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Abstract The aim of this study was to develop a novel biodegradable magnesium (Mg) alloy for bone implant applications. We used scandium (Sc; 2 wt %) and strontium (Sr; 2 wt %) as alloying elements due to their high biocompatibility, antibacterial efficacy, osteogenesis, and protective effects against corrosion. In the present work, we also examined the effect of a heat treatment process on the properties of the Mg‐Sc‐Sr alloy. Alloys were manufactured using a metal casting process followed by heat treatment. The microstructure, corrosion, mechanical properties, antibacterial activity, and osteogenic activity of the alloy were assessed in vitro. The results showed that the incorporation of Sc and Sr elements controlled the corrosion, reduced the hydrogen generation, and enhanced mechanical properties. Furthermore, alloying with Sc and Sr demonstrated a significantly enhanced antibacterial activity and decreased biofilm formation compared to control Mg. Also, culturing Mg‐Sc‐Sr alloy with human bone marrow‐derived mesenchymal stromal cells showed a high degree of biocompatibility (>90% live cells) and a significant increase in osteoblastic differentiation in vitro shown by Alizarin red staining and alkaline phosphatase activity. Based on these results, the Mg‐Sc‐Sr alloy heat‐treated at 400°C displayed optimal mechanical properties, corrosion rate, antibacterial efficacy, and osteoinductivity. These characteristics make the Mg‐Sc‐Sr alloy a promising candidate for biodegradable orthopedic implants in the fixation of bone fractures such as bone plate‐screws or intramedullary nails. 

Introduction: With an average of 6.8 million fractures per year in the United States, the current method for surgical intervention involves bioinert materials that do not promote osteogenesis and can have inflammatory reactions that hinder bone healing. Magnesium has emerged in research due to the material’s biodegradability and biocompatibility; however, it has a low corrosion resistance, which can lead to hydrogen gas evolution and tissue necrosis. Therefore, magnesium is typically alloyed with rare earth elements (REEs) to increase corrosion resistance. The main goal of this study involves fabricating a magnesium (Mg)-based metal matrix nanocomposite (MMNC) containing scandium (Sc) and strontium (Sr) as alloying elements, as well as diopside (CaMgSi2O6) -based bioactive glass-ceramic nanoparticles for reinforcement. Methods: MMNCs were processed using ultrasonic melt processing and hot rolling to disperse nanoparticles and refine their microstructure. These MMNCs have undergone detailed tests to determine microstructure and degradation properties, followed by in vitro and in vivo tests to determine the MMNC’s biodegradation and biocompatibility characteristics. Results: Through cell culture with human bone marrow-derived mesenchymal stem cells (hBM-MSCs) we determined that MMNCs provide in vitro cytocompatibility of >80%. Next, MMNC pins were implanted into rat femoral defects and monitored for 3 months post-implantation with the WE43 Mg alloy used as a control. Utilizing in vivo and ex vivo X-ray imaging and histology of these defects implanted with MMNC or WE43 pins, we found that our composite allows for no or minimal hydrogen gas evolution and fibrotic body response with osteointegration and new bone formation. Discussion: This allows for an understanding of potential applications of our composite as a biomaterial. 

A novel magnesium (Mg)-based metal matrix nanocomposite (MMNC) was fabricated using ultrasonic melt treatment to promote the de-agglomeration of the bioactive glass–ceramic nanoparticles and the homogenization of the melt. The cast samples were then heat treated, machined, and hot rolled to reduce grain size and remove structural defects. Standard mechanical and electrochemical tests were conducted to determine the effect of fabrication and processing on the mechanical and corrosion properties of MMNCs. Compression tests, potentiodynamic polarization tests, electrochemical impedance spectroscopy, and static immersion testing were conducted to determine the characteristics of the MMNCs. The results showed that the combination of ultrasonic melt processing and thermomechanical processing caused the corrosion rate to increase from 8.7 mmpy after 10 days of immersion to 22.25 mmpy when compared with the ultrasonicated MMNCs but remained stable throughout the immersion time, showing no statistically significant change during the incubation periods. These samples also experienced increased yield stress (135.5 MPa) and decreased elongation at break (21.92%) due to the significant amount of grain refinement compared to the ultrasonicated MMNC (σY = 59.6 MPa, elongation = 40.44%). The MMNCs that underwent ultrasonic melt treatment also exhibited significant differences in the corrosion rate calculated from immersion tests. 

Magnesium (Mg) and its alloys are considered to be biodegradable metallic biomaterials for potential orthopedic implants. While the osteogenic properties of Mg alloys have been widely studied, few reports focused on developing a bifunctional Mg implant with osteogenic and angiogenic properties. Herein, a Mg-Sc-Sr alloy was developed, and this alloy’s angiogenesis and osteogenesis effects were evaluated in vitro for the first time. X-ray Fluorescence (XRF), X-ray diffraction (XRD), and metallography images were used to evaluate the microstructure of the developed Mg-Sc-Sr alloy. Human umbilical vein/vascular endothelial cells (HUVECs) were used to evaluate the angiogenic character of the prepared Mg-Sc-Sr alloy. A mix of human bone-marrow-derived mesenchymal stromal cells (hBM-MSCs) and HUVEC cell cultures were used to assess the osteogenesis-stimulating effect of Mg-Sc-Sr alloy through alkaline phosphatase (ALP) and Von Kossa staining. Higher ALP activity and the number of calcified nodules (27% increase) were obtained for the Mg-Sc-Sr-treated groups compared to Mg-treated groups. In addition, higher VEGF expression (45.5% increase), tube length (80.8% increase), and number of meshes (37.9% increase) were observed. The Mg-Sc-Sr alloy showed significantly higher angiogenesis and osteogenic differentiation than pure Mg and the control group, suggesting such a composition as a promising candidate in bone implants.