A Tunable Approach to Formulate Sacrificial Molds Using Vat Photopolymerization 3D Printing

Vat photopolymerization (VPP) 3D printing typically produces thermosetting polymer networks from (meth)acrylate resins, leveraging their fast cure kinetics and commercial availability to achieve a high cross-linking density and adequate mechanical properties. Herein, we demonstrate a tunable and systematic approach that employs commercially available components to enable VPP printing of dissolvable or disintegrable structures, used as sacrificial tooling to cast materials that cannot be directly 3D printed into complex geometries. The developed resin is capable of feature sizes as low as 40 μm, and its printability and speed are similar to those of common commercial VPP resins. To achieve dissolution in a mildly basic aqueous solution, hydrophilic and hydrophobic constituents are evaluated to understand their contribution to the kinetics of network degradation and ultimately disintegration. It is shown that the inclusion of a nonreactive plasticizer is necessary to achieve a printed preswollen network that is disintegrable; however, the hydrophilicity of the plasticizer is not critical. The chemical identity of the reactive diluent, which chemically reacts with the main chain polymer to modulate cross-linking density, requires significant hydrophilic character to allow for the diffusion of the base into the network to participate in the hydrolysis of ester bonds comprising the cross-links of the network. To demonstrate the utility of the process, a mold for interpenetrating tetrahedral lattices is 3D printed, followed by the casting of 15 vol % carbon fiber-loaded urethane elastomer into the mold. The same mold was used to cast Shore 20A silicone with >500% elongation to failure to show the fabrication of highly elastomeric geometries with mechanical properties unattainable with directly printed materials.