Ultraviolet-assisted material extrusion of silicones with largely enhanced mechanical properties and isotropy

3D printed silicone elastomers, combining the favorable physiochemical performances of silicones with the unparalleled advantages of additive manufacturing, have gained significant attention from academia and industry owing to their attractive applications. However, there were several limitations in their existing printing techniques, such as the poor mechanical robustness of the products by vat polymerization and the conflicting rheological requirements for material extrusion. Herein, we report 3D printing of an ultraviolet (UV)-induced, platinum-catalyzed hydrosilylation silicone composite via UV-assisted material extrusion. It was found that UV assistance could enhance the shape-retaining capability during printing, and the achieved materials presented remarkably enhanced mechanical properties by almost an order of magnitude compared to other UV-cured silicones for 3D printing. The material was UV-curable and heat-curable, which allowed for manipulating the tensile, tearing, and relaxation properties by adjusting the curing technique. Moreover, the UV-cured silicone composites exhibited much enhanced mechanical isotropy compared to their heat-cured counterparts, indicating the potential to minimize the intrinsic hurdle of anisotropy for 3D printed products. Structural origins for the excellent properties were discussed in detail. This work will open new opportunities for developing highperformance 3D-printed silicones for engineering applications.