Kokubo Solution Research Articles

A degradation kinetics model of Mg–Zn–Mn–Ca alloys in Kokubo solution

In this work, a model of the degradation of the Mg–Zn–Mn–Ca alloy system in SBF (Simulated Body Fluid) is proposed by applying the isoconversion method. Alloy ingots with nominal compositions of Mg–2Zn–0.2Mn–0.2Ca (wt.%) designed A.2 alloy and Mg–4Zn–0.2Mn–0.2Ca (wt.%), A.4 alloy, was induction melted at 680 °C. In a eudiometer, the alloys were immersed for 600 min in Kokubo solution at temperatures of 23.5 °C, 36.5 °C, 49.5 °C, and the evolution of hydrogen was monitored. In the isoconversion method, the Arrhenius' equations and the kinetic mechanism models of chemical and diffusion control were used to construct the model. The degradation rate in A.2 alloy varied from 6.66 mg of Mg/cm2 to 9.40 mg of Mg/cm2, and in A.4 alloy, from 5.48 mg to 6.70 mg of Mg/cm2 with a test temperature variation of 23.5–49.5 °C. The control mechanism observed was the mixed one, being predominantly of chemical control. The activation energy found for the isoconversion model that used the kinetic mechanism model of chemical control was 3.24 kJ/mol for A.2 alloy and 3.45 kJ/mol for A.4 alloy, the pre-exponential factor of 4.34 × 10−3 mm−1 for A.2 alloy and 4.21 × 10−3 mm−1 for A.4 alloy. It is concluded that the isoconversion model that best represents the degradation of A.2 and A.4 alloys in Kokubo solution is the model of the kinetics mechanism of chemical control associated with the Arrhenius equation, which presents good correlations results comparing the experimental results with the proposed model.

EIS Analysis of Electro Sprayed Chitosan Membranes as Coating Over Magnesium in SBF as Used in Biomedical Applications

Magnesium and its alloys have been used as biodegradable materials with high potential in biomedical applications such as temporary and absorbable implants. A biodegradable coating system was evaluated here from a chitosan solution and a gelatin additive in acetic acid, which was applied by means of the electrospray procedure and another glutaraldehyde crosslinking additive was used. Magnesium and the coatings system in a Kokubo solution at 37°C to simulate body conditions and the Electrochemical Impedance Spectroscopy (EIS) technique for corrosion studies was studied. The obtained electrochemical response was analyzed using a proposed equivalent circuits, composed of circuit elements, such as resistors (R), capacitances (C), inductances (L), and considering the influence of the finite diffusion (O) and the Warburg type (W). The electrochemical parameters allow us to estimate the time constants of each studied corrosion system and the sought interpretation of the phenomenon with the physical processes that occur at the electrochemical interface of Mg and its anticorrosive protection.

Особенности растворимости и цитосовместимости in vitro костных цементов на основе сульфата кальция, содержащих фосфат-ионы

Cement materials have based on calcium sulfate were obtained, which have introduced up to 20 mol. % of phosphate groups to improve their cytocompatibility and solubility. It was found that during exposure of cement materials based on calcium sulfate, containing of 0, 5, 10 and 20 mol. % phosphate - groups, in model solutions SBF (Kokubo solution, simulating the composition of human blood plasma) and DPBS (Dulbecco's phosphate-buffered saline) in dynamics up to 28 days of were formation of a calcium-phosphate layer on the surface of the samples. At the same time, in SBF solution, the process of recrystallization of sulfate and phosphate phases occurs more pronounced than in DPBS solution. In vitro studies on the cell culture of the human osteosarcoma line MG-63, cement samples showed cytocompatibility with the presence of moderate surface matrix properties

Investigation of the corrosion behavior of phosphate coated magnesium in a Kokubo Solution.

Investigation of the corrosion behavior of phosphate coated magnesium in a Kokubo Solution.

Microstructure, mechanical properties, corrosion behavior and film formation mechanism of Mg-Zn-Mn-xNd in Kokubo's solution

In this work, the mechanical properties and corrosion behavior of Mg-2Zn-0.2Mn-xNd with various Nd contents were investigated using correlative microscopy, electrochemical evaluations and immersion tests in a simulated body fluid (SBF). Additionally, the surface potential distributions and phase characteristics were detected using SEM, TEM, AFM/SKPFM and EPMA, and the film layer's adhesive features and localized corrosion mechanism were investigated by XRD, CLSM and EIS measurement. The results indicate that the corrosion initiates as a consequence of micro-galvanic coupling between the cathode phases such as the ellipsoid-like/strip shape of Mg75Zn20Nd5 with a nanoscale size and matrix. For a prolonged immersion time, the holes with different sizes and depths mutually interacted and were connected, which was observed at the dendrite arms and the surrounding the Nd-enriched phases. Both the immersion and electrochemical tests illustrated #2 (0.6% Nd) has the best corrosion performance, and exhibits a uniform corrosion morphology on the surface, which due to the dense and adhesive products could reduce the corrosion sensitivity and alleviate the current exchange density between the medium and the electrode. Moreover, a corrosion model was proposed to interpret the corrosion mechanism.

Wear Behavior of Biomedical Co-Cr-Mo F75 Alloys in Simulated Body Fluid

Pin-on-disk wear test using Co-Cr-Mo-C-N-Si-Mn cast alloy pins and alumina disks was conducted in Kokubo and 1mass% lactic acid solutions. The precipitates in the as-cast alloys were M23X6 type, π-phase and M2X type. After wear test, it was found that the ratio of the amount of eluted ions in 1mass% lactic acid solution corresponded to the chemical composition of alloys. The detached of M2X type precipitate was observed in as-cast alloy after wear test in 1mass% lactic acid solution. Meanwhile, the elution of metallic ions in Kokubo solution was much less that in 1mass% lactic acid solution. Concentration of Cr was extremely low in Kokubo solution. The formation of CrOOH during test in Kokubo solution might suppress the concentration of Cr.

Calcium phosphate crystallization on titania in a flowing Kokubo solution.

Dry titania layers on air-oxidized titanium substrates have been found to be active enough to cause apatite to be deposited in Kokubo's simulated body fluid (SBF) in narrow confined spaces, such as those in narrow grooves and thin gaps. Such in vitro apatite deposition is the basis of the GRAPE(®) technique. The aim of the present study is to determine why GRAPE conditions favor apatite deposition when laminar SBF flow (at 0.01-0.3ml/min) passes through a shallow channel (0.5mm) between a pair of titanium substrates each with a dry layer of titania. Assessing the factors that control the heterogeneous nucleation process led to the proposal of the working hypothesis that there are nucleation pre-embryos, ion assemblies that can be stabilized to form embryos, on the titania layer but that they are removed by the SBF flow. Specimens were subjected to different combinations of processes. One combination was that titania layers were exposed to still or flowing SBF, and the other was that half of a specimen, the inlet or outlet side, was exposed to still or flowing SBF with the other half being covered. The surface morphologies of the specimens were then compared in detail. The conclusion was that exposure to still SBF for 2days before exposure to flowing SBF was required for apatite to be deposited. Some complicated apatite deposition modes were observed, e.g., apatite was deposited even on areas unexposed to still SBF. All of the results were successfully interpreted using the working hypothesis. The conclusion was that the GRAPE(®) technique depends on the confined space holding pre-embryo and embryo assemblies.

Microstructural and Corrosion Behavior of Biodegradable Magnesium Alloys for Biomedical Implant

Magnesium and its alloys have great potential as biodegradable metallic implant materials with good mechanical properties. However, the poor corrosion rate and the production of hydrogen during degradation hindered its application. Binary alloy, Mg-3Ca and ternary alloy, Mg-3Ca-3Zn alloy were studied to investigate their bio-corrosion properties. Microstructure evolution and surfaces of corroded alloys were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The bio-corrosion behavior of the Mg alloys was investigated using immersion and electrochemical tests in Kokubo solution. Microstructural analysis showed that binary Mg-3Ca alloy consisted of α-Mg and Mg2Ca phases and ternary Mg-3Ca-3Zn alloy consisted of α-Mg, Ca2Mg6Zn3 and Mg2Ca phases. These phases had significant effect on the corrosion resistant of the alloy. Electrochemical test showed an improvement in ternary alloys where the corrosion current density reduced from 0.497 mA/cm2 in Mg-3Ca to 0.312 mA/cm2 in Mg-3Ca-3Zn alloy. Ternary Mg-3Ca-3Zn showed significant lower corrosion rate (1.1 mg/cm2/day) compared to binary Mg-3Ca (5.8 mg/cm2/day) alloy after 14 days immersion test.

Hydroxyapatite formation on titania-based materials in a solution mimicking body fluid: Effects of manganese and iron addition in anatase.

Hydroxyapatite formation on the surfaces of implanted materials plays an important role in osteoconduction of bone substitutes in bone tissues. Titania hydrogels are known to instigate hydroxyapatite formation in a solution mimicking human blood plasma. To date, the relationship between the surface characteristics of titania and hydroxyapatite formation on its surface remains unclear. In this study, titania powders with varying surface characteristics were prepared by addition of manganese or iron to examine hydroxyapatite formation in a type of simulated body fluid (Kokubo solution). Hydroxyapatite formation was monitored by observation of deposited particles with scale-like morphology on the prepared titania powders. The effect of the titania surface characteristics, i.e., crystal structure, zeta potential, hydroxy group content, and specific surface area, on hydroxyapatite formation was examined. Hydroxyapatite formation was observed on the surface of titania powders that were primarily anatase, and featured a negative zeta potential and low specific surface areas irrespective of the hydroxy group content. High specific surface areas inhibited the formation of hydroxyapatite because calcium and phosphate ions were mostly consumed by adsorption on the titania surface. Thus, these surface characteristics of titania determine its osteoconductivity following exposure to body fluid.

Effect of Fluoride Conversion Coating on Corrosion of Behavior of Mg-Ca-Zn Alloy

Magnesium and its alloys have been received huge attention as new kind of degradable biomaterials. However its application hindered by poor carrion resistance fluoride conversion coating was performed due to improve the corrosion resistance of Mg-Ca-Zn alloy. In the present work ccorrosion of behaviour and degradation bahaviour of fluoride treated Mg-Ca-Zn alloy were investigated. Microstructural evolutions were characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy. The corrosion resistance was examined in vitro by potentiodynamic polarization and immersion test in Kokubo solution at room temperature. The coating characterization indicated that the dense and uniform film with 6 μm thickness consists of MgO and MgF2 formed on the alloy. Polarization tests recorded a significant reduction in the corrosion current density from 188 μAcm-2 in bare Mg-Ca-Zn to 6.11 μAcm-2 in fluoride treated alloy as a result of formation MgF2 protective layer. The in vitro degradation tests showed that the average weight loss of the untreated specimens significantly higher than that of fluoride treated Mg-Ca-Zn alloy. The results revealed that the fluoride conversion coating noticeably improve the corrosion resistance of Mg-Ca-Zn alloy resistance of Mg in Kokubo solution.

Bioactivity of Calcium Aluminate Endodontic Cement

IntroductionCalcium aluminate endodontic cement (CAEC) developed for use in root canal therapy has been produced with additives that improve handling properties and provide higher mechanical strength than mineral trioxide aggregate (MTA) according to prior studies. The aim of this study was to evaluate the bioactivity of CAEC containing accelerating additives (A-CAEC) in comparison with MTA, both in contact with simulated body fluid (SBF) solutions. MethodspH measurements were taken for set cement samples immersed in water or SBF solutions prepared according to the Kokubo and Rigo techniques. The surface of these materials kept in contact with SBF solutions were also evaluated by means of scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction. ResultsBecause of the calcium hydroxide dissociation, MTA cement is able to release more Ca2+ ions and results in a higher pH increase compared with A-CAEC. This behavior enhances the supersaturation of Kokubo solution, resulting in the precipitation of calcium phosphate phases on the MTA surface. On the other hand, for MTA in Rigo SBF solution, the pH value attained was higher than for the Kokubo SBF solution as a result of the Mg2+ ion precipitation, which inhibited the calcium phosphate phase formation. For A-CAEC, the optimal precipitation conditions of calcium phosphate phases are achieved in Rigo SBF solution. ConclusionsMTA and A-CAEC present bioactivity in contact with SBF solution although the composition of this solution defines the type of phase precipitated.

Effect of fluoride treatment on corrosion behavior of Mg–Ca binary alloy for implant application

The influence of hydrofluoric acid (HF) treatment on the corrosion behavior of the Mg-0.5Ca alloys was investigated by immersion specimen in sodium hydroxide and HF solutions with various concentrations and durations at room temperature. Microstructural evolutions of the specimens were characterized by atomic force microscopy, X-ray diffraction, field-emission scanning electron microscopy. The corrosion resistance was examined through potentiodynamic polarization and immersion test in Kokubo solution. The results revealed that the fluoride treated Mg-0.5Ca alloys produced by immersion in 40% HF provided more uniform, dense and thicker coating layer (12.6 μm) compared with the 35% HF treated specimen. The electrochemical test showed that the corrosion resistance of fluoride treated specimen was 35 times higher compared with the untreated Mg-0.5Ca alloy specimen in Kokubo solution. In vitro degradation rate of the fluoride treated specimens was much lower than untreated Mg-0.5Ca alloy in Kokubo solution. After immersion test the surface of 40% HF treated sample showed a few corrosion dots, while untreated specimens were fully covered by corrosion products and delamination. Fluoride treated Mg-0.5Ca alloy with 40% HF is a promising candidate as biodegradable implants due to its low degradation kinetics and good biocompatibility.

Synthesis and in vitro degradation evaluation of the nano-HA/MgF2 and DCPD/MgF2 composite coating on biodegradable Mg–Ca–Zn alloy

In the present study, nano-hydroxyapatite/magnesium fluoride (nano-HA/MgF2) and dicalcium phosphate dehydrate/magnesium fluoride (DCPD/MgF2) composite coating was synthesized via fluoride conversion coating process followed by an electrochemical deposition (ED) method on biodegradable magnesium (Mg) alloy. The surface morphology, crystalline structures, and compositions of coated specimens were characterized by X-ray diffraction (XRD), atomic-force microscopy (AFM), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The influence of the coatings on the corrosion behaviour of the specimens was evaluated by potentiodynamic polarization and immersion test in Kokubo solution at room temperature. AFM examination of the composite coating specimen indicated that root mean square roughness (RMS) of the nano-HA/MgF2 and DCPD/MgF2 composite coatings was approximately 395nm and 468nm respectively. However, fluoride treated and untreated showed lower RMS compared with the composite coated. The needle-like morphology of HA crystals had a diameter of 80nm–150nm and a length of about 7μm. However, plate-like morphology of DCPD was relatively larger. Electrochemical tests exhibited a significant decline in corrosion current density from 365.2 to 5.23μA/cm2 after composite coating of HA/MgF2 on Mg alloy. However, no significant reduction in corrosion rate was observed between the composite coated and fluoride treated specimens. Immersion tests also showed that HA/MgF2 and DCPD/MgF2 composite coatings reduced the hydrogen evolution and improved the nucleation site of apatite greater than that of the uncoated sample. However, DCPD/MgF2 showed lower corrosion resistance and hence composite coating of HA/MgF2 on Mg–Ca–Zn alloy is a promising candidate for biodegradable medical applications.

Effect of Hydroxyapatite on Reaction of Dicalcium Phosphate Dihydrate DCPD) and Fluoride Ion

DCPD, dicalcium phosphate dihydrate (CaHPO4•2H2O) reacts with fluoride ion in an aqueous solution, and forms fluorapatite (FAp, Ca10(PO4)6F2). In previous study, we have found that DCPD does not react with fluoride ion directly, but show few hours of induction period by reaction with fluoride. In this study, effect of hydroxyapatite (HA, Ca10(PO4)6(OH)2) on the reactivity of DCPD with fluoride ion was investigated. By mixing HA with DCPD, it was appeared that the induction period of the reaction was shortened. Morphology of the obtained FAp was similar to HA paricles. We carried on coating of HA on the DCPD particle by soaking DCPD in simulated body fluid (SBF, Kokubo Solution). By coating HA on DCPD particles, particle morphology of the obtained FAp was consistency to the DCPD particles. These results suggest that the shape and particle size of FAp after reaction of DCPD is controllable by DCPD particle as template, and coating with HA.

Fabrication of chitosan/magnesium phosphate composite coating and the in vitro degradation properties of coated magnesium alloy

A composite coating was fabricated on home-developed Mg–Zn–Ca alloy to improve its biocorrosion resistance in simulated body fluid (SBF, Kokubo solution). The coating was prepared by micro arc oxidation (MAO) of the alloy, followed by dip-coating in chitosan solution. The coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrochemical performance of the MAO, chitosan and chitosan/MAO coated alloys was evaluated by anodic polarization measurements in SBF. After being coated by composite coating, anticorrosion performance was significantly enhanced, while single MAO or chitosan coating only improved anticorrosion properties within a limited range. The barrier effect and interface condition of composite coating were analyzed and related with the improvement in electrochemical performance. The present result indicates that fabrication of composite coatings is a significant strategy to slow down the degradation of Mg alloys, thus enhancing the potential of using Mg alloys as bio-implants.

Composite coating prepared by micro-arc oxidation followed by sol–gel process and in vitro degradation properties

A Mg phosphate coating was prepared on home-developed Mg–Zn–Ca alloy to improve its anticorrosion performance in simulated body fluid (SBF, Kokubo solution). The coating was prepared by micro-arc oxidation (MAO) method at the working voltage of 120–140V. Evident improvement of anticorrosion was obtained even through the surface was porous. To further diminish the contact with SBF, a TiO2 layer was coated on the porous MAO layer by sol–gel dip coating followed by an annealing treatment. The coatings were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The electrochemical performance of the MAO and TiO2/MAO coated alloys was evaluated by anodic polarization measurements. The pores on Mg phosphate layer provided accommodation sites for the subsequent TiO2 sol–gel coating which sealed the pores and hence significantly enhanced the anticorrosion while single MAO coating only improve anticorrosion within a limited range. The present result indicates that fabrication of composite coatings is a significant strategy to improve the corrosion resistance of Mg–Zn–Ca alloy and other alloys, thus enhancing the potential of using Mg alloys as bio-implants.

Characterization and Corrosion Behavior of Biodegradable Mg-Ca and Mg-Ca-Zn Implant Alloys

In the present study binary Mg-xCa (x=0.5 and 1.25wt.%) and ternary Mg-1Ca-xZn (x=0.5 and 1.5wt.%) alloys are produced by casting the molten metal in a metal die at a temperature of 740°C. The microstructure analysis of the Mg-Ca and Mg-Ca-Zn alloys were studied by OM, SEM and EDX. The corrosion behavior of alloys was evaluated via potentiodynamic polarization test in Kokubo solution. The result exhibited that the grain size decrease with rising Ca content in Mg-Ca alloys and degree of grain size reduction further decreased by adding Zn to Mg-1Ca-Zn alloys. The microstructure of Mg-Ca alloys were constituted of primary Mg and lamellar eutectic (α-Mg+Mg2Ca) phase, Whilst Mg–1Ca-Zn alloys were composed of primary Mg and eutectic (α-Mg+Mg2Ca+Ca2Mg6Zn3) phases. In addition with increasing Ca and Zn the amount of Mg2Ca and Ca2Mg6Zn3 increased respectively in grain boundaries. Electrochemical test shows that the addition of Zn leads to improve corrosion resistance of the Mg–1Ca-Zn alloys as a result of the formation of Ca2Mg6Zn3 phase, whilst the addition of more than 0.5 wt% Ca to Mg-Ca alloys result in decrease corrosion resistance due to the formation Mg2Ca.

Microstructure analysis and corrosion behavior of biodegradable Mg–Ca implant alloys

The calcium content in binary Mg– xCa alloys affects the microstructure, corrosion and solidification behavior of the alloys. In this study, binary Mg– xCa alloys with various Ca contents from 0.5 to 10 wt.% were produced by casting process. Microstructural evolutions were characterized by optical microscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Solidification behavior was assessed via two thermocouple thermal analysis method. The corrosion resistance was examined in vitro by potentiodynamic polarization and immersion test in Kokubo solution at room temperature. The results revealed that the grain size and dendrite cell size decreased significantly with rising Ca content, whilst the content of Mg 2Ca intermetallic phase in grain boundaries increased with increasing Ca content. Potentiodynamic polarization tests in simulated body fluid (SBF) indicated that corrosion rates of Mg– xCa alloy increased significantly with rising Ca content. Immersion tests in Kokubo solution also showed that dissolution rate of Mg– xCa alloy increased with increasing Mg 2Ca content which lead to an increase in pH value. It was observed that corrosion damage in specimens with lower Ca content was more moderate and uniform than higher Ca content. Thermal analysis results showed that the fraction of primary α-Mg at dendrite coherency point ( f α DCP ) decreased with increasing Ca content but the liquid fraction f L increased causing the rise in eutectic Mg 2Ca intermetallic phase in grain boundaries, thus increasing the corrosion rate. Our analyses showed that Mg–0.5Ca alloy is a promising alloy to be used as biodegradable implants.

Surface modification of titanium by pack cementation treatment using calcium phosphate powders for biomedical applications

The surface modification of commercially pure titanium by pack cementation treatment using hydroxyapatite (HAp) or tetracalcium phosphate (TTCP) powder was investigated for temperatures ranging from 773 K to 1073 K. An HAp phase was detected on the surface of the titanium substrates after pack cementation treatment at temperatures of 973 K and 1073 K. After treatment using HAp and TTCP powders, a reaction layer with small HAp particles and pores containing small HAp particles, respectively, was observed. Apatite crystallites with a network pattern formed on the pack-cementation-treated titanium substrates after the substrates were immersed in Kokubo solution for 43.2 ks; such rapid apatite formation suggests that pack cementation treatment improves the biocompatibility of titanium.

Synthesis and in vitro characterization of freeze-dried doxorubicin-loaded silica/PEG composite

Freeze-dried doxorubicin-loaded silica/poly(ethylene glycol) composites have been prepared by a two-step acid/base catalyzed sol–gel process from tetraethylorthosilicate in the presence of poly(ethylene glycol) (PEG). PEG was used as a pore-forming agent, followed by liberation process of PEG during the in vitro doxorubicin release study. Simulated body fluid (SBF, Kokubo solution) at 37 °C with ion concentrations nearly equal to those of human blood plasma (pH 7.4) was used for in vitro evaluation. The characteristics of these composites before and after drug release, including the infrared absorption spectra, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) in combination with IR and nitrogen gas adsorption/desorption, were measured and analyzed. The relationship between the liberation process of PEG and rate of drug release is discussed mainly in terms of molecular and structural features of the silica composites before and after drug release study. It was shown that an increase in the proportion of PEG in the silica network was associated with an increase in degree of hydration (higher hydrophilicity) and average pore size, and with a decrease in bulk density, specific surface area, and also degree of polymerization of silica. The rate of drug release increases with an increase in PEG content. These results are in line with the increase in specific surface area and mesopore size of these composites and also correspond to a more polymerized and thermally stable silica network obtained after drug release study.