Biological structural materials, despite consisting of limited kinds of compounds, display multifunctionalities due to their complex hierarchical architectures. While some biomimetic strategies have been applied in artificial materials to enhance their mechanical stability, the simultaneous optimization of other functions along with the mechanical properties via biomimetic designs has not been thoroughly investigated. Herein, iron oxide/carbon nanotube (CNT)-based artificial nacre with both improved mechanical and electromagnetic interference (EMI) shielding performance is fabricated via the mineralization of Fe₃O₄ onto a CNT-incorporated matrix. The micro- and nano-structures of the artificial nacre are similar to those of natural nacre, which in turn improves its mechanical properties. The alternating electromagnetic wave-reflective CNT layers and the wave-absorptive iron oxide layers can improve the multiple reflections of the waves on the surfaces of the reflection layers, which then allows sufficient interactions between the waves and the absorption layers. Consequently, compared with the reflection-dependent EMI-shielding of the non-structured material, the artificial nacre exhibits strong absorption-dependent shielding behavior even with a very low content of wave-absorptive phase. Owing to the high mechanical stability, the shielding effectiveness of the artificial nacre that deeply cut by a blade is still maintained at approximately 70%−96% depending on the incident wave frequency. The present work provides a new way for designing structural materials with concurrently enhanced mechanical and functional properties, and a path to combine structural design and intrinsic properties of specific materials via a biomimetic strategy.

Chitin hydrogel has been recognized as a promising material for various biomedical applications because of its biocompatibility and biodegradability. However, the fabrication of strong chitin hydrogel remains a big challenge because of the insolubility of chitin in many solvents and the reduced chain length of chitin regenerated from solutions. We herein introduce the fabrication of chitin hydrogel with biomimetic structure through the chemical transformation of chitosan, which is a water-soluble deacetylated derivative of chitin. The reacetylation of the amino group in chitosan endows the obtained chitin hydrogel with outstanding resistance to swelling, degradation, extreme temperature and pH conditions, and organic solvents. The chitin hydrogel has excellent mechanical properties while retaining a high water content (more than 95 wt.%). It also shows excellent antifouling performance that it resists the adhesion of proteins, bacteria, blood, and cells. Moreover, as the initial chitosan solution can be feasibly frozen and templated by ice crystals, the chitin hydrogel structure can be either nacre-like or wood-like depending on the freezing method of the precursory chitosan solution. Owing to these anisotropic structures, such chitin hydrogel can exhibit anisotropic mechanics and mass transfer capabilities. The current work provides a rational strategy to fabricate chitin hydrogels and paves the way for its practical applications as a superior biomedical material.

The biomineralization of CaCO₃ often involves the transformation of amorphous precursors into crystalline phases, which is regulated by various proteins and inorganic ions such as Mg²⁺ ions. While the effects of Mg²⁺ ions on the polymorph and shape of the crystalline CaCO₃ have been observed and studied, the interplay between Mg²⁺ ions and CaCO₃ during the mineralization remains unclear. This work focuses on the mechanism of Mg²⁺ ion-regulated mineralization of CaCO₃. By tracing the Mg isotope fractionation, the different mineralization pathways of CaCO₃ under different Mg²⁺ ion concentrations had been clarified. Detailed regulatory role of Mg²⁺ ions at the different stages of mineralization had been proposed through combining the fractionation data with the analyses of the CaCO₃ polymorph and shape evolution. These results provide a clear view of the Mg-mediated crystallization process of amorphous CaCO₃, which can be used to finely control the phase of the crystalline products according to different needs.