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Recently, breakthroughs have been made in the use of mesenchymal stem cells (MSCs) to treat various diseases. Several stem cell types have been authorized as drugs by the European Medicines Agency and the U.S. Food and Drug Administration. The Chinese official document "Notification of the management of stem cell clinical research (trial)" was also published in August 2015. Currently, China has approved 106 official stem cell clinical research filing agencies and 62 clinical research projects, which are mostly focused on MSC therapy. Hence, the optimization and development of stem cell drugs is imperative. During this process, maximizing MSC expansion, minimizing cell loss during MSC transplantation, improving the homing rate, precisely regulating the differentiation of MSCs, and reducing MSC senescence and apoptosis are major issues in MSC preclinical research. Similar to artemisinin extracted from the stems and leaves of Artemisia annua, ginsenoside Rg1 (Rg1) is purified from the root or stem of ginseng. In the human body, Rg1 regulates organ function, which is inseparable from its regulation of adult stem cells. Rg1 treatment may effectively regulate the proliferation, differentiation, senescence, and apoptosis of MSCs in different microenvironments in vitro or in vivo. In this review, we discuss recent advances in understanding the effect of Rg1 on MSCs and describe the issues that must be addressed and prospects regarding Rg1 regulation of MSCs in preclinical or clinical studies.

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A mixed lubrication model of textured cylinder liner-piston ring was built to investigate the effects of four array modes namely, square array, stagger array, stretching, and shortening along liner axis array of micro-dimples on the tribological properties of cylinder liner-piston ring pair. The simulation results indicate that micro-dimples can enhance the hydrodynamic effects of lube oil, improving the film bearing capability. However, the effects differ significantly under the four dimple array modes: for square array, the cylinder liner-piston ring pair is well lubricated due to the synergistic effects of uniformly spaced micro-dimples that form homogeneous bearing film even around the fired top dead center where the lubrication condition is harsh; while the film of stagger array is the thinnest among the four schemes, which means its lubrication is also the worst. From square array mode, to shortening and stretching along liner axis array, then to stagger array mode, the total friction force of cylinder liner-piston ring shows an upward trend. By utilizing laser surface texturing method, square array, stretching along liner axis array, and stagger array of micro-dimples were textured on the gasoline engine cylinder bores, followed by a set of engine bench tests. The experimental results demonstrate that the engine motored torque of the three array modes increases in turns, which validates that the anti-friction effect of square array is optimal whereas that of stagger array is the most inefficient.

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