Concentration Of Mg Ions Research Articles

Three in One: Preparation of High-Performance High-Voltage LiCoO2 Cathodes via Introducing High Concentrations of Mg Ions

Three in One: Preparation of High-Performance High-Voltage LiCoO₂ Cathodes via Introducing High Concentrations of Mg Ions

SELECTIVE SODIUM PUMP INHIBITOR CALIX[4]ARENE C-1130 INCREASES CONCENTRATION OF Ca IONS IN SMOOTH MUSCLE CELLS

Aim. This work aimed to determine the biochemical regularities of calix[4]arene C-1130 effect on the activity of Nа+,К+-АТРase and Са2+ level in PM of smooth muscle cells (SMCs). Methods. Calix[4]arene C-1130 was synthesized and characterized in the Institute of Organic Chemistry of NAS of Ukraine. Biochemical studies were carried out in the Department of Muscle Biochemistry of Palladin Institute of Biochemistry, NAS of Ukraine. The experiments were performed on a suspension of myometrial cells and the PM fraction. Determination of the intracellular Са2+ concentration was done by confocal microscopy. The hydrodynamic diameter of myocytes was determined by dynamic light scattering. Results. We have studied the dependence of the activity of Nа+,К+-АТРase of PM on the concentration of Mg ions and ATP at different concentrations of calix[4]arene C-1130. The affinities of Nа+,К+-АТРase for ATP and Mg ions remained unaffected by the presence of calix[4]arene C-1130. However, a notable reduction in the initial maximum velocity of enzymatic ATP hydrolysis was observed. Overall, it indicates a non-competitive mechanism of inhibition of Nа+,К+-АТРase by C-1130. Confocal microscopy analysis showed that calix[4]arene C-1130 elevates Са2+ concentration within myometrial myocytes. Photon-correlation spectroscopy revealed that C-1130 reduces the effective hydrodynamic diameter of SMCs. Conclusions. We have shown that calix[4]arene C-1130 does not affect the activation coefficient for Mg ions and the apparent Michaelis constant Кm for ATP, but it reduces the maximum initial velocity Vmax of the ATP hydrolysis reaction. Thus, calix[4]arene C-1130 acts as a complete non-competitive inhibitor of Nа+,К+-АТРase of PM.

Co-utilization of aqueous carbonated basic oxygen furnace slag (BOFS) and carbonated filtrate in cement pastes considering reaction duration effect

It is generally agreed that aqueous carbonation of basic oxygen furnace slag (BOFS) is a promising and effective strategy to sequestrate CO2 and enhance the slag properties for use as a construction material. However, the handling of wastewater produced in the aqueous carbonation route is still a challenge. This work investigates the impact of co-utilizing carbonated BOFS as a partial cement replacement and carbonated filtrate as a mixing solution on the fresh and mechanical properties as well as the hydration and microstructural characteristics of cement paste. The carbonation duration of BOFS via the aqueous route (0, 10, 20, 30, 40, 80, and 120 min) was studied, and it was found that calcite was the dominant CaCO3 polymorph with different crystal shapes depending on the concentration of Mg ion in the slurry solution. The early-age compressive strength of blended cement pastes improved with the addition of 15% BOFS slurry carbonated for 40 min compared to as-received BOFS since the in-situ produced fine CaCO3 particles in the former could promote nucleation sites for cement hydration. However, the strength of pastes containing BOFS slurry carbonated for a longer duration was decreased due to the inhibited hydration reaction induced by the nesquehonite (MgCO3∙3H2O). At later ages of hydration, the nucleation effect was less obvious and the strength of cement paste was limited by the lower cement content. Moreover, the volume expansion issue caused commonly by f-CaO/MgO in BOFS can be improved through the precipitation of CaCO3 and nesquehonite.

Magnesium Effects on Carbohydrate Characters in Leaves, Phloem Sap and Mesocarp in Wax Gourd (Benincasa hispida (Thunb.) Cogn.)

Magnesium (Mg) is critical for agricultural production and human health. The wax gourd yield was greatly affected by Mg fertilizer and it serves as an excellent crop to study Mg functioning in sink growth; however, as a Cucurbitaceae plant which is called a raffinose family oligosaccharides (RFOs)-transporting plant, its adaptive mechanism of photoassimilates transportation and distribution to Mg nutrients remains unknown. Herein, we used two Mg treatments (+Mg 90 kg ha−1; CK as control 0 kg ha−1) to observe the effects of Mg on the photoassimilates status in the leaves, phloem sap and fruit of wax gourd grown across the entire growth stage under a field condition. For the first time, we confirmed that stachyose and raffinose, which accounted for 54.9–78.0% of the total carbohydrates across the whole growth phase in the phloem sap, were the most predominant sugars used for the long-distance transport of wax gourds. They were strongly increased by Mg application which started from the seedling stage to the end of growing season. This response was earlier and more dramatic than the over-accumulation of sucrose in leaves regardless of positions. Hexoses (glucose plus fructose) were the main soluble sugars in the source leaves as well as in the mesocarp tissues, and their responses to Mg varied with temporal and spatial differences. The difference in the sugar status in the leaves between the upper, middle and lower positions is closely related to the concentration of Mg ions. Compared with Mg deficiency (CK), Mg application stimulated sugar accumulation in the leaves at the seedling and flowering stages by 10.6–24.5%. On the contrary, after fruit set, Mg supplementation significantly reduced the soluble sugar concentration in leaves by 33.5–67.9%. Mg treatment also spiked the fructose and glucose in fruit at the fruit expansion stage by 26.7% and 16.4%, respectively. Taken together, our results showed that Mg tailors the carbohydrate status in the source (leaves), flow (phloem sap) and sink (mesocarp tissues) in wax gourds, especially during the fruit growth period. The lower stachyose in the phloem at the beginning of fruit setting may be an early indication of a curtailed sink process in wax gourds grown in Mg deficient soil.

Study of Hydroxyapatite-coated High-strength Biodegradable Magnesium-based Alloy in Repairing Fracture Damage in Rats.

Hydroxyapatite (HA) coating can improve the degradation rate and biological activity of metallic implants. This study aimed to fabricate a hydroxyapatite-coated ultrafine-grained biodegradable WE43 magnesium (HA/UFG-WE43 Mg) implant for repairing bone fractures. A hybrid approach, including parallel tubular-channel angular pressing (PTCAP) and physical vapour deposition (PVD) magnetron sputtering, was employed. The HA/UFG-WE43 Mg samples were tested in terms of their physicochemical and biological properties. The processed tubes exhibited ultrafine structures and the uniformity of microstructures improved following the two-pass PTCAP. The phase composition of the coating formed on UFG-WE43 Mg implant at 250 W for 90 min after heat treatment at 500°C for 60 min confirmed the presence of the HA characteristic peaks. Rat skeletal muscle cells were inoculated on the specimens and cultured for 1, 2, 6, 12, and 24 h, followed by evaluation of cell adhesion and morphology. The growth rates of cells were examined by the Cell Counting Kit8 (CCK-8) and cell survival was observed after 3 days of culture by fluorescence microscopy. The concentration of Mg ions in the blood of rats on 1, 3, 5, 7, and 15 days showed a reduction in Mg concentration after deposition of HA. Combination of PTCAP processing followed by surface modification led to tibial fracture healing, and histological analysis of implanted areas demonstrated an efficient biodegradation of the implanted material and a moderate inflammatory reaction.

Magnesium‐Substituted Zinc Ferrite as a Promising Nanomaterial for the Development of Humidity Sensors

Herein, the synthesis of zinc ferrite (ZnFe2O4) nanomaterials, substituted with magnesium (Mg), using the sol–gel autocombustion method, is reported. Powder X‐ray diffraction (PXRD), Fourier‐transform infrared (FTIR), field‐emission scanning electron microscopy (FESEM), and energy‐dispersive X‐ray spectroscopy (EDX) are used to characterize the synthesized Mg‐substituted ZnFe2O4. PXRD results show that unit cell volume and crystallite size decrease when the concentration of Mg ions rises. PXRD confirms that the nanomaterial has a single phase with the Fd3m space group. EDX confirms that the material is composed of Mg, Zn, Fe, and O elements. The FTIR spectra show a clear indication of the spinel ferrite structure, and the bands in the high‐frequency region reveal the hygroscopic nature of the prepared materials. The synthesized nanomaterial is used as a sensing element for the development of a humidity sensor. The average sensitivity (2.93 MΩ/%RH) is found to be highest for the composition Mg0.1Zn0.9Fe2O4. The response and recovery times of the fabricated thin‐film humidity sensor are 31 and 53 s, respectively. The developed sensing material has good repeatability (≈98%) and excellent stability.

Endothelial function after the exposition of magnesium degradation products

One of the most common magnesium (Mg) applications in the biomedical field is in cardiovascular stents. Although Mg is an essential element for homeostasis, Mg is highly reactive, and locally high Mg concentrations can have toxic effects on the surrounding tissue. One strategy to circumvent the Mg toxicity is using coatings or surface modifications that prevent the leaching of excessive Mg ions. In the current study, commercially pure magnesium (c.p Mg) was modified through plasma electrolytic oxidation (PEO) to produce a protective coating primarily composed of Mg oxide (MgO) and Mg hydroxide (Mg(OH)2), which limits leaching of free Mg ions from the base material. As we intend to use this material to produce vascular stents, a biological evaluation of its performance is warranted. Primary human umbilical vein endothelial cells (HUVECs) and smooth muscle cells (SMCs) were the study object. The leaching of free Mg ions from the oxidized materials was investigated, as was its effect on local pH changes. We also investigated the influence of corrosion products, the effects of elevated free Mg concentrations and pH on the cellular behavior on the integrity of monolayers of HUVECs was studied in a static and dynamic model. Results showed that the harmful effect of Mg on cells due to changes in pH and a high concentration of Mg ions could decrease with the influence of flow diffusing corrosion products such as MgO, Mg(OH)2, and H2 among the system. Independently, Mg concentration and pH affected the cell activity of SMCs and HUVECs. Finally, to investigate the influence of leachables on vasomotor function, we exposed porcine aortic rings to PEO-modified Mg stents and assessed endothelial-dependent relaxation. Pure Mg reduced vasorelaxation from 100% in control samples to 30%. Oppositely, PEO-modified Mg did not affect the vasomotor function. Overall, we conclude from this study that the use of PEO coatings reduces the degradation rate of the material reducing the Mg release resulting in better cell viability and vessel function compared to the bare material.

Effect of Mg Cation Diffusion Coefficient on Mg Dendrite Formation.

Dendrite formation is an important issue for the metal anode-based battery system. The traditional perception that Mg metal anode does not grow dendrite during operation has been challenged recently. Herein, we investigate the Mg electrodeposition behavior in a 0.3 M all-phenyl-complex (APC) electrolyte and confirm that Mg dendrites are readily formed at high current densities. A semiquantitative model indicates that the Mg-ion concentration on the electrode surface, limited by the intrinsic diffusion coefficient of the Mg cation group, decreases with increasing current density, resulting in an extra concentration polarization. However, Mg deposition at the tip of a protrusion on the electrode surface is hardly affected by the concentration polarization, and thus dendrite growth is more prone to occur at the tips. We find that the addition of LiCl in conventional APC electrolytes can suppress the Mg dendrite formation, mainly as a result of the enhanced Mg cation diffusion coefficient due to the influence of the LiCl additive, rather than the less pronounced electrostatic shield effect provided by Li cations.

Multifunctional Magnesium Anastomosis Staples for Wound Closure and Inhibition of Tumor Recurrence and Metastasis.

Biodegradable magnesium (Mg) implants spontaneously releasing therapeutic agents against tumors are an intriguing therapeutic approach for both tissue repair and tumor treatment. Anastomotic staples are extensively used for wound closure after surgical resection in patients with colorectal tumors. However, the safety of Mg anastomosis implants for intestinal closure and the effect of tumor suppression remain elusive. Here, we used a high-purity Mg staple to study these issues. Based on the results, we found that it has the potential to heal wounds produced after colorectal tumor resection while inhibiting relapse of residual tumor cells in vitro and in vivo. After implantation of Mg staples for 7 weeks in rabbits, the intestinal wound gradually healed with no adverse effects such as leakage or inflammation. Furthermore, the implanted Mg staples inhibit the growth of colorectal tumor cells and block migration to normal organs because of the increased concentration of Mg ions and released hydrogen. Such an antitumor effect is further confirmed by the in vitro cell experiments. Mg significantly induces apoptosis of tumor cells as well as inhibits cell growth and migration. Our work presents a feasible therapeutic opinion to design Mg anastomotic staples to perform wound healing and simultaneously release tumor suppressor elements in vivo to decrease the risk of tumor recurrence and metastasis.

Evaluación electroquímica de la degradación de la aleación de Mg-Zn-Ca en la solución fisiológica de Hanks

En el presente trabajo se ha investigado el efecto de los elementos aleantes Zn (0,95% en masa) y Ca (0,15% en masa) en el mecanismo de degradación del Mg. Las superficies del Mg puro y de la aleación Mg-Zn-Ca han sido caracterizadas durante su exposición a la solución fisiológica de Hanks (a 37 °C) hasta siete días, utilizando las técnicas SEM-EDS y XPS. La capa formada en la superficie de la aleación contiene Ca10(PO4)6(OH)2, que puede mejorar la compatibilidad ósea. Las partículas intermetálicas compuestas de la fase Mg2Ca, así como la presencia de Zn, han promovido la formación de una capa protectora más uniforme. Las pruebas de EIS y ruido electroquímico (EN) han indicado que la resistencia a la polarización (Rp) del Mg puro es un orden de magnitud menor y la resistencia al ruido de la corriente (Rn) ≈ 5 veces menor, que los de la aleación de Mg-Zn-Ca. Los valores del índice de picadura (PI) de cada material fueron inferiores a 0,6; lo que sugiere que el ataque de corrosión no está altamente localizado. Al final de las pruebas de inmersión, la concentración de iones de Mg liberados durante la degradación ha sido ≈ 4,5 veces mayor para Mg puro (1,63 ± 0,02 mg·cm−2) que para Mg-Zn-Ca (0,35 ± 0,03 mg·cm−2). En consecuencia, la densidad de corriente de corrosión (jcorr) calculada para el Mg puro fue dos veces mayor (1,33 μA·cm−2) que la de la aleación de Mg ZX10 (0,59 μA·cm−2).

Silicon carbide and III-Nitrides nanosheets: Promising anodes for Mg-ion batteries

In this article anode materials of silicon carbide and III-nitride nanosheets are investigated for magnesium ion batteries (MIBs) as possible alternative of lithium and sodium ion batteries. The calculated density functional theory results reveal higher values of internal energy change and cell voltage for MIBs with silicon carbide, boron nitride, aluminum nitride and gallium nitride anode material than the previously reported carbon nanomaterials. The nanosheet shows stronger binding capacity for Mg ion both in monolayer and bulk phase. The adsorption energies and cell voltage decreases as the concentration of Mg ions over nanosheet increased. The lower values (0.05–0.37 eV) of diffusion barriers prove the faster mobility of Mg ion in 2D nanosheet. The boron nitride and silicon carbide exhibit a high storage capacity of 1619.90 mA h/g and 1002.64 mA h/g respectively. Therefore, silicon carbide and III-nitride nanosheets based anode MIBs could be a promising alternative of lithium ion batteries and needs further studies.

In vitro antibacterial activity and cytocompatibility of magnesium-incorporated poly(lactide-co-glycolic acid) scaffolds

BackgroundBone defects are often combined with the risk of infection in the clinic, and artificial bone substitutes are often implanted to repair the defective bone. However, the implant materials are carriers for bacterial growth, and biofilm can form on the implant surface, which is difficult to eliminate using antibiotics and the host immune system. Magnesium (Mg) was previously reported to possess antibacterial potential.MethodsIn this study, Mg was incorporated into poly(lactide-co-glycolic acid) (PLGA) to fabricate a PLGA/Mg scaffold using a low-temperature rapid-prototyping technique. All scaffolds were divided into three groups: PLGA (P), PLGA/10 wt% Mg with low Mg content (PM-L) and PLGA/20 wt% Mg with high Mg content (PM-H). The degradation test of the scaffolds was conducted by immersing them into the trihydroxymethyl aminomethane–hydrochloric acid (Tris–HCl) buffer solution and measuring the change of pH values and concentrations of Mg ions. The antibacterial activity of the scaffolds was investigated by the spread plate method, tissue culture plate method, scanning electron microscopy and confocal laser scanning microscopy. Additionally, the cell attachment and proliferation of the scaffolds were evaluated by the cell counting kit-8 (CCK-8) assay using MC3T3-E1 cells.ResultsThe Mg-incorporated scaffolds degraded and released Mg ions and caused an increase in the pH value. Both PM-L and PM-H inhibited bacterial growth and biofilm formation, and PM-H exhibited higher antibacterial activity than PM-L after incubation for 24 and 48 h. Cell tests revealed that PM-H exerted a suppressive effect on cell attachment and proliferation.ConclusionsThese findings demonstrated that the PLGA/Mg scaffolds possessed favorable antibacterial activity, and a higher content of Mg (20%) exhibited higher antibacterial activity and inhibitory effects on cell attachment and proliferation than low Mg content (10%).

Mg-Phenolic Network Strategy for Enhancing Corrosion Resistance and Osteocompatibility of Degradable Magnesium Alloys.

Magnesium-based alloys are the most widely used materials for degradable metallic implants and have considerable potential for bone applications owing to their excellent stimulating effect on osteogenesis. However, their high corrosion rate limits their structural stability and causes oxygen deficiency and an excessive increase in the pH around the defect area during bone healing. Magnesium oxides, which are the main corrosion products of Mg, are nontoxic materials with useful effects on new bone formation and pH neutralization. Metal–phenolic networks were introduced recently as a cost-effective and efficient surface modifier and were fabricated by deposition of nanosized metal oxides on different types of substrates using the chemical reaction between phenolic groups and metallic ions. In this study, magnesium oxide films were formed successfully on a Mg-based substrate using Mg–phenolic networks. The effects of various coating parameters on the surface morphology, corrosion resistance, degradation behavior, wettability, and osteocompatibility of degradable metallic materials after surface modification with Mg–phenolic networks were thoroughly investigated for the first time. The results showed that the initial concentration of Mg ions was the main parameter affecting the corrosion resistance, which was almost as much as 3 times that of uncoated samples. Additionally, cytotoxicity and viability assessment and observation of the morphological changes in bonelike cells showed that the in vitro osteocompatibility was significantly enhanced by coatings with Mg concentrations of 2.4–3.6 mg mL–1. Finally, in vivo animal studies using the rat calvarial defect model confirmed that the proposed coating method mitigated the formation of gas cavities around the implantation area by reducing the corrosion rate of the Mg-based implant. The nanosized metal oxides produced by the Mg–phenolic network significantly improved the biodegradability and osteocompatibility of Mg alloys, suggesting a potential approach to advancing the clinical application of Mg alloys.

A Magnesium-Enriched 3D Culture System that Mimics the Bone Development Microenvironment for Vascularized Bone Regeneration.

The redevelopment/regeneration pattern of amputated limbs from a blastema in salamander suggests that enhanced regeneration might be achieved by mimicking the developmental microenvironment. Inspired by the discovery that the expression of magnesium transporter‐1 (MagT1), a selective magnesium (Mg) transporter, is significantly upregulated in the endochondral ossification region of mouse embryos, a Mg‐enriched 3D culture system is proposed to provide an embryonic‐like environment for stem cells. First, the optimum concentration of Mg ions (Mg2+) for creating the osteogenic microenvironment is screened by evaluating MagT1 expression levels, which correspond to the osteogenic differentiation capacity of stem cells. The results reveal that Mg2+ selectively activates the mitogen‐activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway to stimulate osteogenic differentiation, and Mg2+ influx via MagT1 is profoundly involved in this process. Then, Mg‐enriched microspheres are fabricated at the appropriate size to ensure the viability of the encapsulated cells. A series of experiments show that the Mg‐enriched microenvironment not only stimulates the osteogenic differentiation of stem cells but also promotes neovascularization. Obvious vascularized bone regeneration is achieved in vivo using these Mg‐enriched cell delivery vehicles. The findings suggest that biomaterials mimicking the developmental microenvironment might be promising tools to enhance tissue regeneration.

First-principles study of Fe:Mg:LiTaO<sub>3</sub> crystals

The electronic structures and absorption spectra of LiTaO<sub>3</sub> (LT) crystal and Fe:Mg:LiTaO<sub>3</sub> crystal with different Mg concentrations are investigated by first-principles through using the density functional theory. The supercell crystal structures are established with 60 atoms with four models: the near-stoichiometric pure LiTaO<sub>3</sub> crystal (LT); the iron doped LiTaO<sub>3</sub> crystal (Fe:LT), with the charge compensation model expressed as Fe<sub>Li</sub><sup>2+</sup>-2V<sub>Li</sub><sup>–</sup>; the iron and magnesium co-doped LiTaO<sub>3</sub> crystal (Fe:Mg:LT), with the charge compensation model taken as Fe<sub>Li</sub><sup>2+</sup>-Mg<sub>Li</sub><sup>+</sup>-3V<sub>Li</sub><sup>–</sup>; the other iron and magnesium co-doped LiTaO<sub>3</sub> crystal (Fe:Mg(E):LT), with Mg ion concentration near threshold value (slightly less than 6 mol%) and taking the charge compensation model as 2Mg<sub>Li</sub><sup>+</sup>-Fe<sub>Ta</sub><sup>2–</sup>. The geometry optimization results show that the total energy values of all models can achieve certain stable values, which means that the models used in this paper are very close to the actual crystal structures. In the electronic structures, the extrinsic defect energy levels in the forbidden band of Fe:LT crystal are mainly contributed from the Fe 3d orbital, and the band gap of Fe:LT about 3.05 eV is narrower than that of LT, the band gap of Fe:Mg:LT and Fe:Mg(E):LT sample are 2.72 eV and 2.45 eV respectively. The results show that the orbit of Fe 3d, Ta 5d and O 2p are superposed with each other, forming covalent bonds, which results in conduction band and valence band shifting toward low energy in iron doped LiTaO<sub>3</sub> crystal. The Fe 3d orbit is split into E<sub>g</sub> orbit and T<sub>2g</sub> orbit under the influence of the crystal field. There are two absorption peaks at 417 nm (2.97 eV) and 745 nm (1.66 eV) in the Fe:LiTaO<sub>3</sub> crystal. The first one is attributed to the transfer of the T<sub>2g</sub> orbital electron to conduction band. The last one can be taken as the result of E<sub>g</sub> electron transfer of Fe<sup>2+</sup> in crystal. The intensities and positions of these peaks vary with the concentration of Mg ion. Specially, with the concentration of Mg ion attaining the threshold value, the peak at 745 nm disappears, and the other peak moves slightly to 457 nm (2.71 eV). With the Mg ion concentration at the threshold value, the Fe ions can occupy Ta positions. This occupying condition makes the E<sub>g</sub> orbital energy change greatly compared with the scenario in the Fe<sub>Li</sub> condition, and it affects hardly the T<sub>2g</sub> orbital energy. So, if the absorption nearby 745 nm waveband can be taken as the useful process in holographic storage application, it is better to take smaller concentration of Mg ions (less than threshold value). On the other hand, nearby 457 nm waveband, concentration of Mg ions can be chosen as a large value.

Mechanical and in vitro degradation behavior of magnesium-bioactive glass composites prepared by SPS for biomedical applications.

In order to make magnesium (Mg) a successful candidate for fracture fixation devices, it is imperative to control the corrosion rate and enhance its elastic modulus. In the present work, we have prepared bioactive glass (BG) reinforced magnesium composite using spark plasma sintering (SPS). Simultaneous application of heat and pressure during SPS decreased the softening point of BG (600°C), allowing it to coat the Mg particles partially. As a result, BG was found along the Mg particle boundaries, which was confirmed by elemental mapping. Addition of BG improved microhardness and elastic modulus of Mg-BG composites. Corrosion behavior was studied by hydrogen evolution and immersion corrosion in phosphate buffered saline (PBS). After 64 h of immersion, Mg-10 wt % BG composite showed highest corrosion resistance. Quantitative micro-computed tomography (micro-CT) results indicated porosity increase in Mg-BG composites during immersion. The maximum increase in porosity (1.66%) was noticed for pure Mg while the minimum for Mg-10 wt % BG composite. MG63 cell-material interactions, using extract method, showed good cytocompatibility for Mg-10 wt % BG composite. The concentration of Mg ion in cell culture media was measured using atomic absorption spectroscopy after 24 h immersion of Mg/BG composites. The results indicated that using BG as reinforcement and SPS as sintering method; we can prepare corrosion resistant and high modulus Mg-BG composites that can be used for fabricating bone fracture fixation plates. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 352-365, 2019.

Development of a Novel Degradation-Controlled Magnesium-Based Regeneration Membrane for Future Guided Bone Regeneration (GBR) Therapy

This study aimed to develop and evaluate the ECO-friendly Mg-5Zn-0.5Zr (ECO505) alloy for application in dental-guided bone regeneration (GBR). The microstructure and surface properties of biomedical Mg materials greatly influence anti-corrosion performance and biocompatibility. Accordingly, for the purpose of microstructure and surface modification, heat treatments and surface coatings were chosen to provide varied functional characteristics. We developed and integrated both an optimized solution heat-treatment condition and surface fluoride coating technique to fabricate a Mg-based regeneration membrane. The heat-treated Mg regeneration membrane (ARRm-H380) and duplex-treated regeneration membrane group (ARRm-H380-F24 h) were thoroughly investigated to characterize the mechanical properties, as well as the in vitro corrosion and in vivo degradation behaviors. Significant enhancement in ductility and corrosion resistance for the ARRm-H380 was obtained through the optimized solid-solution heat treatment; meanwhile, the corrosion resistance of ARRm-H380-F24 h showed further improvement, resulting in superior substrate integrity. In addition, the ARRm-H380 provided the proper amount of Mg-ion concentration to accelerate bone growth in the early stage (more than 80% new bone formation). From a specific biomedical application point of view, these research results point out a successful manufacturing route and suggest that the heat treatment and duplex treatment could be employed to offer custom functional regeneration membranes for different clinical patients.

Dissolution behavior of CaO-MgO-SiO2 -based multiphase bioceramic powders and effects of the released ions on osteogenesis.

In the present study, the dissolution behavior of the CaO-MgO-SiO2 -based multiphase bioceramic powders as well as the effects of released ions on osteogenesis was investigated. In the dissolution process, Ca, Mg, and Si ions could be dissolved out from the powders. The incorporation of Mg could slow down the degradation rate of the powders so that to reduce the local concentration of Ca and Si ions. In return, the dissolution of Ca and Si ions leading to the formation of a porous SiO2 -rich layer could enhance the readsorption of free Mg ions in solution and thus down-regulate the concentration of Mg ions. In addition, the released ions exhibited both positive and negative synergistic effects on osteogenesis with a concentration-dependent manner. Trace amount of released Si ions could stimulate cell proliferation and osteogenic differentiation in the presence of Ca and Mg ions. The optimal concentration of Ca-Mg-Si ion combination to promote osteogenesis was existed in the 1/4 diluted extract, whereas a slightly inhibitory effect on cell proliferation and ALP activity was observed in the 1/2 diluted extract with higher concentration of Ca and Si ions . All above results suggested that the ion dissolution behavior of the CaO-MgO-SiO2 -based multiphase bioceramic could be regulated via adjustment of the composition so that released ions could be maintained at an appropriate composite concentration to cooperatively regulate the osteogenesis. This research provided an experimental basis for further optimization and application of CaO-MgO-SiO2 -based multiphase bioceramics with controlled ion dissolution and excellent physicochemical and biological properties. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3159-3168, 2017.

Corrosion Behavior of Calcium Phosphate-Coated Biomedical Magnesium Alloy Under in Vitro and In Vivo Environments

Magnesium alloys attract attention as a biodegradable/bioabsorbable medical device because of the biodegradability and good mechanical integrity. Corrosion rate of the magnesium alloys should be controlled depending on the implantation part of body as well as the biocompatibility should be improved. Hydroxyapatite (HAp) and octacalcium phosphate (OCP) coatings were developed to control the corrosion rate and to improve the hard tissue compatibility. Corrosion behavior of HAp- and OCP-coated Mg-3mass% Al-1mass% Zn (AZ31) was examined in cell culture medium (in vitro) or in subcutaneous tissue of mouse (in vivo). Effect of medium-replacement and addition of gelatin in medium on the corrosion behavior was also examined. Chemically polished AZ31 was used as a reference. Concentration of Mg ions in medium was quantified. Apparent corrosion initiation of substrate AZ31 was delayed for ca. 1 week with HAp and OCP coatings in medium while Mg ion release from as-polished AZ31 initiated from the beginning. Filiform corrosion took place, but visible growth of filiform corrosion stopped within several days. Afterwards, Mg ion release continued for 1 year with almost a constant corrosion rate. The corrosion rate of AZ31 alloy in medium was reduced by more than 50% with HAp and OCP coatings. HAp coating showed superior corrosion protection effect than OCP coating. After 1 year of immersion, cross section of the immersed specimens showed that uniform corrosion took place underneath the coatings. The wall of filiform corrosion pits was covered with thick corrosion products layer. These results indicate that corrosion continued for long time under the coating and corrosion products layer in medium. The periodical medium replacement during immersion test did not significantly change the initial corrosion rate for 4 weeks. However, the medium-replacement rather reduced the corrosion rate of HAp-coated AZ31 comparing to the result without medium-replacement. Deposition of calcium phosphate from medium was enhanced with the medium-replacement, leading to the improvement of corrosion protection effect of HAp coating. As-polished AZ31 caused the formation of gas cavity in subcutaneous tissue of mouse due to H2 gas generated in corrosion reaction. Such a gas cavity formation was not observed around the implanted HAp- and OCP-coated specimens, indicating that corrosion of substrate AZ31 was also reduced by HAp and OCP coating in subcutaneous tissue. After 16 weeks of implantation, the specimens were retrieved from the mouse and surface and cross section was observed using SEM. Macro- and micro-pits were observed on the surface and underneath the coatings. Unlike in medium, corrosion pits appeared to grow in depth direction rather than in lateral direction in subcutaneous tissue. Because body fluid circulation in the subcutaneous tissue is limited, to simulate the soft tissue environment, gelatin was added in medium and HAp-coated AZ31 was immersed for 4 weeks. Then, the similar corrosion morphology with macro- and micro-pits was obtained in the gelatin-added medium. These results indicate that corrosion of HAp- and OCP-coated AZ31 is localized in diffusion limited environment. The developed HAp and OCP coatings reduced the corrosion rate of Mg alloy in medium and in soft tissue. The corrosion morphology, especially shape of local corrosion, depended on the corrosion environment. The decrease of mass transfer in the environment caused the localization of corrosion of Mg alloy.

Changes in mineral assemblages during serpentine carbonation

The carbonation of serpentine (lizardite [Mg3Si2O5(OH)4]) was investigated at a fixed temperature of 290°C under a 30-bar CO2 atmosphere in aqueous solutions of different alkalinities to understand the pH-dependence of the process. To activate the carbonation, the serpentine was heat-treated at 650°C beforehand for 2h. At pH6, the main reaction products were magnesite (MgCO3) and well-crystallized saponite [NaxMg3(Si4Al4−x)O10(OH)2]. The carbonation rate of the Mg ions was limited at acidic pH, and thermogravimetry (TG) analysis of the solid product showed that only 13% carbonation rate of serpentine to magnesite was achieved. The partial dissolution of SiOSi and the resultant Mg-rich solution provided a favorable environment for the formation of saponite. In weakly alkaline and neutral solutions, the rate of carbonation was dramatically enhanced well-faceted rhombohedral magnesite crystals of approximately 1μm in size with a round shape appeared together with a small amount of “curled-flaky type” saponite. The conversion of silicate to carbonate was found to be approximately 45%. As the pH of the solution increased further, the dissociation of carbonic acid accelerated and the free Mg2+ cations then reacted with the bicarbonate ions to form magnesium carbonate. Thus, active conversion to magnesite resulted in poor formation of saponite because of the low concentration of Mg ions in the solution. At pH2, well-crystallized saponite appeared, but magnesite was not observed. Under strongly alkaline conditions, saponite may form by a mechanism wherein the undissolved Mg layer of serpentine is available to act as a substrate for saponite precipitation. The transformation of serpentine to saponite and magnesite was influenced mostly by temperature, alkalinity, and mineral composition.