Roll-to-roll tomographic volumetric additive manufacturing for continuous production of microstructures on long flexible substrates

Tomographic volumetric additive manufacturing (VAM) has proven viable to 3D-print diverse materials including polymer, glass, ceramic, and hydrogel at the centimeter scale. As tomographic VAM is extended to the microscale, many of its advantages are translatable, including smooth layer-less surfaces, support-free and shear force-free printing, material flexibility, and speed of production. However, as we shrink the patterning scale, the depth of field shrinks much more rapidly and does so roughly with the square of the patterning scale. Consequently, the build volume is substantially reduced as the numerical aperture of the system is increased. Additionally, microscale tomographic VAM is currently limited to batch production, i.e., the photoresist container must be exchanged after the exposure phase is completed. In this work, we introduce roll-to-roll (R2R) tomographic VAM in which these limitations are addressed by unwrapping the precursor material into a film enabling continuous production of microstructures with theoretically unlimited length. We elaborate the design of a focus-multiplexed projection optical system that can scan the projection focal plane axially in sync with the refresh cycle of a digital micromirror device. We describe the process of iteratively optimizing and segmenting sinograms to produce long aperiodic microstructures with the focus tunable optical system. Furthermore, we formulate a thermally reversible organogel photoresist which is deposited onto the substrate in films multiple millimeters in thickness with slot-die coating. Finally, we present progress on printing with the R2R tomographic VAM system.