Multicolor tomographic volumetric printing: property modulation and beyond

Volumetric additive manufacturing based on the principles of tomographic reconstruction has seen inspiring advancements in the past three years. Here we discuss the desirability and challenges associated with using more than one color in computed axial lithography to realize multiple functionalities. We first recap the implementation of a dual color system for spatial control of workpiece stiffness. The orthogonal polymerization of two independent yet interlaced networks allows fine tuning of the end product’s mechanical property from hydrogel-like to thermoset-like. The challenge in maximizing achievable property contrast led us to develop a sinogram computation strategy that differentially prioritize voxels. However, such a strategy puts a stringent requirement on the projecting resolution. We discuss the feasibility of alleviating such a requirement by lifting the non-negativity constraint for tomographic printing. We laid out the theoretical framework for a binary photoinhibitory system, which creates a stationary state with controllable stability on the phase diagram. We show that if illumination of two wavelengths are coordinated to steer a system such that it revolves counterclockwise about the origin, the two wavelengths become effectively negative to each other in the context of polymerization initiation. We further explain why creating negative illumination helps alleviate the resolution requirement. Combined, these efforts lead us to a hypothetically tri-color system that holds the potential of realizing full orthogonality between geometric control and property modulation.