Piezoelectric structures, in forms that allow mere in-surface deformations under large strains, are attractive for bio-integrated systems. Here, mechano-electrospinning (MES) is presented to direct-write straight nanofibers of polyvinylidene fluoride onto a prestrained poly(dimethylsiloxane) (PDMS) substrate, to position and polarize a piezoelectric nanofiber array in one-step. Wrinkled/non-wrinkled buckling modes are found when the substrates are released, and the morphology of the direct-written fiber proved the key to determine the buckling modes, which can be tuned precisely by MES parameters. The non-wrinkled, stretchable piezoelectric devices with a highly synchronized serpentine fiber array exhibit their in-surface deformation and stable piezoelectric performance up the failure strain of PDMS (∼110% in our study), which may be used as stretchable sensors and energy converters/providers.

This paper describes the design and characterization of microfluidic serpentine antennas with reversible stretchability and designed mechanical frequency modulation (FM).

Flexible and stretchable electronics technologies have been attracting increasing attention owing to their potential applications in personal consumed electronics, wearable human–machine interfaces (HMI) and the Internet of Things (IoTs). This paper proposes an HMI based on a polyvinylidene difluoride (PVDF) sensor and laminated it onto the surface of the skin for signal classification and controlling the motion of a mobile robot. The PVDF sensor with ultra-thin stretchable substrate can make conformal contact with the surface of the skin for more accurate measurement of the electrophysiological signal and to provide more accurate control of the actuators. Microelectro-mechanical system (MEMS) technologies and transfer printing processes are adopted for fabrication of the epidermal PVDF sensor. Sensors placed on two wrists would generate two different signals with the fist clenched and loosened. It can be classified into four signals with a combination of the signals from both wrists, i.e. four control modes. Experiments demonstrated that PVDF sensors may be used as an HMI to control the motion of a mobile robot remotely.

Flexible and stretchable self-powered sensors are widely applied to Internet of the Things (IoT), human motion monitoring, and human robot interaction (HRI), and it reveals more and more attentions due to the flexibility and self-powered function. The paper focuses on the stretchable triboelectric nanogenerator (TENG) sensor for human gesture monitoring and HRI application based on conductive ionic gels and machine learning. Stretchable self-powered TENG sensor is fabricated by solution method based on Polyacrylamide (PAAM)/NaCl conductive hydrogel and silicone rubber. Self-powered triboelectric nanogenerator sensor array (TENG-SA) is applied to gesture detection at different parts (wrist, elbow, knee and neck) of human body successfully without external power supply. Conductive PAAM/NaCl hydrogel could be stretched up to 307%, which satisfies the deformation of the human joints. Intelligent sensing system is designed and developed to control the motion of two-wheeled robot through TENG-SA and long and short time memory (LSTM) neural network via Bluetooth. Experiments have demonstrated that the neck motion signals are collected and recognized by intelligent TENG-SA system with LSTM neural network during the neck rotation process, which is applied to control the motion of two-wheeled robot successfully. HRI based on self-powered TENG sensor will promote the interaction among humans and machines/robots to improve the disabled for rehabilitation, medical monitoring and human-robot cooperation.