Lightweight high-strength metal matrix nano-composites (MMNCs) can be used in a wide variety of applications, e.g., aerospace, automotive, and biomedical engineering, owing to their sustainability, increased specific strength/stiffness, enhanced elevated temperature strength, improved wear, or corrosion resistance. A metallic matrix, commonly comprising of light aluminum or magnesium alloys, can be significantly strengthened even by very low weight fractions (~1 wt%) of well-dispersed nanoparticles. This review discusses the recent advancements in the fabrication of metal matrix nanocomposites starting with manufacturing routes and different nanoparticles, intricacies of the underlying physics, and the mechanisms of particle dispersion in a particle-metal composite system. Thereafter, the microstructural influences of the nanoparticles on the composite system are outlined and the theory of the strengthening mechanisms is also explained. Finally, microstructural, mechanical, and tribological properties of the selected MMNCs are discussed as well.

Flame-retardant and thermal management structures have attracted great attention due to the requirement of high-temperature exposure in industrial, aerospace, and thermal power fields, but the development of protective fire-retardant structures with complex shapes to fit arbitrary surfaces is still challenging. Herein, we reported a rotation-blade casting-assisted 3D printing process to fabricate nacre-inspired structures with exceptional mechanical and flame-retardant properties, and the related fundamental mechanisms are studied. 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) modified boron nitride nanoplatelets (BNs) were aligned by rotation-blade casting during the 3D printing process to build the “brick and mortar” architecture. The 3D printed structures are more lightweight, while having higher fracture toughness than the natural nacre, which is attributed to the crack deflection, aligned BN (a-BNs) bridging, and pull-outs reinforced structures by the covalent bonding between TMSPMA grafted a-BNs and polymer matrix. Thermal conductivity is enhanced by 25.5 times compared with pure polymer and 5.8 times of anisotropy due to the interconnection of a-BNs. 3D printed heat-exchange structures with vertically aligned BNs in complex shapes were demonstrated for efficient thermal control of high-power light-emitting diodes. 3D printed helmet and armor with a-BNs show exceptional mechanical and fire-retardant properties, demonstrating integrated mechanical and thermal protection.

Background Bone tissue engineering (BTE) is considered a promising technology for repairing bone defects. Mg 2+ promotes osteogenesis, which makes Mg-based scaffolds popular for research on orthopedic implant materials. Angiogenesis plays an important role in the process of bone tissue repair and regeneration, and it is one of the important problems in BTE urgently needs to be solved. Methods Mg was firstly coated with Ca-deficient hydroxyapatite (CDHA) via hydrothermal treatment, and polydopamine (DOPA) was then used as the connecting medium to immobilize vascular endothelial growth factor (VEGF) on the CDHA coating. The physicochemical properties of the coatings were characterized by SEM, EDS, XPS, FTIR and immersion experiment in SBF. The ahesion, proliferation, and angiogenesis potential of the coatings were determined in vitro. Results The composite coating significantly improved the corrosion resistance of Mg and prohibited excessively high local alkalinity. VEGF could be firmly immobilized on Mg via polydopamine. The CCK-8, live/dead staining and adhesion test results showed that the VEGF-DOPA-CDHA coating exhibited excellent biocompatibility and could significantly improve the adhesion and proliferation of MC3T3-E1 cells on Mg. Microtubule formation, immunofluorescence and Quantitative Real-Time PCR (qRT-PCR) experiments showed that VEGF immobilized on Mg still possessed bioactivity in promoting the differentiation of rat mesenchymal stem cells into endothelial cells. Conclusion In this study, we enabled the angiogenic biological activity of Mg by immobilizing VEGF on Mg. Mg was successfully coated with a functional VEGF-DOPA-CDHA composite coating. The CDHA coating significantly increased the corrosion resistance of Mg and prohibited the negative effect of excessively high local alkalinity on the biological activity of VEGF. As an intermediate layer, the DOPA coating protects Mg, and DOPA provides a binding site for VEGF so that VEGF can be firmly immobilized on Mg and give Mg angiogenic bioactivity during the initial period of implantation. The translational potential of this article The treatment of large bone defect is still one of the orthopedic trauma diseases that are difficult to be completely treated in clinic. The development of tissue engineering technology provides a new option for the treatment of large bone defects. The regeneration of blood vessels is of great significance for the repair of bone defects. In this study, VEGF was connected on the surface of degradable magnesium by covalent bonding. Vascular biofunctionalized magnesium scaffolds are expected to regenerate bone tissue with blood transport and be used in the clinical treatment of large bone defects.

No abstract

In this study, hexagonal-packed Si nanorods (SiNRs) arrays were fabricated and conjugated with Au nanoparticles (AuNPs) in different spatial distributions for surface-enhanced Raman spectroscopy (SERS). The AuNPs were functionalized on the bottom of SiNRs (B-SiNRs@AuNPs), top of SiNRs (T-SiNRs@AuNPs) and sides of SiNRs (S-SiNRs@AuNPs), respectively. Our results demonstrated that the SiNRs conjugated with AuNPs on the sides achieved high reproducibility in detection of R6G molecules, while the AuNPs on the top of the SiNRs obtained the strongest Raman enhancement. In addition, the substrate with S-SiNRs@AuNPs obtained the highest spatial uniformity of enhancement. The finite-difference time-domain simulation gave further evidence that the incident light could be confined in the space of SiNRs arrays and yield a zero-gap enhancement coupled with the AuNPs. Our study provided a spatially tunable SiNRs@AuNPs substrate with high sensitivity and reproducibility in molecular detection.