Comparison study of different coatings on degradation performance and cell response of Mg-Sr alloy

Magnesium Alloys in Orthopedics: A Systematic Review on Approaches, Coatings and Strategies to Improve Biocompatibility, Osteogenic Properties and Osteointegration Capabilities

There is increasing interest in using magnesium (Mg) alloy orthopedic devices because of their mechanical properties and bioresorption potential. Concerns related to their rapid degradation have been issued by developing biodegradable micro- and nanostructured coatings to enhance corrosion resistance and limit the release of hydrogen during degradation. This systematic review based on four databases (PubMed®, Embase, Web of Science™ and ScienceDirect®) aims to present state-of-the-art strategies, approaches and materials used to address the critical factors currently impeding the utilization of Mg alloy devices. Forty studies were selected according to PRISMA guidelines and specific PECO criteria. Risk of bias assessment was conducted using OHAT and SYRCLE tools for in vitro and in vivo studies, respectively. Despite limitations associated with identified bias, the review provides a comprehensive analysis of preclinical in vitro and in vivo studies focused on manufacturing and application of Mg alloys in orthopedics. This attests to the continuous evolution of research related to Mg alloy modifications (e.g., AZ91, LAE442 and WE43) and micro- and nanocoatings (e.g., MAO and MgF2), which are developed to improve the degradation rate required for long-term mechanical resistance to loading and excellent osseointegration with bone tissue, thereby promoting functional bone regeneration. Further research is required to deeply verify the safety and efficacy of Mg alloys.

An osteogenic magnesium alloy with improved corrosion resistance, antibacterial, and mechanical properties for orthopedic applications

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.

Microstructure, Mechanical, In Vitro Biodegradation, and Antimicrobial Behavior of a Mg-Zn-Ca-Sr/ZrO2 Composite Prepared Using Powder Metallurgy

Biodegradable materials, especially Mg alloys, have an exceptional advantage over nonbiodegradable materials in orthopedic applications, such as avoiding second surgery for removal/replacement, stress shielding, but not enough mechanical strength, and so forth. By further improving the Mg alloy to get all the remaining required properties, it can be used for better biodegradable implants, which depend adequately on material optimization, processing, and so forth. A Mg-Zn-Ca-Sr/ZrO₂ composite has been prepared using powder metallurgy by adding 0, 1, 2, and 3 wt % of ZrO₂, which also contains Zn, Ca, and Sr as nutrient elements. Microstructure characterization, as well as mechanical and in vitro biodegradation, have been investigated by hardness, compression, and immersion tests. The highest compressive strength, contraction, and hardness of about 185.6 MPa, 9.5%, and 65.2 HRB are observed in the 2% ZrO₂-containing composite, respectively, whereas a minimum biodegradation rate of 2.76 mm/year is observed on the same. The antibiotic sensitivity observations against Staphylococcus aureus suggest that the alloy C3 has superior biological activity against the pathogen which ranks this alloy on top in merit. Overall, Mg-Zn-Ca-Sr/ZrO₂ exhibits impressive potential for use as a biodegradable and antibiotic material for orthopedic applications.

In vivo comparison of the degradation and osteointegration properties of micro-arc oxidation-coated Mg-Sr and Mg-Ca alloy scaffolds

BACKGROUND

Magnesium (Mg) alloy have biodegradation and mechanical properties that are similar to those of human bone, making it a promising candidate material for inclusion in implantable medical devices.

OBJECTIVE

The osteointegration effect of Mg alloy scaffolds with different corrosion rates were studied and evaluated in large bone defect models.

METHOD

Mg-Sr and Mg-Ca alloy scaffolds with a 20-μm Micro-arc oxidation (MAO) coating were used to repair critical bone defects for subsequent assessment of each alloy's degradation and osteointegration by X-ray, Micro-CT, fluorescence and histological examination.

RESULTS

At 12 weeks post-implantation, each defect was found to be effectively reconstructed by either of the Mg alloys based on X-ray and Micro-CT images. The corrosion rate (CR) of each Mg alloy - as calculated based on micro-computed tomography information - demonstrated that the MAO coating could provide effective protection for only 4 weeks post-surgery. From weeks 8 to 12, the CR of the Mg-Ca alloy scaffold increased from 1.34 ± 0.23 mm/y to 1.57 ± 0.16 mm/y. In contrast, the CR of the Mg-Sr alloy scaffold decreased from 0.58 ± 0.14 mm/y to 0.54 ± 0.16 mm/y. However, fluorescence and histological examination revealed more mature, closely and regularly arranged newborn osteocytes at the Mg-Ca scaffold-fracture interface e from weeks 8 to 12 after surgery.

RESULTS

The Mg-Sr scaffold was more corrosion resistant and the Mg-Ca scaffold yielded a better overall repair, which indicates that the CR of magnesium alloys matches the rate of new bone formation and is the key to repair bone defects as a bone substitute.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys, including stainless steel, titanium and its alloys, cobalt alloys, and other metals and alloys have been widely used clinically as implant materials, but implant-related infection or inflammation is still one of the main causes of implantation failure. The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint. Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability, good mechanical properties and good biocompatibility in vitro and in vivo. In this review, common antibacterial alloying elements, antibacterial standards and testing methods were introduced. Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail, including antibacterial stainless steel, antibacterial titanium alloy, antibacterial zinc and alloy, antibacterial magnesium and alloy, antibacterial cobalt alloy, and other antibacterial metals and alloys. Researches on the antibacterial properties, mechanical properties, corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time. It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner, thereby could promote the development of antibacterial metal alloys and the clinical application.

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This paper focuses the recent development of several antibacterial metals and alloys as biomedical materials.

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The possible antibacterial mechanisms of antibacterial metals and alloys are summarized in this paper.

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This review discusses the feasibility of antibacterial metals and alloys as biomedical implants in the future.

Study on repairing canine mandibular defect with porous Mg-Sr alloy combined with Mg-Sr alloy membrane

To discuss the feasibility of the application of porous Mg–Sr alloy combined with Mg–Sr alloy membrane in the repair of mandibular defects in dogs. The second and third mandibular premolars on both sides were extracted from six dogs. The model of mandible buccal fenestration bone defects were prepared after the sockets healed. Twelve bone defects were randomly divided into groups A and B, then Mg–Sr alloy was implanted in bone defects of group A and covered by Mg–Sr alloy membrane while Mg–Sr alloy was implanted in bone defects of group B and covered by mineralized collagen membrane. Bone defects observed on cone beam computed tomographic images and comparing the gray value of the two groups after 4, 8 and 12 weeks. After 12 weeks, the healing of bone defects were evaluated by gross observation, X-ray microscopes and histological observation of hard tissue. Bone defects in each group were repaired. At 8 and 12 weeks, the gray value of group A was higher than that of group B (P < 0.05). At 12 weeks, the bone volume fraction of group A was higher than that of group B (P < 0.05). The newly woven bone in group A is thick and arranged staggered, which was better than that of group B. Porous Mg–Sr alloy combined with Mg–Sr alloy membrane could further promote the repair of mandibular defects, and obtain good osteogenic effect.

Biodegradable Mg/HA/TiO2 Nanocomposites Coated with MgO and Si/MgO for Orthopedic Applications: A Study on the Corrosion, Surface Characterization, and Biocompatability

In the field of orthopedics, magnesium (Mg) and magnesium-based composites as biodegradable materials have attracted fundamental research. However, the medical applications of magnesium implants have been restricted owing to their poor corrosion resistance, especially in the physiological environment. To improve the corrosion resistance of Mg/HA/TiO2 nanocomposites, monolayer MgO and double-layer Si/MgO coatings were fabricated layer-by-layer on the surface of a nanocomposite using a powder metallurgy route. Then, coating thickness, surface morphology, and chemical composition were determined, and the corrosion behavior of the uncoated and coated samples was evaluated. Field-emission scanning electron microscopy (FE-SEM) micrographs show that an inner MgO layer with a porous microstructure and thickness of around 34 μm is generated on the Mg/HA/TiO2 nanocomposite substrate, and that the outer Si layer thickness is obtained at around 23 μm for the double-layered coated sample. Electrochemical corrosion tests and immersion corrosion tests were carried out on the uncoated and coated samples and the Si/MgO-coated nanocomposite showed significantly improved corrosion resistance compared with uncoated Mg/HA/TiO2 in simulated body fluid (SBF). Corrosion products comprising Mg(OH)2, HA, Ca3(PO4)2, and amorphous CaP components were precipitated on the immersed samples. Improved cytocompatibility was observed with coating as the cell viability ranged from 73% in uncoated to 88% for Si/MgO-coated Mg/HA/TiO2 nanocomposite after nine days of incubation.