Chalcones as Wavelength-Selective Cross-Linkers: Multimaterial Additive Manufacturing of Macro- and Microscopic Soft Active Devices

Photopolymerization-driven additive manufacturing (AM) is a well-established technique to generate polymeric 3D structures with both high resolution and formation in complex geometries. Recent approaches focus on AM techniques that enable multiproperty architectures using wavelength orthogonal photochemistry. Herein, a dual-cure, single-vat resin was developed, based on the radical photopolymerization of a thiol-methacrylate monomer system containing covalently bound chalcone moieties as dimerizable cross-linkers. Thermo-mechanical properties were spatially and systematically controlled via the wavelength-selective [2 + 2] cycloaddition reaction of the chalcone groups. Reaction kinetics were studied with infrared and ultraviolet-visible spectroscopy to ensure sequence-dependent λ-orthogonality during the two-stage illumination process. 3D-structures were fabricated by dynamic light processing (DLP), imprinting, and two-photon lithography (TPL). In particular, the ability to excite both the radical photoinitiator and the chalcone groups separately with TPL in high spatial resolution enabled the production of multifunctional microstructures and represents a versatile concept for the fabrication of soft active devices along various length scales.