A preprogrammed force field generated in a confined space enables external-module-free anisotropic vat-photopolymerization 3D printing

Abstract

Additive Manufacturing, commonly known as 3D printing (3DP), continuously drives a paradigm shift in manufacturing processes from traditional mass production to individually optimized on-demand manufacturing. Vat-photopolymerization (VP) 3DP is a well-established methodology that enables highly precise high-speed modeling of intricate objects from photoresins with an inexpensive 3DP device. However, it remains a challenge to fabricate anisotropic objects without an external-field-applying module, which induces the alignment of molecular or particulate components in the photoresins. Herein, a simple, affordable, and easily accessible approach for fabricating precise and intricate anisotropic composite materials based on external-module-free anisotropic VP (AVP)-3DP. Preprogrammed force field, i.e., compressional stress in a confined space within a layer to be cured generated during the repetitive descending and ascending motion of a platform for anchoring printed objects in typical VP-3DP processes effectively stack mica flakes within a layer to be cured. While the AVP-3DP of composite resin containing mica flakes with the size of 3 μm, which is sufficiently smaller that the thickness of a layer to be cured, afforded a more isotropic material, those with the sizes down to 10 μm afforded highly anisotropic printed objects, suggesting tunability in anisotropy simply by changing the type of mica flakes. The proposed AVP-3DP methodology leads to anisotropy in the mechanical properties of the 3D-printed object by direction, allowing for up to a 4-fold differentiation for flexural strength and up to a 2-fold differentiation for flexural modulus (E). Moreover, with AVP-3DP of a composite resin containing specific mica flakes, exceptionally high average E of 13.6 GPa has been achieved, which is surprisingly comparable to that of metal lead (E = 13–15 GPa). The ability to create anisotropic composites through AVP-3DP paves the way for the development of next-generation highly precise functional anisotropic objects having intricate geometries with tailored mechanical performance for diverse applications.