Roll-to-roll tomographic volumetric additive manufacturing

Abstract: Additive manufacturing (AM) has revolutionized the fabrication of devices with precisely controlled optical, fluidic, mechanical, and filtering properties, offering greater design freedom than conventional manufacturing methods. Tomographic volumetric additive manufacturing (TVAM) has many advantages compared to other AM methods including smooth layer-less surfaces, support-free and shear force-free printing, material versatility, and speed of production which are translatable to the microscale and evident in printed microfluidic devices and micro-optical components. However, as the patterning scale is reduced, the depth of field of the optical projection system 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) TVAM 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 several millimeters in thickness. Finally, we demonstrate printing of complex lattice structures with length more than 60 cm and minimum feature size of 200 um with the R2R TVAM system.