In order to meet the requirements of wearable devices, sensor materials need to be light, soft and corrosion-resistant. At present, the main materials used in wearable devices include flexible materials, paper-based materials, nano materials and organic materials.
Figure 2 common materials of wearable devices: (a) flexible materials; (b) paper-based materials; (c) nano materials; (d) organic materials
As the common materials of wearable devices, flexible materials mainly include polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), poly (naphthalene ethylene), polyurethane, polyimide and latex, etc. their compatibility and bending properties are very good. Mechanical and temperature stability is relatively good. In many flexible materials, PDMS
And pet are the most commonly used. As shown in Figure 2 (a), the flexible microfluidic chip for long-term continuous detection of sweat is made of three layers of PET film. During detection, the chip on the skin surface absorbs the liquid on the body surface through a filter integrated in the inlet, and then enters the microchannel and sensing cavity through capillary action for detection. The ultra light weight, high mobility, scalability, low cost and its dual objectivity of flexible materials make it possible to integrate many other components. The flexibility provided by the retractable can not only relieve the mechanical strain caused by bending, but also relieve the compression. Mechanical strain caused by other disturbances such as tension and torsion. The flexible and stretchable wearable device can be firmly combined with the skin to reduce the stress at the interface as much as possible, and realize the monitoring of human activities and personal health under the strong pressure generated in the process of normal body movement and muscle movement.
Paper based materials
Due to its unique characteristics, paper-based paper has the advantages of easy recycling, low cost, strong water absorption and good flexibility. The unique characteristics of paper-based wearable devices make it can be well used in respiratory monitoring. The wearable paper-based moisture sensor can detect the moisture changes caused by respiration by making use of the good water absorption of paper-based. Compared with traditional devices, its cost is very low. By combining paper with other materials, we can improve the strength of paper-based devices. Based on microfluidic paper-based chip, we combine cotton thread with filter paper to design and prepare wearable devices for glucose detection, which provides a new idea for the development of paper-based wearable devices.
Common nanomaterials for wearable devices include carbon nanotubes. Metal nanowires, metal oxide nanowires and conductive polymer nanowires. As shown in Fig. 2 (c), a pH sensor based on dielectrophoretic carboxyl functionalized single-walled carbon nanotubes (SWCNTs) has been fabricated. Its performance can be changed in different aspects by the arrangement of carbon nanotubes. Many techniques have been developed to prepare carbon nanotubes with different morphologies, including vertical carbon nanotubes, curved carbon nanotubes and suspended carbon nanotubes. For metal nanomaterials, there are mainly gold, silver and copper nanowires. A pressure sensor is developed by combining silver nanowires with PDMS, which can monitor such actions as touching, swallowing, bending and twisting.
In recent years, organic sensors based on organic semiconductors or conductive materials have become one of the commonly used materials for wearable devices due to their flexibility, extensibility, low cost and light weight. The unique advantage of organic semiconductors and conductive materials is that their electrical, mechanical, chemical and optical properties can be reasonably analyzed
Sub design to optimize. The tunable optical range of organic semiconductor optical sensors can achieve the absorption wavelength from near infrared to ultraviolet region through molecular design. Therefore, these sensors are widely used for continuous and real-time monitoring of individual physiological state. As shown in Figure 2 (d), based on the photoelectric volume sensor of high sensitivity organic photoelectric crystal, the ultra-thin wearable device can continuously monitor the change of heart rate and accurately track the change of pulse pressure in various parts of the body.
Editor in charge: CC