![]() 3D printing of microstructured composites reinforced by 1D fillers is easier to achieve as the fillers only need to be aligned along one direction. Current methods that utilise inks containing stiff fillers generally make use of shear-induced or field-assisted alignment of the fillers 11, 12. However, such techniques are usually limited to printing polymers with varied mechanical properties and cannot fully realise the same properties as composites containing actual stiff fillers. One strategy to print microstructured composites is to use multimaterial methods such as polyjet printing or fused deposition modelling to print combinations of soft and stiff materials 8, 9, 10. Although exciting progress has been made in the field of 3D printing, it is still challenging to fabricate these microstructured composites due to the complex anisotropic and multimaterial layered structure required. Aside from mechanical properties, microstructured composites containing functional fillers such as aligned graphene or hexagonal boron nitride (hBN) microplatelets also display enhanced thermal and electrical properties 6, 7. ![]() These structures have high stiffness owing to the high filler content, while their layered architecture toughens the structure 5. For example, bioinspired Bouligand and nacre-like structures are formed by stacked layers of aligned stiff fibres and platelets respectively, within a soft matrix. Microstructured composites are interesting as they give rise to superior properties. More recently, 3D printing has been extended to fabricate microstructured composites consisting of orderly arranged 1D fibrous or 2D plate-shaped anisotropic reinforcement fillers. However, recent advancements have allowed more classes of materials to be 3D printed for use in multidisciplinary fields such as aerospace, robotics, biomedical and electronic applications 1, 2, 3, 4. Traditionally, 3D printing is used for small batch prototyping with limited material compatibilities. Three-dimensional (3D) printing is a manufacturing technology that generates freeform 3D structures using layer-by-layer deposition. MDOD thus creates a large design space to enhance the mechanical and functional properties of 3D printed electronic or sensing devices using a wide range of materials. We showcase the capabilities of MDOD by printing multimaterial piezoresistive sensors with tunable performances based on the local microstructure and composition. Moreover, MDOD allows multimaterial printing with voxelated control. By performing drop-on-demand printing using aqueous slurry inks while applying an external magnetic field, MDOD can print composites with microplatelet fillers aligned at set angles with high filler concentrations up to 50 vol%. In this study, we develop a magnetically assisted drop-on-demand 3D printing technique (MDOD) to print aligned microplatelet reinforced composites. However, it is still challenging to achieve good control of the filler arrangement and high filler concentration simultaneously, which limits the printed material’s properties. Microstructured composites with hierarchically arranged fillers fabricated by three-dimensional (3D) printing show enhanced properties along the fillers’ alignment direction.
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