The mechanical properties of mineral-based structural composite materials can be notably improved by bioinspired multiscale structure designs, which benefits their practical applications. Matrix-induced mineralization process has proved an efficient way to synthesize bioinspired mineral-based composites. However, although it is much faster than the growth of natural biominerals, this process still consumes considerable time to produce a composite with limited size. We herein report a combinational fabrication strategy that integrates rapid organic matrix layer-induced mineralization and layer lamination. While the strategy is featured for time saving compared with previous methods based on mineralization, the size of the final composite can be increased simply by using larger layers. Macroscopic and microscopic mechanical characterizations of the composite reveal its good mechanical performance. More importantly, by spraying a water-insoluble polymer coating on each mineralized layer, the composite exhibits enhanced tolerance to water that wet samples retain good mechanical properties. Besides, the composite inherits the biocompatibility of its raw materials. These advantages ensure the application of such composite as compact bone repair material.

Calcium phosphate salts, which have a similar composition with the mineral phase in natural bone, have been extensively studied for their applications in bone regeneration. However, another calcium-based mineral, calcium carbonate, which is also frequently found in biological materials, is seldom considered for this purpose despite their high biocompatibility and bioactivity. Herein, we report the performance of five types of biomimetic mineral films that are fabricated via the mineralization of calcium carbonate and calcium phosphate on chitin. These films have different in vitro degradation dynamics because of their varied stability. They also show distinct surface roughness, modulus and hardness. Cytological analyses reveal that, although these films all display high biocompatibility, they exhibit diverse osteogenic differentiation behavior, which can be attributed to their respective physicochemical properties. Real-time polymerase chain reaction assays suggest that the aragonite group can lead to higher expression of the six representative osteogenic genes, which even surpasses the amorphous calcium phosphate group and the aragonite-crystalline calcium phosphate composite group. These results illustrate that calcium carbonate and its composites with calcium phosphate are potential bone repair materials. We anticipate these mineral-based materials with controlled physiochemical properties, along with their specific fabrication techniques, can facilitate the design and production of mineral-based bone repair materials with optimized performance.

As a renewable, biocompatible, biodegradable soft material, chitin hydrogels have better advantages in stability, antibacterial activity, antifouling, cost, immunogenicity, and so on than most polymer hydrogels. However, compared with other widely used polymer hydrogels with high strength and toughness, the practical applications of chitin-based hydrogels have been limited by their weak mechanical properties, such as cartilage repair and meniscus replacement. Here, we present the design and fabrication of chitin hydrogels with excellent mechanical strength and toughness by a dehydration and rehydration strategy. By sequential dehydration and rehydration processes, the crystalline domains in the chitin hydrogels can be properly controlled. With optimized crystallinity, the elastic modulus of the chitin hydrogels exceeds all previously reported values, and the fracture toughness is even comparable to some synthetic polymer hydrogels, while maintaining a high-water-content of about 80 wt.%. At the same water content, the mechanical properties of the chitin hydrogels are positively correlated with the hydrogel crystallinity, which proves that the change of mechanical properties of hydrogels is not simply dependent on weight concentration. The hydrogels can be further strengthened by incorporating other biopolymers that are intrinsically weak, which makes the hydrogels promising for applications in fields such as cartilage repair and meniscus replacement. Moreover, the hydrogels enable loading and release of water-soluble and poorly water-soluble drugs. This highly extendable strengthening and toughening strategy of chitin and chitin-based biopolymer hydrogels paves the way for their widely applications.

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.