Red-Light Tomographic Volumetric 3D Printing in Seconds for Fabrication of Colorless Structures

Non-pulsed red light photopolymerization is attractive for volumetric additive manufacturing because longer wavelengths can improve light penetration, lower scattering, and reduce photodamage compared with ultra-violet or blue irradiation. In this work, we utilized methylene blue and triethanolamine as a sacrificial type II photoinitiating system for poly(ethylene glycol) diacrylate (PEGDA) hydrogel printing with a custom-made red-light tomographic volumetric additive manufacturing system. With the optimized formulation, PEGDA hydrogel structures were printed by red light within 30 s. The resulting constructs were colorless, extractable, and contained fully formed internal channels. This work establishes a type II photochemistry system as a promising route for extending tomographic volumetric 3D printing toward lower-energy visible-light irradiation and rapid fabrication of colorless hydrogel constructs.