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In the present study, porous magnesium-xzeolite (x= 0, 3, 5 and 7 wt.%) composite scaffolds containing different amounts of zeolite were synthesized through combination of powder metallurgy (PM) and space holder (SH) techniques. The findings demonstrated that incorporation of zeolite into Mg composite scaffolds leads to higher compressive strength and corrosion resistance than Mg scaffolds without Zeo. Moreover, the Mg/Zeo composite scaffold presented good bioactivity, high capability in MG63 cell attachment and viability whereas a smaller number of cells could attach to the Mg scaffold without Zeo. The antibacterial response of these Mg/Zeo-Ag composite scaffolds against Gram-positive Staphylococcus aureus (S. aureus) and Gram negative Escherichia coli (E. coli) indicates the positive role of silver-zeolite in suppressing the bacteria growth. The aforementioned tests indicated that the articulated magnesium composite scaffold containing 7 wt.% Zeo with suitable mechanical strength and excellent biological activity may be considered as a promising biomaterial for bone substitution. [ABSTRACT FROM AUTHOR]

In this work, binary Zn-0.5Al and ternary Zn-0.5Al- x Mg alloys with various Mg contents were investigated as biodegradable materials for implant applications. Compared with Zn-0.5Al (single phase), Zn-0.5Al- x Mg alloys consisted of the α-Zn and Mg 2 (Zn, Al) 11 with a fine lamellar structure. The results also revealed that ternary Zn-Al-Mg alloys presented higher micro-hardness value, tensile strength and corrosion resistance compared to the binary Zn-Al alloy. In addition, the tensile strength and corrosion resistance increased with increasing the Mg content in ternary alloys. The immersion tests also indicated that the corrosion rates in the following order Zn-0.5Al-0.5Mg < Zn-0.5Al-0.3Mg < Zn-0.5Al-0.1Mg < Zn-0.5Al. The cytotoxicity tests exhibited that the Zn-0.5Al-0.5Mg alloy presents higher viability of MC3T3-E1 cell compared to the Zn-0.5Al alloy, which suggested good biocompatibility. The antibacterial activity result of both Zn-0.5Al and Zn-0.5Al-Mg alloys against Escherichia coli presented some antibacterial activity, while the Zn-0.5Al-0.5Mg significantly prohibited the growth of Escherichia coli . Thus, Zn-0.5Al-0.5Mg alloy with appropriate mechanical properties, low corrosion rate, good biocompatibility and antibacterial activities was believed to be a good candidate as a biodegradable implant material. [ABSTRACT FROM AUTHOR]

In this work, a hybrid dual layer surface coating consisting of a silicon (Si) underlayer and poly(ε-caprolactone) (PCL) overlayer was investigated that was designed to reduce the corrosion rates of magnesium-based biomaterials. The Si underlayer was 1.2 μm thick and composed of spherical nanoparticles. The overlayer of PCL was 75.2 μm thick and comprised network of pores. Corrosion-induced reduction of the compressive strength of a Si/PCL-coated Mg–Ca–Bi alloy was lower than that of the uncoated or Si layer-coated alloys. However, the bonding strength of the Si coating (24.6 MPa) was significantly higher than that of the Si/PCL-coated samples (6.8 MPa). The Si/PCL coating dramatically enhances the charge transfer resistance of the Mg alloy (2.11 kΩ cm 2 ) in simulated body fluid when compared with a Si-coated sample (2265.12 kΩ cm 2 ). Si/PCL coatings are considered a promising route to control the corrosion rate and mechanical properties of Mg-based biomaterials. [ABSTRACT FROM AUTHOR]

In the present study, a novel nano-silica (SiO 2 )/graphene oxide (GO) coating was deposited on Mg alloy via physical vapor deposition (PVD) combined with dip coating. The structural characterization clearly revealed that the nano-SiO 2 underlayer had a compact columnar microstructure with a thickness of 1 μm, while the GO overlayer presented a sheet-like morphology with a thickness of around 30 μm. The in-vitro degradation rate revealed that the presence of GO as an overlayer on the nano-SiO 2 layer significantly decreased the corrosion rate of the Mg alloy. The antibacterial results demonstrated that the both nano-SiO 2 /GO and nano-SiO 2 coatings exhibited a strong antibacterial activity against the Streptococcus mutans . However, the nano-SiO 2 /GO coating exhibited better antibacterial activity compared to the nano-SiO 2 coated and uncoated samples. These results exhibit that nano-SiO 2 /GO coating has effective antibacterial activity and high corrosion resistance in vitro, thus, it can be considered as a promising material for implant applications. [ABSTRACT FROM AUTHOR]

In this study, a novel bi-layered nanostructured silica (SiO 2 )/ silver-doped fluorohydroxyapatite (Ag-FHAp) coating was deposited on biodegradable Mg-1.2Ca-4.5Zn alloy via physical vapor deposition (PVD) combined with electrodeposition (ED). The nano-SiO 2 underlayer had a compact columnar microstructure with thickness of around 1 µm while the Ag-FHAp overlayer presented large plate-like crystals accompanied with small rounded particles with thickness about 10 µm. Potentiodynamic polarization test exhibited that the double layer SiO 2 /Ag-FHAp coated Mg alloy has superior corrosion resistance compared to uncoated and single layer SiO 2 coated samples. Contact angle measurement showed that Ag-FHAp coating over nano-SiO 2 layers significantly increased surface wettability which is favorable for the attachment of cells. Cytotoxicity tests indicated that the nanostructured SiO 2 /Ag-FHAp coating enabled higher cell viability compared to nano-SiO 2 coating and uncoated samples. In addition, bi-layer and single-layer coatings considerably improved the ability of cell attachment than that of the uncoated samples. The cell viability of coated and uncoated samples increased with increasing incubation time. The double layer SiO 2 /Ag-FHAp coated biodegradable Mg alloy possessed high corrosion resistance and cytocompatibility and can be considered as a promising material for implant applications. [ABSTRACT FROM AUTHOR]

In this study, microstructural evolution, mechanical properties and corrosion behavior of plasma sprayed NiCrAlY/nano-yttria stabilized zirconia (nano-YSZ) dual-layered coating on Mg–1.2Ca–3Zn alloy were investigated. NiCrAlY underlayer is composed of large amount of porosities and micro-cracks with thickness around 80–90 μm. However, nano-YSZ overlayer shows bimodal microstructure consisting of columnar grains and some partially molten parts of the nanostructured powders with thickness around 270–300 μm. The microhardness of dual-layered NiCrAlY/nano-YSZ coating is significantly higher than that of single-layered NiCrAlY. Despite that, the bonding strength of dual-layered coating is slightly higher than single-layered plasma sprayed coating. Results also showed that both single-layer NiCrAlY and dual-layer NiCrAlY/nano-YSZ coatings decreased the corrosion current density of Mg alloy from 217.1 μA/cm 2 to 114.5 and 82.4 µA/cm 2 , respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quaternary alloy show better mechanical and corrosion properties than binary alloy. [•] Mg–2Ca–0.5Mn–2Zn alloy showed suitable mechanical properties for bone application. [•] The improved corrosion resistance with addition of Mn and Zn into the Mg–Ca alloy. [•] Formation of protective surface film Mn-containing magnesium on quaternary alloy. [•] Secondary phases have strong effect on micro-galvanic corrosion of Mg alloys. [ABSTRACT FROM AUTHOR]

Abstract: Effects of secondary phases on corrosion behaviour of the Mg–0.5Ca–xZn alloys were investigated by polarization, immersion and hydrogen evolution tests. The Mg2Ca phase nucleated at 520°C while, Ca2Mg6Zn3 and Mg51Zn20 phases were formed at 420°C and 330°C respectively. The corrosion resistance of Mg–0.5Ca alloy was enhanced with the addition of Zn up to 1%, while further addition reversed the effect. The Mg–0.5Ca–1Zn alloys with (α-Mg+Ca2Mg6Zn3 +Mg2Ca) phase showed lower corrosion rate than the alloys with (α-Mg+Ca2Mg6Zn3) and (α-Mg+Ca2Mg6Zn3 +Mg51Ca20) phases. The amount of corrosion product, composed of Mg(OH)2 and hydroxyapatite on the surface of the alloy, increased with increasing Zn content. [Copyright &y& Elsevier]

Magnesium (Mg) was considered as a new kind of biomaterial implant due to its biodegradability and biocompatibility. Nevertheless, sufficient mechanical properties and low degradation rates in physiological environments are required. In this research, we have demonstrated that a network structure is developed from the reduced graphene oxide (rGO) and carbon nanotubes (CNTs), which inhibited face-to-face aggregation of rGO nano-platelets by straight CNTs inserted into adjacent rGO nano-platelets. The combination of rGO and CNTs was then used to strengthen the Mg-based nanocomposite fabricated using semi-powder metallurgy. The compressive strength and strain to fracture were maximally achieved 326.7 MPa and 11.58%, respectively for composite with 0.16 wt% CNTs and 0.5 wt% rGO. It was due to the effective load transfer and energy absorption of rGO and CNTs. Mechanisms for crack tip shielding, crack bridging and crack deflection was found to be responsible for mechanical enhancement. The electrochemical tests showed that the composite with the lowest CNTs concentration has the best corrosion resistance. In addition, the apatite-forming ability of composite in simulated body fluid (SBF) and cell culture experiments demonstrated favorable composite bioactivity and biocompatibility. Evaluation of the antibacterial activity showed that the growth and penetration of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria could be significantly inhibited with increasing rGO-CNTs hybrid content in Mg alloy. This study may open the doors to the fabrication of Mg-based nanocomposite implants containing rGO-CNTs hybrid fillers for load-bearing applications. [Display omitted] • ZM31/0.5rGO-xCNTs (x = 0.12, 0.16, 0.25 and 0.5 wt%CNTs) composite were prepared by semi powder metallurgy. • Crack tip shielding effect, crack bridging and crack deflection were determined as crucial toughening mechanisms. • Composite with the lowest CNTs concentration has the best corrosion resistance. • ZM31/rGO-CNTs nanocomposite has appropriate biocompatibility for the use as biomaterials. [ABSTRACT FROM AUTHOR]

In this study the influence of various Bi additions on the microstructure and corrosion behavior of the Mg–1.2Ca– x Bi alloys ( x = 0.5, 1.5, 3, 5, 12 wt.%) were evaluated by using optical and scanning electron microscopy, immersion and electrochemical tests. Microstructural observations showed that the refinement efficiency became more pronounced with increased Bi amount. Microstructural results of Mg–1.2Ca– x Bi ( x = 0.5, 1.5, and 3) indicated that the formation of three distinct phases—namely α-Mg, Mg 2 Ca and Mg 3 Bi 2 . However, further addition of Bi to 5 and 12 wt.% leads to evolution of α-Mg, Mg 3 Bi 2 , and Mg 2 Bi 2 Ca phases. The addition of Bi up to 0.5 wt.% enhanced corrosion resistance while further addition from 1.5 to 12 wt.% accelerated the degradation rate because of the emergence of more galvanic coupling between the α-Mg phases and secondary phases. The analyses showed that the Mg–1.2Ca–0.5Bi alloy gives the best corrosion resistance behavior, which makes it ideal for biodegradable medical applications. [ABSTRACT FROM AUTHOR]