RESUMEN
Graphene sitting on hexagonal boron nitride (h-BN) always exhibits excellent electrical properties. And the properties of graphene onh-BN are often dominated by its domain size and boundaries. Chemical vapor deposition (CVD) is a promising approach to achieve large size graphene crystal. However, the CVD growth of graphene onh-BN still faces challenges in increasing coverage of monolayer graphene because of a weak control on nucleation and vertical growth. Here, an auxiliary source strategy is adapted to increase the nucleation density of graphene onh-BN and synthesis continuous graphene films. It is found that both silicon carbide and organic polymer e.g. methyl methacrylate can assist the nucleation of graphene, and then increases the coverage of graphene onh-BN. By optimizing the growth temperature, vertical accumulation of graphitic materials can be greatly suppressed. This work provides an effective approach for preparing continuous graphene film onh-BN, and may bring a new sight for the growth of high quality graphene.
RESUMEN
Loading of an appropriate amount of rhBMP-2 and avoiding its "burst-release" are key challenges for upgrading the biological performance of thin bioactive coatings on metal implants. In this study, we adopted incorporation of chitosan nanospheres into thin mineralized collagen coatings to enhance rhBMP-2 loading and improve releasing behavior based on the good affinity of chitosan for proteins and the large surface area of nanospheres. We realized the incorporation process by electrophoretic injection. Using chitosan nanospheres, we were able to increase the rhBMP-2 loading amount in the thin coating by 2.7-fold (from 446 ng cm-2 to 1186 ng cm-2), and showed that the rhBMP-2 exhibited sustained release behavior. MC3T3-E1 cells cultured on the rhBMP-2/chitosan nanosphere-incorporated thin coatings (Col/Cs/BMP) showed good cell attachment and proliferative behavior, and high levels of differentiation and mineralization. In in vivo tests, spiral CT analysis and histological observations demonstrated that Col/Cs/BMP coatings on metal implants were able to increase bone density and accelerate new bone growth after implantation for 4 to 8 weeks, and the boundary between host bones and new bones disappeared after implantation for 8 weeks. The pull-out tests further confirmed that the Col/Cs/BMP coatings could significantly enhance osseointegration. The present results indicate that incorporation of chitosan nanospheres into thin coatings is an effective way to enhance the loading amount properly, improve the release behavior of rhBMP-2 and finally accelerate the osseointegration process.
RESUMEN
It is desired that the coatings on metallic implants have both excellent biological responses and good loading-release capacities of biological factors or drugs. So far, the challenge still remains, because the morphology and composition of the bioactive coatings are usually not favorable for accommodating drug molecules. In this study, we adopted an approach of incorporating chitosan nanospheres into a thin mineralized collagen coating; this approach is based on the good loading-release behavior of the nanospheres and the good cytocompatibility of the thin coating. The incorporation of chitosan nanospheres into the mineralized collagen coatings was realized by electrolytic co-deposition. The morphologies and microstructures of the resulting coatings were characterized by SEM, and the phase and chemical compositions of the coatings were measured by XRD and FTIR. The loading-release capacity for vancomycin hydrochloride (VH) was determined by ultraviolet spectrophotometry. MTS assay was used to evaluate cytocompatibility, and in vitro bacterial adhesion was tested for assessing the antibacterial effects of the VH-loaded coatings. The chitosan nanospheres adhered tightly to collagen fibrils. The incorporated coatings facilitated the sustained release of VH, and had a clear antibacterial effect. The incorporation of chitosan nanospheres into mineralized collagen coatings demonstrates an effective way to improve the drug loading-release capacity for the thin coatings. This formulation had a highly effective biological response.
