The influence of HF treatment on corrosion resistance and <Emphasis Type="Italic">in vitro</Emphasis> biocompatibility of Mg-Zn-Zr alloy

The samples made of a Mg-2.5wt.%Zn-0.5wt.%Zr alloy were immersed in the 20% hydrofluoric acid (HF) solution at room temperature for different time, with the aim of improving the properties of magnesium (Mg) alloy in applications as biomaterials. The corrosion resistance and in vitro biocompatibility of untreated and fluoride-coated samples were investigated. The results show that the optimum process is to immerse Mg alloys in the 20% HF solution for 6 h. After the immersion, a dense magnesium fluoride (MgF₂) coating of 0.5 μm was synthesized on the surface of Mg-Zn-Zr alloy. Polarization tests recorded a reduction in the corrosion current density from 2.10 to 0.05 μA/cm² due to the MgF₂ protective coating. Immersion tests in the simulated body fluid (SBF) also reveal a much milder corrosion on the fluoride-coated samples, and its corrosion rate was calculated to be 0.05 mm/yr. Hemolysis test suggests that the conversion coated Mg alloy has no obvious hemolysis reaction. The hemolysis ratio (HR) of the samples decreases from 11.34% to 1.86% with the HF treatment, which meets the requirements of biomaterials (HR < 5%). The coculture of 3T3 fibroblasts with Mg alloy results in the adhesion and proliferation of cells on the surface of fluoride-coated samples. All the results show that the MgF₂ conversion coating would markedly improve the corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy.     

In situ composite coating of titania-hydroxyapatite on titanium substrate by micro-arc oxidation coupled with electrophoretic deposition processing

In situ composite coating of hydroxyapatite (HA)/TiO₂ were produced on titanium (Ti) substrate by micro-arc oxidation coupled with electrophoretic deposition (MAO&EPD) technique with different concentrations of HA particles in the 0.2 M NaOH electrolyte solution. The surface morphology and chemical composition of the hybrid coating were effected by HA concentration. The amount of HA particles incorporated into coating layer increased with increasing HA concentration used in the electrolyte solution. The corrosion behavior of the coating layer in simulated body fluids (SBF) was evaluated using a potentiodynamic polarization test. The corrosion resistance of the coated sample was increased compared to the untreated Ti sample. The in vitro bioactivity assessment showed that the MAO&EPD treated Ti substrate possessed higher apatite-forming ability than the untreated Ti. Moreover, the apatite-forming ability had a positive correlation with HA concentration. In addition, the cell behavior was also examined using cell proliferation assay and alkaline phosphatase ability. The coating formed at HA concentration of 5 g/L exhibited the highest cell ability.     

The influence of HF treatment on corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy

The samples made of a Mg-2.5wt.%Zn-0.5wt.%Zr alloy were immersed in the 20% hydrofluoric acid (HF) solution at room temperature for different time, with the aim of improving the properties of magnesium (Mg) alloy in applications as biomaterials. The corrosion resistance and in vitro biocompatibility of untreated and fluoride-coated samples were investigated. The results show that the optimum process is to immerse Mg alloys in the 20% HF solution for 6 h. After the immersion, a dense magnesium fluoride (MgF₂) coating of 0.5 μm was synthesized on the surface of Mg-Zn-Zr alloy. Polarization tests recorded a reduction in the corrosion current density from 2.10 to 0.05 μA/cm² due to the MgF₂ protective coating. Immersion tests in the simulated body fluid (SBF) also reveal a much milder corrosion on the fluoride-coated samples, and its corrosion rate was calculated to be 0.05 mm/yr. Hemolysis test suggests that the conversion coated Mg alloy has no obvious hemolysis reaction. The hemolysis ratio (HR) of the samples decreases from 11.34% to 1.86% with the HF treatment, which meets the requirements of biomaterials (HR < 5%). The coculture of 3T3 fibroblasts with Mg alloy results in the adhesion and proliferation of cells on the surface of fluoride-coated samples. All the results show that the MgF₂ conversion coating would markedly improve the corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy.     

Effect of MgF<Subscript>2</Subscript> on hot pressed hydroxylapatite and monoclinic zirconia composites

Hydroxylapatite (HA) has been widely used in biomedical applications because of its excellent biocompatibility in the human body. A total of 25 wt% monoclinic (m) zirconia–HA composites (with and without 5 wt% MgF₂) were synthesized to investigate their mechanical properties and phase stability. In HA–m-ZrO₂ composites, HA and m-ZrO₂ reacted to form CaZrO₃ when there was no F⁻ present in the composite and m-ZrO₂ partially transformed to tetragonal ZrO₂. When MgF₂ was added into the system, it improved the thermal stability of the phases, densification, hardness, and fracture toughness of the composites and it caused the m-ZrO₂ to transform completely to t-ZrO₂ by incorporating the Mg²⁺ ions present in MgF₂ in the ZrO₂. Moreover, the stability of HA was improved by incorporating the F⁻ ions from MgF₂ in place of OH⁻ ions in HA. Substitution of OH⁻ by F⁻ ions was verified by the change in HA’s hexagonal lattice parameters. A fracture toughness of 2.0 MPa√m was calculated for the composite containing MgF₂.     

Characterization of electrolytic HA/ZrO2 double layers coatings on Ti–6Al–4V implant alloy

Hydroxyapatite (HA) coating was proved having bioactive property and hence improving the bonding strength on bone tissue without inducing the growth of fiber tissue. However, the weak adhesion between HA and metal implants is still the major problem. In this study, a novel method of electrolytic HA/ZrO₂ double layers coating was successfully conducted on F-136 Ti–6Al–4V implant alloy in ZrO₂(NO₃)₂ aqueous solution and subsequently in the mixed solution of Ca(NO₃)₂ and NH₄H₂PO₄. After annealing at 400 °C, 500 °C and 600 °C for 4 h in air, the coated specimens were evaluated by X-ray diffraction analyses, surface morphology observations, scratch tests, dynamic polarization tests, immersion tests and cell culture assays. In addition to corrosion resistance, the adhesion strength of electrolytic deposited HA on Ti alloy was dramatically improved from the critical scratch load 2 N to 32 N by adding the intermediate electrolytic deposition of ZrO₂, which showed the strong bonding effects between Ti alloy substrate and HA coating. Based on the cell morphology and cell proliferation data, HA/ZrO₂ double layers coating revealed the better substrate for the adhesion and proliferation of osteoblasts than the others. It was also found that the crystallization of HA had positive effect on the proliferation of osteoblasts.     

In vitro degradation behavior and biocompatibility of Mg–Nd–Zn–Zr alloy by hydrofluoric acid treatment

In this paper, Mg–Nd–Zn–Zr alloy (denoted as JDBM) coated with hydrofluoric acid (HF) chemical conversion film (MgF₂) was researched as a potential biodegradable cardiovascular stent material. The microstructures, in vitro degradation and biocompatibility were investigated. The field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) showed that a compact MgF₂ film was formed on the surface of JDBM. The corrosion rate decreased in artificial plasma from 0.337 to 0.253 mm·y^? 1 and the electrochemical measurement demonstrated that the corrosion resistance of JDBM alloy could be obviously improved due to the protective MgF₂ film on the surface of the substrate. Meanwhile, the hemolysis ratio of JDBM decreased from 52.0% to 10.1% and the cytotoxicity met the requirement of cellular application after HF treatment. In addition, JDBM and MgF₂ film showed good anti-platelet adhesion, which is a very favorable property for implant material in contact with blood directly.     

Enhanced corrosion resistance and cytocompatibility of biomimetic hyaluronic acid functionalised silane coating on AZ31 Mg alloy for orthopaedic applications

This paper reports the corrosion resistant and cytocompatible properties of the hyaluronic acid-silane coating on AZ31 Mg alloy. In this study, the osteoinductive properties of high molecular weight hyaluronic acid (HA, 1–4?MDa) and the corrosion protection of silane coatings were incorporated as a composite coating on biodegradable AZ31 Mg alloy for orthopaedic applications. The multi-step fabrication of coatings first involved dip coating of a passivated AZ31 Mg alloy with a methyltriethoxysilane-tetraethoxysilane sol-gel to deposit a dense, cross-linked and corrosion resistant silane coating (AZ31-MT). The second step was to create an amine-functionalised surface by treating coated alloy with 3-aminopropyl-triethoxy silane (AZ31-MT-A) which facilitated the immobilisation of HA via EDC-NHS coupling reactions at two different concentrations i.e 1?mg.ml^?1 (AZ31-MT-A-HA1) and 2?mg.ml^?1 (AZ31-MT-A-HA2). These coatings were characterised by Fourier transform infrared spectroscopy, atomic force microscopy and static contact angle measurements which confirmed the successful assembly of the full coatings onto AZ31 Mg alloy. The influence of HA-silane coating on the corrosion of Mg alloy was investigated by electrical impedance spectroscopy and long-term immersion studies measurements in HEPES buffered DMEM. The results showed an enhanced corrosion resistance of HA functionalised silane coated AZ31 substrate over the uncoated equivalent alloy. Furthermore, the cytocompatibility of MC3T3-E1 osteoblasts was evaluated on HA-coated AZ31-MT-A substrates by live-dead staining, quantification of total cellular DNA content, scanning electron microscope and alkaline phosphatase activity. The results showed HA concentration-dependent improvement of osteoblast cellular response in terms of enhanced cell adhesion, proliferation and differentiation. These findings hold great promise in employing such biomimetic multifunctional coatings to improve the corrosion resistance and cytocompatibility of biodegradable Mg-based alloy for orthopaedic applications.

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Characterization and bond strength of electrolytic HA/TiO<Subscript>2</Subscript> double layers for orthopaedic applications

Insufficient bonding of juxtaposed bone to an orthopaedic/dental implant could be caused by material surface properties that do not support new bone growth. For this reason, fabrication of biomaterials surface properties, which support osteointegration, should be one of the key objectives in the design of the next generation of orthopaedic/dental implants. Titanium and titanium alloy have been widely used in several bioimplant applications, but when implanted into the human body, these still contain some disadvantages, such as poor osteointegration (forming a fibrous capsule), wear debris and metal ion release, which often lead to clinical failure. Electrolytic hydroxyapatite/titanium dioxide (HA/TiO₂) double layers were successfully deposited on titanium substrates in TiCl₄ solution and subsequently in the mixed solution of Ca(NO₃)₂ and NH₄H₂PO₄, respectively. After annealing at 300∘C for 1 h in the air, the coated specimens were evaluated by dynamic cyclic polarization tests, immersion tests, tensile tests, surface morphology observations, XRD analyses and cells culture. The adhesion strength of the HA coating were improved by the intermediate coating of TiO₂ from 11.3 to 46.7 MPa. From cell culture and immersion test results, the HA/TiO₂ coated specimens promoted not only cells differentiation, but also appeared more bioactive while maintaining non-toxicity.     

MAO-DCPD composite coating on Mg alloy for degradable implant applications

Magnesium (Mg) is a promising metallic material for use as degradable orthopedic implants. The density and Young's modulus of Mg are close to those of human bone, and it is non-toxic and degradable in body fluids. However, the realization of Mg as an implant material is hampered by its high corrosion rate. The present article aims at improving the corrosion resistance and bioactivity of a Mg alloy AZ80 via surface treatment. AZ80 was coated with a composite coating consisting of an oxide layer formed by micro-arc oxidation (MAO) and a top layer of dicalcium phosphate dihydrate (DCPD, CaHPO₄·2H₂O) fabricated by electrodeposition. The corrosion behavior and apatite-forming ability in simulated body fluids (SBFs) were studied using hydrogen evolution measurements and SEM. The results show that the MAO-DCPD composite coating significantly reduces the corrosion rate of AZ80 and at the same time enhances the deposition of apatite on the coating.     

Electrolytic deposition of hydroxyapatite coating on thermal treated Ti-40Zr

In this study, hydroxyapatite (HA) was coated on both thermal treated and untreated Ti-40Zr substrates by means of electrolytic deposition. It was predicted that the HA layer would increase the bioactivity and osteoconductivity of the Ti-40Zr substrate, and a thermal treatment would improve the bonding strength between the HA layer and Ti-40Zr substrate, and prevent the corrosion of the Ti-40Zr substrate. First, the Ti-40Zr samples were annealed at various temperatures (200, 300, 400, 500 and 600°C respectively). After annealing, samples were immersed in a Ca(NO₃)₂ · 4H₂O and (NH₄)₃PO₄ · 3H₂O solution for the electrolytic deposition of the HA coating. Various analyses of the coating were conducted, including surface morphology, phase structure, corrosion resistance, biocompatibility, and bond strength between HA and Ti-40Zr. Experimental results indicated that the bonding strength of the HA coating on the thermal treated Ti-40Zr was markedly improved when compared to that of the HA coating on an untreated Ti-40Zr alloy. The corrosion resistance of Ti-40Zr was also improved by the use of the thermal treatment, as shown by a potentiodynamic polarization test. Finally, osteoblast-like cells cultured on the HA coating surface were found to have proliferated on all samples.     

Effect of applied potential on the microstructure,composition and corrosion resistance evolution of fluoride conversion film on AZ31 magnesium alloy

AZ31 magnesium (Mg) alloy was potentiostatic polarized in 0.1?M deaerated KF solution with pH 7.5 from ?0.4?V to ?1.4?V with an interval of ?0.2?V. The polarization process was described by the potentiostatic current decay. The resultant film was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the deposited film included a Mg(OH)₂/MgF₂ containing inner layer and a Mg(OH)₂/MgF₂/KMgF₃ comprising outer layer. The high polarized potential produced high content of MgF₂ but low content of KMgF₃ and thin film. Conversely, the low polarized potential produced small content of MgF₂ but high content of KMgF₃ and thick film. The optimal corrosion resistance of the deposited film was obtained at ?1.4?V, which was closely related with the content of MgF₂ and KMgF₃ and the film thickness.     

PEO/Mg-Al LDH涂层增强金属镁的生物相容性和成骨作用:体内外研究

镁(Mg)及其合金因具有生物可降解和促成骨效应而成为理想的骨内固定材料,但其抗腐蚀能力差、体内降解快的缺点限制了其临床应用.开发稳定的防腐涂层是镁基金属临床应用的主要挑战.本研究首先通过等离子体电解氧化法(PEO)在Mg表面形成多孔的PEO涂层,然后通过水热处理制备Mg-Al层状双氢氧化物(LDH)层来封闭MgO层的多...     

Effects of hydroxyapatite/Zr and bioglass/Zr coatings on morphology and corrosion behaviour of Rex-734 alloy

To improve corrosion resistance of metallic implant surfaces, Rex-734 alloy was coated with two different bio-ceramics; single-Hydroxyapatite (HA), double-HA/Zirconia(Zr) and double-Bioglass (BG)/Zr by using sol–gel method. Porous surface morphologies at low crack density were obtained after coating and sintering processes. Corrosion characteristics of coatings were determined by Open circuit potential and Potentiodynamic polarization measurements during corrosion tests. Hardness and adhesion strength of coating layers were measured and their surface morphologies before and after corrosion were characterized by scanning electron microscope (SEM), XRD and EDX. Through the SEM analysis, it was observed that corrosion caused degradation and sphere-like formations appeared with dimples on the coated surfaces. The coated substrates that exhibit high crack density, the corrosion was more effective by disturbing and transmitting through the coating layer, produced CrO₃ and Cr₃O₈ oxide formation. It was found that the addition of Zr provided an increase in adhesion strength and corrosion resistance of the coatings. However, BG/Zr coatings had lower adhesion strength than the HA/Zr coatings, but showed higher corrosion resistance.     

ZrO2/hydroxyapatite coating on titanium by electrolytic deposition

In this study, hydroxyapatite (HA) was coated on a titanium (Ti) substrate over a ZrO(2) layer by the electrolytic deposition method, this double layer coating was then compared with a single layer coating of HA. The HA layer was used to increase the bioactivity and osteoconductivity of the Ti substrate, and the ZrO(2) layer was intended to improve the bonding strength between the HA layer and Ti substrate, and to prevent the corrosion of the Ti substrate. The electrolytic deposition formed an HA layer with a thicknesses of approximately 20 mum, which adhered tightly to the Ti substrate. The bonding strength of the HA/ZrO(2) double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The improvement in bonding strength with the use of a ZrO(2) base layer was attributed to the resulting increase in chemical affinity of the ZrO(2) to the HA layer and to the Ti substrate. The osteoblast-like cells cultured on the HA/ZrO(2) coating surface, proliferated in a similar manner to those on the HA single coating and on the pure Ti surfaces. At the same time, the corrosion resistance of Ti was improved by the presence of the ZrO(2) coating, as shown by a potentiodynamic polarization test.     

Anti-corrosion mechanism of epoxy-resin and different content Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings on magnesium alloy

In this study, anti-corrosion coatings were prepared and coated successfully on magnesium alloy substrates by mixing nanopowders, solvent, curing agent with epoxy resin. The effect of the amount of iron trioxide (Fe₂O₃) on the adhesion strength and corrosion resistance on magnesium alloy was investigated with standard protocols, and electrochemical measurements were also made in 3.5 wt.% NaCl solutions. The surface morphology and corrosion mechanism after corrosion tests was characterized using FESEM analysis. Nanoparticles in matrix acted as filler, and interstitial cross-linked spaces and other coating artifacts regions (micro cracks and voids) would all affect the anti-corrosion properties of coating. The results showed the proper powder content not only provided adhesion strength to these coatings but also improved obviously their anticorrosion. Hydrogen bound to the amine nitrogen (¹N) could take part in the curing process rather than hydrogen of the amide site due to the smaller ΔG and the more stable configuration.     

In vivo comparative property study of the bioactivity of coated Mg–3Zn–0.8Zr alloy

In this in vivo study, degradable Mg–3Zn–0.8Zr cylinders were coated with a calcium phosphorus compound (Ca–P) layer or a magnesium fluoride (MgF₂) layer; uncoated Mg–3Zn–0.8Zr alloy was used as a control. These were then implanted intramedullary into the femora of nine Japanese big-ear white rabbits for implantation periods of 1, 2 and 3 months. During the postoperative observation period with radiographic examination, the results showed that the MgF₂-coated implants were tolerated well compared to the Ca–P-coated implants and uncoated implants. Moreover, large amounts of cells, rich fibrillar collagen and calcium and phosphorus products were found on the surface of the MgF₂-coated implants using scanning electron microscopy. Micro-computed tomography further showed a slight decrease in volume (23.85%) and a greater increase in new bone mass (new bone volume fraction = 11.56%, tissue mineral density = 248.81 mg/cm³) for the MgF₂-coated implants in comparison to uncoated and Ca–P compound-coated implants after 3 months of implantation.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Surface Engineering of Biodegradable Magnesium Alloys for Enhanced Orthopedic Implants

Magnesium (Mg) alloys have been promised for biomedical implants in orthopedic field, however, the fast corrosion rate and mode challenge their clinical application. To push Mg alloys materials into practice, a composite coating with biodegradable and high compatible components to improve anticorrosion property of an Mg alloy (i.e., AZ31) is designed and fabricated. The inner layer is micro‐nano structured Mg(OH)₂ through hydrothermal treatment. Then stearic acid (SA) is introduced to modify Mg(OH)₂ for better reducing the gap below a surface‐degradation polymer layer of poly(1,3‐trimethylene carbonate). Benefited by the SA modification effect, this sandwiched coating avoids corrosive medium penetration via enhancing the adhesion strength at the interface between outer and inner layers. Both in vitro and in vivo tests indicate that the composite coating modified AZ31 perform a better anticorrosion behavior and biocompatibility compared to bare AZ31. Strikingly, a 1.7‐fold improvement in volume of newly formed bone is observed surrounding the composite coating modified implant after 12 week implantation. The sandwiched biocompatible coating strategy paves a hopeful way for future translational application of Mg alloys orthopedic materials in clinics.     

Effects of SiO<Subscript>2</Subscript> substitution on wettability of laser deposited Ca-P biocoating on Ti-6Al-4V

Silicon (Si) substitution in the crystal structure of calcium phosphate (CaP) ceramics has proved to generate materials with improved bioactivity than their stoichiometric counterpart. In light of this, in the current work, 100 wt% hydroxyapatite (HA) precursor and 25 wt% SiO₂-HA precursors were used to prepare bioactive coatings on Ti-6Al-4V substrates by a laser cladding technique. The effects of SiO₂ on phase constituents, crystallite size, surface roughness, and surface energy of the CaP coatings were studied. Furthermore, on the basis of these results, the effects and roles of SiO₂ substitution in HA were systematically discussed. X-ray diffraction analysis of the coated samples indicated the presence of various phases such as CaTiO₃, Ca₂SiO₄, Ca₃(PO₄)₂, TiO₂ (Anatase), and TiO₂ (Rutile). The addition of SiO₂ in the HA precursor resulted in the refinement of grain size. Confocal laser microscopy characterization of the surface morphology demonstrated an improved surface roughness for samples with 25 wt% SiO₂-HA precursor compared to the samples with 100 wt% HA precursor processed at 125 cm/min laser speed. The addition of SiO₂ in the HA precursor resulted in the highest surface energy, increased hydrophilicity, and improved biomineralization as compared to the control (untreated Ti-6Al-4V) and the sample with 100 wt% HA as precursor. The microstructural evolution observed using a scanning electron microscopy indicated that the addition of SiO₂ in the HA precursor resulted in the presence of reduced cracking across the cross-section of the bioceramic coating.     

Corrosion behaviour of single (Ti) and duplex (Ti–TiO2) coating on 304L stainless steel in nitric acid medium

Sputter deposited single titanium (Ti) layer, and duplex Ti–TiO₂ coating on austenitic type 304L stainless steel (SS) was prepared, and the corrosion performance was evaluated in nitric acid medium using surface morphological and electrochemical techniques. Morphological analysis using atomic force microscope of the duplex Ti–TiO₂ coated surface showed minimization of structural heterogeneities as compared to single Ti layer coating. The electrochemical corrosion results revealed that, titanium coated 304L SS showed moderate to marginal improvement in corrosion resistance in 1 M, and 8 M nitric acid, respectively. Duplex Ti–TiO₂ coated 304L SS specimens showed improved corrosion resistance as compared to Ti coating from dilute (1 M) to concentrated medium (8 M). The percentage of protection efficiency for base material increases significantly for duplex Ti–TiO₂ coating as compared to single Ti layer coating. The oxidizing ability of nitric acid on both the coatings as well as factors responsible for improvement in protection efficiency are discussed and highlighted in this paper.