Bringing Mechanically-Activated Chemical Reactions into Additive Manufacturing

Targeted chemical reactions can be achieved in fluid flow using mechanical forces alone to activate a stress-sensitive functional molecule embedded within a polymer chain [1]. This polymeric mechanically-activated chemistry can deliver changes in colour or conductivity and can trigger cascade reactions or crosslinking. These stress-sensitive 'mechanophores' have been extensively studied at the molecular level but there have only recently been steps to understand how they react to macroscopic stresses, such as when included in additive manufacturing techniques or translated into real applications [2,3].<br/><br/>This presentation studies the highly controllable and repeatable velocity gradients and forces experienced within the nozzles of additive manufacturing processes such as inkjet printing and extrusion-based additive manufacturing. Most often these are studied to ensure functional and biological materials do not experience significant stresses and retain their structure after printing [4]. Here, instead, we present a range of custom-made experimental techniques to precisely control the fluid flow and forces experienced by solutions and hydrogels within nozzles to deliberately drive chemical changes and then couple these experiments with significant rheological analyses and simulations to reveal new insights and tools for the translation of mechanochemistry to direct-write additive manufacturing. This new level of understanding, along with our ability to better control the forces experienced by mechanically sensitive molecules, suggest an exciting future with spatial tuning of physico-chemical properties by simply tuning flow properties from a single material.<br/><br/>[1] D.A. Davis, A. Hamilton, J. Yang, L.D. Cremar, D. Van Gough, S.L. Potisek, M.T. Ong, P.V. Braun, T.J. Martínez, S.R. White, J.S. Moore, N.R. Sottos. Nature, 459, 68 (2009).<br/>[2] E. Rognin, N. Willis-Fox, R. Daly. RSC Mechanochemistry, 1, 138 (2024).<br/>[3] N. Willis-Fox, E. Watchorn-Rokutan, E. Rognin, R. Daly. Trends in Chemistry 5, 415 (2023).<br/>[4] S.E. Evans, T. Harrington, M.C.R. Rivero, E. Rognin, T. Tuladhar, R. Daly. International Journal of Pharmaceutics, 599, 120443 (2021).