Prospects and strategies for magnesium alloys as biodegradable implants from crystalline to bulk metallic glasses and composites-A review

Co-immobilization of natural marine polysaccharides and bioactive peptides on ZE21B magnesium alloy to enhance hemocompatibility and cytocompatibility

Degradable magnesium alloy stents are considered to be ideal candidates to replace the traditional non-degradable stents for the treatment of cardiovascular diseases. However, bare magnesium alloy stents usually degrade too fast and show poor hemocompatibility and cytocompatibility, which seriously affects their clinical use. In this study, surface modification based on the MgF2 layer, polydopamine (PDA) coating, fucoidan and CAG peptides was performed on the Mg-Zn-Y-Nd (ZE21B) magnesium alloy with the purpose of improving its corrosion resistance, hemocompatibility and cytocompatibility for vascular stent application. After modification, the ZE21B alloy showed better corrosion resistance. Moreover, the lower hemolysis rate, platelet adhesion and activation, and fibrinogen adsorption and denaturation proved the improved hemocompatibility of modified ZE21B alloy in in vitro blood experiments. Furthermore, the co-immobilization of fucoidan and CAG peptides significantly promoted the adhesion, proliferation, migration and NO release of endothelial cells (ECs) on the modified ZE21B alloy, and meanwhile the modification with fucoidan and CAG peptides inhibited the adhesion and proliferation of smooth muscle cells (SMCs) and suppressed the expression of proinflammatory factors in the macrophages (MAs). The surface modification obviously enhanced the corrosion resistance, hemocompatibility and cytocompatibility of ZE21B alloy, and provided an effective strategy for the development of degradable vascular stents.

Silk Fibroin-Laponite Porous Microspheres as Cell Microcarriers for Osteogenic Differentiation

Silk fibroin (SF) has garnered significant attention as a natural polymer for fabricating porous scaffolds in various engineering applications. However, the limited osteoinductive property of SF has hindered its efficacy in bone repair applications. In this study, we constructed an SF-based injectable porous microcarrier that is doped with laponite (LAP), containing magnesium ions (Mg2+). The influence of freezing temperatures and concentrations of SF and LAP on the structural parameters of SF-LAP microcarriers was investigated. The SF-LAP microcarrier exhibited a porosity of 76.7 ± 1.2% and a controlled pore size of 24.6 ± 4.0 μm. At the 6 weeks of in vitro degradation test, a mild alkaline level in culture medium containing SF-LAP microcarriers was detected. The release of Mg2+ from the SF-LAP microcarrier was maintained at a concentration within the range of 1.2-2.3 mM during the 6 weeks. The seeded human adipose-derived stem cells in the SF-LAP microcarrier demonstrated a significant enhancement in osteogenic differentiation compared with cells seeded in the pure SF microcarrier, as evidenced by quantitative alkaline phosphatase activity and the expression of osteogenic marker genes. These findings underscore the potential of the SF-LAP microcarrier as an ideal cell carrier in the treatment of bone defects.

Enhanced Mechanical Properties, Corrosion Resistance, Cytocompatibility, Osteogenesis, and Antibacterial Performance of Biodegradable Mg-2Zn-0.5Ca-0.5Sr/Zr Alloys for Bone-Implant Application

Magnesium (Mg) alloys are widely used in bone fixation and bone repair as biodegradable bone-implant materials. However, their clinical application is limited due to their fast corrosion rate and poor mechanical stability. Here, the development of Mg-2Zn-0.5Ca-0.5Sr (MZCS) and Mg-2Zn-0.5Ca-0.5Zr (MZCZ) alloys with improved mechanical properties, corrosion resistance, cytocompatibility, osteogenesis performance, and antibacterial capability is reported. The hot-extruded (HE) MZCZ sample exhibits the highest ultimate tensile strength of 255.8 ± 2.4 MPa and the highest yield strength of 208.4 ± 2.8 MPa and an elongation of 15.7 ± 0.5%. The HE MZCS sample shows the highest corrosion resistance, with the lowest corrosion current density of 0.2 ± 0.1 µA cm-2 and the lowest corrosion rate of 4 ± 2 µm per year obtained from electrochemical testing, and a degradation rate of 368 µm per year and hydrogen evolution rate of 0.83 ± 0.03 mL cm-2 per day obtained from immersion testing. The MZCZ sample shows the highest cell viability in relation to MC3T3-E1 cells among all alloy extracts, indicating good cytocompatibility except at 25% concentration. Furthermore, the MZCZ alloy shows good antibacterial capability against Staphylococcus aureus.

Enhancing Bone Implants: Magnesium-Doped Hydroxyapatite for Stronger, Bioactive, and Biocompatible Applications

Hydroxyapatite (HAp) with the chemical formula Ca10(PO4)6(OH)2 is an inorganic material that exhibits morphology and composition similar to those of human bone tissues, making it highly desirable for bone regeneration applications. As one of the most biocompatible materials currently in use, HAp has undergone numerous attempts to enhance its mechanical strength. This research focuses on investigating the influence of magnesium (Mg) incorporation on the structural and mechanical properties of synthesized magnesium-doped hydroxyapatite (MgHAp) samples. Apart from its biocompatibility, Mg possesses a density and elasticity comparable to those of human bone. Therefore, incorporating Mg into HAp can be pivotal for improving bone formation. Previous studies have not extensively explored the structural changes induced by Mg substitution in HAp, which motivated us to revisit this issue. Hydrothermal synthesis technique was used to synthesize MgHAp samples with varying molar concentrations (x = 0, 0.5, 1.0, and 1.5). Theoretical simulation of HAp and MgHAp for obtaining 3D structures has been done, and theoretical X-ray diffraction (XRD) data have been compared with the experimental XRD data. Rietveld analysis revealed the alteration and deviation of lattice parameters with an increase in the Mg content, which ultimately affect the structure as well the mechanical properties of prepared samples. The findings revealed an increase in compressive stress and fracture toughness as the Mg concentration in the composition increased. Furthermore, using a finite-element analysis technique and modeling of the mechanical testing data, the von Mises stress distribution and Young's modulus values were calculated, demonstrating the similarity of the prepared samples to human cortical bone. Biocompatibility assessments using NIH-3T3 fibroblast cells confirmed the biocompatible and bioactive nature of the synthesized samples. MgHAp exhibits great potential for biomedical applications in the dental, orthopedic, and tissue engineering research fields.

Effect of acid proticity on the thermodynamic parameters of charge transfer resistance in corrosion and passivation of nickel based glass alloy

The effect of temperature on electrochemical properties of Ni82.3Cr7Fe3Si4.5B3.2 glassy alloy in different acid proticity has been investigated utilizing AC and DC methods. Firstly, the handling of experimental data on the temperature dependence of charge transfer resistance, as well as corrosion current density permits us to determine the values of classical Arrhenius parameters as well as the thermodynamic ones considered approximately independent of temperature. This leads us to deduce a global interpretation on the phenomenon of corrosion and polarization. Secondly, the deviation to the linearity of the Arrhenius behavior and the real dependence on temperature of the thermodynamic parameters, permit us to clearly quantify the effect of the acid proticity and define, for the first time, the concept of current Arrhenius parameters and the current thermodynamic ones, as well as the modeling of the enthalpy-enthalpy compensation. Moreover, the effect of temperature can be investigated using the Vogel-Fulcher-Tammann model to reveal that the corresponding Vogel temperature has an interesting physical meaning.

Comprehensive Study on the Age-Strengthened Mg-Zn-Mn-Ca/ZnO Composites for Fracture Fixation: Microstructure, Mechanical, and In Vitro Biocompatibility Evaluation

The present work investigates the use of age-strengthened Mg-Zn-Mn-Ca/xZnO as resorbable materials in temporary orthopedic implants. Quaternary Mg-Zn-Mn-Ca alloy, reinforced with zinc oxide particles, was stir-cast, followed by solution treatment and a range of aging treatments. Optical and electron microscopy, mechanical, electrochemical, immersion, and dynamic mechanical testing, with biocompatibility assessment were carried out. The observed 2θ shift in the (101) peaks of ZMX611/ZnO-ST and ZMX611/ZnO-H indicated lattice shrinkage. The formation of Mg7Zn3 and Ca2Mg6Zn3 in the grain boundary compositions was observed. ZMX611/ZnO-ST had a smaller β-phase fraction, indicating a finer microstructure. ZMX611/ZnO-H had the highest tensile yield strength (102.97 ± 3.92 MPa), and ZMX611/ZnO-ST showed the highest ultimate tensile strength (127.21 ± 7.48 MPa), indicating precipitation hardening of Zn enrichment. The uniformly dispersed secondary phases played a dual role in corrosion behavior. ZMX611/ZnO-ST showed a better cytocompatibility response among all samples. Composite materials exhibited satisfactory biocompatibility and mechanical compatibility as indicated by in silico results of deviatoric strain-based mechanical stimuli at the fracture interface.

Annealing Effect on Mechanical and Tribological Behaviors of Nanoscale Mechanics of Zr60Cu25Al5Ag5Ni5 Thin-Layer Metallic Glasses for Engineering Materials Applications

A new and unique alloy formulation design strategy has been developed in order to fabricate thin-layered metallic glasses (TLMGs) with superior fracture resistance and low coefficient of friction (COF) during the nanoscratching test. Due to the outstanding properties, TFMG could be applied for different uses, such as for surface coating, biomedical, bioimprinting, electronic devices, spacecraft, and railway, all of which need surface fracture resistance. The fabricated Zr-based metallic glass was prepared from Zr, Al, Cu, Ni, and Ag above 99.9 Wt % in purity by arch melting techniques. TFMGs were coated on silicon wafer by sputtering the vapor deposition method from bulk metallic glass then annealed below glass transition temperature Tg ∼ 450 °C for 10, 30, and 60 min. Nanoindentation and nanoscratch tests were used to investigate nanomechanical and nanotribological properties, and atomic force microscopy (AFM) was used to examine the surface morphology and microstructures of TLMG. The nanoindentation data indicated that the average hardness of metallic glasses increased from 9.75 (as-cast MG) to 13.4 GPa (annealed for 60 min). Coefficients of friction for the cast sample, annealed for unannealed, 10, 30, and 60 min, were 0.062, 0.049, 0.039, and 0.03, respectively, as well as the wear depths were 201.56, 148.43, 37.32, and 25.27 nm, respectively. These studies show that the coefficient of friction and wear rate decreases when the annealing time increases as a result of atomic reordering and structural relaxation that occurred at longer annealing times. Furthermore, continuous wear process, wear depth, wear track volume, and contact area decrease with increasing annealing time. This study can be used to design protocols to prepare novel TLMGs, which have outstanding mechanical and tribological properties for engineering materials applications.

Evaluation of toxicity and biocompatibility of a novel Mg-Nd-Gd-Sr alloy in the osteoblastic cell

BACKGROUND

We investigated the toxicity and biocompatibility of a novel Mg-3Nd-1Gd-0.3Sr-0.2Zn-0.4Zr (abbreviated to Mg-Nd-Gd-Sr) alloy in the osteoblastic cell line MC3T3-E1 as osteoblasts play an important role in bone repair and remodeling.

METHODS

We used cytotoxicity tests and apoptosis to investigate the effects of the Mg-Nd-Gd-Sr alloy on osteoblastic cells. Cell bioactivity, cell adhesion, cell proliferation, mineralization, ALP activity, and expression of BMP-2 and OPG by osteoblastic cells were also used to investigate the biocompatibility of Mg-Nd-Gd-Sr alloy.

RESULTS

The results showed that the Mg-Nd-Gd-Sr alloy had no obvious cytotoxicity, and did not induce apoptosis to MC3T3-E1 cells. Compared with the control group, the number of adherent cells within 12 h was increased significantly in each experimental group (P < 0.05); the OD value of MC3T3-E1 cells was increased significantly in each experimental group on days 1 and 3 of culture (P < 0.05); the number of mineralized nodules formed in each experimental group was significantly increased (P < 0.05), and ALP activity was significantly increased in each experimental group (P < 0.05). RT-PCR results showed that the mRNA expression of BMP-2 and OPG was significantly higher in each experimental group compared with the control group (P < 0.05). Western blotting showed that the Mg-Nd-Gd-Sr alloy extract significantly increased the protein expression of BMP-2 and OPG compared with the control group (P < 0.05).

CONCLUSIONS

Our data indicated that the novel Mg-Nd-Gd-Sr-Zn-Zr alloy had no obvious cytotoxic effects, and did not cause apoptosis to MC3T3-E1 cells; meanwhile it promoted cell adhesion, cell proliferation, mineralization, and ALP activity of osteoblasts. During this process, there was an increase in the expressions of BMP-2 and OPG mRNAs and proteins.

Microstructures, mechanical and corrosion properties of graphene nanoplatelet-reinforced zinc matrix composites for implant applications

Zinc (Zn)-based alloys and composites are gaining increasing interest as promising biodegradable implant materials due to their appropriate biodegradation rates and biological functionalities. However, the inadequate mechanical strength and ductility of pure Zn have restricted its application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) fabricated via powder metallurgy were investigated as potential biodegradable implant materials. The microstructures, mechanical properties, and corrosion behaviors of the GNP-reinforced ZMCs were characterized using optical microscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, Raman spectroscopy, compression testing, and electrochemical and immersion testing in Hanks' balanced salt solution (HBSS). The microstructural study revealed that the GNP was uniformly dispersed in the ZMCs after ball milling and sintering at 420°C for 6 h. The microhardness, compressive yield strength, ultimate compressive strength, and compressive strain of the ZMC-0.2GNP were 69 HV, 123 MPa, 247 MPa, and 23 %, respectively, improvements of ∼ 18 %, 50%, ∼ 28%, and ∼ 15% compared to pure Zn. The corrosion rate of the ZMCs were lower than that of the pure Zn in HBSS, and the ZMC-0.2GNP composite exhibited the lowest corrosion rate of 0.09 mm/y as measured by electrochemical testing. Biocompatibility assessment indicated that the diluted extracts of pure Zn and GNP-reinforced ZMCs with concentrations of 12.5% and 6.25% exhibited no cytotoxicity after cell culturing for up to 5 days, and the diluted extracts of ZMC-0.2 GNP composite revealed more than 90% cell viability after cell culturing of 3 days, showing the satisfying cytocompatibility. STATEMENT OF SIGNIFICANCE: Biodegradable Zn is a promising candidate material for orthopedic implant applications. Nonetheless, the inadequate mechanical strength and ductility of pure Zn limited its clinical application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) were developed via powder metallurgy, and the reinforcing efficacy of GNP on their mechanical properties was investigated. The addition of GNP significantly improved the compressive properties of ZMCs, with the Zn-0.2GNP composite exhibiting the best compressive properties, including 123 MPa compressive yield strength, 247 MPa ultimate compressive strength, and 22.9% compressive strain. Further, the 12.5% concentration extract of the ZMCs exhibited no cytotoxicity after cell culturing for 5 d toward SaOS2 cells.

Effect and mechanism of a novel Mg-Nd-Gd-Sr alloy on osteogenic differentiation of bone marrow mesenchymal stem cells

We investigated the effect and mechanism of a novel Mg-3Nd-1Gd-0.3Sr-0.2Zn-0.4Zr (abbreviated to Mg-Nd-Gd-Sr) alloy on the osteogenic differentiation of bone marrow mesenchymal stem cells extracted from Sprague-Dawley rats. Cultured cells were divided into five groups: a control group cultured in osteogenic induction medium alone without Mg-Nd-Gd-Sr alloy extract, and four experimental groups cultured in the same medium with 25%, 50%, 75%, and 100% Mg-Nd-Gd-Sr alloy extracts, respectively. After 14 days of culture, ALP activity was determined and expressions of osteogenesis-related factors Runx2, OCN, and OPN at the mRNA level and Runx2, OCN, and OPN at the protein level were detected by RT-PCR and western blot, respectively. After 21 days of culture, mineralized nodules were detected by alizarin red staining. The results showed that bone marrow mesenchymal stem cells from Sprague-Dawley rats were successfully isolated in vitro using the whole bone marrow adherence method. Flow cytometry revealed that the cells expressed high levels of CD44 and CD90, but low levels of CD31 and CD45. Alizarin red staining indicated the formation of mineralized nodules in all five groups. Compared with the control group, the number of mineralized nodules was increased significantly in the four experimental groups (p < 0.05). The ALP activity in each group was significantly higher on day 14 than on day 7, and was significantly higher in the four experimental groups compared with the control group (p < 0.05). Moreover, the ALP activity was highest when the concentration of Mg-Nd-Gd-Sr alloy extract was 75% (p < 0.05). RT-PCR results showed that, compared with the control group, the mRNA expression of Runx2, OPN, and OCN was significantly higher in the four experimental groups (p < 0.05), and the highest mRNA expression of Runx2, OPN, and OCN was observed in the 75% experimental group (p < 0.05). Western blotting showed that Mg-Nd-Gd-Sr alloy extract significantly increased the protein expression of Runx2, OCN, and OPN compared with the control group (p < 0.05). Our data indicate that the novel Mg-Nd-Gd-Sr alloy can promotes the osteogenic differentiation of bone marrow mesenchymal stem cells isolated from Sprague-Dawley rats. During this process, there is an increase in the expressions of Runx2, OPN, and OCN mRNAs and Runx2, OCN, and OPN proteins.

Potential bioactive coating system for high-performance absorbable magnesium bone implants

Magnesium alloys are considered the most suitable absorbable metals for bone fracture fixation implants. The main challenge in absorbable magnesium alloys is their high corrosion/degradation rate that needs to be controlled. Various coatings have been applied to magnesium alloys to slow down their corrosion rates to match their corrosion rate to the regeneration rate of the bone fracture. In this review, a bioactive coating is proposed to slow down the corrosion rate of magnesium alloys and accelerate the bone fracture healing process. The main aim of the bioactive coatings is to enhance the direct attachment of living tissues and thereby facilitate osteoconduction. Hydroxyapatite, collagen type I, recombinant human bone morphogenetic proteins 2, simvastatin, zoledronate, and strontium are six bioactive agents that show high potential for developing a bioactive coating system for high-performance absorbable magnesium bone implants. In addition to coating, the substrate itself can be made bioactive by alloying magnesium with calcium, zinc, copper, and manganese that were found to promote bone regeneration.

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Bioactive-coated magnesium implant could accelerate bone fracture healing time to match with magnesium degradation.

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Hydroxyapatite, collagen type I, recombinant human bone morphogenetic proteins 2, simvastatin, zoledronate, and strontium are high potential bioactive coating materials.

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The incorporation of Ca, Zn, Cu, Sr, and Mn in Mg base-metal could further enhance bone formation.

In vivo performance of a rare earth free Mg–Zn–Ca alloy manufactured using twin roll casting for potential applications in the cranial and maxillofacial fixation devices

A magnesium alloy containing essential, non-toxic, biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process (TRC). Microstructure, mechanical properties, in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth (RE) element containing WE43 alloy. TRC Mg-0.5 wt% Zn- 0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150 μm. Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%. The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51 ± 0.07 mm/y similar to that of the WE43 alloy (0.47 ± 0.09 mm/y) in the rat model after 1 week of implantation. By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant. The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation. The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

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Mg-0.5Zn-0.5Ca alloy plates were fabricated by a twin-roll casting (TRC) process.

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TRC alloy showed an ultimate strength and elongation of 221 ± 2 MPa and 9 ± 2%.

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Gas development during in vivo degradation was analysed using μ-CT techniques.

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Histological analysis revealed a good biocompatibility and promoted healing.

Fluorescent In Situ 3D Visualization of Dynamic Corrosion Processes of Magnesium Alloys

Magnesium (Mg) alloys as implant materials with excellent biodegradation ability have promising clinical applications for tissue repair and restoration. Although the corrosion processes of Mg alloys in biophysiological media are closely related with their biodegradation ability, only limited methods have been developed for characterization of their corrosion processes, including electrochemical analysis, weight loss measurement, and hydrogen evolution analysis. Moreover, these methods suffer from drawbacks of poor spatiotemporal resolution, static observation, and tedious operation. To tackle these challenges, we herein developed a fluorescent probe PSPA for in situ 3D monitoring of the dynamic corrosion processes of Mg alloys on the basis of its selective turn-on detection ability toward magnesium hydroxide [Mg(OH)₂], which is the main corrosion product of Mg alloys in biophysiological media. As far as we know, this is the first example of a fluorescent probe for the monitoring of corrosion processes of Mg alloys in biophysiological media. We believe this fluorescence analysis method with easy operation and high spatiotemporal resolution advantages will contribute greatly to the clinical applications of Mg alloy implants.

Facile fabrication of biodegradable endothelium-mimicking coatings on bioabsorbable zinc-alloy stents by one-step electrophoretic deposition

The zinc-alloy stent is one of the best potential candidates for bioabsorbable metal stents because of its appropriate corrosion rate aligned to the duration of the healing process of the surrounding vessel tissues. However, excessive release of zinc ions, causing cytotoxicity of endothelial cells, and insufficient surface bio-functions of Zn-alloy stents lead to considerable challenge in their application. Herein, one-step electrophoretic deposition was employed to apply a hybrid coating of polycarbonate, tannic acid, and copper ions with tailored functions on Zn-alloy stents to enhance their corrosion resistance and provide an endothelium-mimicking surface. Specifically, the synthesized amino-functionalized aliphatic polycarbonates endowed the hybrid coating with specific surface-erosion properties, resulting in superior corrosion resistance and long-term stability in degradation tests both in vitro and in vivo. The immobilized copper ions enabled the catalytic generation of nitric oxide and promoted the adhesion and proliferation of endothelial cells on zinc alloy. The added tannic acid firmly chelated the copper ions and formed durable phenolic-copper-amine crosslinked networks by electrostatic interaction, resulting in long-term stability of the hybrid coating during the 21 day dynamic immersion test. Tannic acid exerted a synergistic antibacterial effect with copper ions as well as a reduction in the inflammatory response to the zinc substrate. In addition, the hybrid coating improved the in vitro hemocompatibility of zinc alloys. By adjusting the amount of chelated copper in the coating system, the biological function of the corresponding coatings can be controlled, providing a facile surface treatment strategy to promote the progress of zinc-alloy stents in clinical applications.

In vitro and in vivo assessment of the effect of biodegradable magnesium alloys on osteogenesis

Magnesium (Mg) and some of its alloys are considered promising biodegradable metallic biomaterials for bone implant applications. The osteogenesis effect of Mg alloys is widely reported; however, the underlying mechanisms are still not clear. In this study, pure Mg, Mg-3Zn, and Mg-2Zn-1Mn were prepared, and their degradation behavior, biocompatibility, and osteogenesis effect were systematically assessed both in vitro and in vivo. Primary rat bone marrow-derived mesenchymal stem cells (BMSCs) were used to evaluate the biocompatibility of the prepared Mg alloys, and a rat femur fracture model was used to assess the stimulating effect of these alloys on bone-tissue formation. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. Extracts of the three materials showed significant stimulating effects on osteogenic differentiation of BMSCs along with non-cytotoxicity. Implantation of Mg-2Zn-1Mn wires into the femur of rats demonstrated superior histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. Moreover, the results of both in vitro and in vivo assessments demonstrated that bone morphogenetic proteins and fibroblast growth factor receptors are involved in the stimulating effect of Mg alloys. STATEMENT OF SIGNIFICANCE: This work reports the degradation behavior, biocompatibility, and osteogenic effect of pure Mg and Mg-3Zn and Mg-2Zn-1Mn alloys in both in vitro and in vivo conditions. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. The extracts of the three materials showed a significant stimulating effect on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs) along with non-cytotoxicity. Mg-2Zn-1Mn wires implanted into the femur of rats showed good histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. The results of the present study suggest that bone morphogenetic proteins (BMPs) and fibroblast growth factor receptors (FGFRs) are involved in the stimulating effect of Mg alloys on osteogenesis.

Biodegradable Mg-Zn-Ca-Based Metallic Glasses

Biodegradable Mg-Zn-Ca-based metallic glasses (MGs) present improved strength and superior corrosion resistance, compared to crystalline Mg. In particular, in vivo and in vitro attempts reveal that biodegradable Mg-Zn-Ca-based MGs possess excellent biocompatibility, suggesting that they are ideal candidates for temporary implant materials. However, the limited size and severe brittleness prevent their widespread commercialization. In this review, we firstly summarize the microstructure characteristic and mechanical properties of Mg-Zn-Ca-based MGs. Then, we provide a comprehensive and systematic understanding of the recent progress of the biocorrosion and biocompatibility of Mg-Zn-Ca-based MGs. Last, but not least, the outlook towards the fabrication routes, composition design, structure design, and reinforcement approaches of Mg-Zn-Ca-based MGs are briefly proposed.

Enhanced Plasticity and Corrosion Resistance in Mg-Zn-Ca-Cu Amorphous Alloy Composite via Plasma Electrolytic Oxidation Treatment

In this study, a dendrite-reinforced Mg-based amorphous alloy composite was prepared through an in situ precipitation strategy. After plasma electrolytic oxidation (PEO) treatment, the Mg85.1Zn12.7Ca2Cu0.2 amorphous alloy composite exhibited enhanced plasticity and corrosion resistance in a simulated body fluid solution (SBF). The PEO-treated composite showed a significant plastic strain of 10.5 ± 1.1%, as well as outstanding strain-hardening behavior. The enhancement of plasticity may be attributed to the in-situ formed coating, which can not only serve as a propagation barrier for shear bands but can also introduce nucleation sites in the bands as a result of stress mismatch and compositional heterogeneity. The corrosion density in the SBF decreased by three orders compared with the composite substrate. The spontaneous formation of apatite on the porous layer demonstrated that the prepared PEO coating has high bioactivity. The current work may provide a fundamental basis for developing biomedical Mg-based alloys with excellent comprehensive mechanical properties and corrosion resistance.

In vitro evaluation of freeze-drying chitosan-mineralized collagen/Mg-Ca alloy composites for osteogenesis

Magnesium (Mg) alloy with good mechanical properties and biodegradability is considered as one of the ideal bone repair materials. However, the rapid corrosion of Mg-based metals can pose harm to the function of an implant in clinical applications. In this study, micro-arc oxidation coating was prepared on the surface of the Mg-Ca matrix, then the chitosan and mineralized collagen (nano-hydroxyapatite/collagen; nHAC) were immobilized on the surface of the MAO/Mg-Ca matrix to construct the CS-nHAC/Mg-Ca composites of different component proportions (the ratio of CS to nHAC is 2:1, 1:1, and 1:2, respectively). The corrosion resistance, osteogenic activity, and angiogenic ability were extensively investigated. The results indicated that the CS-nHAC reinforcement materials can improve the corrosion resistance of the Mg matrix significantly and promote the proliferation and adhesion of mouse embryo osteoblast precursor cells (MC3T3-E1) and human umbilical vein endothelial cells (HUVECs). In addition, the CS-nHAC/Mg-Ca composites can not only promote the alkaline phosphatase (ALP) activity and extracellular matrix mineralization of MC3T3-E1 cells but also enhance the migration motility and vascular endothelial growth factor (VEGF) expression of HUVECs. Meanwhile, the 2CS-1nHAC/Mg-Ca composite exhibited the optimum function characteristics compared with other samples. Therefore, considering the improvement of corrosion resistance and biocompatibility, the CS-nHAC/Mg-Ca composites are expected to be a promising orthopedic implant.

Effect of Magnesium Addition and High Energy Processing on the Degradation Behavior of Iron Powder in Modified Hanks’ Solution for Bioabsorbable Implant Applications

This paper shows the results of applying a combination of high energy processing and magnesium (Mg) as an alloying element in a strategy for enhancing the degradation rate of iron (Fe) for applications in the field of non-permanent medical implants. For this purpose, Fe powder was milled with 5 wt% of Mg (Fe5Mg) and its microstructure and characterized degradation behavior. As-received Fe powder was also milled in order to distinguish between the effects due to high energy processing from those due to the presence of Mg. The powders were prepared by high energy planetary ball milling for 16 h. The results show that the initial crystallite size diminishes from >150 nm to 16 nm for Fe and 46 nm for Fe5Mg. Static degradation tests of loose powder particles were performed in Hanks’ solution. Visual inspection of the immersed powders and the X-ray diffraction (XRD) phase quantification indicate that Fe5Mg exhibited the highest degradation rate followed by milled Fe and as received Fe, in this order. The analysis of degradation products of Fe5Mg showed that they consist on magnesium ferrite and pyroaurite, which are known to present good biocompatibility and low toxicity. Differences in structural features and degradation behaviors of milled Fe and milled Fe5Mg suggest the effective dissolution of Mg in the Fe lattice. Based on the obtained results, it can be said that Fe5Mg powder would be a suitable candidate for non-permanent medical implants with a higher degradation rate than Fe.

Biodegradable magnesium phosphates in biomedical applications

As an essential element, magnesium is involved in a variety of physiological processes. Magnesium is the second most abundant cation in cells and the fourth most abundant cation in living...

Biofunctional magnesium-coated Ti6Al4V scaffolds promote autophagy-dependent apoptosis in osteosarcoma by activating the AMPK/mTOR/ULK1 signaling pathway

The recurrence of osteosarcoma (OS) after reconstruction using Ti6Al4V prostheses remains a major problem in the surgical treatment of OS. Modification of the surfaces of Ti6Al4V prostheses with antitumor functions is an important strategy for improving therapeutic outcomes. Magnesium (Mg) coating has been shown to be multifunctional: it exhibits osteogenic and angiogenic properties and the potential to inhibit OS. In this study, we determined the proper concentration of released Mg²⁺ with respect to OS inhibition and biosafety and evaluated the anti-OS effects of Mg-coated Ti6Al4V scaffolds. We found that the release of Mg²⁺ during short-term and long-term degradation could significantly inhibit the proliferation and migration of HOS and 143B cells. Increased cell apoptosis and excessive autophagy were also observed, and further evidence of AMPK/mTOR/ULK1 signaling pathway activation was obtained both in vitro and in vivo, which suggested that the biofunctional scaffolds induce OS inhibition. Our study demonstrates the ability of an Mg coating to inhibit OS and may contribute to the further application of Mg-coated Ti6Al4V prostheses.

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Multifunctional Mg coating is considerable surface modification for Ti6Al4V prostheses.

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Mg²⁺ releasing by the scaffolds could significantly inhibit the proliferation and migration of OS cells.

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The biofunctional scaffolds could inhibit OS by activating autophagy-dependent apoptosis.

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The AMPK/mTOR/ULK-1 pathway was involved in autophagy-depended apoptosis induced by the scaffolds.

Interfacial Compatibilization into PLA/Mg Composites for Improved In Vitro Bioactivity and Stem Cell Adhesion

The present work highlights the crucial role of the interfacial compatibilization on the design of polylactic acid (PLA)/Magnesium (Mg) composites for bone regeneration applications. In this regard, an amphiphilic poly(ethylene oxide-b-L,L-lactide) diblock copolymer with predefined composition was synthesised and used as a new interface to provide physical interactions between the metallic filler and the biopolymer matrix. This strategy allowed (i) overcoming the PLA/Mg interfacial adhesion weakness and (ii) modulating the composite hydrophilicity, bioactivity and biological behaviour. First, a full study of the influence of the copolymer incorporation on the morphological, wettability, thermal, thermo-mechanical and mechanical properties of PLA/Mg was investigated. Subsequently, the bioactivity was assessed during an in vitro degradation in simulated body fluid (SBF). Finally, biological studies with stem cells were carried out. The results showed an increase of the interfacial adhesion by the formation of a new interphase between the hydrophobic PLA matrix and the hydrophilic Mg filler. This interface stabilization was confirmed by a decrease in the damping factor (tanδ) following the copolymer addition. The latter also proves the beneficial effect of the composite hydrophilicity by selective surface localization of the hydrophilic PEO leading to a significant increase in the protein adsorption. Furthermore, hydroxyapatite was formed in bulk after 8 weeks of immersion in the SBF, suggesting that the bioactivity will be noticeably improved by the addition of the diblock copolymer. This ceramic could react as a natural bonding junction between the designed implant and the fractured bone during osteoregeneration. On the other hand, a slight decrease of the composite mechanical performances was noted.

Magnesium Promotes the Regeneration of the Peripheral Nerve

Peripheral nerve injury is a common complication in trauma, and regeneration and function recovery are clinical challenges. It is indispensable to find a suitable material to promote peripheral nerve regeneration due to the limited capacity of peripheral nerve regeneration, which is not an easy task to design a material with good biocompatibility, appropriate degradability. Magnesium has captured increasing attention during the past years as suitable materials. However, there are little types of research on magnesium promoting peripheral nerve regeneration. In this review, we conclude the possible mechanism of magnesium ion promoting peripheral nerve regeneration and the properties and application of different kinds of magnesium-based biomaterials, such as magnesium filaments, magnesium alloys, and others, in which we found some shortcomings and challenges. So, magnesium can promote peripheral nerve regeneration with both challenge and potential.

Titanium alloy cannulated screws and biodegradable magnesium alloy bionic cannulated screws for treatment of femoral neck fractures: a finite element analysis

Background

Cannulated screws (CS) are one of the most widely used treatments for femoral neck fracture, however, associated with high rate of complications. In this study, we designed a new type of cannulated screws called degradable magnesium alloy bionic cannulated screws (DMBCS) and our aim was to compare the biomechanical properties of DMBCS, the traditionally used titanium alloy bionic cannulated screws (TBCS) and titanium alloy cannulated screws (TTCS).

Methods

A proximal femur model was established based on CT data of a lower extremity from a voluntary healthy man. Garden type III femoral neck fracture was constructed and fixed with DMBCS, TBCS, and TTCS, respectively. Biomechanical effect which three type of CS models have on femoral neck fracture was evaluated and compared using von Mises stress distribution and displacement.

Results

In the normal model, the maximum stress value of cortical bone and cancellous bone was 76.18 and 6.82 MPa, and the maximum displacement was 5.52 mm. Under 3 different fracture healing status, the stress peak value of the cortical bone and cancellous bone in the DMBCS fixation model was lower than that in the TTCS and TBCS fixation, while the maximum displacement of DMBCS fixation model was slightly higher than that of TTCS and TBCS fixation models. As the fracture heals, stress peak value of the screws and cortical bone of intact models are decreasing, while stress peak value of cancellous bone is increasing initially and then decreasing.

Conclusions

The DMBCS exhibits the superior biomechanical performance than TTCS and TBCS, whose fixation model is closest to the normal model in stress distribution. DMBCS is expected to reduce the rates of post-operative complications with traditional internal fixation and provide practical guidance for the structural design of CS for clinical applications.

Influence of the second phase on protein adsorption on biodegradable Mg alloys' surfaces: Comparative experimental and molecular dynamics simulation studies

The effect of the second phase on the mechanical properties and corrosion resistance of Mg alloys has been systematically studied. However, there is limited information on the effect of the second phase on protein adsorption behavior. In the present study, the effect of the second phase on protein adsorption on the surfaces of biodegradable Mg alloys was investigated using experimental methods and molecular dynamics (MD) simulations. The experimental results showed that the effect of the second phase on fibrinogen adsorption was type-dependent. Fibrinogen preferentially adsorbed on Y-, Ce-, or Nd-involved second phases, while the second phase containing Zn inhibited its adsorption. MD simulations revealed the mechanism of the second phase that influenced protein adsorption in terms of charge distribution, surface-protein interaction energy, and water molecule distribution. Our studies proposed a deep understanding of the design of Mg-based biomaterials with superior biocompatibility. STATEMENT OF SIGNIFICANCE: Mechanical properties, uniform degradation, and biocompatibility must be considered while designing biomedical Mg alloys. To improve the mechanical properties and corrosion resistance of Mg alloys, the second phase is usually required. However, the effects of the second phase on biocompatibility of Mg alloys have been rarely reported. Here, the influence of the second phase on protein adsorption was experimentally studied by designing Mg alloys with different types of second phase. The first principle calculation and MD simulation were used to reveal the mechanism by which the second phase influences protein adsorption. This work could be used to better elucidate the protein adsorption mechanisms and design principles to improve the biocompatibility of Mg alloys.

Recent advances and directions in the development of bioresorbable metallic cardiovascular stents: Insights from recent human and in vivo studies

Over the past two decades, significant advancements have been made regarding the material formulation, iterative design, and clinical translation of metallic bioresorbable stents. Currently, magnesium-based (Mg) stent devices have remained at the forefront of bioresorbable stent material development and use. Despite substantial advances, the process of developing novel absorbable stents and their clinical translation is time-consuming, expensive, and challenging. These challenges, coupled with the continuous refinement of alternative bioresorbable metallic bulk materials such as iron (Fe) and zinc (Zn), have intensified the search for an ideal absorbable metallic stent material. Here, we discuss the most recent pre-clinical and clinical evidence for the efficacy of bioresorbable metallic stents and material candidates. From this perspective, strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations. STATEMENT OF SIGNIFICANCE: Recent efforts in using Mg, Fe, and Zn based materials for bioresorbable stents include elemental profile changes as well as surface modifications to improve each of the three classes of materials.  Although a variety of alloys for absorbable metallic stents have been developed, the ideal absorbable stent material has not yet been discovered. This review focuses on the state of the art for bioresorbable metallic stent development. It covers the three bulk materials used for degradable stents (Mg, Fe, and Zn), and discusses their advances from a translational perspective. Strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations.

Cardiovascular Stents: A Review of Past, Current, and Emerging Devices

One of the leading causes of morbidity and mortality worldwide is coronary artery disease, a condition characterized by the narrowing of the artery due to plaque deposits. The standard of care for treating this disease is the introduction of a stent at the lesion site. This life-saving tubular device ensures vessel support, keeping the blood-flow path open so that the cardiac muscle receives its vital nutrients and oxygen supply. Several generations of stents have been iteratively developed towards improving patient outcomes and diminishing adverse side effects following the implanting procedure. Moving from bare-metal stents to drug-eluting stents, and recently reaching bioresorbable stents, this research field is under continuous development. To keep up with how stent technology has advanced in the past few decades, this paper reviews the evolution of these devices, focusing on how they can be further optimized towards creating an ideal vascular scaffold.

Microstructural, Electrochemical and In Vitro Analysis of Mg-0.5Ca-xGd Biodegradable Alloys

The subject of Mg-based biodegradable materials, used for medical applications, has been extensively studied throughout the years. It is a known fact that alloying Mg with biocompatible and non-toxic elements improves the biodegradability of the alloys that are being used in the field of surgical applications. The aim of this research is to investigate the aspects concerning the microstructure, electrochemical response (corrosion resistance) and in vitro cytocompatibility of a new experimental Mg-based biodegradable alloy—Mg–0.5%Ca with controlled addition of Gd as follows: 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%—in order to establish improved biocompatibility with the human hard and soft tissues at a stable biodegradable rate. For this purpose, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), light microscopy (LM) and X-ray diffraction (XRD) were used for determining the microstructure and chemical composition of the studied alloy and the linear polarization resistance (LPR) method was used to calculate the corrosion rate for the biodegradability rate assessment. The cellular response was evaluated using the 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test followed by fluorescence microscopy observation. The research led to the discovery of a dendritic α-Mg solid solution, as well as a lamellar Mg2Ca and a Mg5Gd intermetallic compound. The in vivo tests revealed 73–80% viability of the cells registered at 3 days and between 77 and 100% for 5 days, a fact that leads us to believe that the experimental studied alloys do not have a cytotoxic character and are suitable for medical applications.

The Effect of Equal-Channel Angular Pressing on Microstructure, Mechanical Properties, and Biodegradation Behavior of Magnesium Alloyed with Silver and Gadolinium

The effect of equal channel angular pressing (ECAP) on the microstructure, texture, mechanical properties, and corrosion resistance of the alloys Mg-6.0%Ag and Mg-10.0%Gd was studied. It was shown that ECAP leads to grain refinement of the alloys down to the average grain size of 2–3 μm and 1–2 μm, respectively. In addition, in both alloys the precipitation of fine particles of phases Mg54Ag17 and Mg5Gd with sizes of ~500–600 and ~400–500 nm and a volume fraction of ~9% and ~8.6%, respectively, was observed. In the case of the alloy Mg-6.0%Ag, despite a significant grain refinement, a drop in the strength characteristics and a nearly twofold increase in ductility (up to ~30%) was found. This behavior is associated with the formation of a sharp inclined basal texture. For alloy Mg-10.0%Gd, both ductility and strength were enhanced, which can be associated with the combined effect of significant grain refinement and an increased probability of prismatic and basal glide. ECAP was also shown to cause a substantial rise of the biodegradation rate of both alloys and an increase in pitting corrosion. The latter effect is attributed to an increase in the dislocation density induced by ECAP and the occurrence of micro-galvanic corrosion at the matrix/particle interfaces.

Effect of GelMA Hydrogel Coatings on Corrosion Resistance and Biocompatibility of MAO-Coated Mg Alloys

Micro-arc oxidation (MAO) treatment is a simple and effective technique to improve the corrosion resistance for magnesium alloys. However, the presence of micro-pores and cracks on the coatings provides paths for corrosive ions to penetrate into and react with the substrate, limiting the long-term corrosion resistance. In this paper, we designed a composite coating with which GelMA hydrogel coatings with varying thicknesses were prepared on the surface of MAO-coated magnesium alloys via a dip-coating method, aiming to improve the biocorrosion resistance and biocompatibility. The surface morphology, the chemical composition of GelMA hydrogels, and the crystallographic structure of magnesium alloys were characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), respectively. The corrosion resistance and biocompatibility of all samples were evaluated through electrochemical and biological experiments. The results demonstrated that the addition of GelMA hydrogel could effectively seal the pores and improve the corrosion resistance and biocompatibility of MAO-coated magnesium alloys, especially for the sample with one layer of GelMA hydrogel, showing high cell proliferation rate, and its current density (Icorr) was two orders of magnitude lower than that of the MAO coating. Besides, the balance mechanism between corrosion and protection was proposed. As a result, the GelMA hydrogel coatings are beneficial to the application of MAO-coated magnesium alloys in bone tissue engineering and other fields.

Biomimetic Design for a Dual Concentric Porous Titanium Scaffold with Appropriate Compressive Strength and Cells Affinity

In repairing or replacing damaged bones, a dual concentric porous titanium scaffold (P-Tix-y) has emerged as a promising bio-mimic design. Herein, various P-Tix-y were made and sintered with relatively dense (x = 10, 20, or 30% porosity) and loose (y = 45, 55, or 65 porosity) structures. Firstly, NaCl was used as the pore-forming additive and followed by a hydrothermal removal method. The compressive strength of the as-formed P-Tix_y and surface morphology, nanomechanical property, and cells' affinity on the cross-sectioned surface of P-Tix_y (CP-Tix_y) were then characterized. The results demonstrate that the compressive strength of P-Ti10_45, P-Ti20_45, or P-Ti20_55 exhibits a relatively mild decline (e.g., in the range of 181 and 97 MPa, higher than the required value of 70 MPa) and suitable porosities for the intended structure. Nano-hardness on the solid surface of CP-Tix_y shows roughly consistent with that of CP-Ti (i.e., ~8.78 GPa), thus, the porous structure of CP-Tix_y remains mostly unaffected by the addition of NaCl and subsequent sintering process. Most of the surfaces of CP-Tix_y exhibit high fibroblast (L929) cell affinity with low cell mortality. Notably, in the hFOB 1.19 cell adhesion and proliferation test, CP-Ti20_55 and CP-Ti20_65 reveal high cell viability, most probably relating with the assembly of dual porosities with interconnected pores. Overall, the sample P-Ti20_55 provides a relatively load-bearable design with high cell affinity and is thus promising as a three-dimensional bio-scaffold.

Formation and In Vitro Evaluation of a Deep Eutectic Solvent Conversion Film on Biodegradable Magnesium Alloy

The chemical conversion films from deep eutectic solvents (DESs) have recently been shown to reduce the corrosion rate of magnesium alloys, which are recognized as a kind of promising materials applied in the human body. However, the biocompatibility of the conversion films has not been investigated. This study proposes an uncommon DES system composed of lithium chloride and urea to fabricate the chemical conversion films on Mg and its alloy. The fabrication process of the conversion film is facile, which is performed by the heat treatment of the substrate in the DES at about 200 °C for 30 min. It is found that the thermal decomposition of the DES can release hydrogen, which diffuses into the Mg substrate to form MgH₂-based conversion films. The DES conversion film possesses a porous structure on pure Mg, whereas it becomes dense on the alloy with some cracks. X-ray photoelectron spectroscopy shows that MgCO₃ and oxides also exist in the DES conversion films, which depends on the substrate. Electrochemical corrosion test and in vitro biocompatibility tests, including hemolysis, cytotoxicity, antibacterial, and cytoskeleton staining experiments, are performed in a simulated body environment, which shows that the corrosion resistance and biocompatibility of the substrates have been improved significantly. We expect that the DES heat treatment method will be applied to the fabrication of corrosion-resistant and biocompatible surfaces for biodegradable Mg alloys.

Mg-Based Materials with Quasiamorphous Phase Produced by Vertical Twin-Roll Casting Process

Metallic materials with micron grains, submicron grains, or amorphous structures have attracted great interest in recent decades owing to their excellent mechanical properties and corrosion resistance. Compared with traditional forming processes, rapid solidification technology has shown great superiority and potential in the preparation of materials in such structures. In this study, fine-grained quasiamorphous Mg-based alloy strips fabricated by a twin-roll strip casting process were explored using simulation and experimental methods. The concept of critical casting speed was proposed to reflect the optimum casting conditions. The product of critical casting speed and strip thickness was used to evaluate the cooling capacity of the casting system. Based on simulation results, a twin-roll strip-casting experiment was performed on a Mg-rare earth alloy. A novel puddle-like microstructure of the as-cast alloy strip was obtained. Tensile testing results showed that the novel strip exhibited improved ductility.