronic/optoelectronic system currently used in animal model studies, and they also have the potential for future treatment of life-threatening diseases and disorders in humans.

Metal ion chelation enhances tissue plasminogen activator (tPA)-induced thrombolysis: an in vitro and in vivo study.

Stroke is the third leading cause of death in the United States and the leading cause of adult disability. Despite enormous research efforts including many clinical trials, tissue plasminogen activator (tPA) remains the only FDA-approved treatment for acute ischemic stroke. Unfortunately, only 1-3% of stroke patients in the US receive this therapy because of the narrow time window and severe side effects for using tPA. The most deadly and damaging side effect is the risk of intracranial bleeding or hemorrhage. For that reason, the dose of tPA and its overall administration are under tight control, which may compromise the effect of thrombolysis. Studies have been focused on improving the effectiveness of tPA for higher rate of reperfusion, and the safety for less adverse bleeding episode. We studied how metal ions (zinc & iron) affect tPA-induced thrombolysis in vitro and in vivo, and proposed a method to improve the rate of thrombolysis. The amount of hemoglobin in the blood clot lysis was measured by a spectrophotometer. The tPA-induced thrombolysis was measured in vivo in femoral artery. Our results showed that Zn2+, Fe3+ and Fe2+ inhibited tPA-induced thrombolysis, with Zn2+ and Fe2+ being the most effective. Metal ion chelating agent EDTA when it was co-applied with tPA significantly enhanced the tPA-induced thrombolysis. The chelation alone did not have noticeable thrombolytic effect. In in vivo study of tPA-induced thrombosis following femoral artery thrombosis, the co-application of tPA and EDTA achieved significant higher rate of reperfusion than that by tPA treatment alone, suggesting that ion chelation facilitates tPA-induced thrombolysis and potentially improves the safety of tPA application by reducing the necessary dose of tPA application. Our results suggest that the co-application of a chelator and tPA improves the efficacy and, potentially, safety of tPA application, by reducing the necessary dose of tPA for thrombolysis.

Gold nanorods doping induced performance improvement of room temperature OTFT NO2sensors.

Solution-processed organic thin-film transistors (OTFTs) are regarded as the promising candidates for low-cost gas sensors due to their advantages of high throughput, large-area and sensitive to various gas analytes. Microstructure control of organic active layers in OTFTs is an effective route to improve the sensing performance. In this work, we report a simple method to modify the morphology of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) thin films via doping gold nanorods (Au NRs) for enhancing the performance of the corresponding OTFT sensors for nitrogen dioxide (NO2) detection. With the optimized doping ratio of Au nanorods, the TIPS-pentacene OTFT snesors not only exhibit a 3-fold increase in mobility, but also obtain a high sensitivity of 70% to 18 ppm NO2with a detection limit of 270 ppb. The microstructures and morphologies of the modified TIPS-pentacene thin film characterized by atomic force microscopy and field scanning electron microscope. The experimental results indicate that the proper addition of Au NRs could effectively regulate the grain size of TIPS-pentacene, and therein control the density of grain boundaries during the crystallization, which is essential for the high-performance gas sensors.

Relation between blood pressure and pulse wave velocity for human arteries.

Continuous monitoring of blood pressure, an essential measure of health status, typically requires complex, costly, and invasive techniques that can expose patients to risks of complications. Continuous, cuffless, and noninvasive blood pressure monitoring methods that correlate measured pulse wave velocity (PWV) to the blood pressure via the Moens-Korteweg (MK) and Hughes Equations, offer promising alternatives. The MK Equation, however, involves two assumptions that do not hold for human arteries, and the Hughes Equation is empirical, without any theoretical basis. The results presented here establish a relation between the blood pressure P and PWV that does not rely on the Hughes Equation nor on the assumptions used in the MK Equation. This relation degenerates to the MK Equation under extremely low blood pressures, and it accurately captures the results of in vitro experiments using artificial blood vessels at comparatively high pressures. For human arteries, which are well characterized by the Fung hyperelastic model, a simple formula between P and PWV is established within the range of human blood pressures. This formula is validated by literature data as well as by experiments on human subjects, with applicability in the determination of blood pressure from PWV in continuous, cuffless, and noninvasive blood pressure monitoring systems.

Materials and processing approaches for foundry-compatible transient electronics.

Foundry-based routes to transient silicon electronic devices have the potential to serve as the manufacturing basis for "green" electronic devices, biodegradable implants, hardware secure data storage systems, and unrecoverable remote devices. This article introduces materials and processing approaches that enable state-of-the-art silicon complementary metal-oxide-semiconductor (CMOS) foundries to be leveraged for high-performance, water-soluble forms of electronics. The key elements are (i) collections of biodegradable electronic materials (e.g., silicon, tungsten, silicon nitride, silicon dioxide) and device architectures that are compatible with manufacturing procedures currently used in the integrated circuit industry, (ii) release schemes and transfer printing methods for integration of multiple ultrathin components formed in this way onto biodegradable polymer substrates, and (iii) planarization and metallization techniques to yield interconnected and fully functional systems. Various CMOS devices and circuit elements created in this fashion and detailed measurements of their electrical characteristics highlight the capabilities. Accelerated dissolution studies in aqueous environments reveal the chemical kinetics associated with the underlying transient behaviors. The results demonstrate the technical feasibility for using foundry-based routes to sophisticated forms of transient electronic devices, with functional capabilities and cost structures that could support diverse applications in the biomedical, military, industrial, and consumer industries.

3D printed microstructures for flexible electronic devices.

Flexible and stretchable electronics have attracted increasing attention and been widely used in wearable devices and electronic skins, where the circuits for flexible and stretchable electronics are typically in-plane-based 2D geometries. Here, we introduce a 3D microprinting technology that can expand one more dimension of the circuit in flexible electronics. We fabricated three-dimensional serpentine microstructures based on direct laser writing. These microstructures with a thin metal coated layer can be used as stretchable conducting meshes. Soft silicone serving as a substrate and encapsulations for these 3D microstructures enables great light transmittance (>90% in visible light range) and flexibility with 114° bending and 24° twisting. Further optimization of the mechanical design of the 3D microstructures can also enhance the stretchability up to 13.8%. These results indicate 3D flexible electronics can be realized by simple microprinting methods. Furthermore, 3D microprinting would also allow for the precise fabrication of other 3D structures, such as mechanically active 3D mesostructures, for the function of mechanical and electrical testing.

Vibration of Mechanically-Assembled 3D Microstructures Formed by Compressive Buckling.

Micro-electromechanical systems (MEMS) that rely on structural vibrations have many important applications, ranging from oscillators and actuators, to energy harvesters and vehicles for measurement of mechanical properties. Conventional MEMS, however, mostly utilize two-dimensional (2D) vibrational modes, thereby imposing certain limitations that are not present in 3D designs (e.g., multi-directional energy harvesting). 3D vibrational microplatforms assembled through the techniques of controlled compressive buckling are promising because of their complex 3D architectures and the ability to tune their vibrational behaviour (e.g., natural frequencies and modes) by reversibly changing their dimensions by deforming their soft, elastomeric substrates. A clear understanding of such strain-dependent vibration behaviour is essential for their practical applications. Here, we present a study on the linear and nonlinear vibration of such 3D mesostructures through analytical modeling, finite element analysis (FEA) and experiment. An analytical solution is obtained for the vibration mode and linear natural frequency of a buckled ribbon, indicating a mode change as the static deflection amplitude increases. The model also yields a scaling law for linear natural frequency that can be extended to general, complex 3D geometries, as validated by FEA and experiment. In the regime of nonlinear vibration, FEA suggests that an increase of amplitude of external loading represents an effective means to enhance the bandwidth. The results also uncover a reduced nonlinearity of vibration as the static deflection amplitude of the 3D structures increases. The developed analytical model can be used in the development of new 3D vibrational microplatforms, for example, to enable simultaneous measurement of diverse mechanical properties (density, modulus, viscosity etc.) of thin films and biomaterials.

Spray-combustion synthesis: efficient solution route to high-performance oxide transistors.

Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations.

Three-Dimensional Multiscale, Multistable, and Geometrically Diverse Microstructures with Tunable Vibrational Dynamics Assembled by Compressive Buckling.

Microelectromechanical systems remain an area of significant interest in fundamental and applied research due to their wide ranging applications. Most device designs, however, are largely two-dimensional and constrained to only a few simple geometries. Achieving tunable resonant frequencies or broad operational bandwidths requires complex components and/or fabrication processes. The work presented here reports unusual classes of three-dimensional (3D) micromechanical systems in the form of vibratory platforms assembled by controlled compressive buckling. Such 3D structures can be fabricated across a broad range of length scales and from various materials, including soft polymers, monocrystalline silicon, and their composites, resulting in a wide scope of achievable resonant frequencies and mechanical behaviors. Platforms designed with multistable mechanical responses and vibrationally de-coupled constituent elements offer improved bandwidth and frequency tunability. Furthermore, the resonant frequencies can be controlled through deformations of an underlying elastomeric substrate. Systematic experimental and computational studies include structures with diverse geometries, ranging from tables, cages, rings, ring-crosses, ring-disks, two-floor ribbons, flowers, umbrellas, triple-cantilever platforms, and asymmetric circular helices, to multilayer constructions. These ideas form the foundations for engineering designs that complement those supported by conventional, microelectromechanical systems, with capabilities that could be useful in systems for biosensing, energy harvesting and others.

Metal oxides for optoelectronic applications.

Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III-V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p-n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Bithiophenesulfonamide Building Block for π-Conjugated Donor-Acceptor Semiconductors.

We report here π-conjugated small molecules and polymers based on the new π-acceptor building block, bithiophenesulfonamide (BTSA). Molecular orbital computations and optical, electrochemical, and crystal structure analyses illuminate the architecture and electronic structure of the BTSA unit versus other acceptor building blocks. Field-effect transistors and photovoltaic cells demonstrate that BTSA is a promising unit for the construction of π-conjugated semiconducting materials.

Zebrafish (Danio rerio) Developed as an Alternative Animal Model for Focal Ischemic Stroke.

Thrombotic cerebral ischemia is one of the leading causes of mortality and chronic disability. Animal models provide an essential tool for understanding the complex cellular and molecular pathophysiology of ischemia and for improving treatment and testing novel neuroprotective drugs in the preclinical setting. In this study, we tested zebrafish as a novel model for thrombotic ischemic brain damage. Zebrafish were intraperitoneally injected with Rose Bengal and light exposure was directed onto the optic tectum region of the brain to induce photothrombosis. After full recovery from anesthesia, zebrafish consistently exhibited abnormal swimming patterns, indicating brain injury from the procedure. The staining of 2,3,5-triphenyltetrazolium chloride (TTC) 24 h after the treatment showed lack of staining of the exposed area of the brain, which further confirmed the ischemic injury. Application of Activase®-tPA improved viability of the brain. The tPA treatment also reduced the occurrence of moving disability as well as the mortality rate, demonstrating that the zebrafish model not only showed focal ischemic injury but also responded well to tPA therapy. Our results suggest that the current photothrombotic method induced focal ischemia in zebrafish and produced consistent brain damage that can be measured by behavioral changes and quantified by histological staining.

Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4-c]pyrrole-4,6-dione and Bithiopheneimide Photovoltaic Copolymers.

As effective building blocks for high-mobility transistor polymers, oligothiophenes are receiving attention for polymer solar cells (PSCs) because the resulting polymers can effectively suppress charge recombination. Here we investigate two series of in-chain donor-acceptor copolymers, PTPDnT and PBTInT, based on thieno[3,4-c]pyrrole-4,6-dione (TPD) or bithiopheneimide (BTI) as electron acceptor units, respectively, and oligothiophenes (nTs) as donor counits, for high-performance PSCs. Intramolecular S···O interaction leads to more planar TPD polymer backbones, however backbone torsion yields greater open-circuit voltages for BTI polymers. Thiophene addition progressively raises polymer HOMOs but marginally affects their band gaps. FT-Raman spectra indicate that PTPDnT and PBTInT conjugation lengths scale with nT catenation up to n = 3 and then saturate for longer oligomer. Furthermore, the effects of oligothiophene alkylation position are explored, revealing that the alkylation pattern greatly affects film morphology and PSC performance. The 3T with "outward" alkylation in PTPD3T and PBTI3T affords optimal π-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm(2)/(V s)). These characteristics contribute to the exceptional ∼80% fill factors for PTPD3T-based PSCs with PCE = 7.7%. The results demonstrate that 3T is the optimal donor unit among nTs (n = 1-4) for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering, transmission electron microscopy, and time-resolved microwave conductivity measurements reveal that the terthiophene-based PTPD3T blend maintains high crystallinity with appreciable local mobility and long charge carrier lifetime. These results provide fundamental materials structure-device performance correlations and suggest guidelines for designing oligothiophene-based polymers with optimal thiophene catenation and appropriate alkylation pattern to maximize PSC performance.