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Recently, Associate Professor Chuanfei Guo’s team from the Department of Materials Science and Technology at Southern University of Science and Technology has made important progresses on bionic flexible electronic skins. The research results have been published in Advanced Functional Materials, Small and Advanced Electronic Materials.
Prof. Guo's team are focusing on micro-and nano-fabrication of thin films, preparation of flexible transparent electrodes, growth of nanostructured thin films, and their application in optoelectronics, biomedicine as well as nano-energy fields.
Tactile sensing, enabled by the mechanoreceptors in skin, is one of the most important routes for biological organisms to obtain information from the external environment. The emulation of the sensory capacity of biosystems is of great significance, leading to the emerging field of electronic skins. For example, prostheses help disabled people perform certain motional functions. However, products on the market typically are not equipped with tactile sensors, thus unable to endow the disabled with perception. Flexible tactile sensors (electronic skins) are an electronic device that converts pressure signals into electrical signals. It shows great promise in wearable electronics, health/motion monitoring, intelligent prosthesis, human-machine interfaces, and artificial intelligence. Previous studies have shown that microstructures (e.g., micropyramids, micropillars, and microspheres) can effectively improve the performance of flexible tactile sensors, resulting in ultra-sensitive flexible tactile sensors. However, these microstructures are mostly fabricated by traditional methods including photolithography and chemical etching methods, which are complex, time-consuming and expensive. The preparation of low-cost, simple and high-performance flexible tactile sensors has become a major challenge.
Prof. Guo's group was inspired by the fact that the superhydrophobic property of lotus leaves originates from the surface micro-and nano-structures. To reduce the cost of fabrication and improve the sensing performance of tactile devices, Prof. Guo’s team decided to use natural materials as templates to construct surface microstructures. A capacitive tactile sensor (Adv. Electron. Mater. 2018, 4, 1700586) was fabricated by adopting natural plants as the original template, which copied the microstructure of the plant surface and became conductive by being sprayed with a layer of silver nanowires. The device shows high sensitivity (1.2 kPa-1), fast response speed (36 ms, comparable with human skin), and good stability (tested over 100,000 cycles without fatigue). The work was rated as one of the top ten monthly papers in Advanced Electronic Materials.
The highly sensitive flexible tactile sensor has become a hot research topic nowadays. In order to improve the performance of capacitive tactile sensors, the research team used the Calathea Zebrine leaf as the template to prepare the ionic gel dielectric layers with microcone arrays. The interfacial electric double layer can effectively improve the device's sensitivity (Adv. Funct. Mater. 2018, 1802343) up to 54.1 kPa-1, which is the highest value for capacitive tactile sensors reported so far. In addition, the device exhibits a detection limit as low as 0.1 Pa and a response speed of 29 ms, which exceeds the response speed of human skin.
Inspired by the three-dimensional porous structure of plants, Prof. Guo’s team adopted dried natural materials (such as petals and leaves) as the dielectric layer of electronic skins (Small 2018, 1801657). The results show that the device has a large capacitive response due to the electric double layer formed between the ionic liquid and the electrode of the fresh natural plant materials. However, the device performance degrades rapidly with the evaporation of water from the natural materials. By means of critical point drying treatment, the geometric structures of the natural materials were preserved, leading to devices with stable performance. Such natural-material-based devices with high sensitivity, low detection limit and high reliability can be used for motion detection and pressure sensing with a good spatial resolution. This work has been selected as a monthly hot topic paper. Using bionic microstructures or natural materials directly to fabricate flexible tactile sensors can greatly simplify the fabrication process and reduce the cost of fabrication, which is in accord with the concept of sustainable development, and of great significance to the construction of environmentally friendly flexible electronic systems.
These studies on electronic skins based on plant templates and natural plant materials can effectively reduce the cost of device fabrication, and meanwhile improve the device performance, opening up a new door to the construction of flexible electronic devices. Such electronic skins can be used in human health monitoring, motion detection, and human-machine interfaces, showing great potential in the fields of intelligent robots, intelligent prosthesis, and wearable electronics.
These researches were mainly completed by graduate student, Yongbiao Wan (currently working at the Chinese Academy of Engineering Physics) and research assistant Zhiguang Qiu. Graduate students, Ying Hong, Jun Huang, and Peng Lu, and undergraduate students, Qi Wang and Jingyi Yang also contributed to part of the experimental work. The Department of Materials Science and Engineering, SUSTech, is the only corresponding research institution. The research was supported by “Guangdong Innovation and Entrepreneurship Team Program”, “National Natural Science Foundation of China”, and “Shenzhen Peacock Plan”.
Contributed: Department of Materials Science and Engineering