Animals can show fascinating biological behaviors in response to environmental cues, such as changing their color or shape. Mimicking such attributes is the objective of developing bionic materials with color- and shape-changing capabilities. However, it is still challenging to fabricate smart soft materials with such a “programmability” that can be manipulated with high spatial resolution.
Shuai Huang, Hong Yang, Southeast University, Nanjing, China, Quan Li, Southeast University and Kent State University, OH, USA, and colleagues have developed bioinspired smart soft actuators—i.e., materials that can change their shape as well as their color upon external stimuli. The team incorporated terminally functionalized aggregation-induced emission (AIE)-active tetraphenylethene derivatives (TPE, pictured below) and photochromic spiropyran moieties (SP, pictured below) into elastomers that contain mesogens, i.e., compounds with liquid-crystal properties, as well as the dye YHD796.
The fluorescent color and shape of the actuator can be adjusted and manipulated with light (pictured). The photochromic SP moiety can reversibly isomerize between the nonfluorescent closed form and the red fluorescent open merocyanine (MC) form, leading to a color change. The liquid-crystal elastomers can be deformed by manipulating the alignment of mesogens, triggered by near-infrared (NIR) light.
The team simulated several biological behaviors using the material, such as the crawling and camouflaging/color-changing of caterpillars and the furling–unfurling action of the frill of a frill-necked lizard, which is accompanied by a color change. According to the researchers, the approach could be useful for incorporating multiple nature-inspired functions into one device.
- Bioinspired Synergistic Photochromic Luminescence and Programmable Liquid Crystal Actuators,
Yinliang Huang, Hari Krishna Bisoyi, Shuai Huang, Meng Wang, Xu-Man Chen, Zhiyang Liu, Hong Yang, Quan Li,
Angew. Chem. Int. Ed. 2021.