Study on morphology optimization of open-pit mine slope based on section and spatial morphology effect.

Reasonable design of the slopes of mining field is an important prerequisite for optimizing open-pit mine boundary, ensuring safe production and improving economic benefits of open-pit mines. This study took the open-pit coal mine coal mine in Block I of Thar coal field in Pakistan as the research background, based on the section morphology effect of slope stability and the occurrence characteristics of coal seam and weak layer, the section morphology of slope was optimized step by step from two-dimensional angle by using the rigid body limit equilibrium method. The three-dimensional numerical simulation method is used to analyze the three-dimensional spatial effect of slope stability and reveal the influence of the spatial geometry of the slope stability. The spatial morphology of the slope was optimized and the evolutionary mechanism of slope instability was revealed. By comparing the optimized slope morphology with the preliminary design and the slope morphology of the straight slope with equal flat plate, the economic benefits were further analyzed. The results showed that under the premise of meeting the safety reserve coefficient, compared with the preliminary design and the design of equal plate. The slope angle of the optimized section morphology was increased by 1° and 3° respectively, and the coal resource recovery was increased by 332 m2 and 1790 m2 respectively, and the economic benefits were $ 18,065,859 and $ 54,408,251 respectively. And the slope angle of the optimized spatial morphology was increased by 3° and 5° respectively, and the coal resource recovery was increased by 1188 m2 and 2726 m2 respectively, and the economic benefits were $ 72,082,808 and $ 108,417,368 respectively.

[Study on cytotoxicity of three-dimensional printed ß-tricalcium phosphate loaded poly (lactide-co-glycolide) anti-tuberculosis drug sustained release microspheres and its effect on osteogenic differentiation of bone marrow mesenchymal stem cells].

Objective: To study the effect of three-dimensional (3D) printed ß-tricalcium phosphate (ß-TCP) scaffold loaded poly (lactide-co-glycolide) (PLGA) anti-tuberculosis drug sustained release microspheres on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and its cytotoxicity. Methods: Isoniazid and rifampicin/PLGA sustained release microspheres were prepared by W/O/W multiple emulsion method. The ß-TCP scaffolds were prepared by 3D printing technique. The microspheres were loaded on the scaffolds by centrifugal oscillation method to prepare composite materials. The BMSCs of Sprague Dawley rat were isolated and cultured by whole bone marrow adherent method, and the third generation cells were used for the following experiments. BMSCs were co-cultured with osteogenic induction medium (group A), PLGA anti-tuberculosis drug sustained release microsphere extract (group B), 3D printed ß-TCP scaffold extract (group C), and 3D printed ß-TCP scaffold loaded PLGA anti-tuberculosis drug sustained release microsphere composite extract (group D), respectively. Cytotoxicity was detected by cell counting kit 8 (CCK-8) method; the calcium deposition was observed by alizarin red staining; and the mRNA expressions of alkaline phosphatase (ALP), osteocalcin (OCN), and bone sialoprotein (BSP) were detected by real-time fluorescence quantitative PCR (RT-qPCR). Results: CCK-8 assay showed that the absorbance ( A) value of groups A, B, C, and D increased gradually with the culture time prolonging. After cultured for 24, 48, and 72 hours, the A value decreased in the order of groups A, C, B, and D. There was no significant difference between groups B and D ( P>0.05), but there were significant differences between other groups ( P<0.05). The cytotoxicity was evaluated as grade 0-2, and the toxicity test was qualified. Alizarin red staining showed that red mineralized nodules were formed in all groups at 21 days after osteogenic induction, but the number of mineralized nodules decreased sequentially in groups C, D, A, and B. RT-qPCR test results showed that the relative expressions of OCN and BSP genes in groups A, B, C, and D increased gradually with the culture time prolonging. The relative expression of ALP gene increased at 7 and 14 days, and decreased at 21 days. After cultured for 7, 14, and 21 days, the relative expressions of ALP, OCN, and BSP genes decreased sequentially in groups C, D, A, and B; the differences were significant between groups at different time points ( P<0.05). Conclusion: 3D printed ß-TCP loaded PLGA anti-tuberculosis drug sustained release microsphere composites have no obvious cytotoxicity to BMSCs, and can promote BMSCs to differentiate into osteoblasts to a certain extent.

[Comparative study of different concentrations of methicillin-resistant Staphylococcus aureus in the preparation of chronic femoral osteomyelitis models].

Objective: To investigate the appropriate concentration of methicillin-resistant Staphylococcus aureus (MRSA) in establishing chronic femoral osteomyelitis model in rabbits. Methods: Forty-eight adult New Zealand white rabbits were randomly divided into 6 groups with 8 rabbits in each group. Animals in groups B, C, D, E, and F were injected 1×10 9, 1×10 8, 1×10 7, 1×10 6, 1×10 5 CFU/mL MRSA on the location of 2 cm of the femoral supracondyle, respectively, and group A was injected with aseptic saline as a control. The general observation were performed at 4 weeks after operation, and the wound secretions were taken for bacteriological examination. The serum C-reactive protein content was detected at preoperation and 2 weeks and 4 weeks after operation. The X-ray, CT scan, and Norden imaging scoring were performed at 4 weeks after operation. At 4 weeks after operation, the animals were sacrificed, and the specimens were observed and evaluated by general scores; and the HE staining and histological score were also performed. Results: Five rabbits died of severe infection in group B, 2 died in group C, and no rabbit died in groups D, E, and F. General observation showed that the incision healed without soft tissue swelling in group A; most animals had visible incision swelling and sinus formation, femoral thickening, bone destruction, and damage decreased with the decreasing of the concentration of liquid bacterial in groups B-D; the infection signs were seen in groups E and F, and the degree of infection were less than that of group D. Bacteriological examination showed that fistula formation animal in groups B, C, D, and E were cultured with positive results, and with the decrease of concentration, the number of animal fistula formation decreased gradually; and bacteriological culture did not be performed in group F because of no sinus formation. There was no significant difference in the content of C-reactive protein between groups before operation ( P>0.05). The contents of C-reactive protein in groups B-F were significantly higher than those in group A at 2 and 4 weeks after operation ( P<0.05). At 4 weeks after operation, the content of C-reactive protein was in the order of groups B, C, D, E, F, and A in turn from high to low, showing significant differences between groups ( P<0.05). Imaging examination showed that there was no soft tissue swelling and bone destruction in group A; bone destruction, massive sequestrum formation, and soft tissue swelling were found in groups B and C; bone destruction was observed in groups D and E, and the degree of sequestrum formation was not as good as that in group C; and there was a small amount of bone infection in group F. The Norden scores in groups B-F were significantly higher than that in group A, and in groups B and C than those in groups D, E, and F, and in groups D and E than that in group F ( P<0.05); there was no significant difference between groups B and C, and between groups D and E ( P>0.05). The specimens general observation scores in groups B-F were significantly higher than that in group A, while in groups B and C than those in groups D, E, and F ( P<0.05); there was no significant difference between groups D, E, and F ( P>0.05). HE staining showed that the structure of bone trabecula in group A was clear and the structure was arranged neatly; in groups B-F, trabecular bone destruction and inflammatory cell infiltration were seen and the degree gradually decreased. The histological scores in groups B-F were significantly higher than that in group A, and in group B than those in groups C-F, in groups C and D than that in group F ( P<0.05); there was no significant difference between groups C, D, and E, and between groups E and F ( P>0.05). Conclusion: The optimal MRSA concentration of rabbit model of chronic osteomyelitis of femur is between 1×10 6 and 1×10 7 CFU/mL.