Fluoridated Hydroxyapatite Coatings Research Articles

Preparation and properties of FHA coatings on micro-arc oxidised AZ91D magnesium alloy with different deposition times

ABSTRACT To improve the corrosion resistance of magnesium (Mg) alloy under the physiological environment, fabrication of fluoridated hydroxyapatite (FHA) coating on micro-arc oxidised AZ91D Mg alloy was carried out by electrochemical deposition. The influence of electrochemical deposition time on surface morphology, phase composition, electrochemical properties, and degradation behaviour of the FHA coating was studied by SEM, XRD, electrochemical testing, and in-vitro immersion test, respectively. The results of the electrochemical test and in-vitro immersion test show that FHA coating can significantly improve corrosion resistance. In particular, the sample with deposition time of 60 min showed the minimum corrosion current density (1.26 × 10−6 A cm−2), which may be attributed to a significant decrease in the imperfections of the coating being achieved after this optimum deposition time.

Suspension plasma-sprayed fluoridated hydroxyapatite coatings: Effects of spraying power on microstructure, chemical stability and antibacterial activity

Nanostructured fluoridated hydroxyapatite (FHA) coatings were deposited on Ti substrates using the suspension plasma spraying (SPS) process. The effects of the plasma spraying power on the microstructure and properties of coatings were intensively studied. The X-ray diffraction pattern showed that the as-sprayed coatings mainly consisted of the hydroxyapatite (HA) phase, and the crystal size was estimated to be dozens of nanometers. With the increase of the spraying power, the amount of decomposed phases, crystallinity, and crystal size increased. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of fluorine in the as-sprayed coatings. The corrosion in simulated body fluid (SBF) was studied using potentiodynamic polarization tests, and the results indicated that the coating greatly enhanced the corrosion resistance of the Ti substrate. The chemical stability was assessed by measuring the weight loss of the coatings before and after immersion in a citric acid-modified phosphate buffered saline (PBS) solution at various intervals. The results showed that increasing the spraying powers decreased the dissolution rate of coatings. The in vitro bioactivity was characterized by soaking coatings in the SBF solution for different times, and the obtained results suggested that the spraying power levels affected the initial nucleation rate of the bone-like apatite on the coating surface. The antibacterial activity was investigated using optical density (OD) growth curves and colony-forming unit assays. The coating prepared at a low spraying power had relatively high antibacterial activity with respect to Staphylococcus aureus.

Fabrication and Characterization of Suspension Plasma-Sprayed Fluoridated Hydroxyapatite Coatings for Biomedical Applications

Fluoridated hydroxyapatite (FHA) coatings were prepared on a Ti substrate using a suspension plasma spraying technique. The crystalline phases and chemical compositions of the coatings were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. The analysis confirmed that the coating consisted of an FHA phase. The corrosion behavior in simulated body fluid was studied using potentiodynamic polarization tests, and the results indicated that the FHA coating greatly enhanced the corrosion resistance of the Ti substrate. The chemical stability of the FHA coatings was assessed by evaluating the release of Ca2+ ions. The results indicated that the substitution of fluorine into the hydroxyapatite (HA) structure had a positive effect on the dissolution resistance of the HA. The antibacterial activity was investigated using a surface-plating method; the results revealed that the antibacterial activity of the FHA coating was greater than that of the pure HA coatings. During cell culture tests, the FHA coating did not exhibit cytotoxicity toward the osteoblast cell line, and the cell proliferation was comparable with that of the HA coatings. The antibacterial activity and cell culture results suggested that the plasma-sprayed FHA coating possesses good antibacterial qualities, but is biocompatible with osteoblasts. The promising features of the FHA coating render it suitable for orthopedic and dental applications.

Preparation and properties of heat treated FHA@PLA composition coating on micro-oxidized AZ91D magnesium alloy

To control the corrosion resistance of magnesium (Mg) alloys in physiology environment, a composite coating composed of fluoridated hydroxyapatite (FHA) and poly-lactic acid (PLA) was fabricated on micro-arc oxidated (MAO) AZ91D alloy via combination electrochemical deposition and dip coating methods (Mg@MAO@FHA@PLA). Then these samples were subjected to different heat treatment. The influence of heat treatment on morphology, phase structure, bonding strength and static contact angle of Mg@MAO@FHA@PLA was investigated. The results of electrochemical test and immersion test in simulated body fluid (SBF) show that the corrosion resistance of Mg@MAO@FHA@PLA with heat treatment is further improved. The sample with melting and annealing duplex treatment has the best corrosion resistance and its corrosion rate is 5.574 × 10−5 mm/yr. At the end of 21 days immersion tests, it has lower hydrogen evolution and pH is still less than 7.60. These results indicate that Mg alloy coated with MAO, FHA and PLA coatings is a promising candidate as orthopedic implants.

Application of fluoridated hydroxyapatite thin film coatings using KrF pulsed laser deposition.

Fluoridated hydroxyapatite (FHA) was investigated for application as an implant coating for titanium bone substitute materials in dental implants. A KrF pulsed excimer deposition technique was used for film preparation on a titanium plate. The compacts were ablated by laser irradiation at an energy density of 1 J/cm2 on an area 1×1 mm2 with the substrate at room temparature. Energydispersive spectrometric analysis of the FHA film revealed peaks of fluorine in addition to calcium and phosphorus. X-ray diffraction revealed the presence of crystalline FHA on the FHA film after a 10 h post annealing treatment at 450°C. The FHA film coating exhibited significant dissolution resistance to sodium phosphate buffer for up to 21 days, and favorable cell attachment of human mesenchymal stem cells compared with HA film. The results of this study suggest that FHA coatings are suitable for real-world implantation applications.

In vitro study of electrodeposited fluoridated hydroxyapatite coating on G-II titanium with a nanostructured TiO2 interlayer

Titanium and its alloys have been widely used as orthopedic and dental implants for several decades due to their superior mechanical properties, corrosion resistance and biocompatibility. Recently, many researches revealed that the hydroxyapatite coatings on biomedical materials can further improve their biocompatibility and bioactivity. However, hydroxyapatite coatings are easily decomposed, weakening the bonding between implants and bone tissues and resulting in a high dissolution rate in the biological environment. Prolonging the lifetime of hydroxyapatite in implants is valuable for improving postoperative quality. Hydroxyapatite is the primary inorganic component of bones and teeth. A suitable amount of fluoride ions would be beneficial for the formation of fluoridated hydroxyapatite, which can enhance bone-cell response and the acid resistance of enamel. In this study, G-II titanium substrate was anodized to form a TiO2 interlayer with a nanotube structure. An electrolyte composed of fluoride, calcium and phosphorus ions was prepared for electroplating fluoridated hydroxyapatite (FHA) coatings onto anodized G-II titanium substrates at a constant voltage. The obtained coatings were examined for their microstructure, mechanical properties; moreover, the changes of apatite structure, surface morphology and corrosion resistance were further investigated after immersion in simulated body fluid (SBF) for a number of weeks. The results show that FHA coatings have a higher surface roughness and hardness than plain hydroxyapatite. After immersion in SBF, the FHA coatings induced the nucleation and growth of apatite on the surface and increased their crystallinity. In a potentiodynamic polarization test, FHA coatings exhibited a better anti-corrosion ability than bare G-II titanium substrate in SBF. Additionally, the anodized TiO2 nanotube improved the adhesion and corrosion resistance of FHA as well.

Electrodeposition of sustainable fluoridated hydroxyapatite coatings on 316L stainless steel for application in bone implant

Abstract Fluoridated hydroxyapatite (FHAp) coatings were deposited on 316L stainless steel (316LSS) substrate by the electrodeposition method. Different concentrations of F– ion were incorporated into the apatite structure by adding NaF into the electrolyte solution. The coating was uniform and dense, with thickness of 9.6 µm, and F– ions were doped on HAp with mass percentage of 1.7%; F– concentration was 0.002 M. Results of IR, energy-dispersive X-ray (EDX), X-ray and scanning electron microscopy (SEM) analysis showed that the obtained coatings were single phase crystals of HAp, of a cylinder shape with average size of about 100 nm×30 nm, and characterized for the molecular structure FHAp. The in vitro test of 316LSS, HAp/316LSS and FHAp/316LSS materials in simulated body fluid (SBF) solution was realized with different immersion times. After 21 immersion days in SBF solution, the apatite crystals have a cactus-like shape, and they grow to form a thick block on the surface of FHAp/316LSS leading to the decrease of the corrosion current density during the immersion process in the SBF solution.

Hydroxyapatite and Fluoridated Hydroxyapatite Coatings and Their Effects on Commercially Pure Magnesium Corrosion Response

Dicalcium-phosphate dehydrate, converted to hydroxyapatite by post-treatment in sodium hydroxide, and fluoridated hydroxyapatite were electrodeposited on commercially pure magnesium substrates that were pretreated with sodium hydroxide. The coatings’ crystalline structure, thickness, scratch hardness, morphology and chemical composition were characterised by GIXRD, microscratch testing platform, SEM and EDS. The results showed that the apatite coatings had highly crystalline structure, acceptable scratch hardness, flake-like morphology and acceptable chemical composition. Corrosion behaviour of the uncoated and coated substrates was investigated by potentiodynamic polarization and immersion tests in simulated body fluid. The coated substrates, especially fluoridated hydroxyapatite coated substrates, showed significantly lower corrosion rates compared to uncoated substrates. The polarisation curves showed that the coatings hindered anodic reactions; the corrosion potentials were shifted toward less-negative. In general, this study concluded that the corrosion rate of commercially pure magnesium could be significantly decreased to be a candidate for future cost-effective biodegradable orthopaedic implants.

Ag-Incorporated FHA Coating on Pure Mg: Degradation and in Vitro Antibacterial Properties.

Fluoridated hydroxyapatite (FHA) coating can help retard the degradation of magnesium, and possess good biocompatibility. However, the antibacterial property of FHA is very limited. In this work, we aimed to incorporate silver into FHA structure to fabricate biocompatible and antibacterial coatings with enhanced anticorrosion property. The results showed that the Ag-FHA coating prepared by electrochemical deposition and subsequent immersion in AgNO3 solution was superior to the Ag-FHA coating prepared by coelectrodeposition in terms of crystal structure, surface morphology and corrosion resistance. The release of Ag(+) ion causing high antiplanktonic bacterial rate and excellent antiadherence property to MRSA. Meanwhile, good cell compatibility of MC3T3-E1 including cell viability, cell adhesion, and cell morphology was achieved under the controlled degradation. The balance of degradation and antimicrobial property of Ag-incorporated FHA coating made it an alternative in the application of surface modification for biodegradable Mg.

In Vitro Analysis of Electrophoretic Deposited Fluoridated Hydroxyapatite Coating on Micro-arc Oxidized AZ91 Magnesium Alloy for Biomaterials Applications

Magnesium (Mg) alloys have been recently introduced as a biodegradable implant for orthopedic applications. However, their fast corrosion, low bioactivity, and mechanical integrity have limited their clinical applications. The main aim of this research was to improve such properties of the AZ91 Mg alloy through surface modifications. For this purpose, nanostructured fluoridated hydroxyapatite (FHA) was coated on AZ91 Mg alloy by micro-arc oxidation and electrophoretic deposition method. The coated alloy was characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, in vitro corrosion tests, mechanical tests, and cytocompatibility evaluation. The results confirmed the improvement of the corrosion resistance, in vitro bioactivity, mechanical integrity, and the cytocompatibility of the coated Mg alloy. Therefore, the nanostructured FHA coating can offer a promising way to improve the properties of the Mg alloy for orthopedic applications.

Biodegradation assessment of nanostructured fluoridated hydroxyapatite coatings on biomedical grade magnesium alloy

The challenges associated with managing Mg degradation rate demand novel technologies to ensure its biological safety and reliability. Here, fluoridated hydroxyapatite nanopowders with different degrees of fluoridation were coated on microarc oxidized AZ91 magnesium alloy via the electrophoretic deposition method. Zeta potential and conductivity monitoring techniques were employed to offer appropriate conditions for the coatings. The bio-corrosion process and the associated mineralization were interpreted during the immersion in simulated body fluid solution. Based on the results, the 25% fluorine substituted hydroxyapatite coating on microarc-treated AZ91 implant was proposed to stimulate bone ingrowth in a minor invasive behavior and without post-operative complications during its lifespan.

Laser Cladding of Fluoridated Hydroxyapatite Coatings on Titanium Alloy: Preparation and Characterization

In this research, Fluoridated hydroxyapatite bio-ceramic coatings were produced by laser cladding on the titanium alloy with hydroxyapatite and CaF2 as raw materials. The microstructures and phase constitutions of coatings were characterized by OM, SEM, EDS and XRD, the mechanical properties was investigated by micro-hardness and simulated body fluid immersion test. The results indicated that Fluoridated hydroxyapatite bio-ceramic coatings with anticipated structure and properties were achieved successfully by laser cladding on the titanium alloy. Compared with CO2 laser, the FHA coatings prepared by fiber laser had better deposition of biological activity phase.

Laser Cladding of Fluoridated Hydroxyapatite Coatings on Titanium Alloy for Bone Replacement Structures

Bone-like fluoridated hydroxyapatite (FHA) coatings were prepared on Ti-6Al-4V substrates (TC4) by using laser cladding. This bioceramic coating was fabricated by adding CaF2 micron-particles into the hydroxyapatite before presetted on the Ti alloy substrate and radiated by laser beam which aimed at obtaining lower solubility, fine thermostability and maintaining the comparable bioactivity and biocompatibility. Coatings, which were processed using a Nd:YAG laser cladding, presented FHA crystallization on the surface with a uniform morphology along the coating cross-section and no significant dilution of the titanium alloy was observed. Phase analysis by X-ray diffraction indicated the generation of fluoridated hydroxyapatite phase in the laser cladded coatings. The coatings showed the formation of a metallurgically sound and diffused substrate-coating interface, which significantly increased bonding strength between the coatings and subtrate. The bioactive coatings afforded favourable bone bioactivity by inducing the rapid precipitation of apatite on their surface when immersed in a simulated body fluid (SBF). The work demonstrated the potential of using laser cladding for fabricating fluoridated hydroxyapatite bioceramic coatings on Ti alloy.

Electrochemical depositions of fluorohydroxyapatite doped by Cu2+, Zn2+, Ag+ on stainless steel substrates

Fluoridated hydroxyapatite (FHA, Ca10(PO4)6(OH)2−xFx where 0<x<2 is the degree of fluoridation) and inorganic ions (Zn2+, Cu2+, Ag+) substituted fluoridated hydroxyapatite coatings (M-FHA) were deposited on the surface of medical grade 316L stainless steel samples by electrochemical deposition technique. The FHA coatings were co-substituted with antibacterial ions (Zn2+, Cu2+ or Ag+) by co-precipitation and ion-exchange methods. Characterization studies of coatings from X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) showed that the obtained layers are monophase crystals FHA and did not contain any discernible crystalline impurity. The particles of all samples are of nano size that gives thin layers. The surface morphology, microstructure and Ca/P atomic ratio of the FHA coatings can be regulated by varying electrolyte temperature. This later affects the porosity of the coating surface and the chemical compositions of the deposits.Quantitative elemental analysis indicates that the copper, zinc and silver ions are incorporated into the Fluorohydroxyapatite.The antimicrobial effects of doped fluorohydroxyapatite coatings against pathogen bacterial strains Staphylococcus aureus were tested in liquid media. The results are promising and demonstrated that all doped FHA samples exhibit excellent antimicrobial activity “in vitro” against the microorganism, so the antimicrobial properties of the coatings developed are improved.

Preparation and characterization of fluoridated hydroxyapatite coatings on HT-C/C composites

Monetite-like coatings were deposited from a solution containing Ca and P ions onto H 2O 2 treated Carbon/Carbon composites (HT-C/C) by ultrasonic induction heating (UIH) and subsequently subjected to ammonia hydrothermal treatment to form hydroxyapatite (HA). Subsequently, this HA coating was placed in a NaF solution and hydrothermally treated to produce fluorinated hydroxyapatite (FHA) coatings. The structure, morphology and chemical composition of the HA and FHA coatings were characterized by SEM, XRD, XPS, EDS and FTIR, and the adhesiveness and dissolution rate were examined by a scratch test and an immersion test respectively. The results showed that incorporation of F into HA led to an increase in the adhesiveness but a decrease in the dissolution rate of HA coating on C/C. With increasing hydrothermally fluoridation temperature, the F content in the FHA coatings increased and their dissolution rate decreased. However, the adhesiveness of these FHA coatings on C/C first increased from 42.7 N to 54.2 N as the hydrothermal fluoridation temperature increased from 353 K to 393 K, and then decreased to 18.3 N at 413 K. The reasons for changes in the adhesiveness and dissolution rate of the coatings were discussed.

Integrity and zeta potential of fluoridated hydroxyapatite nanothick coatings for biomedical applications

Fluoridated hydroxyapatite (FHA) coatings exhibit great potential for applications on implants which require good bioactivity and high antibacterial activity. This work is a comparative study of chemical stability, adhesive strength and zeta potential of a nanothick (about 200 nm) FHA coating which is densely and uniformly deposited on a titanium substrate electrochemically. The chemical stability of the nanothick coatings was evaluated using a dissolution test in a simulated physiological solution. The dissolution tests indicate that the fluorine-containing calcium phosphate (CaP) coating with an appropriate heat treatment is chemically stable in a physiological environment, even more so than its HA counterpart. The adhesive strength of FHA coatings was evaluated by the critical load obtained from nanoscratching tests. The critical load which caused coating failure in scratching was determined by a method which correlated the scratching morphology with a sudden change in friction coefficient. The adhesive strength of a nanothick FHA coating was 147% larger than that of HA coating with the same thickness level. The fluorine addition does not have a significant effect on the characteristics of the negative zeta potential of apatite coatings. The solid integrity of this nanothick FHA coating makes it an excellent candidate for biomedical applications.

Interfacial study of magnesium-containing fluoridated hydroxyapatite coatings

Magnesium-containing fluoridated hydroxyapatite (Mg x FHA) coatings have been developed to improve the biological performances of fluoridated hydroxyapatite (FHA) coatings. The coatings are deposited on Ti6Al4V substrates via a sol–gel process. The interface between the coating and substrate is characterized by scanning electron microscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy for coating thickness, elemental distribution and chemical states. Pull-off test is used to evaluate the adhesion strength. The results show that the interdiffusion of elements happens at the coating/substrate interface. The incorporation of Mg ions into FHA coatings enhances the pull-off adhesion strength between the coating and the substrate, but no significant difference is observed with different Mg concentrations.

Sol-Gel Derived Nanocrystalline Fluoridated Hydroxyapatite Powders and Nanostructured Coatings for Tissue Engineering Applications

Nanocrystalline fluoridated hydroxyapatite (FHA) powders and coatings with a chemical composition of Ca10(PO4)6OH2–x F x (where x values were selected equal to 0.0 ,0.5, 1.0, 1.5, and 2.0) were prepared through a modified simple sol-gel technique in comparison with conventional alkoxide-based sol-gel route. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy, pF-meter with a fluorine-sensitive electrode, and inductively coupled plasma–optical emission spectroscopy (ICP-OES) analysis techniques were employed in order to evaluate phase composition, particle size distribution, morphology, functional groups, fluorine content, and purity of prepared FHA nanopowders, respectively. SEM analysis was used to study the surface morphology and cross section of the FHA coatings, deposited on 316L stainless steel substrate. Results indicated that single-phase and homogeneous FHA nanopowders with carbonate peaks in the FTIR spectrum were synthesized through the modified sol-gel technique. TEM analysis revealed that fluorapatite (FA) powder was composed of nanosized particles, ~25 nm in size, with polyhedron shape and straight corners. In the modified sol-gel technique, polymerization and gelation kinetic of the sol were significantly improved without any need to use additives or pH control. Uniform, dense, well-adhered, and compacted FHA coatings were formed on the 316L stainless steel substrate after 24 hours of aging.

Osteoblastic cell response on fluoridated hydroxyapatite coatings: the effect of magnesium incorporation

Magnesium (Mg) ions were incorporated into fluoridated hydroxyapatite (HA) coating by the sol–gel dip-coating method. Mg in the coating was measured by x-ray photoelectron spectroscopy (XPS). The changes of calcium and magnesium concentrations were recorded to monitor the dissolution behavior of the coatings. In vitro cell responses were evaluated using MG63 cells in terms of cell morphology, proliferation and differentiation. The substitution of Mg and F ions into the HA crystal structure was confirmed by XPS. Only a limited amount of Mg can be incorporated into HA lattice. The dissolution test revealed that Mg incorporation increased the solubility of the coating in the tris-buffered saline solution. The highest solubility was achieved at x = 1.5 (Ca(10-x)Mgx(PO4)6 F(OH). In the cell culture test, well-spread cells were observed on all the coatings. Also, a significantly positive effect of Mg ions on cell proliferation and late differentiation was found at x = 1.5. Mg incorporation stimulates osteoblastic cell responses on fluoridated hydroxyapatite coatings.

Zn-Releasing FHA Coating and Its Enhanced Osseointegration Ability

In this study, we present a novel coating with Zn-releasing ability that promotes osseointegration of Ti6Al4V implants. The coatings were prepared by a sol–gel technique, and nanosized Zn-containing β-tricalcium phosphate particles were added to the Ca(NO3)2–P2O5–HPF6 sol system to incorporate Zn ions into fluoridated hydroxyapatite (FHA) coatings. The derived Zn-releasing fluoridated hydroxyapatite (ZTFHA) coatings demonstrated a slow and sustained Zn release behavior. The ZTFHA coatings were able to support cell growth of osteoblast-like cell cultures and promoted an obvious increase in cell viability compared with FHA coating alone. The histological analysis of the ZTFHA coating showed direct bonding to bony tissue and significantly higher bone contact than with FHA coating alone. The ZTFHA coating with its slow and sustained Zn release shows promise as a medium for significantly enhancing osseointegration and allowing cementless stable fixation of orthopedic implants.