Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.R ecent developments in flexible and stretchable electronics, either through structural consideration or by exploring novel materials 1,2 , have imparted otherwise rigid and brittle electronic devices mechanical compliance and bio-compatibility, paving the way for energy-efficient, lightweight, portable, wearable and even implantable electronics 3 . Examples include stretchable and large area display that can undergo complex deformations 4 , bio-inspired material and structural designs that enable bionic functions 5 , and printable sensory system capable of detecting planar strains, normal pressure, temperature, light, moisture and chemical/biological species 6 . Multifunctional sensors, in particular, with sensing abilities akin to or beyond those of human skin 6-12 , are essential for applications such as interactive electronics 13 , structural health monitoring 14 , smart clothing 15 , robotic systems with advanced sensing capabilities 16 , human motion detection 8 and so on. Among the various types of sensors, strain gauge is one of the most important smart sensors, which have been widely used in the measurements of strain, acceleration and tension, as well as structural health monitoring. Conventional strain gauges, made of metal foils, register resistance changes under tensile strains. Actually, mechanical compliance and large strain range (?5%), obviously not the case of metal foils, are required to meet the demands of wearable electronics 15 , human motion detection 8 and interactive robots 17 . Although mercury-in-rubber strain gauge has been used in the biological measurements for decades 18 , the maximum strain limit and toxicity of mercury still block their practically wide applications. In addition, the combination of conformability and optical transparency will facilitate intelligent electronics and self-powered robot where strain sensors are integrated with optoelectronic devices and direct observation through the devices is ne...

One of the most critical aspects in the preparation of single-walled carbon nanotubes (SWCNTs)/ conducting polymer hybrid electrodes is to improve the energy density without seriously deteriorating their high power capability. Here, we report a ''skeleton/skin'' strategy for the preparation of freestanding, thin and flexible SWCNT/polyaniline (PANI) hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with a continuous reticulate structure as template. In situ electrochemical polymerization can achieve effective deposition of PANI onto the surface of SWCNT bundles in the films and control the morphology and microstructure of the SWCNT/PANI hybrid films. In a SWCNT/PANI hybrid film, the directly grown SWCNT film with continuous reticulate architecture acts as the skeleton and PANI layers act as the skin. This unique continuous ''skeleton/skin'' structure ensures that these hybrid films have much higher conductivity compared to SWCNT/PANI composite films based on post-deposition SWCNT films. Flexible supercapacitors have been fabricated using the SWCNT/PANI hybrid films as both electrodes and charge collectors without metallic current collectors. High energy and power densities (131 W h kg À1 and 62.5 kW kg À1 , respectively) have been achieved for the optimized assembly. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggests that the asprepared ultrathin free-standing SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance. Broader contextThe hybrid electrodes of SWCNT/conducting polymer display high energy density due to pseudocapacitance originating from the conducting polymer. However, their power density is dramatically reduced in comparison with pure SWCNT-based electrodes, due to the poor electrical conductivity of PANI layers and overlapped PANI-PANI contact. Therefore, one of the most critical aspects in the development of SWCNT/conducting polymer supercapacitors is to optimize the energy density without deteriorating their high power capability as these two parameters determine concomitantly the ultimate performance of the supercapacitor. In this work, we report a ''skeleton/skin'' strategy to prepare free-standing, thin and flexible SWCNT/PANI hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with continuous reticulate structure as template. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggest that as-prepared ultrathin freestanding SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance. The flexible supercapacitors based on the SWCNT/PANI hybrid films achieve high energy and power densities. 8726

Free-standing, hierarchical reticulate single-walled carbon nanotube (SWCNT) fi lms are embedded in poly(dimethylsiloxane) (PDMS) to fabricate stretchable conductors (SWCNT/PDMS stretchable conductors). The stretchable conductors are highly transparent in visible light region and retain excellent conductance under large tensile strains. Strain tests reveal a unique strainhistory dependence behavior of the resistance, and resistance stabilization is achieved upon repetitive stretching and releasing, implying that the SWCNT/ PDMS stretchable conductors can be programmed to be reversibly stretched to a defi ned strain without resistance changes. A quantitative description of the increase in resistance is determined by adopting the Weibull distribution. Moreover, a light-emitting diode is illuminated using a repetitively stretched SWCNT/PDMS strip as the connecting wire, demonstrating the utility of the stretchable conductors as interconnects for stretchable electronics. Because of the high transparency, high conductivity, and excellent stretchability, in addition to the facile fabrication, the SWCNT/PDMS stretchable conductors might be widely used as interconnects and electrodes for stretchable intelligent and functional devices.