Conductive films that are both stretchable and flexible could have applications in electronic devices, sensors, actuators and speakers. A substantial amount of research has been carried out on conductive polymer composites, metal electrode-integrated rubber substrates and materials based on carbon nanotubes and graphene. Here we present highly conductive, printable and stretchable hybrid composites composed of micrometre-sized silver flakes and multiwalled carbon nanotubes decorated with self-assembled silver nanoparticles. The nanotubes were used as one-dimensional, flexible and conductive scaffolds to construct effective electrical networks among the silver flakes. The nanocomposites, which included polyvinylidenefluoride copolymer, were created with a hot-rolling technique, and the maximum conductivities of the hybrid silver-nanotube composites were 5,710 S cm⁻¹ at 0% strain and 20 S cm⁻¹ at 140% strain, at which point the film ruptured. Three-dimensional percolation theory reveals that Poisson's ratio for the composite is a key parameter in determining how the conductivity changes upon stretching.

Highly efficient human skin systems transmit fast adaptive (FA) and slow adaptive (SA) pulses selectively or consolidatively to the brain for a variety of external stimuli. The integrated analysis of these signals determines how humans perceive external physical stimuli. Here, a self-powered mechanoreceptor sensor based on an artificial ion-channel system combined with a piezoelectric film is presented, which can simultaneously implement FA and SA pulses like human skin. This device detects stimuli with high sensitivity and broad frequency band without external power. For the feasibility study, various stimuli are measured or detected. Vital signs such as the heart rate and ballistocardiogram can be measured simultaneously in real time. Also, a variety of stimuli such as the mechanical stress, surface roughness, and contact by a moving object can be distinguished and detected. This opens new scientific fields to realize the somatic cutaneous sensor of the real skin. Moreover, this new sensing scheme inspired by natural sensing structures is able to mimic the five senses of living creatures.

Torsional artificial muscles generating fast, large-angle rotation have been recently demonstrated, which exploit the helical configuration of twist-spun carbon nanotube yarns. These wax-infiltrated, electrothermally powered artificial muscles are torsionally underdamped, thereby experiencing dynamic oscillations that complicate positional control. Here, using the strategy spiders deploy to eliminate uncontrolled spinning at the end of dragline silk, we have developed ultrafast hybrid carbon nanotube yarn muscles that generated a 9,800 r.p.m. rotation without noticeable oscillation. A high-loss viscoelastic material, comprising paraffin wax and polystyrene-poly(ethylene-butylene)-polystyrene copolymer, was used as yarn guest to give an overdamped dynamic response. Using more than 10-fold decrease in mechanical stabilization time, compared with previous nanotube yarn torsional muscles, dynamic mirror positioning that is both fast and accurate is demonstrated. Scalability to provide constant volumetric torsional work capacity is demonstrated over a 10-fold change in yarn cross-sectional area, which is important for upscaled applications.

wileyonlinelibrary.comactuators, [ 6 ] and absorbers of environmental pollution. [ 2,7 ] Among graphenebased materials, graphene oxides (GOs) can be described as "up-and-coming" material candidates because they are thin, light, strong, environmentally friendly, and fl exible. They also have high surface area, excellent mechanical-chemical properties, and the ability to conduct electricity within 2D nanostructures. Many research groups [ 8 ] have reported the simple preparation of rGO aerogels from GO solution by hydrothermal and freeze-drying methods or etching methods, employing a spherical template/GO composite. The microstructural features of rGO aerogels make them some of the most promising building blocks for energy-related and environmental applications. This is because these features can greatly improve working-volume deformability, can form a multidimensional conduction network, and can provide 3D interfacing or intercalation with other system components (e.g., electrolytes, reactants). [ 8 ] However, the performance and diversity of such graphene aerogel conductors are limited by the lack of a suffi cient compressive modulus (that is, they are fragile and collapse under stress). [ 4,9 ] Aerogels usually have an extremely low density due to their relatively high rigidity and/or a rather low electrical conductivity (e.g., 0.12 S m −1 with a density of 5.10 mg cm −3 ). [ 10 ] These properties can result from an incomplete reduction if mild chemical reducing conditions are employed without thermal annealing. Zhao et al. [ 11 ] reported the development of a compression-tolerant rGO sponge supercapacitor with a polypyrrole coating, which is conductive and provides mechanical reinforcement. This work showed that the use of rGO sponges in conjunction with other materials can overcome some of the shortcomings of monolithic rGO sponges. Recently, Wu et al. [ 12 ] fabricated a spongy graphene material (density = 1.15 mg cm −3 ; conductivity = 0.37 S m −1 ) that showed compressive elasticity and a near-zero Poisson's ratio by using a solvo-thermal reaction and thermal annealing. The primary remaining challenge is the synthesis of additive-free monolithic rGO aerogels that preserve the low density, high conductivity, and good elasticity inherent in GO nanosheets.In this article, we describe the development of a facile approach for fabricating support-free monolithic nitrogen (N)-doped rGO aerogels using a simple hydrothermal method employing hexamethylenetetramine (HMTA) as a stabilizerThe simple synthesis of ultralow-density (≈2.32 mg cm −3 ) 3D reduced graphene oxide (rGO) aerogels that exhibit high electrical conductivity and excellent compressibility are described herein. Aerogels are synthesized using a combined hydrothermal and thermal annealing method in which hexamethylenetetramine is employed as a reducer, nitrogen source, and graphene dispersion stabilizer. The N-binding confi gurations of rGO aerogels increase dramatically, as evidenced by the change in pyridinic-N/quaternary-N ratio. The conductivity ...

Biological ion channels have led to much inspiration because of their unique and exquisite operational functions in living cells. Specifically, their extreme and dynamic sensing abilities can be realized by the combination of receptors and nanopores coupled together to construct an ion channel system. In the current study, we demonstrated that artificial ion channel pressure sensors inspired by nature for detecting pressure are highly sensitive and patchable. Our ion channel pressure sensors basically consisted of receptors and nanopore membranes, enabling dynamic current responses to external forces for multiple applications. The ion channel pressure sensors had a sensitivity of ∼5.6 kPa(-1) and a response time of ∼12 ms at a frequency of 1 Hz. The power consumption was recorded as less than a few μW. Moreover, a reliability test showed stability over 10 000 loading-unloading cycles. Additionally, linear regression was performed in terms of temperature, which showed no significant variations, and there were no significant current variations with humidity. The patchable ion channel pressure sensors were then used to detect blood pressure/pulse in humans, and different signals were clearly observed for each person. Additionally, modified ion channel pressure sensors detected complex motions including pressing and folding in a high-pressure range (10-20 kPa).