Rapid High Resolution Visible Light 3D Printing
Light-driven 3D printing to convert liquid resins into solid objects (i.e., photocuring) has traditionally been dominated by engineering disciplines, yielding the fastest build speeds and highest resolution of any additive manufacturing process. However, the reliance on high energy UV/violet light derived from decades of photolithography research, limits the materials scope due to degradation and attenuation (e.g., absorption and/or scattering). Chemical innovation to shift the spectrum into more mild and tunable visible wavelengths promises to improve compatibility and expand the repertoire of accessible objects, including those containing biological compounds and multi-material structures. Photochemistry at these longer wavelengths currently suffers from slow reaction times precluding its utility. Herein, novel panchromatic photopolymer resins were developed and applied for the first time to realize rapid high resolution visible light 3D printing. The combination of electron deficient iodonium and rich borate co-initiators were critical to overcoming the speed-limited photocuring with visible light. Furthermore, azo-dyes were identified as vital resin components to confine curing to irradiation zones, improving spatial resolution. A unique screening method was used to streamline optimization (e.g., exposure time and azo-dye loading) and correlate resin composition to resolution, cure rate, and mechanical performance. Ultimately, a versatile and general visible light-based printing method was shown to afford 1) stiff and soft objects with feature sizes < 100 μm, 2) build speeds up to 45 mm/h, and 3) mechanical isotropy, rivaling modern UV-based 3D printing technology and providing a foundation from which bio- and composite-printing can emerge.