Investigation on the <Emphasis Type="Italic">in vitro</Emphasis> cytocompatibility of Mg-Zn-Y-Nd-Zr alloys as degradable orthopaedic implant materials

Mg-Zn-Y-Nd-Zr alloy has been developed as a new type of biodegradable orthopaedic implant material by the authors’ research group with its excellent mechanical properties and controllable degradation rate. In this study, the cytocompatibility of Mg-Zn-Y-Nd-Zr alloy was systematically evaluated through in vitro cell culture method. MTT assay was applied to evaluate the cytotoxicity of Mg-Zn-Y-Nd-Zr alloy and no toxic effect was observed on L929 and MC3T3-E1 cells followed the protocol of ISO 10993 standard. Considering the potential ion accumulation in the bony environment, this study further investigated the cytotoxic effect of accumulated metallic ions during the alloy degradation by extending the extract preparation time. When the extract preparation time was prolonged to 1440?h, the accumulated metallic ions leaded to severe cell apoptosis, of which the combined ion concentration was determined as 39.5–65.8?µM of Mg²⁺, 3.5–5.9?µM of Zn²⁺, 0.44–0.74?µM of Y³⁺, 0.3–0.52?µM of Nd³⁺ and 0.11–0.18?µM of Zr⁴⁺ for L929, and 65.8–92.2?µM of Mg²⁺, 5.9–8.3?µM of Zn²⁺, 0.74–1.04?µM of Y³⁺, 0.52–0.73?µM of Nd³⁺ and 0.18–0.25?µM of Zr⁴⁺ for MC3T3-E1 cells. Besides the cell viability assessment, high expression of ALP activity and calcified nodules implied that metal elements in Mg-Zn-Y-Nd-Zr alloys can promote the osteogenic differentiation. Hence, excellent cytocompatibility has equipped Mg-Zn-Y-Nd-Zr alloy as a promising candidate for orthopaedic implant application, which can remarkably guide the magnesium-based alloy design and provide scientific evidence for clinical practice in future.     

In vitro degradation,hemolysis and MC3T3-E1 cell adhesion of biodegradable Mg–Zn alloy

In this study a kind of patent binary Mg–6 wt.%Zn magnesium alloy was investigated as degradable biomedical material. The results of in vitro degradation including electrochemical measurements and immersion tests in simulated body fluid (SBF) revealed that zinc could elevate both the corrosion potential and Faraday charge transfer resistance of magnesium and thus improve the corrosion resistance. XRD and EDS analysis proved that the corrosion products on the surface of Mg–Zn contained hydroxyapatite (HA), Mg(OH)₂ and other Mg/Ca phosphates, which could reduce the degradation rate. The degradation process of magnesium alloy and the mechanism of corrosion layer formation were also discussed in this work, i.e. the byproducts of degradation of magnesium, Mg²⁺ and OH^?, reacted with the phosphate and Ca²⁺ in the SBF, thus the corrosion layer containing HA, Mg(OH)₂ and other magnesium-substituted apatite precipitated in corrosion pits and covered the surface of magnesium alloy.The hemolysis test found that the hemolysis rate of Mg–Zn was 3.4%, which is lower than the safe value of 5% according to ISO 10993-4. For the cell culture experiments, after 2 h incubation the pre-osteoblastic cell MC3T3-E1 was able to adhere and spread on the corrosion layer of Mg–Zn alloy, indicating that despite the fluctuation of pH value of DMEM culture solution, Mg–Zn alloy could still support the earlier adhesion of pre-osteoblastic cells on the surface. Hemolysis and adhesion of cells display good biocompatibility of Mg–Zn alloy in vitro.     

Microwave assisted synthesis of amorphous magnesium phosphate nanospheres

Magnesium phosphate (MgP) materials have been investigated in recent years for tissue engineering applications, attributed to their biocompatibility and biodegradability. This paper describes a novel microwave assisted approach to produce amorphous magnesium phosphate (AMP) in a nanospherical form from an aqueous solution containing Mg²⁺ and HPO₄ ^2?/PO₄ ^3?. Some synthesis parameters such as pH, Mg/P ratio, solution composition were studied and the mechanism of AMP precursors was also demonstrated. The as-produced AMP nanospheres were characterized and tested in vitro. The results proved these AMP nanospheres can self-assemble into mature MgP materials and support cell proliferation. It is expected such AMP has potential in biomedical applications.     

The use of rat, rabbit or human bone marrow derived cells for cytocompatibility evaluation of metallic elements

Rat, rabbit and human bone marrow cells were cultured according to the method previously reported for cells of rat origin [1] and were exposed, or not (control), to corrosion products of a Co–Cr orthopaedic alloy as well as to metal salts containing Co2+, Cr3+ and Cr6+. Cells were cultured for 21 days and analysed for the following biochemical parameters: intracellular MTT reduction (i.e. cell viability/proliferation), alkaline phosphatase (ALP) activity and protein production. Morphological observations included both histochemistry (detection of ALP-positive cells, calcium and phosphate deposits) and scanning electron microscopy (SEM). Control cultures of rat and rabbit cells showed higher proliferation rates than human cells at the start of culture, but they all reached similar values on day 21. Protein production was parallel to cell proliferation. In contrast, ALP activity of rat cultures was much stronger than rabbit or human cultures. All cell types were able to develop the osteogenic phenotype in vitro.Co–Cr extract caused inhibitory effects on cell viability, on ALP activity and, to a lower extent, on protein production of all rat, rabbit and human cell cultures. Compared to rat and rabbit cultures, human cultures were the most sensitive to metal ions exposure.     

Biosorption of heavy metals and cephalexin from secondary effluents by tolerant bacteria

The biosorption of heavy metal ions and the antibiotic cephalexin from secondary effluents by the cell biomass of tolerant bacterial strains was investigated in this article. A total of 67 bacterial strains were isolated from a secondary effluents generated by sewage treatment plants. These strains were adapted to tolerate 6 mM nickel ions (Ni²⁺) and 10 g L^?1 cephalexin. Bacterial cell biomass that has more than 150 mg g^?1 biosorptive capacity was used for the biosorption under optimal conditions. The biosorption process was efficient in removing heavy metals: 87.63 % of cadmium, 74.61 % of copper, 58.32 % of nickel, 61.9 % of lead, and 94.26 % of zinc, respectively. The maximum biosorptive capacity of the bacterial cell biomass for cephalexin was 60 mg g^?1. The efficiency of cephalexin biosorption was reduced by more than 40.83 and 82.88 % (living and dead cells, respectively) in the presence of 1 mg L^?1 Ni²⁺ ions compared with the control, whereas no biosorption by dead cell biomass was recorded in aqueous solutions contaminated with cadmium, zinc, copper, and lead ions. In conclusion, biosorption which efficiently removes metal ions, but not cephalexin, from secondary effluents is explained.     

Effect of Mg<Superscript>2+</Superscript> concentration on biocompatibility of pure magnesium

The aim of the present study is to find the correlation between the Mg²⁺ concentration degraded from pure magnesium material and the biocompatibility of the material. Hemolysis ratio (HR) of the extracts of pure magnesium with different Mg²⁺ concentration were measured according to ISO 10993.4 standard. The cytotoxicity tests were carried out by both indirect contact with fibroblast L929 and preosteoblasts MC3T3-E1, and MTT tests were used. Cytotoxicity of the pure magnesium with and without surface modification was further evaluated by direct contact method. Samples were cultured with Osteoblast MC3T3-E1 and the effects of the material on viability and activity of cells were discussed. The results showed that the hemolysis rate and cytotoxicity of the modified Mg could meet the requirement for biomaterials. In our test, the hemolysis rate of the extracts was qualified when the concentration of Mg²⁺ ? 42 mg/L; the extracts with 202 mg/L Mg²⁺ met the cytotoxicity requirement, and the extracts with 156 mg/L Mg²⁺ promoted cell proliferation. Therefore, the biocompatibility of magnesium-based materials can be improved by suitable surface modification.     

生物可降解镁合金的发展现状与展望

镁合金作为新型可降解医用金属材料,近年来成为生物材料领域的研究热点,并越来越受到生物、材料和医学界的关注和重视.从工程用镁合金、新型医用镁合金、表面改性镁合金和新颖结构镁合金4个方面综述了国际和国内生物可降解镁合金方面的研究现状,系统地介绍和总结了目前生物可降解镁合金材料的合金设计、力学性能、体液腐蚀特性、细胞毒性和动物体内植入实验的相关结果,展望了未来生物可降解镁合金亟待解决的科学问题和应用前景.     

Improved performance of ZnO thin film solar cells by doping magnesium ions

This study investigates the effect of magnesium doping on the performance of nanocrystalline zinc oxide (ZnO) thin film solar cells. Mg_xZn_1?xO (x = 0.00, 0.05, 0.075 and 0.1 %) nanoparticles were prepared by simple precipitation method. The crystallinity and morphology of the photo-anode was characterized by X-ray diffraction analysis and scanning electron microscopy. The effect of various concentrations of magnesium ions on the structural and optical properties of ZnO nanoparticles was examined. Doping of magnesium ions helps the ZnO nanoparticles to grow larger in size with rod like surface morphologies. Solar cell with 0.075 % magnesium doped ZnO electrode exhibits an enhanced short-circuit current density of 3.36 mA/cm², open-circuit photo voltage of 0.79 V, fill factor of 0.73, and overall power conversion efficiency of 2.1 %.     

Magnesium – der Zukunftswerkstoff für die Automobilindustrie?

Magnesium – future material for automotive industry? Magnesium alloys show a very high potential in automotive applications as constructive metal, whereas the main focus lies on die cast parts. Electronic industry is the major commercial consumer for die castings besides the automobile industry. Room temperature applications like steering wheels and frame components in cars as well as mobile phone‐ or notebook housings are well established. These castings are produced with AZ‐ or AM‐magnesium alloys, which show good room temperature properties and a good castability. The great alloy development challenge in extending the use of magnesium cast alloys are application for higher temperatures. The application in powertrain components is considered to be the benchmark here. Besides alloy development there are also further research activities in development of casting processes. Semi‐solid processes like New‐Rheocasting (NRC), Thoxomolding ? or Thixocasting (TC) are adapted to the requirements of newly developed alloys. Not only cast alloys but also magnesium wrought alloys have moved to the centre of interest in the last decade. Alloy development for improving the formability on the one hand as well as process development in extrusion or rolling has to be done in order to find optimum parameters for deforming magnesium alloys properly.     

Preparation and Performance of Electroless Nickel on AZ91D Magnesium Alloy

The corrosion of magnesium alloy in different plating solutions was researched. The results demonstrated that corrosive condition of the alloy immersed in nickel chloride solution and nickel sulfate solution is serious and in nickel acetate solution and nickel nitrate solution is less. Magnesium alloy was handled with four acid pickling formulas and two activation formulas and the effects of different pickling formulas and activation formulas were researched through comparative experiment. The experimental results indicated that after handed with pickling formula about 500 mL L^?1 H₃PO₄ (85%), 110 mL L^?1 HNO₃ (68%), room temperature for 30 s and activation formula about 375 mL L^?1 HF (40%), room temperature for 10 min, magnesium alloy could realize electroless nickel plating directly and the performance of the prepared plating was much better. The properties of the nickel-plating coating were researched by electrochemical workstation, scanning electron microscope, and X-ray diffraction. The results demonstrated that this Ni–P coating was very uniform and meticulous; the structure of Ni–P coating was amorphous; and comparing with magnesium alloy, the corrosion potential of this plating increased about 799 V and the corrosion current density declined obviously. The nickel-plating coating effectively improved the anticorrosion performance of magnesium alloy.     

Characterization of fold defects in AZ91D and AE42 magnesium alloy permanent mold castings

Casting premium-quality magnesium alloy components for aerospace and automotive applications poses unique challenges. Magnesium alloys are known to freeze rapidly prior to filling a casting cavity, resulting in misruns and cold shuts. In addition, melt oxidation, solute segregation and turbulent metal flow during casting contribute to the formation of fold defects. In this research, formation of fold defects in AZ91D and AE42 magnesium alloys cast via the permanent mold casting process was investigated. Computer simulations of the casting process predicted the development of a turbulent metal flow in a critical casting region with abrupt geometrical transitions. SEM and light optical microscopy examinations revealed the presence of folds in this region for both alloys. However, each alloy exhibited a unique mechanism responsible for fold formation. In the AZ91D alloy, melt oxidation and velocity gradients in the critical casting region prevented fusion of merging metal front streams. In the AE42 alloy, limited solubility of rare-earth intermetallic compounds in the α-Mg phase resulted in segregation of Al₂RE particles at the leading edge of a metal front and created microstructural inhomogeneity across the fold.     

Fatigue of Magnesium Alloys

Magnesium alloys show a high specific strength and are therefore increasingly used for light‐weight constructions in transportation industry.^[1,2] To predict the behaviour of the material under the influence of cyclic loading it is vital to understand the fatigue behaviour of magnesium alloys. Only when understood properly, it is possible to fully apply the potential weight reduction by using magnesium alloys. A very important aspect in fatigue of magnesium alloys is the influence of a corrosive media and elevated temperatures, of which both are relevant in automotive applications. These two factors tend to have deleterious effects on magnesium alloys and therefore also have to be considered in investigations on the fatigue behaviour of magnesium alloys.     

Improvement of <Emphasis Type="Italic">in vitro</Emphasis> behavior of an Mg alloy using a nanostructured composite bioceramic coating

Magnesium (Mg) alloys as a new group of biodegradable metal implants are being extensively investigated as a promising selection for biomaterials applications due to their apt mechanical and biological performance. However, as a foremost drawback of Mg alloys, the high degradation in body fluid prevents its clinical applications. In this work, a bioceramic composite coating is developed composed of diopside, bredigite, and fluoridated hydroxyapatite on the AZ91 Mg alloy in order to moderate the degradation rate, while improving its bioactivity, cell compatibility, and mechanical integrity. Microstructural studies were performed using a transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, and energy dispersive spectroscopy (EDS). The degradation properties of samples were carried out under two steps, including electrochemical corrosion test and immersion test in simulated body fluid (SBF). Additionally, compression test was performed to evaluate the mechanical integrity of the specimens. L-929 fibroblast cells were cultured on the samples to determine the cell compatibility of the samples, including the cell viability and attachment. The degradation results suggest that the composite coating decreases the degradation and improves the bioactivity of AZ91 Mg alloy substrate. No considerable deterioration in the compression strength was observed for the coated samples compared to the uncoated sample after 4 weeks immersion. Cytotoxicity test indicated that the coatings improve the cell compatibility of AZ91 alloy for L-929 cells.     

In vitro degradation of four magnesium–zinc–strontium alloys and their cytocompatibility with human embryonic stem cells

Magnesium alloys have attracted great interest for medical applications due to their unique biodegradable capability and desirable mechanical properties. When designed for medical applications, these alloys must have suitable degradation properties, i.e., their degradation rate should not exceed the rate at which the degradation products can be excreted from the body. Cellular responses and tissue integration around the Mg-based implants are critical for clinical success. Four magnesium–zinc–strontium (ZSr41) alloys were developed in this study. The degradation properties of the ZSr41 alloys and their cytocompatibility were studied using an in vitro human embryonic stem cell (hESC) model due to the greater sensitivity of hESCs to known toxicants which allows to potentially detect toxicological effects of new biomaterials at an early stage. Four distinct ZSr41 alloys with 4 wt% zinc and a series of strontium compositions (0.15, 0.5, 1, and 1.5 wt% Sr) were produced through metallurgical processing. Their degradation was characterized by measuring total mass loss of samples and pH change in the cell culture media. The concentration of Mg ions released from ZSr41 alloy into the cell culture media was analyzed using inductively coupled plasma atomic emission spectroscopy. Surface microstructure and composition before and after culturing with hESCs were characterized using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Pure Mg was used as a control during cell culture studies. Results indicated that the Mg–Zn–Sr alloy with 0.15 wt% Sr provided slower degradation and improved cytocompatibility as compared with pure Mg control.     

Calcium phosphate coating on magnesium alloy by biomimetic method: Investigation of morphology, composition and formation process

Magnesium alloy has similar mechanical properties with natural bone and can degrade via corrosion in the electrolytic environment of the human body. Calcium phosphate has been proven to possess bioactivity and bone inductivity. In order to integrate both advantages, calcium phosphate coating was fabricated on magnesium alloy by a biomimetic method. Supersaturated calcification solutions (SCSs) with different Ca/P ratio and Cl⁻ concentration were used as mimetic solutions. The morphology, composition and formation process of the coating were studied with scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results show that a uniform calcium phosphate coating was observed on magnesium alloy, the properties of which could be adjusted by the SCSs with different Ca/P ratio. The formation process of the coating was explored by immersing magnesium alloy in SCSs with different Cl⁻ concentration which could adjust the hydrogen production. According to SEM results, the hydrogen bubbles were associated with the formation of grass-like and flower-like coating morphologies. In conclusion, the biomimetic method was effective to form calcium phosphate coating on magnesium alloy and the morphology and composition of the coating could be accommodated by the Ca/P ratio and Cl⁻ concentration in SCSs.     

A novel antibacterial titania coating: Metal ion toxicity and <Emphasis Type="Italic">in vitro</Emphasis> surface colonization

Postoperative implant-associated infection is still an unresolved and serious complication in modern surgery. Antibacterial and biocompatible surfaces could both reduce infection rates and promote tissue integration. In this respect, a comparative study of the antibacterial as well as the biocompatible potential of different metal ions in vitro is presented. The assays used were growth inhibition tests with different metal salts carried out with tissue cells and bacteria under corresponding culture conditions. Additionally, in vitro tests in direct surface contact with tissue cells and bacteria onto a novel copper containing sol-gel derived titanium dioxide coating (Cu-TiO₂) and a fourfold Cu-TiO₂ coating were performed. The values were compared to a non-filled titanium dioxide coating and standard Ti6Al4V alloy. SEM-investigations were performed to approve the results of the in vitro tests.Among Ag⁺, Zn²⁺, Co²⁺, Al³⁺ and Hg²⁺, the growth inhibition tests revealed an outstanding position of copper ions as antibacterial but nevertheless bio-tolerant additive. These results were affirmed by the cell tests in direct surface contact and SEM-investigations, where best cell growth was found on the Cu-TiO₂ coatings. Highest antibacterial properties with a tolerable cytocompatibility could be observed on the fourfold Cu-TiO₂ coatings.Consequently, surfaces with custom-tailored antibacterial properties may be established and could be of particular interest in revision and tumor arthroplasty.     

Surface characterization and biocompatibility of titanium alloys implanted with nitrogen by Hardion+ technology

In this study, the new Hardion+ micro-implanter technology was used to modify surface properties of biomedical pure titanium (CP-Ti) and Ti?C6Al?C4V ELI alloy by implantation of nitrogen ions. This process is based on the use of an electron cyclotron resonance ion source to produce a multienergetic ion beam from multicharged ions. After implantation, surface analysis methods revealed the formation of titanium nitride (TiN) on the substrate surfaces. An increase in superficial hardness and a significant reduction of friction coefficient were observed for both materials when compared to non-implanted samples. Better corrosion resistance and a significant decrease in ion release rates were observed for N-implanted biomaterials due to the formation of the protective TiN layer on their surfaces. In vitro tests performed on human fetal osteoblasts indicated that the cytocompatibility of N-implanted CP-Ti and Ti?C6Al?C4V alloy was enhanced in comparison to that of the corresponding non treated samples. Consequently, Hardion+ implantation technique can provide titanium alloys with better qualities in terms of corrosion resistance, cell proliferation, adhesion and viability.     

Preliminary study of biodegradation of AZ31B magnesium alloy

Magnesium alloys are potential to be developed as a new type of biodegradable implant material by use of their active corrosion behavior. Both in vitro and in vivo biodegradation properties of an AZ31B magnesium alloy were investigated in this work. The results showed that AZ31B alloy has a proper degradation rate and much lower hydrogen release in Hank’s solution, with a degradation rate of about 0.3 mm/year and hydrogen release below 0.15 mL/cm². The animal implantation test showed that the AZ31B alloy could slowly biodegrade in femur of the rabbit and form calcium phosphate around the alloy sample, with the Ca/P ratio close to the natural bone.     

医用镁合金降解及其对人体的影响

镁合金具有比高分子更高的强度、比陶瓷材料更好的韧性,与人体自然骨的密度、弹性模量和力学性能也更为接近。更重要的是,其植入人体后将会逐步腐蚀降解,既无毒副作用也无需二次手术,是一种极具潜质的新型可降解生物金属材料。但镁在人体生理环境中腐蚀速度太快,可能导致镁离子、氢气、局部pH值和腐蚀沉淀物在体内发生堆积,同时镁合金的机械完整性和力学性能也会因此丧失,达不到预期的治疗目的,甚至引起不良反应和治疗失败。从镁在人体的腐蚀机理和降解产物对人体造成的影响进行综述,并分析了镁合金在未来的发展方向和挑战。     

In vitro degradation behavior of M1A magnesium alloy in protein-containing simulated body fluid

Magnesium alloys possess unique advantages to be used as biodegradable implants for clinical applications. In this study, in vitro cells responses and degradation behaviors of magnesium alloy M1A in simulated body fluid (SBF) and albumin-containing SBF (A-SBF) were systematically investigated. Cell responses, in terms of Cell morphology and cell proliferation, imply that M1A possesses good viability for MG63 cells. The corrosion behaviors of M1A are strongly affected by the addition of albumin through the combined effects of adsorption and chelation. Electrochemical testing indicates that such an absorbed albumin layer makes M1A to be more noble with a smaller corrosion current. Corrosion rate monitored by hydrogen evolution rate suggests that the quickly adsorbed albumin serves as an effective protective layer, resulting in a much slower hydrogen release rate at initial stage. With increasing immersion time, a higher corrosion rate is observed since the chelation effect exerts more significant acceleration effects on the removal of the passivation layer. The corrosion mode evaluated by surface morphology of the samples changes from a nonuniform-anisotropic mode for M1A in SBF to a uniform-isotropic mode for M1A in A-SBF.