Wrinkled elastomeric templates prepared by stretching and releasing are utilized for demonstrating highly sensitive, simple, and low-cost piezocapacitive pressure sensors over large area.

An electrohydrodynamic (EHD) printing process was optimized for the printing of a (3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) conductive polymer by manipulating the surface tension of a PEDOT:PSS solution. A stable cone-jet mode was confirmed by adjusting the process parameters of the EHD printing process, such as applied voltage, flow rate, and working distance. The addition of a nonionic surfactant, Triton X-100, enabled both printing of PEDOT:PSS conductive lines with widths ranging from 335 μm to 90 μm in a low-power operation (0.5 kV), as well as a 100-fold increase in conductivity of the PEDOT:PSS film compared with that of the pristine one. To utilize printed PEDOT:PSS lines for high functional applications, a multi-deposition technique was carried out, which results in a decrease in line resistance from 1.3 × 10⁴ Ω mm⁻¹ to 0.2 × 10³ Ω mm⁻¹.

Flexible strain sensors are recognized as a key component of electronic-skin technology. One of the important features for strain sensors is that they should be able to sensitively recognize the direction of the external stress to accurately detect the various motions of humans or matter. Herein, we successfully developed a directionally responsive piezoresistive strain sensor with asterisk-shaped CNT sensing electrodes to recognize the direction of an applied external stress, thereby overcoming some of the shortcomings of established sensors. Under 5% strain, the change in relative resistance of the sensor developed here differed by up to a factor of 24.5 for different orientations of the sensor electrode relative to the source of the stress, i.e., a high angular dependence of the sensing performance on the external stress direction was observed. In particular, the asterisk-shaped CNT strain sensors showed a super-linear relationship between response and strain for low strains of up to 5%, allowing them to provide a good sensing platform for recognizing micro-deformations. Finally, we demonstrated that our sensor could recognize the direction of the movement of an applied brush and the magnitude and direction of the tilt of a home-built joystick attached onto the sensor device.