Highly Flexible, Stretchable, and Self-Powered Strain-Temperature Dual Sensor Based on Free-Standing PEDOT:PSS/Carbon Nanocoils-Poly(vinyl) Alcohol Films.

The wearable and self-powered sensors with multiple functions are urgently needed for energy saving devices, economical convenience, and artificial human skins. It is a meaningful idea to convert excess heat sources into power supplies for wearable sensors. In this report, we have fabricated a series of free-standing self-powered temperature-strain dual sensors based on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS)/carbon nanocoils (CNCs)-poly(vinyl) alcohol composite films by a simple drop casting method. The Seebeck coefficients of the composite films were measured to be 19 µV/K. The sensor, with the addition of CNCs, showed a superior sensing performance to that without CNCs. PEDOT:PSS is used to provide a thermoelectric power to detect temperature changes and strain deformations. The minimum detect limit for the temperature difference was 0.3 K. Under a constant temperature gradient of 30 K, strains from 1 to 10% were detected without any external power supply. The films can be easily made into an array to detect the temperature of the fingers and motions of the wrist by attaching it to the human wrist directly. For the first time, due to the independent action of the thermoelectric material and strain sensing material, the thermoelectric voltage which is generated by a constant temperature difference is maintained under different strains. This kind of free-standing self-powered multifunctional sensors has great application prospects in the fields of healthcare and artificial intelligence in the future.

Self-healing and anti-freezing graphene-hydrogel-graphene sandwich strain sensor with ultrahigh sensitivity.

Hydrogels with specially designed structures and adjustable properties have been considered as smart materials with multi-purpose application prospects, especially in the field of flexible sensors. However, most hydrogel-based sensors have low sensitivity, which inevitably affects their promotion in the market. Herein, a strain sensor comprising a poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hybrid hydrogel sandwiched between two graphene layers was successfully constructed in a facile way, and it exhibited many excellent properties including extremely high sensitivity. The incorporation of glycerol ensured the good flexibility and anti-freezing performance of the hydrogel-based sensor even at -15 °C. The dynamic coordination bonds in the hydrogel-based sensor endowed it with excellent self-healing properties. In particular, the sandwich-structured hydrogel sensor showed a very high gauge factor (GF) value of 39 at the strain of 50%, which is much higher than those of most ordinary hydrogel-based strain sensors. A super stable signal value after 5000 strain cycles and a very short response time of 274 ms guaranteed the long-term usability and sensitivity of the hydrogel-based sandwich sensor. More importantly, the hydrogel-based sandwich sensor could detect both large and tiny human motions accurately and instantly in a series of real-time monitoring experiments, showing great potential for intelligent wearable electronic devices.

A carbon nanocoil-based flexible tip for a live cell study of mechanotransduction and electro-physiological characteristics.

The responses of living cells to external mechanical and electrical stimulation play important roles in regulating their biological functions and behaviors, and the response mechanisms have attracted great attention. Global stimulation on cells is generally used in traditional methods, but it is insufficient to investigate the mechanism of a dynamic physiological response at the subcellular level. At present, there is still lack of a low-cost and easy-operated method to apply local mechanical force and electrical stimulation on living cells. In this study, an individual carbon nanocoil (CNC) is used as a microscale noninvasive tool for local stimulation on a single cell, and a living cell imaging technology, fluorescence resonance energy transfer (FRET), is adopted to determine the responses of cells. After demonstrating that CNCs have low cytotoxicity to be applied in the biological field, an individual CNC is used as a needle tip to apply local mechanical force on a single osteosarcoma cell, which is transfected with a Src FRET biosensor to explore the mechano-physiological response. A spatially increasing and polarized Src protein activation is observed on the stimulated cell. Moreover, a single CNC is also used as an electrode to exert periodic local electrical stimulation. Osteosarcoma cells transfected with calcium-FRET biosensors show notable spatial-polarized FRET emission ratio distribution, and the FRET ratio shows a recoverable tendency towards the initial state after withdrawing the electrical stimulation. The cell biofunctions and structures are not damaged during the experiment process, which indicates that CNC is a kind of non-invasive and bio-safe tip. The CNC tip is a powerful tool for exploring the mechanotransduction and electro-physiological characteristics of living cells.

Facile Fabrication of High-Performance Pen Ink-Decorated Textile Strain Sensors for Human Motion Detection.

Recently, wearable strain sensors have increasingly attracted much attention due to their potential applications in human motion detection and personal health monitoring. To date, it is still a challenge to fabricate a flexible strain sensor with both comfort and high performance. In this study, we dip the commercially available spandex/polyamide fabric into carbonic pen ink to prepare a textile strain sensor with good skin affinity. The textile strain sensor exhibits a high gauge factor (∼62.9) and an excellent linearity (R2 ∼ 0.99) in the strain range of 0-30%. Both before and after washing, the sensor exhibits high stability in more than 5000 cycles. Owing to the facile integration of the ink-decorated fabric on clothes, the sensor can be conveniently attached to the human body to monitor human motions, thus showing great potential in practical applications.