At present, diversification and incorporation of electronics in our daily routines has motivated the rapid development of stretchable and wearable electronics. These electronic devices are capable of converting external stimuli into measurable electrical signals, which play a vital role in the fields of human activity monitoring, personal health management, electronic skin, soft robots, and artificial limbs. Such smart interactive electronic devices can dynamically respond to and visualize environmental stimuli. Unfortunately, the brightness perceived by naked eyes is greatly affected by ambient light, reducing the accuracy of visual information acquired. Moreover, human eyes are not sensitive enough to brightness change in order to directly read out the strain or pressure applied to the device. To this end, the introduction of color changing elements is necessary for interactive displays in view of human’s better sensitivity to color perception. To overcome such hurdles, humans can always seek inspiration from nature. Credit to having time on its side, nature developed ingenious yet facile solutions to intricate problems. For instance, the brilliant structural colors produced by periodic microstructures based on photonic crystals that play a pivotal role in many organisms, such as chameleons, squids etc
With regard to the aforementioned color problem, research has shown that current colorimetric sensors are subject to low brightness and low response speed due to inherent limitations of those chromic dyes. Moreover, the dyes used can switch between only two-color states, leading to relatively low contrast and low-resolution visual interaction. As a resolve, a combination of rational mechanochromic materials and the design of geometric structures would be an effective strategy to realize this goal. In quest to resolve these shortfalls, it would be best to look up to nature as it is patent free and yet with proven efficacy. Putting this into consideration, researchers from the Dalian University of Technology, China: Dr. Yunpeng Wang, Professor Wenbin Niu, Guorui Zhang, Professor Suli Wu, Professor Benzhi Ju and Professor Shufen Zhang, in collaboration with Dr. Chiao-Yueh Lo, Dr. Yusen Zhao and Professor Ximin He, at the University of California, proposed a novel interactive sensor by integrating a photonic crystal with tunable structural colors in the entire visible spectrum into an electronic fiber to provide a visual information display. Their work is currently published in the research journal, Advanced Functional Materials 2020.
Inspired by the rapid color changes of natural creatures, an interactive electronic fiber sensor with high stretchability and tunable coloration was designed and manufactured. The interactive electronic fiber sensor was based on an ingenious multi-sheath design on a piezoresistive electronic fiber coupled with a mechanochromic photonic crystal microtubule. Overall, the researchers developed the rational design and fabrication of interactively tunable full-color electronic fiber sensors with high stretchability, rapid optical/electrical response, and dynamic color switching.
The authors showed that the developed interactive electronic fiber sensor had unique capabilities of sensing and visualizing its deformation simultaneously, by reconstructing conductive paths and regulating the lattice spacing of the photonic sheath. In particular, it exhibited dynamic color switching spanning the full visible region (from red to blue), fast optical/electrical response (≈80 ms), and a large working range (0–200%), allowing its application as a user-interactive sensor for dynamically monitoring large joint movements and muscle micro-vibrations of the human body in real time.
In summary, the study demonstrated a novel interactive fiber sensor featuring full-color changes, high stretchability, high sensitivity (GF ≈ 24.2), high resolution (≈1 nm%−1), and rapid response for wearable electronic devices. The team reported remarkable interactive fiber sensor realizing continuous color changes across the entire visible spectrum (from 632 to 439 nm) over a large working range for the first time. In a statement to Advances in Engineering, Professor Wenbin Niu mentioned that he believed their PE strain sensor has broad application prospects in human–machine exchange, e-skin, health monitoring, and other fields.
Yunpeng Wang, Wenbin Niu, Chiao-Yueh Lo, Yusen Zhao, Ximin He, Guorui Zhang, Suli Wu, Benzhi Ju, and Shufen Zhang. Interactively Full-Color Changeable Electronic Fiber Sensor with High Stretchability and Rapid Response. Advanced Functional Materials 2020, volume 30, 2000356.