Natural inorganic-organic composites exhibit an exceptional combination of stiffness, strength, and toughness, owing to their intricate hierarchical composite structures. Firstly, as natural materials form through bottom-up growth, they are assembled from the most basic building blocks in a hierarchical manner. Secondly, their compositions feature (1) aligned stiff anisotropic fibres or particles with a thickness ranging from one to a few hundred nanometres, (2) connected by a soft matrix, and (3) a tight interface in between. This hierarchical organization, from molecular to macro scales, achieves a strong coupling between the inorganic and organic constituents, fostering synergistic interactions across multiple length scales. Inspired by the hierarchical composite design in nature, this presentation introduces a hierarchical design strategy via direct-ink-write (DIW) 3D printing, which integrates shear-induced alignment of ceramic platelets within a polymer matrix at the unit strut level, and further 3D prints the unit struts into macro-structures for desired properties.

In the first study, ceramic nanocomposites with a high inorganic content (95 wt.%) and a minimal organic phase are prepared, which reveal excellent flexibility for shape morphing owing to their bioinspired concentric lamellar microstructure. These flexible ceramic nanocomposites can be used in 4D printing through a programmable prestrain approach to deform into complex structures hardly achievable with conventional 3D printing. With a high inorganic content, the materials also exhibit excellent mechanical properties, anisotropic thermal properties, and resistance to corrosion and high temperatures.[1]

In another study, the hierarchical strategy is leveraged to fabricate strong and tough ceramic-reinforced organo-hydrogels consisting of (1) 5 wt.% ceramic platelets, (2) a highly crystalline poly(vinyl alcohol) (PVA) organo-hydrogel matrix, and (3) silane-treated ceramic-polymer interfaces. By 3D printing unit struts with the above compositions into a selection of bioinspired macro-architectures, this strategy is capable of translating mechanical mechanisms from natural materials into composite organo-hydrogels with a combination of high stiffness, strength, and toughness, through multi-scale energy dissipation mechanisms. Also, the composite organo-hydrogels can be simultaneously endowed with excellent operation tolerance and electrical conductivity for potential applications in flexible electronics under mechanically demanding conditions.[2] Hence, these studies showcase a model strategy that extracts the hierarchical composite design principles from nature and applies them to harness the benefits of both inorganic and organic constituents in composite materials. Being versatile and applicable in diverse material compositions, this strategy shall also inspire future research on the design and fabrication of bioinspired materials.

References

[1] T. Li, Q. Liu, H. Qi, W. Zhai; Small, 2022, 2204032.

[2] Q. Liu, X. Dong, H. Qi, T. Li, Y. Zhao, G. Li, W. Zhai; Under review.