Multimaterial Vat Polymerization Additive Manufacturing

Additive manufacturing is the process of creating an object from a digital three-dimensional (3D) design using hardware that deposits and adds materials successively until the desired object is formed. Vat polymerization is a type of additive manufacturing technique that offers an attractive strategy for fabricating 3D objects due to its high resolution, versatility of feedstock materials, and high dimensional accuracy. However, the ability to spatially control the placement of multiple materials during vat polymerization is limited by mechanical designs that can restrict printing to a single photocurable resin, making it difficult to create complex geometries with embedded functionality. In this review, we highlight work-arounds that have been employed, such as manually switching resins, as well as two key areas of innovation: mechanical hardware design and the chemistry of materials. These methods include systems which automatically switch resin vats, volumetric additive manufacturing which overprints a secondary 3D structure on top of an existing object, and specially formulated, unique material chemistries, such as those which enable dual wavelength light to initiate orthogonal chemistry mechanisms, control of the degree of cross-linking with variation in light parameters, and phase separation of functional materials. Perspectives on the interplay of printer type and material chemistry, the constraints they impose on one another, and the future of multimaterial vat polymerization are described. In order for vat polymerization to emerge as a viable technology for multimaterial additive manufacturing, both mechanical hardware design and chemistry of materials must be codeveloped.