Declined regenerative potential and aggravated inflammation upon aging create an inappropriate environment for arterial regeneration. Macrophages are one of vital effector cells in the immune microenvironment, especially during biomaterials mediated repairing process. Here, we revealed that the macrophage autophagy decreased with aging, which led to aggravated inflammation, thereby causing poor vascular remodeling of artificial grafts in aging body. Through loading the autophagy-targeted drugs, rapamycin and 3-MA (3-methyladenine), in PCL (polycaprolactone) sheath of the PGS (poly glycerol sebacate) - PCL vascular graft, the essential role of macrophage autophagy was confirmed in regulating macrophage polarization and biomaterial degradation. Moreover, the utilization of rapamycin promoted anti-inflammatory polarization of macrophage by activating autophagy, which further promoted myogenic differentiation of vascular progenitor cells and accelerated endothelialization. Our study elucidated the contribution of pharmacological manipulation of macrophage autophagy in promoting regeneration of small caliber artery, which may pave a new avenue for clinical translation of vascular grafts in aging body.
The Jakarta-Bandung high-speed railway is the first overseas project involving China’s high-speed railway. Owing to the high seismic intensity in this area, the optimal selection of earthquake resisting schemes is critical for short-span bridges, and such schemes are related to the safety and cost-effectiveness of the entire line. This study compares the safety and cost-effectiveness of four earthquake resisting schemes: (i) prestressed concrete (PC) simply-supported box beams using common spherical steel bearings; (ii) PC simply-supported box beams using seismic isolation bearings; (iii) steel-concrete (SC) composite simply-supported beams using seismic isolation bearings; (iv) reinforced concrete (RC) rigid frames. The results indicate that PC beams using more expensive seismic isolation bearings reduce the cost of the substructure, making it more cost-effective. In contrast, the scheme of SC composite beams is the most expensive one, and the associated maintenance costs are also the highest. Although the scheme of RC rigid frames is the cheapest among the evaluated schemes, it is only suitable for relatively stiff sites with low pier heights. Overall, PC beams with isolation bearings exhibit good seismic performance and are suitable for prefabricated construction; therefore, this scheme can be applied in various soil conditions with relatively low costs, and it is recommended for use throughout the entire Jakarta-Bandung high-speed railway.
This paper presents inspection, materials testing, field testing and parametric finite element analysis of a pre-stressed concrete box girder bridge after fire exposure. A detailed inspection of the fire-exposed bridge was performed through visual checking, photo examinations, and hammer detection. Samples of the concrete cores and reinforcing bars were tested; the residual strengths of the building materials (concrete, reinforcing bars and prestressed strands) were estimated. Furthermore, the temperatures at various depths were estimated. The data from field studies were used to validate finite element models. The structural behaviors of the original bridge prior to fire exposure were obtained via instrumentation from a reference bridge not exposed to fire. The static proof load test deflection results indicate that the stiffness decreased by approximately 23% after fire exposure and no longer satisfied the design requirement. The measured fundamental frequency of the fire-exposed span was approximately 97% of that of the original span and the theoretical fundamental frequency, indicating that the fire had little influence on the frequency of the concrete structure. Based on this work, the repair requirements of the bridge were determined and undertaken, and the repairs were proven to be effective via a field loading test after strengthening.
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