Background: Previous studies have demonstrated that mesenchymal stem cells (MSCs) can promote the recovery of neural function after cerebral apoplexy by secreting multiple cytokines. In addition, cell factor-derived extracellular vesicles play an important role in recovery of neural function. The aim of this study was to determine the effect of extracellular vesicles on neural functional recovery and brain tissue remodeling after cerebral apoplexy in a rat model. Methods: The rat models with local ischemic stroke was established and three random groups were created. In groups A and B, human bone marrow-derived MSCs and MSC-derived extracellular vesicles were transplanted into rats. In the control group (group C), only normal saline was injected. Then, we evaluated motor coordination ability, pathologic changes of the brain, immune responses in the central and peripheral nervous systems, regeneration of blood vessels, and nervous tissue in 4 weeks after cerebral apoplexy. Results: Obvious regeneration of blood vessels and nervous tissues were identified in groups A and B. There was no significant difference with respect to coordination between groups A and B, but coordination in groups A and B was significantly better than the control group. Immunohistochemical staining of brain tissue showed that extracellular vesicles exerted no effect on infiltration of immune cells in the central nervous system. Weakened immune suppression was noted 1 week after cerebral apoplexy, which provided a favorable environment for remodeling of brain tissue. Conclusion: MSC-derived extracellular vesicles accelerated neural functional recovery after cerebral apoplexy. The weakened immune suppression was beneficial to remodeling of brain tissue.
Applications of a metallic material highly depend on its mechanical properties, which greatly depend on the material’s grain sizes. Reducing grain sizes by severe plastic deformation is one of the efficient approaches to enhance the mechanical properties of a metallic material. In this paper, severe plastic deformation of equal channel angular pressing (ECAP) will be reviewed to illustrate its effects on the grain refinement of some common metallic materials such as titanium alloys, aluminum alloys, and magnesium alloys. In the ECAP process, the materials can be processed severely and repeatedly in a designed ECAP mold to accumulate a large amount of plastic strain. Ultrafine grains with diameters of submicron meters or even nanometers can be achieved through severe plastic deformation of the ECAP. In detail, this paper will give state-of-the-art details about the influences of ECAP processing parameters such as passes, temperature, and routes on the evolution of the microstructure of metallic materials. The evolution of grain sizes, grain boundaries, and phases of different metallic materials during the ECAP process are also analyzed. Besides, the plastic deformation mechanism during the ECAP process is discussed from the perspectives of dislocation slipping and twinning.
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