Tong Cui

Electrodeposition of hydroxyapatite coating on Mg‐4.0Zn‐1.0Ca‐0.6Zr alloy and in vitro evaluation of degradation, hemolysis, and cytotoxicity

A novel biodegradable Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy was successfully produced using a series of metallurgical processes; including melting, casting, rolling, and heat treatment. The hardness and ultimate tensile strength of the alloy sheets increased to 71.2HV and 320 MPa after rolling and then aging for 12 h at 175°C. These mechanical properties were sufficient for load-bearing orthopedic implants. A hydroxyapatite (HA) coating was deposited on the Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy using a novel coating process combining alkali heat pretreatment, electrodeposition, and alkali heat posttreatment. The microstructure, composition, and phases of the Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy and HA coating were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The degradation, hemolysis, and cytocompatibility of the HA-coated and uncoated Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy were studied in vitro. The corrosion potential (E(corr)) of Mg-4.0Zn-1.0Ca-0.6Zr alloy (-1.72 V) was higher than Mg (-1.95 V), Mg-0.6Ca alloy (-1.91 V) and Mg-1.0Ca alloy (-1.97 V), indicating the Mg-Zn-Ca-Zr alloy would be more corrosion resistant. The initial corrosion potential of the HA-coated Mg alloy sample (-1.51 V) was higher than the uncoated sample (-1.72 V). The hemolysis rates of the HA-coated and uncoated Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy samples were both <5%, which met the requirements for implant materials. The HA-coated and uncoated Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy samples demonstrated the same cytotoxicity score as the negative control. The HA-coated samples showed a slightly greater relative growth rate (RGR%) of fibroblasts than the uncoated samples. Both the HA-coated and uncoated Mg-4.0Zn-1.0Ca-0.6Zr (wt %) alloy provided evidence of acceptable cytocompatibility for medical applications.

Development and evaluation of a magnesium–zinc–strontium alloy for biomedical applications — Alloy processing, microstructure, mechanical properties, and biodegradation

A new biodegradable magnesium-zinc-strontium (Mg-Zn-Sr) alloy was developed and studied for medical implant applications. This first study investigated the alloy processing (casting, rolling, and heat treatment), microstructures, mechanical properties, and degradation properties in simulated body fluid (SBF). Aging treatment of the ZSr41 alloy at 175 °C for 8h improved the mechanical properties when compared to those of the as-cast alloy. Specifically, the aged ZSr41 alloy had an ultimate tensile strength of 270 MPa, Vickers hardness of 71.5 HV, and elongation at failure of 12.8%. The mechanical properties of the ZSr41 alloy were superior as compared with those of pure magnesium and met the requirements for load-bearing medical implants. Furthermore, the immersion of the ZSr41 alloy in SBF showed a degradation mode that progressed cyclically, alternating between pitting and localized corrosion. The steady-state average degradation rate of the aged ZSr41 alloy in SBF was 0.96 g/(m(2)·hr), while the pH of SBF immersion solution increased. The corrosion current density of the ZSr41 alloy in SBF solution was 0.41 mA/mm(2), which was much lower than 1.67 mA/mm(2) for pure Mg under the same conditions. In summary, compared to pure Mg, the mechanical properties of the new ZSr41 alloy improved while the degradation rate decreased due to the addition of Zn and Sr alloying elements and specific processing conditions. The superior mechanical properties and corrosion resistance of the new ZSr41 alloy make it a promising alloy for next-generation implant applications.

Microstructures, mechanical properties, and degradation behaviors of heat-treated Mg-Sr alloys as potential biodegradable implant materials

In previous studies, Mg-Sr alloys exhibited great biocompatibility with regard to test animals, and enhanced peri-implant bone formation. The objective of the present study was to investigate the effects of heat treatments on the mechanical and corrosion properties of Mg-Sr alloys. Various heat-treated Mg-xSr (x = 0.5, 1, and 2wt%, nominal composition) alloys were prepared using homogenization and aging treatments. Mechanical tests were performed at room temperature on the as-cast, homogenized, and peak-aged alloys. As the Sr content increased, the volume fraction of Mg17Sr2 phases within the as-cast alloys increased; in addition, the mechanical strength of the alloys initially increased and subsequently decreased, while the ductility decreased. Following the homogenization treatment, the mechanical strength of the alloys decreased, and the ductility increased. Nano-sized Mg17Sr2 phases were re-precipitated during the aging treatment. The age-hardening response at 160°C was enhanced as the Sr content increased. Following the aging treatment, there was an increase in the mechanical strength of the alloys; however, there was a slight reduction in the ductility. Immersion tests were conducted at 37°C for 360h, using Hanks buffered salt solution (HBSS), to study the degradation behavior of the alloys. As the Sr content of the Mg-Sr alloys increased, the corrosion rate (CR) increased owing to the galvanic effect. The homogenization treatment consequently reduced the CR dramatically, and the aging treatment had a slight effect on the CR. The peak-aged Mg-1Sr (wt%) alloy exhibited the best combination of properties. The tensile yield strength (TYS), ultimate tensile strength (UTS), elongation, compressive yield strength (CYS), ultimate compressive strength (UCS), compressibility, and CR of the as-cast Mg-1Sr (wt%) alloy were 56.0MPa, 92.67MPa, 1.27%, 171.4MPa, 243.6MPa, 22.3%, and 1.76mm/year, respectively. The respective results obtained for the peak-aged Mg-1Sr (wt%) alloys were 69.7MPa, 135.6MPa, 3.22%, 183.1MPa, 273.6MPa, 27.6%, and 1.33mm/year. Following immersion in HBSS, the primary corrosion products of the peak-aged Mg-1Sr (wt%) alloy were Mg(OH)2, MgO, MgCO3, Mg3(PO4)2, MgHPO4, and Mg(H2PO4)2, which enhanced the corrosion resistance by forming a composite corrosion film.

New Magnesium Alloys for Potential Application of Implantation Biomaterial

New magnesium alloys with optimized chemical compositions with good biocompatibility were designed. Experimental results show that MZ alloy mainly consists of Ca2Mg5Zn5+α (Mg) and MgZn+MgZn2+Mg2Ca+Zn-Zr compounds. Ca has a strong capability for grain refinement in such alloy. Zr can refine magnesium alloy. Zn addition does not refine the solidification microstructure but plays significant strengthening role during aging treatment. The main strengthening phases of Mg-Zn-Zr alloy are γ(MgZn) and δ(Mg2Zn3). The tensile strength of MZ alloy plate aged at 170°C for 12h is 320MPa, and the elongation-to-failure is 18.4%, the alloy has a potential application of implantation biomaterial.

Microstructure formation mechanism and properties of a Mg-3Sn-1Mn (wt%) magnesium alloy processed by a novel semisolid continuous shearing and rolling process

A novel semisolid Continuous Shearing and Rolling (CSR) process for producing a Mg-3Sn-1Mn (wt%) alloy strip is developed, and the microstructure formation mechanism and properties of the Mg-3Sn-1Mn (wt%) alloy processed by this process are investigated. At a casting temperature of 690°C and a roll speed of 0.052 m·s−1, a Mg-3Sn-1Mn (wt%) alloy strip with a cross section size of 4×160 mm was produced by the proposed process. Under strong cooling and shearing actions, eruptive nucleation, direct globular grain growth and dendrite arm breakage took place during the process, which caused formations of fine spherical grains. The grain size and roundness of the Mg-3Sn-1Mn (wt%) alloy strip increased with increasing increments of the casting temperature. In this perspective, roll speed obviously affects grain shape. The ultimate tensile strength and elongation of the Mg-3Sn-1Mn (wt%) alloy strip reached 205.93 MPa and 7.2%.

In vitro degradation and cytocompatibility of Magnesium-Zinc-Strontium alloys with human embryonic stem cells

Magnesium-based alloys have attracted great interest for medical applications due to their unique biodegradable capability and desirable mechanical properties. When considered for medical applications, the degradation rate of these alloys must be tailored so that: (i) it does not exceed the rate at which the degradation products can be excreted from the body, and (ii) it is slow enough so that the load bearing properties of the implant are not jeopardized and do not conflict prior to and during synthesis of new tissue. Implant integration with surrounding cells and tissues and mechanical stability are critical aspects for clinical success. This study investigated Magnesium-Zinc-Strontium (ZSr41) alloy degradation rates and the interaction of the degradation products with human embryonic stem cells (hESC) over a 72 hour period. An in vitro hESC model was chosen due to the higher sensitivity of ESCs to known toxicants which allows to potentially detect toxicological effects of new biomaterials at an early stage. Four distinct ZSr41 compositions (0.15 wt.%, 0.5 wt.%, 1 wt.%, and 1.5 wt.% Sr) were designed and produced through metallurgical processing. ZSr41 alloy mechanical properties, degradation, and cytocompatibility were investigated and compared to pure polished Magnesium (Mg). Mechanical properties evaluated included hardness, ultimate tensile strength, and elongation to failure. Degradation was characterized by measuring total weight loss of samples and pH change in the cell culture media. Cytocompatibility was studied by comparing fluorescence and phase contrast images of hESCs after co-culture with Mg alloys. Results indicated that the Mg-Zn-Sr alloy with 0.15 wt.% Sr improved cytocompatibility and provided slower degradation as compared with pure Mg.

Biocorrosion of Biodegradable Implant Mg-xCa-4Zn Alloy in Simulated Body Fluid with the Addition of Ca

The affect of adding of Zn on the microstructure and corrosion properties was investigated in this work. Vacuum induce melting was used to obtain the Mg-2Ca-xZn (wt.%) (x = 0%, 1%, 2% and 3%) alloys. Erode test was carried out in the Hank’s simulated body fluid for the alloys and the increasing of weight is carefully measured. The microstructure of the alloys was observed with optical microscope and SEM. It is found that and the Mg-2Ca-1Zn alloy is with the best corrosion resistance. Hardness increases as the adding of Zn in the alloys.

Microstructure and Mechanical Properties of Al-Mg-Sc Alloy Processed by Semi-Solid Continuous Casting-Extrusion

High tensile strength Al-3Mg-0.5Sc alloy wires can be produced by a method called semi-solid continuous casting-extrusion and on-line solution process (CCES). The effects of artificial aging and the combination of the artificial aging and cold drawing on the microstructures and properties of alloy wires were respectively investigated. TEM observations reveal that a large number of dislocations and Al3Sc particles distributed in the Al-matrix of Al-3Mg-0.5Sc alloy produced by semi-solid CCES.After directly artificial aging (DAA), the tensile strength is 353MPa and elongation is 19.9%; After cold drawing following artificial aging (CDAA), the tensile strength is 378MPa and elongation is 17.7%; After artificial aging following cold drawing (AACD), the tensile strength is 435MPa and elongation is 10.4%.

The Impacts of Heat Treatment on the Material Structure and Properties of Mg-4.0Zn-1.0Ca-0.6Zr Bio-Medical Materials

The Mg-4.0Zn-1.0Ca-0.6Zr alloy was prepared through casting-homogenizing-rolling and the study was made on the alloy microstructure as well as mechanical properties under different heat treatment processes. The result shows that, alloy sheets have their hardness and tensile strength rising at the first phase and inclining later with the extension of aging time, in which the maximum values gained at 12h i.e. 71.2HV and 320MPa accordingly. At 8h of aging the extensibility obtained maximum value of 19.2%, then the value reduced gradually with the continuous aging time. The mechanical properties of alloy sheets increased after tempering process, the reason should be that, inside of the crystal particles rich amount of Mg6Ca2Zn3 and MgZn strengthening phases were separated out.

The Microstructures and Mechanical Properties of a Novel Biomaterial Mg-Zn-Sr Alloy Sheet during Aging Treatment

Mg-Zn-Sr alloy sheet; biomaterial; aging treatment; tensile property Abstract. The microstructures and mechanical properties of a novel biodegradable Mg-Zn-Sr alloy sheet aged at 175°C had been studied. The results indicate that the grain size of the casting alloy Mg-Zn-Sr is changed with the change of content of element Sr, and while it is 1.0 (wt.)%, smaller average grain size is gained which is 38μm, as well as it is increased to 1.5 (wt.)%, the grain size is coarsen obviously. The phase precipitated in the alloy sheet is sufficient and distributed in the uniform style at 175°C for 8h which gained the preferable mechanical properties, which the tensile strength reaches 230MPa, hardness 76.1HV as well as prolongation ratio 12.7%.