Lightweight, stretchable, and wearable strain sensors have recently been widely studied for the development of health monitoring systems, human-machine interfaces, and wearable devices. Herein, highly stretchable polymer elastomer-wrapped carbon nanocomposite piezoresistive core-sheath fibers are successfully prepared using a facile and scalable one-step coaxial wet-spinning assembly approach. The carbon nanotube-polymeric composite core of the stretchable fiber is surrounded by an insulating sheath, similar to conventional cables, and shows excellent electrical conductivity with a low percolation threshold (0.74 vol %). The core-sheath elastic fibers are used as wearable strain sensors, exhibiting ultra-high stretchability (above 300%), excellent stability (>10 000 cycles), fast response, low hysteresis, and good washability. Furthermore, the piezoresistive core-sheath fiber possesses bending-insensitiveness and negligible torsion-sensitive properties, and the strain sensing performance of piezoresistive fibers maintains a high degree of stability under harsh conditions. On the basis of this high level of performance, the fiber-shaped strain sensor can accurately detect both subtle and large-scale human movements by embedding it in gloves and garments or by directly attaching it to the skin. The current results indicate that the proposed stretchable strain sensor has many potential applications in health monitoring, human-machine interfaces, soft robotics, and wearable electronics.

Slow deformation seriously restrains application development of IPMC actuator, especially for thick and ionic liquid-based IPMC. Inspired by the action potential of muscle cell, this letter proposes a concept of high electrical pulse stimulus to accelerate IPMC deformation. By analyzing the dynamic process of voltage drop at the electrode-polymer interface, high voltage pulse is proved theoretically to be safe for IPMC in a short time. After charging the electrical double layer at the interface, the voltage pulse should be reduced to a safe level before electrochemical reactions. In our experiments, applying various high voltage pulses to a thick IPMC, the deformation can be sped up a few hundred times at most without any electrolysis damage. The results strongly support the practicability of the impulsive driving method.

Ionic electroactive polymer (iEAP) actuators have attracted great attention in the fields of microelectromechanical systems and biomedicine due to their remarkably large strain under lowvoltage stimulation. As actuation performance is mainly dominated by the electrochemical and electromechanical processes, the electrode layer and its structure are increasingly crucial to the actuators. In this research, we introduced a nanoporous carbon nanotube film with superior conductivity (1000-2000 S cm −1 ) as a cost-effective alternative electrode in fabricating iEAP actuators. The actuators were assembled by hot-pressing a Nafion/EMImBF 4 electrolyte layer between two electrode films under vacuum conditions. Based on the developed porous hierarchal structure and superior electrical and mechanical properties of the electrode film, the actuators showed highly improved electrochemical and electromechanical properties and can operate controllably and durably under various voltage amplitudes and waveforms with a wide frequency range. The generated strain and stress reach up to 1.26% and 5.27 MPa, respectively, which are greater than the performances of the actuators based on polymer-supporting nano carbon electrodes. Once the voltage increases by 1 V, the strain and stress will increase by 0.336% and 1.407 MPa, respectively. The actuators can perform more than 20 000 cycles with an initial drop less than 20% in the operation stroke, showing a relatively durable and controllable cycle life. The newly developed actuators can be promising candidates for artificial muscles in academic interest and industrial applications.

Ionic polymer carbon-composite (IPCC) is a kind of ionic electroactive polymer with a Nafion/ionic liquid electrolyte layer between two multi-walled carbon nanotube (MWCNT) film electrodes. We have fabricated a three-electrode structured IPCC (3E-IPCC) that exhibited a higher safe working voltage and improved electromechanical performance when compared with a traditional two-electrode laminar actuator. An intermediate electrode that was fabricated using MWCNTs was introduced into the matrix membrane, which was then subjected to hot-pressing to form the 3E-IPCC actuator. The effects of the intermediate electrode on the performance of the 3E-IPCC were analyzed. The experiment results indicated that the intermediate electrode connected the two electrolyte layers in series and successfully broadened the window of working voltage by distributing the voltage over the two electrolyte layers. The broadened window of working voltage endowed a higher safe working voltage and then led to enhanced electromechanical performance when compared with the traditional IPCC actuator. The 3E-IPCC exhibited desirable properties, including a large deformation, high output force and excellent stability under high working voltages and so these actuators show great potential for use in a wide range of fields.

Ionic polymer-metal composite (IPMC) actuator can generate large and rapid deformation based on ion migration under a relatively low driving voltage. Under full hydrated conditions, the deformation is always prone to relaxation. At room humidity conditions, the deformation increases substantially at the early stage of actuation, and then decreases gradually. Generally, most researchers considered that the change of water content or relative humidity mainly leads to the deformation instabilities, which severely limits the practical applications of IPMC. In this Letter, a novel actuation mode is proposed to control the deformation behavior of IPMC by employing moisture as an independent or collaborative incentive source together with the electric field. The deformation response is continuously measured under electric field, electric field-moisture coupling stimulus and moisture stimulus. The result shows that moisture can be a favorable driving factor for IPMC actuation. Such an electric field-moisture coupling stimulus can avoid the occurrence of deformation instabilities and guarantee a superior controllable deformation in IPMC actuation. This research provides a new method to obtain stable and large deformation of IPMC, which is of great significance for the guidance of material design and application for IPMC and IPMC-type iEAP materials.