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Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Wireless power transfer can significantly extend the application range and service life of implantable medical devices, such as pacemakers, neurostimulators, and vascular applicators. However, existing transmission schemes are faced with shortcomings such as weak power, discontinuity, or impact on human health. Here, we design a subcutaneously implantable flexible ultrasound energy harvesting system that integrates a triboelectric nanogenerator (TENG) transducer and a power management circuit into a single flexible printed circuit board. We maximize the TENG transducer performance by choosing an attached-electrode TENG with optimized structural parameters, which offers 66% higher output power and lower impedance than the existing work. Such a flexible system shows broad applications in various environments. It can successfully provide a stable direct current voltage of 1.8 V with >1 mW continuous DC output power and >10 mW instantaneous power, which is sufficient to continuously drive various sensor systems, operate micromotors, and apply nerve stimulation.

Neurotransmitters play essential roles in regulating neural circuit dynamics both in the central nervous system as well as at the peripheral, including the gastrointestinal tract1–3. Their real-time monitoring will offer critical information for understanding neural function and diagnosing disease1–3. However, bioelectronic tools to monitor the dynamics of neurotransmitters in vivo, especially in the enteric nervous systems, are underdeveloped. This is mainly owing to the limited availability of biosensing tools that are capable of examining soft, complex and actively moving organs. Here we introduce a tissue-mimicking, stretchable, neurochemical biological interface termed NeuroString, which is prepared by laser patterning of a metal-complexed polyimide into an interconnected graphene/nanoparticle network embedded in an elastomer. NeuroString sensors allow chronic in vivo real-time, multichannel and multiplexed monoamine sensing in the brain of behaving mouse, as well as measuring serotonin dynamics in the gut without undesired stimulations and perturbing peristaltic movements. The described elastic and conformable biosensing interface has broad potential for studying the impact of neurotransmitters on gut microbes, brain–gut communication and may ultimately be extended to biomolecular sensing in other soft organs across the body.

Next-generation light-emitting displays on skin should be soft, stretchable and bright1–7. Previously reported stretchable light-emitting devices were mostly based on inorganic nanomaterials, such as light-emitting capacitors, quantum dots or perovskites6–11. They either require high operating voltage or have limited stretchability and brightness, resolution or robustness under strain. On the other hand, intrinsically stretchable polymer materials hold the promise of good strain tolerance12,13. However, realizing high brightness remains a grand challenge for intrinsically stretchable light-emitting diodes. Here we report a material design strategy and fabrication processes to achieve stretchable all-polymer-based light-emitting diodes with high brightness (about 7,450 candela per square metre), current efficiency (about 5.3 candela per ampere) and stretchability (about 100 per cent strain). We fabricate stretchable all-polymer light-emitting diodes coloured red, green and blue, achieving both on-skin wireless powering and real-time displaying of pulse signals. This work signifies a considerable advancement towards high-performance stretchable displays.

Skin-like intrinsically stretchable soft electronic devices are essential to realize next-generation remote and preventative medicine for advanced personal healthcare1–4. The recent development of intrinsically stretchable conductors and semiconductors has enabled highly mechanically robust and skin-conformable electronic circuits or optoelectronic devices2,5–10. However, their operating frequencies have been limited to less than 100 hertz, which is much lower than that required for many applications. Here we report intrinsically stretchable diodes—based on stretchable organic and nanomaterials—capable of operating at a frequency as high as 13.56 megahertz. This operating frequency is high enough for the wireless operation of soft sensors and electrochromic display pixels using radiofrequency identification in which the base-carrier frequency is 6.78 megahertz or 13.56 megahertz. This was achieved through a combination of rational material design and device engineering. Specifically, we developed a stretchable anode, cathode, semiconductor and current collector that can satisfy the strict requirements for high-frequency operation. Finally, we show the operational feasibility of our diode by integrating it with a stretchable sensor, electrochromic display pixel and antenna to realize a stretchable wireless tag. This work is an important step towards enabling enhanced functionalities and capabilities for skin-like wearable electronics.

An unstable mechanical structure that can self-balance when perturbed is a superior choice for vibration energy harvesting and vibration detection. In this work, a suspended 3D spiral structure is integrated with a triboelectric nanogenerator (TENG) for energy harvesting and sensor applications. The newly designed vertical contact–separation mode TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m2on a load of 6 MΩ. The position of an in-plane vibration source was identified by placing TENGs at multiple positions as multichannel, self-powered active sensors, and the location of the vibration source was determined with an error less than 6%. The magnitude of the vibration is also measured by the output voltage and current signal of the TENG. By integrating the TENG inside a buoy ball, wave energy harvesting at water surface has been demonstrated and used for lighting illumination light, which shows great potential applications in marine science and environmental/infrastructure monitoring.

Skin-like electronics that can adhere seamlessly to human skin or within the body are highly desirable for applications such as health monitoring, medical treatment, medical implants and biological studies, and for technologies that include human–machine interfaces, soft robotics and augmented reality. Rendering such electronics soft and stretchable—like human skin—would make them more comfortable to wear, and, through increased contact area, would greatly enhance the fidelity of signals acquired from the skin. Structural engineering of rigid inorganic and organic devices has enabled circuit-level stretchability, but this requires sophisticated fabrication techniques and usually suffers from reduced densities of devices within an array. We reasoned that the desired parameters, such as higher mechanical deformability and robustness, improved skin compatibility and higher device density, could be provided by using intrinsically stretchable polymer materials instead. However, the production of intrinsically stretchable materials and devices is still largely in its infancy: such materials have been reported, but functional, intrinsically stretchable electronics have yet to be demonstrated owing to the lack of a scalable fabrication technology. Here we describe a fabrication process that enables high yield and uniformity from a variety of intrinsically stretchable electronic polymers. We demonstrate an intrinsically stretchable polymer transistor array with an unprecedented device density of 347 transistors per square centimetre. The transistors have an average charge-carrier mobility comparable to that of amorphous silicon, varying only slightly (within one order of magnitude) when subjected to 100 per cent strain for 1,000 cycles, without current–voltage hysteresis. Our transistor arrays thus constitute intrinsically stretchable skin electronics, and include an active matrix for sensory arrays, as well as analogue and digital circuit elements. Our process offers a general platform for incorporating other intrinsically stretchable polymer materials, enabling the fabrication of next-generation stretchable skin electronic devices.

A bioinspired soft and stretchable triboelectric nanogenerator (TENG) is developed as energy-harvesting skin to drive personal electronics by scavenging biomechanical energy. Drawn inspiration from biological cells, the TENG consists of patterned interconnected cellular structures, with physiological saline as the electrode and silicone rubber as the encapsulation and triboelectric layer. The TENG can withstand a strain of 600% and has a transmittance of as high as 62.5%. The TENG can keep its high performance under various strain. The TENG also has the desirable features of biocompatibility, simple fabrication, light weight and environmental protection. The maximum instantaneous power density (2.3Hz) and direct current power density of the TENG are ~ 11.6W/m2and ~ 2.65mW/m2respectively. Mounted on the skin, the TENG integrating with a power management unit can sustainably drive an electronic watch sorely by harvesting energy from hand motion. A stretchable self-charging power unit with a TENG and a micro supercapacitor sharing the same solution is created, with the solution as both the electrode of the TENG and the electrolyte of the supercapacitor. This work opens up new insights for clean power sources of skin-mounted electronics and promotes the development of sustainable energy supply for wearable and portable electronics.

Vibration is one of the most common energy sources in ambient environment. Harvesting vibration energy is a promising route to sustainably drive small electronics. This work introduces an approach to scavenge vibrational energy over a wide frequency range as an exclusive power source for continuous operation of electronics. An elastic multiunit triboelectric nanogenerator (TENG) is rationally designed to efficiently harvest low-frequency vibration energy, which can provide a maximum instantaneous output power density of 102 W·m–3at as low as 7 Hz and maintain its stable current outputs from 5 to 25 Hz. A self-charging power unit (SCPU) combining the TENG and a 10 mF supercapacitor gives a continuous direct current (DC) power delivery of 1.14 mW at a power management efficiency of 45.6% at 20 Hz. The performance of the SCPU can be further enhanced by a specially designed power management circuit, with a continuous DC power of 2 mW and power management efficiency of 60% at 7 Hz. Electronics such as a thermometer, hygrometer, and speedometer can be sustainably powered solely by the harvested vibration energy from a machine or riding bicycle. This approach has potential applications in self-powered systems for environment monitoring, machine safety, and transportation.

A soft, stretchable, and fully enclosed self-charging power system is developed by seamlessly combining a stretchable triboelectric nanogenerator with stretchable supercapacitors, which can be subject to and harvest energy from almost all kinds of large-degree deformation due to its fully soft structure. The power system is washable and waterproof owing to its fully enclosed structure and hydrophobic property of its exterior surface. The power system can be worn on the human body to effectively scavenge energy from various kinds of human motion, and it is demonstrated that the wearable power source is able to drive an electronic watch. This work provides a feasible approach to design stretchable, wearable power sources and electronics.

Wurtzite structured mateirals such as ZnO, GaN, InN and CdS simultaneously exhibit piezoelectric, semiconducting and photoexcitation properties. The piezotronic effect is to use the inner crystal potential generated by piezoelectric polarization charges for controlling/tuning the charge carrier transport characteristics in these materials. The piezo-phototronic effect is about the use of piezoelectric charges to tube the generation, transport, separation and/or recombination of charge carriers at p-n junction. This article reviews the fundamental theories of piezotronics and piezo-phototronics, forming their basis for electromechancial devices, sensors and energy sciences. Starting from the basic equations for piezoelectricity, semiconductor and photoexcitation, analytical equations for describing the strain-tuned device current were derived. Through analytical calculations and numerical simulations, it was confirmed that the piezoelectric polarization charges can act in the form of inner-crystal charges in the depletion region, resulting in a change in Schottky barrier height, depletion region shift and/or formation of a charge channel, which can be used effectively to enhance the efficiency of LED, solar cell and photon detectors.

In this review, we systematically analyze the enhanced performances of Schottky-structured nanowire sensors by the piezotronic effect. Compared with traditional Ohmic-contact nanowire sensing systems, Schottky-contact provides ultra-high sensitivity and superfast response depending on the barrier height at local metal–semiconductor (M–S) interface. Utilizing the strain-induced piezoelectric polarization charges presented at the vicinity of M–S contact, piezotronic effect is applied to tune/control the charge carriers transport process through the interface by modulating the Schottky barrier height (SBH) at local contact, and thus hugely enhances the performances of Schottky-structured sensors. Our results indicate that piezotronic effect is a universal effect that provides an effective approach to improve the sensitivity, resolution, response time and other general properties of Schottky-contact nanowire sensors in different categories, including bio/chemical sensing, gas sensing, humidity sensing, temperature sensing and others.

Triboelectric nanogenerator (TENG) technology based on contact electrification and electrostatic induction is an emerging new mechanical energy harvesting technology with numerous advantages. The current area power density of TENGs has reached 313W/m2and their volume energy density has reached 490kW/m3. In this review, we systematically analyzed the theoretical system of triboelectric nanogenerators. Starting from the physics of TENGs, we thoroughly discussed their fundamental working principle and simulation method. Then the intrinsic output characteristics, load characteristics, and optimization strategy is in-depth discussed. TENGs have inherent capacitive behavior and their governing equation is their V–Q–xrelationship. There are two capacitance formed between the tribo-charged dielectric surface and the two metal electrodes, respectively. The ratio of these two capacitances changes with the position of this dielectric surface, inducing electrons to transfer between the metal electrodes under short circuit conditions. This is the core working mechanism of triboelectric generators and different TENG fundamental modes can be classified based on the changing behavior of these two capacitances. Their first-order lumped-parameter equivalent circuit model is a voltage source in series with a capacitor. Their resistive load characteristics have a “three-working-region” behavior because of the impedance match mechanism. Besides, when TENGs are utilized to charge a capacitor with a bridge rectifier in multiple motion cycles, it is equivalent to utilizing a constant DC voltage source with an internal resistance to charge. The optimization techniques for all TENG fundamental modes are also discussed in detail. The theoretical system reviewed in this work provides a theoretical basis of TENGs and can be utilized as a guideline for TENG designers to continue improving TENG output performance.

With 70% of the earth’s surface covered with water, wave energy is abundant and has the potential to be one of the most environmentally benign forms of electric energy. However, owing to lack of effective technology, water wave energy harvesting is almost unexplored as an energy source. Here, we report a network design made of triboelectric nanogenerators (TENGs) for large-scale harvesting of kinetic water energy. Relying on surface charging effect between the conventional polymers and very thin layer of metal as electrodes for each TENG, the TENG networks (TENG-NW) that naturally float on the water surface convert the slow, random, and high-force oscillatory wave energy into electricity. On the basis of the measured output of a single TENG, the TENG-NW is expected to give an average power output of 1.15 MW from 1 km2surface area. Given the compelling features, such as being lightweight, extremely cost-effective, environmentally friendly, easily implemented, and capable of floating on the water surface, the TENG-NW renders an innovative and effective approach toward large-scale blue energy harvesting from the ocean.

Triboelectric nanogenerator technology is emerging as a promising candidate for mechanical energy harvesting from ambient environment. Freestanding triboelectric-layer-based nanogenerators (FTENGs) are one of the fundamental operation modes with many advantages. In this paper, the first theoretical model of FTENGs is proposed with thorough analysis of their operation principle. Both contact-mode and sliding-mode FTENGs are discussed to fully uncover their unique characteristics. Contact-mode FTENGs have superior linearity, which is highly beneficial for both energy-harvesting and self-powered sensing applications. Sliding-mode FTENGs have two subcategories based on the material of their freestanding layer. For both of the two subcategories, the coupling effect of the height of the freestanding layer and the electrode gap on their output characteristics are discussed in detail to obtain the strategy for their structural optimization.

In comparison to in-pane sliding friction, rolling friction not only is likely to consume less mechanical energy but also presents high robustness with minimized wearing of materials. In this work, we introduce a highly efficient approach for harvesting mechanical energy based on rolling electrification and electrostatic induction, aiming at improving the energy conversion efficiency and device durability. The rolling triboelectric nanogenerator is composed of multiple steel rods sandwiched by two fluorinated ethylene propylene (FEP) thin films. The rolling motion of the steel rods between the FEP thin films introduces triboelectric charges on both surfaces and leads to the change of potential difference between each pair of electrodes on back of the FEP layer, which drives the electrons to flow in the external load. As power generators, each pair of output terminals works independently and delivers an open-circuit voltage of 425 V, and a short-circuit current density of 5 mA/m2. The two output terminals can also be integrated to achieve an overall power density of up to 1.6 W/m2. The impacts of variable structural factors were investigated for optimization of the output performance, and other prototypes based on rolling balls were developed to accommodate different types of mechanical energy sources. Owing to the low frictional coefficient of the rolling motion, an instantaneous energy conversion efficiency of up to 55% was demonstrated and the high durability of the device was confirmed. This work presents a substantial advancement of the triboelectric nanogenerators toward large-scope energy harvesting and self-powered systems.

A vibration sensor is usually designed to measure the vibration frequency but disregard the vibration amplitude, which is rather challenging to be quantified due to the requirement of linear response. Here, we show the application of triboelectric nanogenerator (TENG) as a self-powered tool for quantitative measurement of vibration amplitude based on an operation mode, the contact-mode freestanding triboelectric nanogenerator (CF-TENG). In this mode, the triboelectrically charged resonator can be agitated to vibrate between two stacked stationary electrodes. Under the working principle with a constant capacitance between two electrodes, the amplitudes of the electric signals are proportional to the vibration amplitude of the resonator (provided that the resonator plate is charged to saturation), which has been illuminated both theoretically and experimentally. Together with its capability in monitoring the vibration frequency, the CF-TENG appears as the triboelectrification-based active sensor that can give full quantitative information about a vibration. In addition, the CF-TENG is also demonstrated as a power source for electronic devices.

In the past years, scientists have shown that development of a power suit is no longer a dream by integrating the piezoelectric nanogenerator (PENG) or triboelectric nanogenerator (TENG) with commercial carbon fiber cloth. However, there is still no design applying those two kinds of NG together to collect the mechanical energy more efficiently. In this paper, we demonstrate a fiber-based hybrid nanogenerator (FBHNG) composed of TENG and PENG to collect the mechanical energy in the environment. The FBHNG is three-dimensional and can harvest the energy from all directions. The TENG is positioned in the core and covered with PENG as a coaxial core/shell structure. The PENG design here not only enhances the collection efficiency of mechanical energy by a single carbon fiber but also generates electric output when the TENG is not working. We also show the potential that the FBHNG can be weaved into a smart cloth to harvest the mechanical energy from human motions and act as a self-powered strain sensor. The instantaneous output power density of TENG and PENG can achieve 42.6 and 10.2 mW/m2, respectively. And the rectified output of FBHNG has been applied to charge the commercial capacitor and drive light-emitting diodes, which are also designed as a self-powered alert system.

Demonstrating integrated triboelectric nanogenerator energy harvesting systems that contain triboelectric nanogenerators, power management circuits, signal processing circuits, energy storage elements, and/or load circuits are core steps for practical applications of triboelectric nanogenerators. Through the design flow of such systems, theoretical simulation plays a critical role. In this manuscript, we provided a new theoretical simulation method for integrated triboelectric nanogenerator systems through integrating the equivalent circuit model of triboelectric nanogenerators into SPICE software. This new simulation method was validated by comparing its results with analytical solutions in some specific triboelectric nanogenerator systems. Finally, we employed this new simulator to analyze the performance of an integrated triboelectric nanogenerator system with a power management circuit. From the study of the influence of different circuit parameters, we outline the design strategy for such kind of triboelectric nanogenerator systems.

The recently introduced triboelectric nanogenerator (TENG) and the traditional electromagnetic induction generator (EMIG) are coherently integrated in one structure for energy harvesting and vibration sensing/isolation. The suspended structure is based on two oppositely oriented magnets that are enclosed by hollow cubes surrounded with coils, which oscillates in response to external disturbance and harvests mechanical energy simultaneously from triboelectrification and electromagnetic induction. It extends the previous definition of hybrid cell to harvest the same type of energy with multiple approaches. Both the sliding-mode TENG and contact-mode TENG can be achieved in the same structure. In order to make the TENG and EMIG work together, transformers are used to match the output impedance between these two power sources with very different characteristics. The maximum output power of 7.7 and 1.9 mW on the same load of 5 kΩ was obtained for the TENG and EMIG, respectively, after impedance matching. Benefiting from the rational design, the output signal from the TENG and the EMIG are in phase. They can be added up directly to get an output voltage of 4.6 V and an output current of 2.2 mA in parallel connection. A power management circuit was connected to the hybrid cell, and a regulated voltage of 3.3 V with constant current was achieved. For the first time, a logic operation was carried out on a half-adder circuit by using the hybrid cell working as both the power source and the input digit signals. We also demonstrated that the hybrid cell can serve as a vibration isolator. Further applications as vibration dampers, triggers, and sensors are all promising.

New technologies that can scavenge ambient environmental energy have attracted increasing interest in the past decades. Recently, triboelectric nanogenerator (TENG) has been demonstrated as a powerful approach for harvesting various forms of mechanical energies. In this work, a newly designed TENG is demonstrated by coaxially integrating multiple layers disk TENGs into a whole system, which transforms the fluid flow into rotation motion of multiple layers disks and generates a multiplied electrical output. To achieve the effective structural integration and output multiplication, a D-shape shaft is adopted to facilitate the synchronized relative rotation of all the segmentally-structured disk layers and light weight and low stiffness springs are employed to ensure the intimate contact of the tribo-surfaces. With the above design, the nanogenerator delivers an open-circuit voltage up to ~470V and a short-circuit current density of 90.6mA/m2, corresponding to an instantaneous maximum power density of 42.6W/m2(2.68kW/m3) at a rotation speed of 1000rpm. By combining the TENG with a water turbine, the device can be effectively driven by a water flow from a common household faucet. This technology represents an important advance of TENGs toward practical applications and shows great potential in hydroelectric power and wind power industries.

In this work, we introduced an innovative noncontact, free-rotating disk triboelectric nanogenerator (FRD-TENG) for sustainably scavenging the mechanical energy from rotary motions. Its working principle was clarified through numerical calculations of the relative-rotation-induced potential difference, which serves as the driving force for the electricity generation. The unique characteristic of the FRD-TENG enables its high output performance compared to its working at the contact mode, with an effective output power density of 1.22 W/m2for continuously driving 100 light-emitting diodes. Ultrahigh stability of the output and exceptional durability of the device structure were achieved, and the reliable output was utilized for fast/effective charging of a lithium ion battery. Based on the relationship between its output performance and the parameters of the mechanical stimuli, the FRD-TENG could be employed as a self-powered mechanical sensor, for simultaneously detecting the vertical displacement and rotation speed. The FRD-TENG has superior advantages over the existing disk triboelectric nanogenerator, and exhibits significant progress toward practical applications of nanogenerators for both energy harvesting and self-powered sensor networks.

Energy harvesting and storage are the two most important energy technologies developed for portable, sustainable, and self-sufficient power sources for mobile electronic systems. However, both have limitations for providing stable direct-current (DC) with an infinite lifetime. Herein, we integrated a triboelectric nanogenerator (TENG)-based mechanical energy harvester with Li-ion-battery (LIB)-based energy storage as a single device for demonstrating a flexible self-charging power unit (SCPU), which allows a battery to be charged directly by ambient mechanical motion. This physical integration enables a new operation mode of the SCPU: the “sustainable mode”, in which the LIB stores the TENG-generated electricity while it is driving an external load. With the LIB being replenished by the ambient mechanical energy, the SCPU can keep providing a constant voltage to the load by utilizing the stable difference between the battery’s intrinsic electrode potentials. This study will impact the traditional trends of battery research and advance the development of the self-powered systems.

We report an innovative, large-area, and self-powered pressure mapping approach based on the triboelectric effect, which converts the mechanical stimuli into electrical output signals. The working mechanism of the triboelectric active sensor (TEAS) was theoretically studied by both analytical method and numerical calculation to gain an intuitive understanding of the relationship between the applied pressure and the responsive signals. Relying on the unique pressure response characteristics of the open-circuit voltage and short-circuit current, we realize both static and dynamic pressure sensing on a single device for the first time. A series of comprehensive investigations were carried out to characterize the performance of the TEAS, and high sensitivity (0.31 kPa–1), ultrafast response time (<5 ms), long-term stability (30 000 cycles), as well as low detection limit (2.1 Pa) were achieved. The pressure measurement range of the TEAS was adjustable, which means both gentle pressure detection and large-scale pressure sensing were enabled. Through integrating multiple TEAS units into a sensor array, the as-fabricated TEAS matrix was capable of monitoring and mapping the local pressure distribution applied on the device with distinguishable spatial profiles. This work presents a technique for tactile imaging and progress toward practical applications of nanogenerators, providing potential solutions for accomplishment of artificial skin, human-electronic interfacing, and self-powered systems.

Harvesting mechanical energy is becoming increasingly important for its availability and abundance in our living environment. Triboelectric nanogenerator (TENG) is a simple, cost-effective, and highly efficient approach for generating electricity from mechanical energies in a wide range of forms. Here, we developed a TENG designed for harvesting tiny-scale wind energy available in our normal living environment using conventional materials. The energy harvester is based on a rotary driven mechanical deformation of multiple plate-based TENGs. The operation mechanism is a hybridization of the contact-sliding-separation-contact processes by using the triboelectrification and electrostatic induction effects. With the introduction of polymer nanowires on surfaces, the rotary TENG delivers an open-circuit voltage of 250 V and a short-circuit current of 0.25 mA, corresponding to a maximum power density of ∼39 W/m2at a wind speed of ∼15 m/s, which is capable of directly driving hundreds of electronic devices such as commercial light-emitting diodes (LEDs), or rapidly charging capacitors. The rotary TENG was also applied as a self-powered sensor for measuring wind speed. This work represents a significant progress in the practical application of the TENG and its great potential in the future wind power technology. This technology can also be extended for harvesting energy from ocean current, making nanotechnology reaching our daily life a possibility in the near future.

A branched ZnO-CdS double-shell NW array on the surface of a carbon fiber (CF/ZnO-CdS) was successfully synthesized viaa facile two-step hydrothermal method. Based on a single CF/ZnO-CdS wire on a polymer substrate, a flexible photodetector was fabricated, which exhibited ultrahigh photon responsivity under illuminations of blue light (1.11 × 105A/W, 8.99 × 10–8W/cm2, 480 nm), green light (3.83 × 104A/W, 4.48 × 10–8W/cm2, 548 nm), and UV light (1.94 × 105A/W, 1.59 × 10–8W/cm2, 372 nm), respectively. The responsivity of this broadband photon sensor was enhanced further by as much as 60% when the device was subjected to a −0.38% compressive strain. This is because the strain induced a piezopotential in ZnO, which tunes the barrier height at the ZnO–CdS heterojunction interface, leading to an optimized optoelectronic performance. This work demonstrates a promising application of piezo-phototronic effect in nanoheterojunction array based photon detectors.

We demonstrated the first piezoelectric effect on the performance of a pH sensor using an MSM back-to-back Schottky contacted ZnO micro/nanowire device. When the device is subjected to an external strain, a piezopotential is created in the micro/nanowire, which tunes the effective heights of the Schottky barriers at the local contacts, consequently increasing the sensitivity and signal level of the sensors. Furthermore, the strain-produced piezopotential along the ZnO micro/nanowire will lead to a nonuniform distribution of the target molecules near the micro/nanowire surface owing to electrostatic interaction, which will make the sensor proactiveto detect the target molecules even at extremely low overall concentration, which naturally improves the sensitivity and lowers the detection limit. A theoretical model is proposed to explain the observed performance of the sensor using the energy band diagram. This prototype device offers a new concept for designing supersensitive and fast-response micro/nanowire sensors by introducing an external strain and piezotronic effect, which may have great applications in building sensors with fast response and reset time, high selectivity, high sensitivity, and good signal-to-noise ratio for chemical, biochemical, and gas sensing.

Objective: Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease that affects 63 in every 100,000 Americans. Its etiology remains unknown, although inflammatory pathways appear to be important. Given the dynamic environment of the lung, we examined the significance of mechanotransduction on both inflammatory and fibrotic signaling during IPF. Innovation: Mechanotransduction pathways have not been thoroughly examined in the context of lung disease and pharmacologic approaches for IPF do not currently target these pathways. The interplay between mechanical strain and inflammation in pulmonary fibrosis remain incompletely understood. Approach: In this study, we used conditional KO mice to block mechanotransduction by knocking out FAK (Focal Adhesion Kinase) expression in fibroblasts, followed by induction of pulmonary fibrosis using bleomycin. We examined both normal human and human IPF fibroblasts and used immunohistochemistry, qRT-PCR, and Western Blot to evaluate the effects of FAK inhibition (FAKI) on modulating fibrotic and inflammatory genes. Results: Our data indicate that deletion of FAK in mice reduces expression of fibrotic and inflammatory genes in lungs. Similarly, mechanical straining in normal human lung fibroblasts activates inflammatory and fibrotic pathways. FAK inhibition decreases these signals but has less effect on IPF fibroblasts as compared to normal human fibroblasts. Conclusion: Administering FAKI at early stages of fibrosis may attenuate the FAK-mediated fibrotic response pathway in IPF, potentially mediating disease progression.

Burn scars and scar contractures cause significant morbidity for patients. Recently, cell-based therapies have been proposed as an option for improving healing and reducing scarring after burn injury, through their known proangiogenic and immunomodulatory paracrine effects. Our laboratory has developed a pullulan-collagen hydrogel that, when seeded with mesenchymal stem cells (MSCs), improves cell viability and augments their proangiogenic capacity in vivo. Concurrently, recent research suggests that prospective isolation of cell subpopulations with desirable transcriptional profiles can be used to further improve cell-based therapies. In this study, we examined whether adipose-derived stem cell (ASC)-seeded hydrogels could improve wound healing following thermal injury using a murine contact burn model. Partial thickness contact burns were created on the dorsum of mice. On days 5 and 10 following injury, burns were debrided and received either ASC hydrogel, ASC injection alone, hydrogel alone, or no treatment. On days 10 and 25, burns were harvested for histologic and molecular analysis. This experiment was repeated using CD26+/CD55+FACS-enriched ASCs to further evaluate the regenerative potential of ASCs in wound healing. ASC hydrogel-treated burns demonstrated accelerated time to reepithelialization, greater vascularity, and increased expression of the proangiogenic genes MCP-1, VEGF, and SDF-1 at both the mRNA and protein level. Expression of the profibrotic gene Timp1and proinflammatory gene Tnfawas downregulated in ASC hydrogel-treated burns. ASC hydrogel-treated burns exhibited reduced scar area compared to hydrogel-treated and control wounds, with equivalent scar density. CD26+/CD55+ASC hydrogel treatment resulted in accelerated healing, increased dermal appendage count, and improved scar quality with a more reticular collagen pattern. Here we find that ASC hydrogel therapy is effective for treating burns, with demonstrated proangiogenic, fibromodulatory, and immunomodulatory effects. Enrichment for CD26+/CD55+ASCs has additive benefits for tissue architecture and collagen remodeling postburn injury. Research is ongoing to further facilitate clinical translation of this promising therapeutic approach.Impact statementBurns remain a significant public health burden. Stem cell therapy has gained attention as a promising approach for treating burns. We have developed a pullulan-collagen biomimetic hydrogel scaffold that can be seeded with adipose-derived stem cells (ASCs). We assessed the delivery and activity of our scaffold in a murine contact burn model. Our results suggest that localized delivery of ASC hydrogel treatment is a promising approach for the treatment of burn wounds, with the potential for rapid clinical translation. We believe our work will have broad implications for both hydrogel therapeutics and regenerative medicine and will be of interest to the general scientific community.