Titanium alloy scaffolds have recently gained substantial interest for the treatment of critical-size bone defect, particularly along with the maturity of the 3D printing technology that is capable of turning scaffold design ideas into real implants. As titanium alloys lack surface osteogenic activity, for improved biological performance of such scaffolds, surface modification is necessary. Various coating materials and coating methods have been explored. In this study, we developed a unique surface modification method to provide the surface of 3D printed titanium scaffolds with nano-sized structure and bioactive agent. Uniform, ordered TiO₂ nanotube arrays were formed by applying two-step anodization, and then mesoporous bioactive glass (MBG) was loaded into nanotubes. The results of in vitro immersion testing showed that bioactive ions, i.e., Si and Ca ions, could be steadily and continuously released from MBG into basal medium. The assessment of the responses of hBMSCs confirmed that the surface-modified scaffolds supported the adhesion and proliferation of hBMSCs, indicating good surface cytocompatibility. The developed method of combining surface nanostructure and bioactive agent could be used as a new strategy to improve the osteogenic activity of 3D printed titanium alloy scaffolds.

The effects of pore throat structure on gas permeability in tight sand reservoir were investigated using helium-measured porosity, pulse decay permeability, casting thin sections, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and constant-rate mercury injection for five sandstone samples from the Upper Triassic Yanchang Formation in the Western Ordos Basin, China. Results show that permeability values are in the range of 0.474-2.290 mD. The strong variation may be due to the effect of mineral composition and pore-throat structure. Generally, sandstone samples of higher content of quartz, chlorite film, and slit-shaped throat tend to have higher permeability. The movable fluid porosity numerically equals to the product of porosity and the movable fluid saturation based on the film bound water, which can comprehensively reflect the influence of fluid flow channels on porosity while neglecting the influence of bound fluids in the fine pores of clay minerals in the tight reservoirs. Larger movable fluid porosity values mean larger pore spaces for the movable fluids, which contribute to larger permeability. It is more reasonable to analyze the movable fluid pore-throat radius as a range. The homogeneous pore throat structure lead to a narrow lower limit range of the movable fluid pore-throat radius, which is favorable for the fluid flow. Meanwhile, if the lower bound of the lower limit range of the movable fluid pore-throat radius is small, pores and throats are less plugged, and thus make the conditions favorable for fluid flow. The contribution of throats to the pore volume is critical in influencing reservoir permeability as it can directly control the lower limit of the movable fluid pore-throat size. The pore-throat radius where throats account for the smallest amount in the pore space increases with the permeability, which indicates that larger proportions of large throats result in larger throat radius and higher pore connectivity, leading to higher permeability.