![]() Robocasting is a promising AM process which emerged two decades ago 14, and was initially used to produce ceramic woodpile scaffold structures 15. This is in part due to the inherent difficulties in melting these materials which limit the applicable AM techniques to powder bed processes 11, wet processes 12 and fused deposition 13. Most work has focused on printing molten polymers 9 and metals 10, while ceramics and glasses have received less attention. Its value is now recognised across a wide range of sectors from aerospace to biomedical engineering. In some cases the precision and fine detail that 3D printing affords has enabled the production of parts which would have been impossible using traditional manufacturing techniques. In recent decades 3D printing/additive manufacturing (AM) has progressed enormously, revolutionising the fields of rapid prototyping and the production of complex geometries. These materials exhibit microstructural designs able to direct crack propagation in three dimensions and to control fracture, generating strengths and toughness that are well beyond that of their constituent materials. Some well-studied examples include mammalian cortical bone 6, nacre 7 and certain areas of crustacean exoskeletons 8. In contrast, many natural materials exhibit a remarkable level of complexity, with intricate structures at a range of length scales. In particular they offer hints about how to combine strength and toughness, a goal that has been difficult to reach with synthetic composites as they are limited to relatively simple microstructures 5. Natural materials offer blueprints for the design of composites to achieve this objective 1, 2, 3, 4. In order to improve the mechanical properties of materials their structure and architecture need to be carefully controlled at a range of scales from nm to cm. In this way we can retain strength while enhancing toughness by using strategies taken from crustacean shells. To demonstrate the versatility of the approach we have fabricated highly mineralized composites with microscopic Bouligand structures that guide crack propagation and twisting in three dimensions, which we have followed using an original in-situ crack opening technique. This is achieved by manipulating the rheology of ceramic pastes and the shear forces they experience during printing. ![]() Here we show that robocasting can be used to build ceramic-based composite parts with a range of geometries, possessing microstructures unattainable by other production technologies. Natural structures provide blueprints to overcome this, however this approach introduces another trade-off between fine structural manipulation and manufacturing complex shapes in practical sizes and times. ![]() In modern composites there is a critical trade-off between strength and toughness. Natural structural materials like bone and shell have complex, hierarchical architectures designed to control crack propagation and fracture. ![]()
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