Dancing Artificial Muscles: enabling multidirectional bending in helically twisted polymeric fibers

Presented as an oral session at the CMD-General Conference of the Condensed Matter Division (CMD31) held in Braga, Portugal, on the 3rd of September 2024. Abstract of the presentation: Sunflowers perform a daily choreography tracking the sun during their growing period. This movement is promoted by a differential growth in their stem, which leads to the bending of the flower head. This striking strategy allows the plant to optimize the sunlight capture.[1] Inspired by the heliotropism in sunflowers, we developed a method to generate spatially selective motion, guided by light, in helically twisted polymeric fibers. Typically, the twist introduced in monofilament polyamide coiled yarns (artificial muscles) can generate contraction and expansion due to an asymmetric expansion of the material upon stimuli like heat.[2] However, the type of motion is limited to linear actuation. By adding a photothermal component, allowing the conversion of light into thermal energy, we tested the possibility of partial untwisting of the helical structure through the application of a localized stimulus. The interplay between localized heating and thermal diffusion allows polymeric fibers to perform dynamic and multidirectional bending at the irradiation site. Furthermore, the performance of this actuator is not dictated by a predetermined deformation, allowing it to bend toward the light deliberately.[3]Together, these discoveries form a promising leap in the realms of artificial muscles and biomimetic technologies. They depict a world where textiles are not just passive entities, but active accomplices responding to environmental stimuli, paving the way for adaptive, shape-changing systems. [1] J. P. Vandenbrink, E. A. Brown, S. L. Harmer, B. K. Blackman, Plant Science (2014), 224, 20. [2] Haines CS, Lima MD, Li N, Spinks GM, Foroughi J, Madden JD, Kim SH, Fang S, Jung de Andrade M, Göktepe F, Göktepe Ö, Mirvakili SM, Naficy S, Lepró X, Oh J, Kozlov ME, Kim SJ, Xu X, Swedlove BJ, Wallace GG, Baughman RH. Science (2014) 343.[3] Z. Madani, P. E. S. Silva, H. Baniasadi, M. Vaara, S. Das, J. C. Arias, J. Seppälä, Z. Sun, J. Vapaavuori, Light-Driven Multidirectional Bending in Artificial Muscles. Adv. Mater. 2024, 36, 2405917. https://doi.org/10.1002/adma.202405917