Abstract

Computed Axial Lithography For Volumetric Printing of Soft Structures

Hayden Taylor, Assistant Professor, Mechanical Engineering, University of California-Berkeley

Volumetric additive manufacturing is defined as producing the entire volume of a component or structure simultaneously — rather than by layering — and has been envisioned as a possible way to increase the speed of additive manufacturing. Until recently, however, no practicable technique existed for creating arbitrary 3D geometries volumetrically. Recently, we have demonstrated Computed Axial Lithography (CAL) to meet this need. CAL essentially reverses the principles of computed tomography (widely used in imaging, but not previously in fabrication) to synthesize a three-dimensionally controlled illumination dose within a volume of photocurable resin. The photosensitive volume rotates steadily while a video projector illuminates the material from a direction perpendicular to the axis of rotation. The illumination pattern typically changes >1000 times per revolution, so that light from many different projection angles contributes to the cumulative dose. Where the dose exceeds a threshold, the resin solidifies and the part is formed. In this talk I will discuss the CAL process in the context of its possible bioprinting applications. The CAL printing technique has several potential advantages. Because there is no relative motion between the component being printed and the resin during printing, the printing speed is not limited by resin flow effects, as it can be in layer-by-layer photopolymerization-based printing. The absence of relative motion also allows highly viscous resins or soft, highly compliant materials such as hydrogels to be printed. Because layers are not used in CAL, the surfaces of printed components are very smooth (c. 1–4 µm roughness in preliminary experiments), which may open up new applications. Additionally, it is possible to print objects around pre-existing solid objects that could have been made using a different material or process. This ‘overprinting’ capability suggests applications in mass-customization for end users and also potentially in fabricating biological structures with highly heterogeneous mechanical properties.