Orientation Control for Nickel-Based Single Crystal Superalloys: Grain Selection Method Assisted by Directional Columnar Grains.

The service performance of single crystal blades depends on the crystal orientation. A grain selection method assisted by directional columnar grains is studied to control the crystal orientation of Ni-based single crystal superalloys. The samples were produced by the Bridgman technique at withdrawal rates of 100 µm/s. During directional solidification, the directional columnar grains are partially melted, and a number of stray grains are formed in the transition zone just above the melt-back interface. The grain selected by this method was one that grew epitaxially along the un-melted directional columnar grains. Finally, the mechanism of selection grain and application prospect of this grain selection method assisted by directional columnar grains is discussed.

Mg(OH)2 nanoparticles enhance the antibacterial activities of macrophages by activating the reactive oxygen species.

Infection often causes disastrous consequences in all fields of clinical medicine, especially orthopedics. Hence, critical efforts are being made to engineer novel nanomaterials for the treatment of orthopedic infections due to the high biocompatibility and antibacterial properties they possess. The purpose of this study was to investigate the antibacterial effects of magnesium hydroxide (Mg(OH)2 ) nanoparticles (NPs) in vitro and determine their possible mechanisms of action. In this study, Escherichia coli was selected as the pathogenic bacteria and it was found that Mg(OH)2 NPs significantly inhibited the growth of E. coli by promoting nucleic acid leakage, inhibiting protein synthesis, and suppressing the metabolic activity. The minimum inhibitory concentration for these bacteria was determined to be 4.4 µg/ml. In vitro flow cytometry and immunofluorescence tests indicated that Mg(OH)2 NPs induced the macrophages to generate reactive oxygen species to kill the bacteria. To understand the mechanisms involved in this process, western blotting was performed and it was found that Mg(OH)2 NPs activated the phosphatidylinositol-3-kinase/serine-threonine kinase (PI3K/Akt) signaling pathway of macrophages to enhance their phagocytosis with no obvious cytotoxicity. Thus, Mg(OH)2 NPs are a suitable choice to develop promising agents or coating materials for the treatment of clinically widespread infections in view of their safety, biocompatibility, and powerful antibacterial properties.

LOC103691336/miR-138-5p/BMPR2 axis modulates Mg-mediated osteogenic differentiation in rat femoral fracture model and rat primary bone marrow stromal cells.

Intramedullary stabilization is frequently used to treat long bone fractures. Since implant removal can become technically very challenging with the potential to cause further tissue damage, biodegradable materials are emerging as alternative options. Magnesium (Mg)-based biodegradable implants have a controllable degradation rate and good tissue compatibility, which makes them attractive for musculoskeletal research. Herein, the degradation of Mg and steel implants, the pathological characteristics and osteoblast differentiation in mice femora were examined. To investigate the molecular mechanism, we analyzed the differentially expressed long noncoding RNAs (lncRNAs) and messenger RNAs (mRNAs) in Mg-implanted or stain-steel-implanted callus tissues. lncRNA LOC103691336 was upregulated in Mg-implanted tissues and most relevant to BMPR2, a kinase receptor of BMPs with an established role in osteogenesis. The knockdown of LOC103691336 attenuated Mg-mediated osteogenic differentiation. Furthermore, miR-138-5p, previously reported to inhibit osteogenic differentiation, could bind to LOC103691336 and BMPR2 in bone marrow stromal cells (BMSCs). LOC103691336 competed with BMPR2 for miR-138-5p binding in BMSCs to attenuate the inhibitory effect of miR-138-5p on BMPR2 expression. Finally, the effect of LOC103691336 knockdown on Mg-mediated osteogenic differentiation could be attenuated by miR-138-5p inhibition. In conclusion, we provided a novel mechanism of Mg implants mediating the osteogenesis differentiation and demonstrated that Mg implants may be promising for improving fracture healing.

Mg-Zn-Mn alloy extract induces the angiogenesis of human umbilical vein endothelial cells via FGF/FGFR signaling pathway.

Magnesium (Mg) and its alloys as a type of different biodegradable materials have been used in the musculoskeletal field because of their excellent biocompatibility, biodegradability and mechanical properties similar to bone; besides, Mg could promote osteoblast differentiation in vitro and induce the formation of new bone in vivo. In the present study, we prepared the extracts of Mg-Zn-Mn alloy and examined their effects on the angiogenesis of human umbilical vein endothelial cells (HUVECs). In the present study, we prepared Mg-Zn-Mn alloy extracts of different concentrations and cultured HUVECs with these extracts. The DNA synthesis capacity, the cell viability, and the tube formation capacity of HUVECs could be significantly induced by 6.25% Mg alloy extract. In the meantime, the ratios of p-FGFR/FGFR, p-PI3K/PI3K, and p-AKT/AKT were significantly increased by 6.25% Mg alloy extract treatment, while decreased by FGFR/FGFR signaling pathway inhibitor BFJ398, indicating that 6.25% Mg alloy extract could promote the angiogenesis of HUVECs via activating FGF/FGFR signaling pathway. In conclusion, these data indicate that 6.25% Mg-Zn-Mn alloy extract induces the angiogenesis of HUVECs via FGF signaling pathway. Further in vivo experiments are needed to further confirm the present in vitro findings.

Investigation on the microstructure, mechanical properties, in vitro degradation behavior and biocompatibility of newly developed Zn-0.8%Li-(Mg, Ag) alloys for guided bone regeneration.

In order to develop a biodegradable guided bone regeneration membrane with the required mechanical properties and high corrosion resistance, Zn-0.8%Li(wt), Zn-0.8%Li-0.2%Mg(wt), and Zn-0.8%Li-0.2%Ag(wt) alloys were cast and hot rolled into 0.1-mm thick sheets. The main secondary phase in Zn-0.8%Li-(Mg, Ag) alloys was the LiZn4 nanoprecipitate. Following the addition of minimal amounts of Mg, the tensile strength of the Zn-0.8%Li-0.2%Mg alloy improved, albeit with a greatly reduced elongation and corrosion resistance. The addition of minimal amounts of Ag refined the microstructure, producing fine equiaxed grains (2.3 µm) in the Zn-0.8%Li-0.2%Ag alloy, and promoted a uniform distribution of LiZn4 nanoprecipitates with increased density and refined size. Therefore, the Zn-0.8%Li-0.2%Ag alloy exhibited optimal tensile strength and the highest corrosion resistance, with its elongation reaching 97.9 ±â€¯8.7%. The corrosion products of Zn-0.8%Li-(Mg, Ag) alloys immersed in Ringer's solution for 35 days mainly consisted of zinc oxide and zinc carbonate. In addition, the cytotoxicity test using L929 cells and the evaluation of bone marrow mesenchymal stem cell proliferation indicated that the Zn-0.8%Li-0.2%Ag alloy had good biocompatibility.

Evaluation of the mechanisms and effects of Mg-Ag-Y alloy on the tumor growth and metastasis of the MG63 osteosarcoma cell line.

Osteosarcoma is a malignant primary bone tumor, which often associates with pulmonary metastasis. The radical surgery of osteosarcoma often requires internal orthopedic implants. Therefore, implants with antitumor properties should be developed. Magnesium (Mg) and its alloys possess great potential as orthopedic materials, given their biodegradable properties, superior osteogenesis performance, and antitumor features. However, problems arise with their uncontrolled degradation rates and their unknown antitumor mechanisms. In our study, when compared with pure Mg, the rare element silver alloyed with yttrium (Ag-Y) could extremely enhance the corrosion resistance of these elements, giving the Ex-Mg-1Ag-1Y alloy better anticorrosion rates. Here, we implanted the Ex-Mg-1Ag-1Y alloy and pure Mg and Ti alloy in vivo around tumors in nude mice (BALB/c). Notably, the local tumor weight in Mg alloy and pure Mg groups were much smaller than that in Ti alloy group in 36 days after surgery (6.59 ± 0.70, 6.76 ± 0.62, and 8.54 ± 0.56 g), while the general scores of lung metastasis in Mg alloy and pure Mg groups were also lower than Ti alloy group (64.50 ± 7.64, 62.73 ± 7.84, and 87.60 ± 9.43). Therefore, the Mg and Ex-Mg-1Ag-1Y alloy, both demonstrated resisting effects against local tumor growth and pulmonary metastasis, which could be performed by changing the extracellular acidosis microenvironment, elevating the Mg concentration, suppressing C-X-C chemokine receptor type 4 (CXCR4) levels, and increasing prostacyclin (PGI2 ) synthesis. Our work revealed that the Ex-Mg-1Ag-1Y alloy may be a promising orthopedic implant for treating osteosarcoma due to its better corrosion resistance and antitumor attributes. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2537-2548, 2019.

In vitro and in vivo evaluation of novel biodegradable Mg-Ag-Y alloys for use as resorbable bone fixation implant.

Magnesium (Mg) alloy is gaining more interest because of its degradability and osteogenic potential. Still, it has some deficiencies, such as its rapid degradation rate, insufficient mechanical property. This research aimed to design a novel biodegradable Mg-argentum (Ag)-yttrium (Y) alloy, and Y was added to improve degradable and mechanical property. Mg-Ag-Y alloys were characterized for mechanical features, practicabilities in vitro and in vivo. The mechanical features results shown that this novel component was similar to native bone tissue in elastic moduli, tensile, and compressive stress. Then mesenchymal stem cells (MSCs) were seeded in alloys to assess cell toxicity in vitro. The results showed that its aqueous extract was suitable for MSCs adhesion and proliferation. Then the alloy was evaluated for biomedical applications in nonfractured distal femora of Sprague Dawley rats for 6 weeks, compared with those of pure-Mg and stainless steel groups. All rats survived, and hematological and histological evaluation showed no abnormal physiology 6 weeks postimplantation, and measurements of serum Mg2+ concentration were within normal levels. X-ray scanning, microcomputed tomography, and histological examinations were performed to evaluate the degradability and osteogenic potential. The results indicated that the degradation rate of alloy was 0.91 mm per year, (range 0.77-1.22 mm), and pure-Mg 1.80 mm per year (1.43-2.26 mm). The new bone quantity was 3.18 mm3 (1.46-4.44 mm3 ) in Mg-Ag-Y alloys group, 1.39 mm3 (0.54-2.32 mm3 ) in pure-Mg group, and none in stainless steel group. These promising results suggest potential clinical application of Mg-Ag-Y alloys for use as resorbable bone fixation implant. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2059-2069, 2018.

Biodegradation performance of a chitosan coated magnesium-zinc-tricalcium phosphate composite as an implant.

A Mg-Zn-tricalcium phosphate composite with a chitosan coating was prepared in this investigation to study its biodegradation performance both in vitro and in vivo conditions. The in vitro test results show that the immersion corrosion rate, the pH values of the simulated body fluids and the released metal ion concentration of the chitosan coated composite are all lower than those of the uncoated composite. The in vitro cytotoxicity test shows that the chitosan coated specimens is safe for cellular applications. When the chitosan coated composite is tested in vivo, the concentration of metal ions from the composite observed in the venous blood of Zelanian rabbits is less than the uncoated composite specimens. The chitosan coating slows down the in vivo degradation of the composite after surgery. In vivo testing also indicates that the chitosan coated composite is harmless to important visceral organs, including the heart, kidneys, and liver of the rabbits. The new bone formation surrounding the chitosan coated composite implant shows that the composite improves the concrescence of the bone tissues. The chitosan coating is an effective corrosion resistant layer that reduces the hydrogen release of the implant composite, thereby decreasing the subcutaneous gas bubbles formed.