4D printing of light activated shape memory polymers with organic dyes Clara Vazquez-Martel 1 , Christoph A. Spiegel 1 , Matteo Gastaldi 2,3 , Claudia Barolo 2 , Ignazio Roppolo 3 ,Eva Blasco 1 1 Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Germany, 2 ICxT Interdepartmental Center, University of Turin, Italy, 3 Department of Applied Science and Technology, Politecnico di Torino, Italy 4D printing combines responsive materials and 3D printing technologies to produce smart, time-evolving (4 th dimension) structures that respond to external stimuli. 1,2 Light is an extremely attractive stimulus due to its tunability, which permits precise spatiotemporal control. 3 Moreover, among all 3D printing technologies, light- based 3D printing technologies, such as digital light processing (DLP), provide the best performance due to the complexity and resolution of the structures that can be printed at high speed. Consequently, based on our previous work on the design of a shape memory polymer (SMP) ink system utilising a temperature stimulus, 4 we aim to expand the state-of-the-art of SMPs within this work. Therefore, we utilise push-pull azobenzene (azo) pigments not only improve printing resolution, but also to facilitate a light response in 3D printed SMPs without the need for inorganic additives. 5 Specifically, a library of azo-dyes with various substituents in ortho-position was synthesised and added to the printing formulation as photoactive dyes. The light activated shape memory effect could be demonstrated for all printed structures that include the dyes, with the chlorine-substituted azo dyes displaying the best performance. Importantly, adding only 0.1 wt% of dye in the formulation is sufficient to attain the desired effect. By using visible light irradiation, temperature could be increased within the 4D geometry with high local precision, allowing for spatiotemporal activation of SMP properties. The reliability of this approach was demonstrated by performing shape memory recovery processes for a range of different structures, thus illustrating the potential of visible light as stimulus. Due to its simplicity, adaptability, and reliability, the presented system opens new opportunities in numerous disciplines, including soft robotics, actuators, and smart sensing applications. References 1. P. Fu, H. Li, J. Gong, Z. Fan, A. T. Smith, K. Shen, T. O. Khalfalla, H. Huang, X. Qian, J. R. McCutcheon, L. Sun, Prog. Polym. Sci., 2022, 126, 101506. 2. X. Kuang, D. J: Roach, J. Wu, C. M. Hamel, Z. Ding, T. Wang, M. L. Dunn, H. J. Qi, Adv. Funct. Mater., 2019, 29, 1805290. 3. M. Herath, J. Epaarachchi, M. Islam, L. Fang, J. Leng, Eur. Polym. J., 2020, 136, 109912. C. A. Spiegel, M. Hackner, V. P. Bothe, J. Spatz, E. Blasco, Adv. Funct. Mater., 2022, 2110580. 4. M. Gastaldi, C. A. Spiegel, C. Vazquez-Martel, C. Barolo, I. Roppolo, E. Blasco, Mol. Syst. Des. Eng., 2023, 8, 323-329
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