Magnesium-calcium Alloy Research Articles

Surface integrity of biodegradable orthopedic magnesium–calcium alloy by high-speed dry face milling

Biodegradable magnesium–calcium (MgCa) implants have the ability to gradually dissolve and be absorbed in human body after implantation. Since the implant surface is in direct interaction with body fluids, surface integrity of MgCa implants are key factors influencing degradation rate of the biodegradable implants. Machining is often very necessary to make geometric features of implants. The effects of process parameters in dry high-speed face milling of MgCa0.8 (wt%) alloy on surface integrity characteristics, i.e. surface topography, surface roughness, microstructure, microhardness, and residual stresses, are investigated in this study. Polycrystalline diamond inserts are used to avoid material adhesion in milling MgCa alloy. High cutting speeds of up to 2,800 m/min and a broad range of feed and depth-of-cut values are selected to cover the regimes of finish and rough cutting. Average roughness value of 0.4 μm and shallow strain hardened depths are achieved. Little change of grain size can be observed in the near surface even for very slow feed value of 0.05 mm/rev. The surface residual stresses are measured to be highly compressive.

Cutting mechanics in high speed dry machining of biomedical magnesium–calcium alloy using internal state variable plasticity model

Magnesium–Calcium (MgCa) alloys become attractive orthopedic biomaterials due to their biodegradability, biocompatibility, and congruent mechanical properties with bone tissues. However, process mechanics of cutting biomedical MgCa alloys is poorly understood. Mechanical properties of the biomedical magnesium alloy at high strain rates and large strains are determined using the split-Hopkinson pressure bar testing method. Internal state variable (ISV) plasticity model is implemented to model the material behavior under cutting regimes. A finite element analysis (FEA) model has been developed to study the chip formation during high speed dry cutting of MgCa0.8 (wt%) alloy. Continuous chip formation predicted by finite element simulation is verified by high speed dry face milling of MgCa0.8 using polycrystalline diamond (PCD) inserts. Chip ignition as the most hazardous aspect in machining Mg alloys does not occur in high-speed dry cutting with sharp PCD tools. The predicted temperature distribution well explains the reason for the absence of chip ignition in high speed dry cutting of MgCa0.8 alloy. In addition, sporadic surface deterioration and void marks on the back face of chips are explained.

Surface integrity of magnesium-calcium implants processed by synergistic dry cutting-finish burnishing

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive orthopedic biomaterial compared to permanent metallic alloys. However, the critical issue is that MgCa alloy corrodes too fast in the human organism. It is expected that surface integrity of an MgCa implant has significant impact on the corrosion performance. Compared to dry cutting, the synergistic dry cutting-finish burnishing of MgCa0.8 alloy is capable of producing superior surface integrity including good surface finish, high compressive hook-shaped residual stress profile, extended strain hardening in subsurface, and little change of grain size.

Biomechanical testing and degradation analysis of MgCa0.8 alloy screws: A comparative in vivo study in rabbits

The aim of this study was to compare the biomechanical properties of degradable magnesium calcium alloy (MgCa0.8) screws and commonly used stainless steel (S316L) screws and to assess the in vivo degradation behavior of MgCa0.8. MgCa0.8 screws (n=48) and S316L screws (n=32) were implanted into both tibiae of 40 adult rabbits for a follow-up of 2, 4, 6 and 8weeks. This resulted in a testing group of MgCa0.8 (n=12) and S316L (n=8) screws for each follow-up. Uniaxial pull-out tests were carried out in an MTS 858 Mini Bionix at a rate of 0.1mms−1. For degradation analysis of MgCa0.8 in vivo micro-computed tomography (μCT) was performed to determine the volume of metal alloy remaining. Retrieved MgCa0.8 screws were analysed for degradation by determination of weight changes, scanning electron microscopy and energy dispersive X-ray analyses. No significant differences could be noted between the pull-out forces of MgCa0.8 and S316L 2weeks after surgery (P=0.121). Six weeks after surgery the pull-out force of MgCa0.8 decreased slightly. In contrast, the S316L pull-out force increased with time. Thus, significantly higher pull-out values were detected for S316L from 4weeks on (P<0.001). The volume and weight of MgCa0.8 gradually reduced. A corrosion layer, mainly composed of oxygen, magnesium, calcium and phosphorus, formed on the implants. Since MgCa0.8 showed good biocompatibility and biomechanical properties, comparable with those of S316L in the first 2–3weeks of implantation, its application as a biodegradable implant is conceivable.

Evaluation of the soft tissue biocompatibility of MgCa0.8 and surgical steel 316L in vivo: a comparative study in rabbits

BackgroundRecent studies have shown the potential suitability of magnesium alloys as biodegradable implants. The aim of the present study was to compare the soft tissue biocompatibility of MgCa0.8 and commonly used surgical steel in vivo.MethodsA biodegradable magnesium calcium alloy (MgCa0.8) and surgical steel (S316L), as a control, were investigated. Screws of identical geometrical conformation were implanted into the tibiae of 40 rabbits for a postoperative follow up of two, four, six and eight weeks. The tibialis cranialis muscle was in direct vicinity of the screw head and thus embedded in paraffin and histologically and immunohistochemically assessed. Haematoxylin and eosin staining was performed to identify macrophages, giant cells and heterophil granulocytes as well as the extent of tissue fibrosis and necrosis. Mouse anti-CD79α and rat anti-CD3 monoclonal primary antibodies were used for B- and T-lymphocyte detection. Evaluation of all sections was performed by applying a semi-quantitative score.ResultsClinically, both implant materials were tolerated well. Histology revealed that a layer of fibrous tissue had formed between implant and overlying muscle in MgCa0.8 and S316L, which was demarcated by a layer of synoviocyte-like cells at its interface to the implant. In MgCa0.8 implants cavities were detected within the fibrous tissue, which were surrounded by the same kind of cell type. The thickness of the fibrous layer and the amount of tissue necrosis and cellular infiltrations gradually decreased in S316L. In contrast, a decrease could only be noted in the first weeks of implantation in MgCa0.8, whereas parameters were increasing again at the end of the observation period. B-lymphocytes were found more often in MgCa0.8 indicating humoral immunity and the presence of soluble antigens. Conversely, S316L displayed a higher quantity of T-lymphocytes.ConclusionsModerate inflammation was detected in both implant materials and resolved to a minimum during the first weeks indicating comparable biocompatibility for MgCa0.8 and S316L. Thus, the application of MgCa0.8 as biodegradable implant material seems conceivable. Since the inflammatory parameters were re-increasing at the end of the observation period in MgCa0.8 it is important to observe the development of inflammation over a longer time period in addition to the present study.

Development and biocompatibility of a novel corrodible fluoride‐coated magnesium‐calcium alloy with improved degradation kinetics and adequate mechanical properties for cardiovascular applications

Recently, corrodible magnesium-based alloys have been introduced for use as cardiovascular stents and orthopedic implants. However, rapid corrosion rates have raised questions about their biocompatibility. Therefore, we developed a binary fluoride-coated magnesium-calcium alloy with improved degradation kinetics. Biocompatibility of the alloys was evaluated with metabolic assays (colorimetric WST-1 test). Furthermore, five different probes of magnesium-calcium alloys (MgCa 0.4, 0.6, 0.8, 1.2, and 2.0 wt %) were cocultivated with human smooth muscle cells and endothelial cells. To investigate the decomposition kinetics in a physiological environment the alloys were used untreated and fluoride coated (MgF(2)). Mg and Ca decreased the metabolic activity in vascular cells dose-dependently, with cytotoxic effects only at unphysiological concentrations. Uncoated magnesium alloys showed signs of decomposition after a short incubation time of 24 h in contrast to MgF(2) coated alloys. After 10 days smooth muscle and endothelial cells around the alloys were still alive, whereas colonization of the surfaces was only observed for smooth muscle cells. The fluoride-coated MgCa alloys exhibited good results concerning mechanical properties, degradation kinetics, and biocompatibility in vitro. We conclude that a binary fluoride magnesium-calcium alloy is a promising candidate for the production of cardiovascular stents.

Optical properties of switchable mirrors based on magnesium-calcium alloy thin films

Switchable mirrors based on magnesium-calcium alloy thin films were prepared using a direct-current magnetron sputtering method and their gasochromic properties have been investigated. Pd-capped Mg1−zCaz (0.04&amp;lt;z&amp;lt;0.20) films showed excellent switchable mirror properties. The visible transmittance in the transparent state increased with Ca composition, z, and after reaching a maximum of ∼46% at z∼0.06, the transmittance decreased gradually with increasing Ca composition. In the transparent state with z&amp;lt;0.08, the optical transmittance spectra of these switchable mirrors were fairly flat in the visible range and their color looked completely neutral. The achromatic properties with high visible transmittance may be because the hydrogenated switchable mirrors are composed of MgH2 and MgCaH3.72 with grayish neutral color appearance.

Preparation and characterization of a new biomedical magnesium–calcium alloy

Magnesium alloys are currently used in many structural applications. It is believed that magnesium and its alloys may also find applications in biomedical fields. In this study, a new biomedical magnesium-based alloy, i.e., magnesium–calcium (Mg–Ca) has been designed from biological and metallurgical viewpoints. The microstructure, mechanical and corrosion behaviors of Mg–Ca alloys with varying calcium content were investigated. The results show that a magnesium alloy with 0.6 wt.% calcium content (denoted as Mg–0.6Ca) shows good corrosion and mechanical properties. Our preliminary results demonstrate a good potential of this Mg–0.6Ca alloy as a new biomedical material.

Influence of zinc ion implantation on surface nanomechanical performance and corrosion resistance of biomedical magnesium–calcium alloys

It is believed that magnesium and its alloys may find applications in biomedical fields as implants, bone fixation devices, and tissue engineering scaffolds. However, their corrosion rate must be controlled. In this study, biomedical magnesium–calcium (Mg–Ca) alloys were ion-implanted with zinc. The surface nanomechanical performance and corrosion behavior of the ion-implanted Mg–Ca alloys are determined. The results show that zinc ion implantation at a dose of 0.9 × 10 17 ions/cm 2 significantly improves the surface hardness and modulus. However, the results on corrosion resistance reveal that zinc ion implantation degrades the corrosion behavior of Mg–Ca alloys. Thus, zinc is not a favorable element for the ion implantation treatment of biomedical Mg–Ca alloys.

Activated solid–fluid reactions in ultrasound reactors

Reactions of solids with liquid reactants can be accelerated in ultrasound fields. Transient bubbles create liquid microjets and increase the amount of dislocations on metallic surfaces. Dynamic experiments and models for the activation of magnesium turnings in the Grignard reaction of chlorobutane and phenylchloride show a relation between the degree of activation and the local energy distribution in the ultrasound field. The local action of transient bubbles and microjets in cavitating sound fields was measured and calculated. This allows the prediction of reaction rates, optimum process parameters and the behavior of different metals in noncatalytic as well as catalytic solid–fluid reactions. A further optimization of reaction rates and safer production of organometallic compounds was reached by applying mixtures of calcium donated magnesium. These alloys are very brittle and can be cleaved under ultrasound. High reaction rates with a variety of organic chlorides and phenyl fluoride are observed with sonicated magnesium calcium alloys.

Internal Friction in Magnesium and Magnesium Calcium Alloys Prepared by Rapid Solidification

Internal Friction in Magnesium and Magnesium Calcium Alloys Prepared by Rapid Solidification

Advances in the refining and alloying of low-bismuth lead

A programme has been initiated to improve the performance and eliminate the environmental concerns of the traditional Kroll-Betterton process for bismuth removal from lead. The work has resulted in the development of a new generation of debismuthizing reagents that are comprised of a magnesium-calcium alloy, specially designated at Mag-Cal™. The most common Mag-Cal™ alloy contains 70 wt.% magnesium and 30 wt.% calcium. Extensive testing has revealed that addition of Mag-Cal™ to the vortex at approximately 480–500 °C, followed by mixing for 5–15 min, provides the best results. With Mag-Cal™, bismuth levels of 0.005 wt.% Bi, or less, are readily achieved without the need for supplemental calcium and antimony additions. Calcium-aluminum master alloys (known as CAL-AL™) have been developed which enable battery-grid manufacturers to achieve target calcium and aluminum specifications with consistently high and predictable recoveries. A new process has been developed for alloying calcium and aluminum into lead. The process has been proven in an extensive campaign of pilotscale trials. The process uses pure calcium and aluminum in the form of granules of particulates and offers many advantages that will be of significant benefit to lead-calcium alloy producers.

Fabrication and properties of PM magnesium-calcium alloys : F.M. Knoop et al (Zentrum Funktionswerkstoffe GmbH, Germany)

Fabrication and properties of PM magnesium-calcium alloys : F.M. Knoop et al (Zentrum Funktionswerkstoffe GmbH, Germany)