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The aim of this study was to improve the dissolution rate and bioactivity of nanophase hydroxyapatite (HA). For this purpose, simultaneous structural and surface modifications of nanophase HA was made by incorporating SiO 4 4 - into the HA structure and creating a silica layer on its surface via the sol–gel method. Characterization of the prepared nanopowders was performed by transmission electron microscopy, X-ray diffractometer, Fourier transformed infrared spectroscopy, and acid dissolution testing. An atomic absorption spectrometer was used to determine calcium ions concentration in physiological saline solution. Results revealed that the simultaneous structural and surface modifications of nanophase HA had a considerable increasing effect on calcium ion release from nanophase HA, and on surface reprecipitation rate of calcium ions, respectively. The obtained results suggest that this modified nanophase HA could be used as a new bioceramic for bone repair. [ABSTRACT FROM AUTHOR]

Magnesium has been recently introduced as a novel biodegradable material for bone healing. However, the fast degradation of this material results in the fast release of hydrogen which limits its clinical applications. In view of that, in the present study, we attempt to overcome this drawback using a bredigite (Ca 7 MgSi 4 O 16 ) coating. In our previous work, we have coated AZ91 magnesium implants with bredigite through the combination of anodic spark deposition (ASD) and electrophoretic deposition (EPD) techniques. As continuation to that work, in this paper, we have focused on the in vivo examination of the bredigite/ASD compared to the plain ASD coated and the uncoated AZ91 substrates. The results of the in vivo animal test in the greater trochanter of rabbits indicated improved regeneration of bone and less bone inflammation upon employing bredigite/ASD coated implants. In addition, an enhancement in in vivo biodegradation was observed by the reduction in magnesium ion released in the blood plasma. In summary, a surface treatment using bredigite on magnesium implants promotes their bone healing capabilities for future clinical applications. [ABSTRACT FROM AUTHOR]

Synthesis conditions of biomaterials have a key role on their final properties, which affect their performance in the human body. So, the aim of this study was to evaluate the effect of acid and base catalysts used in processing of silica synthesis, on phase purity and dissolution behavior of the in situ silica coated apatite composite nanopowders prepared via the sol–gel method. Composite nanopowders were synthesized in the presence of 0.1 N HNO 3 and acetic acid as the acid catalyst (A-S-AP composite nanopowder) and ammonium hydroxide as the base catalyst (B-S-CP composite nanopowder). The prepared composite nanopowders were characterized by XRD, FTIR, TEM, and BET techniques, acid dissolution test, and AAS spectroscopy. Results indicated that the base catalyst, rather than the acid catalyst, induced a nano-scale phase separation, which paved the way for the creation of a new crystalline phase (whitelockite) along with HA. In addition, the results of dissolution behavior evaluations in physiological saline solution showed that A-S-AP composite nanopowder, rather than B-S-CP composite nanopowder, had more calcium ions release and faster in vitro biomineralization, which are very important for bone repair and regeneration. [ABSTRACT FROM AUTHOR]

The main aim of this research was the preparation of the forsterite (Mg 2 SiO 4 ) coating on the surface of 316L stainless steel (316L SS) substrate. For this purpose, the nanostructured forsterite was coated on the 316L SS substrate using the sol–gel dip coating technique. Structural characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX) were utilized to investigate the phase structure, morphology and elemental composition of the uncoated and coated samples. Corrosion properties of samples were studied using the electrochemical measurements in simulated body fluid (SBF). The in vitro bioactivity evaluation of the forsterite coated samples was conducted by soaking the samples in the SBF at the temperature of 37 °C. The results showed that, a crack-free and homogeneous forsterite coating with the crystallite size of around 40 nm was successfully achieved on the surface of 316L SS substrate. The corrosion current density of the forsterite coated samples was lesser than that of the uncoated ones indicating the improvement of corrosion resistance of the metallic substrate using the forsterite coating. Deposition of Ca and P-contained products on the surface of coated samples during the incubation in the SBF solution confirmed the bioactivity behavior of the forsterite coated samples. Consequently, the 316L SS substrate coated with nanostructured forsterite may be an appropriate selection for dental and orthopedic implant applications. [ABSTRACT FROM AUTHOR]

Although magnesium (Mg) is a unique biodegradable metal which possesses mechanical property similar to that of the natural bone and can be an attractive material to be used as orthopedic implants, its quick corrosion rate restricts its actual clinical applications. To control its rapid degradation, we have modified the surface of magnesium implant using fluoridated hydroxyapatite (FHA: Ca 10 (PO 4 ) 6 OH 2 − x F x ) through the combined micro-arc oxidation (MAO) and electrophoretic deposition (EPD) techniques, which was presented in our previous paper. In this article, the biocompatibility examinations were conducted on the coated AZ91 magnesium alloy by implanting it into the greater trochanter area of rabbits. The results of the in vivo animal test revealed a significant enhancement in the biocompatibility of FHA/MAO coated implant compared to the uncoated one. By applying the FHA/MAO coating on the AZ91 implant, the amount of weight loss and magnesium ion release in blood plasma decreased. According to the histological results, the formation of the new bone increased and the inflammation decreased around the implant. In addition, the implantation of the uncoated AZ91 alloy accompanied by the release of hydrogen gas around the implant; this release was suppressed by applying the coated implant. Our study exemplifies that the surface coating of magnesium implant using a bioactive ceramic such as fluoridated hydroxyapatite may improve the biocompatibility of the implant to make it suitable as a commercialized biomedical product. [ABSTRACT FROM AUTHOR]

In order to improve the corrosion resistance and bioactivity of a biodegradable magnesium alloy, we have recently prepared a nanostructured diopside (CaMgSi2O6) coating on AZ91 magnesium alloy through a combined micro-arc oxidation (MAO) and electrophoretic deposition (EPD) method (reported elsewhere). In this work, we performed a detailed biocompatibility analysis of the implants made by this material and compared their performance with those of the uncoated and micro arc oxidized magnesium implants. The biocompatibility evaluation of samples was performed by culturing L-929 cells and in vivo animal study, including implantation of samples in greater trochanter of rabbits, radiography and histological examinations. The results from both the in vitro and in vivo studies indicated that the diopside/MAO coated magnesium implant significantly enhanced cell viability, biodegradation resistance and new bone formation compared with both the uncoated and the micro-arc oxidized magnesium implants. Our data provides an example of how the proper surface treatment of magnesium implants can overcome their drawbacks in terms of high degradation rate and gas bubble formation under physiological conditions. [ABSTRACT FROM AUTHOR]

Abstract: The high corrosion rate of Mg alloys has hindered their application in various areas, particularly for orthopedic applications. In order to decrease the corrosion rate and to improve the bioactivity, mechanical stability and cytocompatibility of the Mg alloy, nanostructured diopside (CaMgSi2O6) has been coated on AZ91 Mg alloy using a combined micro arc oxidation (MAO) and electrophoretic deposition (EPD) method. The crystalline structure, the morphology and the composition of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Electrochemical corrosion test, immersion test, and compression test were used to evaluate the corrosion resistance, the in vitro bioactivity and the mechanical stability of the samples, respectively. The cytocompatibility of the samples was tested by the cell viability and the cell attachment of L-929 cells. The results confirmed that the diopside coating not only slows down the corrosion rate, but also enhances the in vitro bioactivity, mechanical stability and cytocompatibility of AZ91 Mg alloy. Therefore, Mg alloy coated with nanostructured diopside offers a promising approach for biodegradable bone implants. [Copyright &y& Elsevier]

Abstract: Magnesium (Mg) alloys have recently attracted much attention as degradable metallic implants for bone fracture healing. A biodegradable osteosynthetic implant material will remove the need for the implant removal surgery after the bone healing process. However, the high corrosion rate of the Mg alloys in the body fluid has prevented their clinical application as implants. In the present study, a nanostructured merwinite (Ca3MgSi2O8) bioceramic coating was prepared on AZ91 Mg alloy in order to improve its corrosion resistance, bioactivity, mechanical stability and cytocompatibility. The coating was deposited by electrophoretic deposition assisted micro arc oxidation. The phase composition and the surface morphology of the samples were characterized by X-ray diffraction and electron microscopy. The corrosion, bioactivity and mechanical behavior of the samples were investigated by electrochemical measurements, immersion into simulated body fluid (SBF) and compression tests. The cytocompatibility of the samples was evaluated by a cell culture test. The results showed that the nanostructured merwinite coating not only improved the corrosion resistance, but also enhanced the bioactivity, mechanical stability and cytocompatibility of the AZ91 Mg alloy. [Copyright &y& Elsevier]

Highlights: [•] The corrosion resistance of biodegradable Mg alloy was increased by akermanite coat. [•] The mechanical stability of biodegradable Mg alloy was increased by akermanite coat. [•] The cytocompatibility of biodegradable Mg alloy was increased by akermanite coat. [Copyright &y& Elsevier]

Abstract: Magnesium and its alloys have been recently investigated as biodegradable metallic biomaterials for bone implants. However, rapid corrosion rate and low bioactivity have been two limiting factors for their biomedical applications. In this work we aimed to improve these two properties for AZ91 magnesium alloy using the nanostructured bredigite (Ca7MgSi4O16) coating made by micro-arc oxidation and electrophoretic deposition methods. The results indicated that this surface treatment enhanced both corrosion resistance and the bioactivity of AZ91 substrate, making it suitable for biomedical applications. [Copyright &y& Elsevier]

Highlights: [•] Nano-hydroxyapatite (n-HAp) particles synthesized using a sol–gel process. [•] Stable suspension of n-HAp powders was prepared in methanol medium. [•] Fluoride and MAO pre-treatments were applied on AZ91 samples as intermediate layers. [•] Electrophoretic deposition process was used for coating n-HAp particles. [•] The MAO/n-HAp/AZ91 system is highly prone to be utilized as bio-absorbable implants. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium (Mg) alloys have been introduced as new generation of biodegradable orthopedic materials in recent years since it has been proved that Mg is one of the main minerals required for osseous tissue revival. The main goal of the present study was to establish a desired harmony between the necessities of orthopedic patient body to Mg2+ ions and degradation rate of the Mg based implants as a new class of biodegradable/bioresorbable materials. This prospect was followed by providing a sol–gel derived nanostructured hydroxyapatite (n-HAp) coating on AZ91 alloy using dip coating technique. Phase structural analysis, morphology study, microstructure characterization, and functional group identification were performed using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The prepared samples were immersed in simulated body fluid in order to study the formation of apatite-like precipitations, barricade properties of the n-HAp coating, and to estimate the dosage of released Mg2+ ions within a specified and limited time of implantation. Electrochemical polarization tests were carried out to evaluate and compare the corrosion behavior of the n-HAp coated and uncoated samples. The changes of the in vitro pH values were also evaluated. Results posed the noticeable capability of n-HAp coating on stabilizing alkalization behavior and improving the corrosion resistance of AZ91 alloy. It was concluded that n-HAp coated AZ91 alloy could be a good candidate as a type of biodegradable implant material for biomedical applications. [Copyright &y& Elsevier]

In this research, a novel nanostructured forsterite coating was deposited on AISI 316L stainless steel substrates by the electrophoretic deposition (EPD) method. Forsterite nanopowders were synthesized using the mechanical activation method. The as-milled nanoparticles were then immersed in a slurry containing 0.5 wt% polyvinyl alcohol (PVA) in order to obtain PVA-coated forsterite nanopowders. The PVA-coated powder particles were electrophoretically deposited on metallic substrates under various conditions (times and voltages). As-deposited coatings were then subjected to a two-step sintering process. The forsterite coatings deposited under different conditions were characterized in terms of microstructural and bioactivity properties. The bioactivity of the prepared specimens was evaluated in simulated body fluid (SBF) at 37 °C for up to 28 days. Results showed that the coating which was deposited after 5 min under a voltage of 25 V was homogeneous and crack-free. The nanostructured forsterite coated samples possessed apatite-formation ability during immersion in SBF. [ABSTRACT FROM AUTHOR]

In the present study, Co-based machining chips (P1) and Co-based atomized alloy (P2) has been processed through planetary ball mill in order to obtain nanostructured materials and also to comprise some their physical and mechanical properties. The processed powders were investigated by X-ray diffraction technique in order to determine several microstructure parameters including phase fractions, the crystallite size and dislocation density. In addition, hardness and morphological changes of the powders were investigated by scanning electron microscopy and microhardness measurements. The results revealed that with increasing milling time, the FCC phase peaks gradually disappeared indicating the FCC to HCP phase transformation. The P1 powder has a lower value of the crystallite size and higher degree of dislocation density and microhardness than that of the P2 powder. The morphological and particle size investigation showed the role of initial HCP phase and chemical composition on the final processed powders. In addition results showed that in the first step of milling the crystallite size for two powders reach to a nanometer size and after 12 h of milling the crystallite size decreases to approximately 27 and 33 nm for P1 and P2 powders, respectively. [ABSTRACT FROM AUTHOR]