Biocompatibility of magnesium particles evaluated by in vitro cytotoxicity and genotoxicity assays

Corrosion Behavior in Magnesium-Based Alloys for Biomedical Applications

Magnesium alloys exhibit superior biocompatibility and biodegradability, which makes them an excellent candidate for artificial implants. However, these materials also suffer from lower corrosion resistance, which limits their clinical applicability. The corrosion mechanism of Mg alloys is complicated since the spontaneous occurrence is determined by means of loss of aspects, e.g., the basic feature of materials and various corrosive environments. As such, this study provides a review of the general degradation/precipitation process multifactorial corrosion behavior and proposes a reasonable method for modeling and preventing corrosion in metals. In addition, the composition design, the structural treatment, and the surface processing technique are involved as potential methods to control the degradation rate and improve the biological properties of Mg alloys. This systematic representation of corrosive mechanisms and the comprehensive discussion of various technologies for applications could lead to improved designs for Mg-based biomedical devices in the future.

Water-powered self-propelled magnetic nanobot for rapid and highly efficient capture of circulating tumor cells

Nanosized robots with self-propelling and navigating capabilities have become an exciting field of research, attributable to their autonomous motion and specific biomolecular interaction ability for bio-analysis and diagnosis. Here, we report magnesium (Mg)-Fe₃O₄-based Magneto-Fluorescent Nanorobot ("MFN") that can self-propel in blood without any other additives and can selectively and rapidly isolate cancer cells. The nanobots viz; Mg-Fe₃O₄-GSH-G4-Cy5-Tf and Mg-Fe₃O₄-GSH-G4-Cy5-Ab have been designed and synthesized by simple surface modifications and conjugation chemistry to assemble multiple components viz; (i) EpCAM antibody/transferrin, (ii) cyanine 5 NHS (Cy5) dye, (iii) fourth generation (G4) dendrimers for multiple conjugation and (iv) glutathione (GSH) by chemical conjugation onto one side of Mg nanoparticle. The nanobots propelled efficiently not only in simulated biological media, but also in blood samples. With continuous motion upon exposure to water and the presence of Fe₃O₄ shell on Mg nanoparticle for magnetic guidance, the nanobot offers major improvements in sensitivity, efficiency and speed by greatly enhancing capture of cancer cells. The nanobots showed excellent cancer cell capture efficiency of almost 100% both in serum and whole blood, especially with MCF7 breast cancer cells.

Characterization and In Vitro Evaluations of Injectable Calcium Phosphate Cement Doped with Magnesium and Strontium

Injectable calcium phosphate cement is a promising biomaterial for hard tissue repair due to its osteoinductivity, biocompatibility properties, and its use to correct defect areas involving narrow cavities with limited accessibility by the minimally invasive technique. Microwave-synthesized hydroxyapatite (HA) was used for the preparation of cement. In recent years, both magnesium and strontium calcium phosphate cements have exhibited rapid setting, improved mechanical strength, and a good resorption rate. A big step still remains to develop injectable magnesium and strontium phosphate cements with ideal self-setting properties, adequate mechanical strength, and good biocompatibility for clinical applications. In this study, both magnesium and strontium were doped with synthesized semiamorphous and crystalline hydroxyapatite (HA). The powder mixture was mixed with Na₂HPO₄, NaH₂PO₄, and a carboxymethyl cellulose (CMC) solution to develop the novel magnesium and strontium calcium phosphate cement. The setting time, physiochemical properties of hardened cement, microstructure, mechanical strength, and injectability of the prepared cement were studied. The toxicity evaluation and cell adhesion, which are necessary to identify the suitability of the material for different applications, were quantified and investigated using fibroblast cells. The setting time of cement was reduced substantially for magnesium- or strontium-doped cement by 2 min. The phase composition of the hardened cement expresses the semiamorphous or crystalline phase of HA with additives. Smooth and complete injection of cement paste was observed in semiamorphous HA-based cement. The intercellular reactive oxygen stress (ROS) of the Sr²⁺-doped cement sample showed varied degrees of toxicity to cells in terms of different concentrations. The Mg²⁺-doped cement showed significant attachment of cells after treatment at varying incubation times.

A study of Titanium and Magnesium particle-induced oxidative stress and toxicity to human osteoblasts

Hybrid implants combine both Titanium (Ti) and Magnesium (Mg) are prevalent nowadays. The long-term implications of Ti and Mg implants within the human body are not yet fully understood. Many implant failure cases due to inflammation, allergic responses, and aspect loosening have been reported frequently. Particles generated through daily wear and tear of implants may worsen the situation by causing acute complications. An in-depth understanding of the behavior of metal particles with human osteoblasts is necessary. In this study, a novel and systematic attempt was made to understand the effects of different concentrations of Ti and Mg particles to the osteoblastic SAOS2 cell: toxicity, alterations to mitochondria, and changes to the specific gene and protein expression. Ti particles were found toxic to SAOS2 cells at different dosages, while Mg particles at lower concentrations could improve cell viability. To understand this phenomenon better, we have measured cellular reactive oxygen species (ROS) production and cell apoptosis & necrosis percentage. We also have checked the mitochondrial structure with transmission electron microscope (TEM), and mitochondrial function using Tetramethyl rhodamine, ethyl ester staining (TMRE). NDUFB6, SDHC, and ATP5F1 were the essential mitochondrial genes involved in the ROS production and ATP production. Immunocytochemistry (ICC) and real-time polymerase chain reaction (qPCR) were implemented to check the regulations of these related genes.

Micro-/Nanomotors toward Biomedical Applications: The Recent Progress in Biocompatibility

Inspired by the highly versatile natural motors, artificial micro-/nanomotors that can convert surrounding energies into mechanical motion and accomplish multiple tasks are devised. In the past few years, micro-/nanomotors have demonstrated significant potential in biomedicine. However, the practical biomedical applications of these small-scale devices are still at an infant stage. For successful bench-to-bed translation, biocompatibility of micro-/nanomotor systems is the central issue to be considered. Herein, the recent progress in micro-/nanomotors in biocompatibility is reviewed, with a special focus on their biomedical applications. Through close collaboration between researches in the nanoengineering, material chemistry, and biomedical fields, it is expected that a promising real-world application platform based on micro-/nanomotors will emerge in the near future.

The effect of cell density, proximity, and time on the cytotoxicity of magnesium and galvanically coupled magnesium-titanium particles in vitro

Magnesium (Mg) and galvanically coupled magnesium-titanium (Mg-Ti) particles in vitro have been reported previously to kill cells in a dosage-dependent manner. Mg-Ti particles kill cells more effectively than Mg alone, due to the galvanic effect of Mg and Ti. This study further investigated the in vitro cytotoxicity of Mg and Mg-Ti in terms of particle concentration, cell density, time, and proximity. Cell density has an effect on cell viability only at low particle concentrations (below 250 µg/mL), where cell viability dropped only for lower cell densities (5000-10,000 cells/cm² ) and not for higher cell densities (20,000-30,000 cells/cm² ), showing that the particles cannot kill if there are more cells present. Cytotoxicity of Mg and Mg-Ti particles is quick and temporary, where the particles kill cells only during particle corrosion (first 24 h). Depending on the percentage of surviving cells, particle concentrations, and ongoing corrosion activity, the remaining live cells either proliferated and recovered, or just remained viable and quiescent. The particle killing is also proximity-dependent, where cell viability was significantly higher for cells far away from the particles (greater than ∼1 mm) compared to those close to the particles (less than ∼1 mm). Although the increase of pH does affect cell viability negatively, it is not the sole killing factor since cell viability is significantly dependent on particle type and proximity but not pH. Mg and Mg-Ti particles used in this study are large enough to prevent direct cell phagocytosis so that the cell killing effect may be attributed to solely electrochemical reactions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1428-1439, 2018.

Time-Lapse Evaluation of Interactions Between Biodegradable Mg Particles and Cells

Mg-based implants have promising applications as biodegradable materials in medicine for orthopedic, dental, and cardiovascular therapies. During wear and degradation microdebris are released. Time-lapse multidimensional microscopy (MM) is proposed here as a suitable tool to follow, in fixed intervals over 24-h periods, the interaction between cells and particles. Results of MM show interactions of macrophages (J774) with the magnesium particles (MgPa) that led to modifications of cell size and morphology, a decrease in duplication rate, and cell damage. Corrosion products were progressively formed on the surface of the particles and turbulence was generated due to hydrogen development. Changes were more significant after treating MgPa with potassium fluoride. In order to complement MM observations, membrane damage as detected by a lactase dehydrogenase (LDH) assay and mitochondrial activity as detected by a WST-1 assay with macrophages and osteoblasts (MC3T3-E1) were compared. A more significant concentration-dependent effect was detected for macrophages exposed to MgPa than for osteoblasts. Accordingly, complementary data showed that viability and cell cycle seem to be more altered in macrophages. In addition, protein profiles and expression of proteins associated with the adhesion process changed in the presence of MgPa. These studies revealed that time-lapse MM is a helpful tool for monitoring changes of biodegradable materials and the biological surrounding in real time and in situ. This information is useful in studies related to biodegradable biomaterials.

Cytotoxic, genotoxic, and neurotoxic effects of Mg, Pb, and Fe on pheochromocytoma (PC-12) cells

Metals such as lead (Pb), magnesium (Mg), and iron (Fe) are ubiquitous in the environment as a result of natural occurrence and anthropogenic activities. Although Mg, Fe, and others are considered essential elements, high level of exposure has been associated with severe adverse health effects including cardiovascular, hematological, nephrotoxic, hepatotoxic, and neurologic abnormalities in humans. In the present study we hypothesized that Mg, Pb, and Fe are cytotoxic, genotoxic and neurotoxic, and their toxicity is mediated through oxidative stress and alteration in protein expression. To test the hypothesis, we used the pheochromocytoma (PC-12) cell line as a neuro cell model and performed the LDH assay for cell viability, Comet assay for DNA damage, Western blot for oxidative stress, and HPLC-MS to assess the concentration levels of neurological biomarkers such as glutamate, dopamine (DA), and 3-methoxytyramine (3-MT). The results of this study clearly show that Mg, Pb, and Fe, respectively in the form of MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 induce cytotoxicity, oxidative stress, and genotoxicity in PC-12 cells. In addition, exposure to these metallic compounds caused significant changes in the concentration levels of glutamate, dopamine, and 3-MT in PC-12 cells. Taken together the findings suggest that MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 have the potential to induce substantial toxicity to PC-12 cells.

Cytotoxicity of corrosion products of degradable Fe-based stents: relevance of pH and insoluble products

Fe-based biodegradable metallic materials (Fe-BMMs) have been proposed for cardiovascular applications and are expected to disappear via corrosion after an appropriate period. However, in vivo studies showed that Fe ions release leads to accumulation of orange and brownish insoluble products at the biomaterial/cell interface. As an additional consequence, sharp changes in pH may affect the biocompatibility of these materials. In the present work, the experimental protocols were designed with the aim of evaluating the relative importance that these factors have on biocompatibility evaluation of BMMs. Mitochondrial activity (MTT assay) and thiobarbituric acid reactive substances (TBARS) assay on mammalian cells, exposed to 1-5 mM of added Fe3+ salt, were assessed and compared with results linked exclusively to pH effects. Soluble Fe concentration in culture medium and intracellular Fe content were also determined. The results showed that: (i) mitochondrial activity was affected by pH changes over the entire range of concentrations of added Fe3+ assayed, (ii) at the highest added Fe3+ concentrations (≥3 mM), precipitation was detected and the cells were able to incorporate the precipitate, that seems to be linked to cell damage, (iii) the extent of precipitation depends on the Fe/protein concentration ratio; and (iv) lipid peroxidation products were detected over the entire range of concentrations of added Fe3+. Hence, a new approach opens in the biocompatibility evaluation of Fe-based BMMs, since the cytotoxicity would not be solely a function of released (and soluble) ions but of the insoluble degradation product amount and the pH falling at the biomaterial/cell interface. The concentration of Fe-containing products at the interface depends on diffusional conditions in a very complex way that should be carefully analyzed in the future.

Magnesium corrosion particles do not interfere with the immune function of primary human and murine macrophages

Magnesium is currently under investigation as a prospective biodegradable implant material. Biodegradation of magnesium causes a release of magnesium, hydroxide ions and hydrogen gas but it can also lead to the formation of particulate debris. Implant-derived particles may have immunotoxic effects. To investigate the influence of magnesium-derived particles on the immune functions of primary macrophages, up to 500 μg/ml magnesium or magnesium corrosion particles were added to the cell culture medium. No major effects were observed on cell viability and on the release of the proinflammatory cytokine tumor necrosis factor (TNF)α. In addition, the ability of macrophages to stimulate proliferation of allogenic lymphocytes in a mixed leukocyte reaction remained unaffected. When macrophages were incubated with magnesium particles and then infected with the apathogenic Mycobacterium smegmatis, infection-induced TNFα secretion from murine macrophages was inhibited but not from human macrophages. However, the bactericidal activity of either cell type was not influenced. In conclusion, magnesium-related particles did not restrict the immune function of macrophages, suggesting that magnesium implants and corrosion particles derived thereof are highly biocompatible and have a low inflammatory potential.

Effects of fluctuant magnesium concentration on phenotype of the primary chondrocytes

Magnesium (Mg) and its alloys have attracted much research interest as degradable implant materials. Mg ions may enhance phenotype of chondrocytes at optimal concentrations. In this study, we investigated the effects of fluctuant concentrations of Mg ion released from in vitro degradation of pure Mg microspheres on the phenotype of chondrocytes. The chondrocytes were cultured with 250 μg/mL, 500 μg/mL, and 1000 μg/mL of Mg microspheres (75-150 μm) either on tissue culture plates or within alginate hydrogels, with 5, 10, and 20 mM of MgCl2 solution set as the control group. Concentrations of Mg ions and pH values of the culture medium were measured at 3 days' interval. Cytotoxicity was evaluated while glycosaminoglycan (GAG) content and gene expression of collagen type I/II/X, aggrecan were quantified. Results showed that peak concentrations of Mg ion reached 10, 20, 30 mM, respectively, at day 3 in groups containing Mg-250 μg/mL, Mg-500 μg/mL, and Mg-1000 μg/mL, respectively, whereas pH values increased mildly to approximately 8 in all experimental groups. No significant cytotoxic effects were found at day 1 and day 3 in all experimental groups. GAG content increased 6% at day 14 in Mg-250 μg/mL group in tissue culture plate, but not in the hydrogel culture. Gene expression of collagen type I/II/X and aggrecan in Mg-1000 μg/mL group decreased significantly when chondrocytes were cultured in cell culture plates. Increase of gene expression of collagen type X in Mg-250 μg/mL group at day 7 was observed. However, gene expressions of collagen type I/II/X and aggrecan in Mg groups increased significantly at day 7 when chondrocytes were cultured in hydrogels. It was concluded that the phenotype of chondrocytes was regulated with dynamic concentration of Mg ions and pH values in a dose- and time-dependant manners. Fine-tuned degradation of Mg microspheres could be used to facilitate layered structures of articular cartilage. Furthermore, it would be cautious to extrapolate from results from 2D chondrocyte cultures.

Mechanical property, biocorrosion and in vitro biocompatibility evaluations of Mg-Li-(Al)-(RE) alloys for future cardiovascular stent application

Mg-Li-based alloys were investigated for future cardiovascular stent application as they possess excellent ductility. However, Mg-Li binary alloys exhibited reduced mechanical strengths due to the presence of lithium. To improve the mechanical strengths of Mg-Li binary alloys, aluminum and rare earth (RE) elements were added to form Mg-Li-Al ternary and Mg-Li-Al-RE quarternary alloys. In the present study, six Mg-Li-(Al)-(RE) alloys were fabricated. Their microstructures, mechanical properties and biocorrosion behavior were evaluated by using optical microscopy, X-ray diffraction, scanning electronic microscopy, tensile tests, immersion tests and electrochemical measurements. Microstructure characterization indicated that grain sizes were moderately refined by the addition of rare earth elements. Tensile testing showed that enhanced mechanical strengths were obtained, while electrochemical and immersion tests showed reduced corrosion resistance caused by intermetallic compounds distributed throughout the magnesium matrix in the rare-earth-containing Mg-Li alloys. Cytotoxicity assays, hemolysis tests as well as platelet adhesion tests were performed to evaluate in vitro biocompatibilities of the Mg-Li-based alloys. The results of cytotoxicity assays clearly showed that the Mg-3.5Li-2Al-2RE, Mg-3.5Li-4Al-2RE and Mg-8.5Li-2Al-2RE alloys suppressed vascular smooth muscle cell proliferation after 5day incubation, while the Mg-3.5Li, Mg-8.5Li and Mg-8.5Li-1Al alloys were proven to be tolerated. In the case of human umbilical vein endothelial cells, the Mg-Li-based alloys showed no significantly reduced cell viabilities except for the Mg-8.5Li-2Al-2RE alloy, with no obvious differences in cell viability between different culture periods. With the exception of Mg-8.5Li-2Al-2RE, all of the other Mg-Li-(Al)-(RE) alloys exhibited acceptable hemolysis ratios, and no sign of thrombogenicity was found. These in vitro experimental results indicate the potential of Mg-Li-(Al)-(RE) alloys as biomaterials for future cardiovascular stent application and the worthiness of investigating their biodegradation behaviors in vivo.