Bioinspired flexible high-strength hydrogel with hierarchically ordered structure

What is it about?

The synthetic hydrogels with high water contents are promising for various applications, however, they usually exhibit low mechanical properties. In this work, inspired by the natural biological soft tissues, whose hierarchically ordered fibrous structures result in high strength and good flexibility, a flexible, high-strength, and versatile hydrogel with the fiberboard-and-mortar hierarchically ordered structure (HFMOS) is developed based on ultralong hydroxyapatite (HAP) nanowires and polyacrylic acid (PAA). The as-prepared HFMOS hydrogel has a high water content (∼ 70 wt.%), dense structure, and excellent mechanical properties, and these properties are similar to those of the human cartilage and are superior to many hydrogels reported in the literature. The excellent mechanical properties of the HFMOS hydrogel originate from the combination of the fiberboard-and-mortar hierarchically ordered structure, reinforcement of ultralong HAP nanowires, strong interfacial strength, and multiple energy dissipation pathways. Moreover, thanks to the controllable components and injection procedure, the HFMOS hydrogel with a Janus structure is prepared for particular applications. The HFMOS hydrogel possesses abundant ordered water channels, and can be used for loading, release, and directed delivery of various functional substances. Thus, the as-prepared flexible, high-strength, and versatile HFMOS hydrogel possesses a great potential for various applications such as water purification, pollution treatment, biomedicine, nanofluidic devices, and high-performance structural materials.

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Why is it important?

In this work, we have developed a new kind of flexible, high-strength and versatile hydrogel with the fiberboard-and-mortar hierarchically ordered structure (HFMOS) based on ultralong HAP nanowires and polyacrylic acid (PAA), as shown in Scheme 1. The as-prepared HFMOS hydrogel is a inorganic/organic nanocomposite with a high water content (~70 wt.%), dense structure, and excellent mechanical properties (high strength and high Young’s modulus), and it has an anisotropic hierarchically ordered structure similar to the biological soft tissues, which are superior to many synthetic hydrogel materials reported in the literature. The HFMOS hydrogel possesses abundant ordered water channels, and can be used for loading, release and directed delivery of various functional substances. Moreover, the hierarchically ordered structure of the HFMOS hydrogel enables multiple energy dissipation pathways, such as the nanowire fracture, nanowire pull-out and deformation, and crack bridge after fracture, which can effectively reduce the stress concentration. The ordered PAA mortar layers between lamellar fiberboards serve as the water channels for the loading, release and directed transportation of various functional substances. In addition, the HFMOS hydrogel with a Janus structure can be prepared by controlling the spatial distribution of different ion-doped ultralong HAP nanowires during the injection process of the ultralong HAP nanowire slurry. The as-prepared HFMOS hydrogel with the ultralong HAP nanowire-based fiberboard-and-mortar hierarchically ordered structure and excellent mechanical properties is promising for various applications.

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