No abstract

Bone defects resulting from trauma or tumor are one of the most challenging problems in clinical settings. Current tissue engineering (TE) strategies for managing bone defects are insufficient, owing to without using optimal osteoconductive material and seeding cells capable of superior osteogenic potential; thus their efficacy is instable. Herein, a novel TE strategy was developed for treating bone defects. First, the decellularized bone matrix (DBM) was manufactured into powders, and these DBM powders preserved the ultrastructural and compositional properties of native trabecular bone, are non-cytotoxic and low-immunogenic, and are capable of inducing the interacted stem cells differentiating into osteogenic lineage. Then, a subtype of osteoprogenitors was isolated from mouse long bones, and its high osteogenic potential was identified in vitro. After that, we constructed a “bone-forming unit” by seeding the special subtype of osteoprogenitors onto the DBM powders. In vivo performance of the “bone-forming units” was determined by injecting into the defect site of a mouse femoral epiphysis bone defect model. The results indicated that the “bone-forming unit” was capable of enhancing bone defect healing by regulating new bone formation and remodeling. Overall, the study establishes a protocol to construct a novel “bone-forming unit,” which may be an alternative strategy in future bone TE application.

Gas foil bearing has been used in high-speed turbomachinery for its high speed, high adaptability, and eco-friendly. The stability of the rotor bearing system is greatly enhanced due to the flexible foil support structure. In the foil supporting structure, vibration energy of the rotor bearing system can be absorbed by the Coulomb friction dissipation. In order to evaluate the frictional dissipation on bearing performance, a quasi-2-dimensional mechanical model is proposed considering the Coulomb friction. The Coulomb damping dissipation characteristics of the bearing in operating conditions are analyzed by coupling gas film. Frictional analysis is conducted on the bump foil bearing with different structural parameters, such as bump height, foil thickness, friction coefficient and number of bump foil strips. The stiffness of the foil bump is less affected by the base load. In the process of foil bearing design, the optimal friction coefficient, bump height should be properly selected in favor of either foil bearing stiffness or damping characteristics. In addition, the overall performance of bump foil bearing is strongly affected by the number of bump foil strips.

No abstract

The liquefaction of hydrogen is considered to be a crucial process in the large-scale utilization of hydrogen energy. In hydrogen liquefaction, hydrogen turbo-expander is a key refrigerating machine for high liquefaction efficiency. Performance of the turbo-expander is directly affected by the hydrogen gas bearings. To obtain a deep understanding of the performance characteristics of hydrogen gas bearings, the static and dynamic characteristics of herringbone grooved journal bearings under hydrogen and other lubricating gases were numerically calculated and compared. The bearing load capacity and critical mass of hydrogen gas bearings were slightly lower than those of helium-, air- and nitrogen-lubricated bearings. To improve the performance of the hydrogen gas bearings used in high-speed turbo-machinery, the influence of working conditions was analyzed. It is found that the load capacity of hydrogen gas bearings can be improved by increasing the ambient pressure, reducing the gas film clearance, and raising the bearing eccentricity ratio. Meanwhile, the critical mass increases, and the bearing dynamic stability is enhanced.