Super-robust superhydrophobic concrete for anti-icing, anti-freeze–thaw, and anti-corrosion.

Fluid bath-assisted three-dimensional (3D) printing is an innovative 3D printing strategy that extrudes liquid ink materials into a fluid bath to form various 3D configurations. Since the support bath can provide in situ support, extruded filaments are able to freely construct complex 3D structures. Meanwhile, the supporting function of the fluid bath decreases the dependence of the ink material's cross-linkability, thus broadening the material selections for biomedical applications. Fluid bath-assisted 3D printing can be divided into two subcategories: embedded 3D printing and support bath-enabled 3D printing. This review will introduce and discuss three main manufacturing processes, or stages, for these two strategies. The stages that will be discussed include preprinting, printing, and postprinting. In the preprinting stage, representative fluid bath materials are introduced and the bath material preparation methods are also discussed. In addition, the design criteria of fluid bath materials including biocompatibility, rheological properties, physical/chemical stability, hydrophilicity/hydrophobicity, and other properties are proposed in order to guide the selection and design of future fluid bath materials. For the printing stage, some key technical issues discussed in this review include filament formation mechanisms in a fluid bath, effects of nozzle movement on printed structures, and design strategies for printing paths. In the postprinting stage, some commonly used postprinting processes are introduced. Finally, representative biomedical applications of fluid bath-assisted 3D printing, such as standalone organoids/tissues, biomedical microfluidic devices, and wearable and bionic devices, are summarized and presented.

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Nanoclay-enabled self-supporting printing has been emerging as a promising filament-based extrusion fabrication approach for different biomedical and engineering applications including tissue engineering. With the addition of nanoclay powders, liquid build materials may exhibit solid-like behavior upon extrusion and can be directly printed in air into complex three-dimensional structures. The objective of this study is to investigate the effect of nanoclay on the extrudability of N -isopropylacrylamide (NIPAAm) and the effect of standoff distance on the print quality during nanoclay-enabled direct printing. It is found that the addition of nanoclay can significantly improve the NIPAAm extrudability and effectively eliminate die swelling in material extrusion. In addition, with the increase of standoff distance, deposited filaments change from over-deposited to well-defined to stretched to broken, the filament width decreases, and the print fidelity deteriorates. A mathematical model is further proposed to determine the optimal standoff distance to achieve better print fidelity during nanoclay-enabled direct printing. Based on the extrudability and standoff distance knowledge from this study, NIPAAm-Laponite nanoclay and NIPAAm-Laponite nanoclay-graphene oxide nanocomposite hydrogel precursors are successfully printed into a three-layered one-dimensional responsive pattern, demonstrating the good extrudability and print quality during nanoclay-enabled printing under optimal printing conditions.

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