Fluorapatite Coatings Research Articles

Porous Mg–Zn–Ca scaffolds for bone repair: a study on microstructure, mechanical properties and in vitro degradation behavior

Biodegradable porous Mg scaffolds are a promising approach to bone repair. In this work, 3D-spherical porous Mg–1.5Zn–0.2Ca (wt.%) scaffolds were prepared by vacuum infiltration casting technology, and MgF2 and fluorapatite coatings were designed to control the degradation behavior of Mg-based scaffolds. The results showed that the pores in Mg-based scaffolds were composed of the main spherical pores (450–600 μm) and interconnected pores (150–200 μm), and the porosity was up to 74.97%. Mg-based porous scaffolds exhibited sufficient mechanical properties with a compressive yield strength of about 4.04 MPa and elastic modulus of appropriately 0.23 GPa. Besides, both MgF2 coating and fluorapatite coating could effectively improve the corrosion resistance of porous Mg-based scaffolds. In conclusion, this research would provide data support and theoretical guidance for the application of biodegradable porous Mg-based scaffolds in bone tissue engineering.Graphical

Hydrothermal Synthesis of Fluorapatite Coatings over Titanium Implants for Enhanced Osseointegration-An In Vivo Study in the Rabbit.

This work aims at the development and characterization of fluorapatite coatings, innovatively prepared by the hydrothermal method, aiming for enhanced osseointegration of titanium implants. Fluoride-containing coatings were prepared and characterized by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy-attenuated total reflectance, and X-ray photoelectron spectroscopy. The biological response was characterized by microtomographic evaluation and histomorphometric analysis upon orthotopic implantation in a translational rabbit experimental model. Physic-chemical analysis revealed the inclusion of fluoride in the apatite lattice with fluorapatite formation, associated with the presence of citrate species. The in vivo biological assessment of coated implants revealed an enhanced bone formation process-with increased bone-to-implant contact and bone volume. The attained enhancement of the osteogenic process may be attributable to the conjoined modulatory activity of selected fluoride and citrate levels within the produced coatings. In this regard, the production of fluorapatite coatings with citrate, through the hydrothermal method, entails a promising approach for enhanced osseointegration in implant dentistry and orthopedic applications.

Deposition and characterization of a sol-gel Mg-substituted fluorapatite coating with new stoichiometries

The calcium substitution for magnesium on fluorapatite is attractive because this element is a natural substitute in biological apatites. There are several published stoichiometries for calcium substituted by magnesium fluorapatites and most works point out that the formation and fixation of biomimetic Ca-P coatings in Ringer’s solution were strongly related to Mg2+ content and furthermore the Mg replacement improves the bioactivity of apatite. In the present study, fluorapatite (FA) and fluorapatite substituted with 6% and 7% of magnesium were obtained by deposition via sol-gel coating on substrates of AISI 316L stainless steel to investigate the effect of magnesium substitution on fluorapatite with not yet investigated stoichiometry. Characterization of coating thickness, chemical composition and crystalline structure was performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The coating adhesion was evaluated using the pull-out test and the corrosion resistance was undertaken using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The electrochemical results showed improvement in the corrosion resistance of magnesium-fluorapatite compared to fluorapatite coated on AISI 316L stainless steel substrates. The improvement corrosion protection and adhesion performance indicate that such magnesium fluorapatites coatings are very interesting candidates as bioactive coatings for implants.

Does Fluorapatite Coating Impart Osteoinductive Capabilities? In Vivo Study of Rat Calvarial Defects

Does Fluorapatite Coating Impart Osteoinductive Capabilities? In Vivo Study of Rat Calvarial Defects

Optimisation of fluorapatite coating synthesis applied to a biodegradable substrate

ABSTRACT Fluorapatite was synthesised using the sol–gel route at three different pH values and aged for a number of days. The coating that was determined to be of optimal morphology was then applied to a pure iron substrate and to an austenitic stainless steel, the latter serving as a control. Deposited fluorapatite coatings were characterised by means of X-ray diffraction and Fourier transform infrared spectroscopy. Crystalline fluorapatite was successfully produced at temperatures as low as 250°C. Temperatures of 250°C and higher caused carbonated fluorapatite, present at 150°C, to transform into fluorapatite. Neutralisation of the sol before coating was found to give rise to a less soluble product when immersed in Hank’s solution at 37°C and 5% CO2. Coatings on pure iron and stainless steel substrates were produced by neutralising the sol to pH 7 and heat treatment at 250°C. This generated a morphology which could potentially aid in cellular attachment.

Physicochemical and Antibacterial Characterization of a Novel Fluorapatite Coating.

Peri-implantitis remains the major impediment to the long-term use of dental implants. With increasing concern over the growth in antibiotic resistance, there is considerable interest in the preparation of antimicrobial dental implant coatings that also induce osseointegration. One such potential coating material is fluorapatite (FA). The aim of this study was to relate the antibacterial effectiveness of FA coatings against pathogens implicated in peri-implantitis to the physicochemical properties of the coating. Ordered and disordered FA coatings were produced on the under and upper surfaces of stainless steel (SS) discs, respectively, using a hydrothermal method. Surface charge, surface roughness, wettability, and fluoride release were measured for each coating. Surface chemistry was assessed using X-ray photoelectron spectroscopy and FA crystallinity using X-ray diffraction. Antibacterial activity against periodontopathogens was assessed in vitro using viable counts, confocal microscopy, and scanning electron microscopy (SEM). SEM showed that the hydrothermal method produced FA coatings that were predominately aligned perpendicular to the SS substrate or disordered FA coatings consisting of randomly aligned rodlike crystals. Both FA coatings significantly reduced the growth of all examined bacterial strains in comparison to the control. The FA coatings, especially the disordered ones, presented significantly lower charge, greater roughness, and higher area when compared to the control, enhancing bacteria–material interactions and therefore bacterial deactivation by fluoride ions. The ordered FA layer reduced not only bacterial viability but adhesion too. The ordered FA crystals produced as a potential novel implant coating showed significant antibacterial activity against bacteria implicated in peri-implantitis, which could be explained by a detailed understanding of their physicochemical properties.

Comparison of microstructure and chemical composition of hydroxyapatite and fluorapatite coatings deposited on Ti-6Al-4V substrates by Nd-YAG laser

In this paper, hydroxyapatite or fluorapatite, was clad on the Ti-6Al-4V substrate by Nd-YAG laser technology, respectively. Scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction were utilised to compare the differences of microstructures, chemical compositions and the compounds in the coating layer and transition layer of samples. The results show that CaTiO3, TiO2, Al2O3 and Ca2P2O7 are compounds in the coating layer of hydroxyapatite cladding sample, and CaTiO3 is the main phase which appears a dendrite-like structure feature. Besides, the dendrite-like CaTiO3 phase, few compounds of TiO2, Al2O3 and the granular residual FA were found that dispersed between interdendritic areas in the coating layer of fluorapatite cladding sample. Compared with these hydroxyapatite and fluorapatite cladding samples, the distribution feature of elements Ca, P, Ti in the coating layer and transition layer is similar, but relatively higher amount of Ca, P and lower Ca/P ratio were found in the coating layer of fluorapatite cladding sample.

Hydroxyapatite and fluorapatite coatings on dental screws: effects of blast coating process and biological response.

This paper describes the deposition of hydroxyapatite (HA) and fluorapatite (FA) onto titanium dental screws using a novel ambient temperature coating technique named CoBlast. The process utilises a coating medium and a blast medium sprayed simultaneously at the substrate surface. The blast medium was a sintered apatite (sHA) and two particles sizes (<106 and <180 µm) were used to assess their influence on the coating process. The influence of the coating process on the coating composition, coating adhesion, screw morphology and screw microstructure was examined. XRD analysis revealed the coating crystallinity was the same as the original HA and FA feedstock powders. Examining the screw's morphology, the threads of the CoBlasted screws exhibited rounding compared to the unmodified screw. This is due to the abrasive nature of the CoBlast process. The degree of rounding was more significant for the screws blasted with the 180 µm sHA than the 106 µm sHA. The blast media particle size significantly influences the surface roughness of both the substrate and coating and the microstructure of the substrate. The screws did not exhibit any loss of coating after insertion into a model bone material, indicating that the coating was strongly adhered to the substrate. There was no statistically significant difference in cell attachment and cell morphology on the unmodified substrates compared to the coated substrates. In conclusion, the CoBlast process can be used to deposit HA and FA onto complex geometries such as dental screws. The choice of blast medium particle size influences the screws morphology. The coating process does not negatively impact on the cell attachment and morphology in vitro.

Synthesis and characterization of nanosized magnesium-doped fluorapatite powder and coating for biomedical application

Nanosized hydroxyapatite (HA) powders exhibit a greater surface area and are expected to have better bioactivity than coarser crystals. In addition, properties of HA can be tailored over a wide range by incorporating different ions into HA lattice. In this study nanosized magnesium-doped fluorapatite powders with different magnesium content are prepared by sol–gel method and calcinated at different temperatures. Moreover, magnesium-doped fluorapatite coatings are applied on 316L stainless steel substrates by sol–gel dip coating method. Results confirmed the incorporation of magnesium and fluoride ions into HA lattice. Increasing calcination temperature not only alters the crystallinity and crystallite size, but also affects the phase composition of obtained powders. The crystallite size and crystallinity of obtained nanopowders were in the range of 40–70 nm and 75–85 %, respectively. Magnesium-doped fluorapatite coating obtained after 24 h aging and one time dip coating was thinner in thickness and morphologically was more homogeneous and had less cracks. Since the obtained magnesium-doped fluorapatite has structural properties similar to biological apatite, they are expected to be appropriate candidates for bone substitution materials and body implants.

VEGF promotes osteogenic differentiation of ASCs on ordered fluorapatite surfaces.

Vascular endothelial growth factor (VEGF) has been reported to mediate both osteogenesis and angiogenesis in bone regeneration. We previously found an upregulation of VEGF in adipose-derived stem cells (ASCs) when obvious mineralization occurred on a novel fluorapatite (FA)-coated surfaces. This study investigated the effect of FA and VEGF on the growth, differentiation and mineralization of (ASC) grown on ordered FA surfaces. Cells grown on FA and treated with VEGF demonstrated osteogenic differentiation as measured with ALP staining, and obvious mineralization as measured by Alizarin red staining. A combined stimulating effect of FA and VEGF was seen using both indicators. VEGF signaling pathway perturbation using a specific VEGF receptor inhibitor showed the lowest levels of ALP and Alizarin red staining, which was partially rescued when the cells were grown on FA and/or treated with the addition of VEGF. The osteogenic differentiation of ASCs stimulated by these FA surfaces as well as VEGF has been shown to be mediated through, but probably not only, the VEGF signaling pathway. The enhancement of osteogenic differentiation and mineralization supports the potential use of therapeutic VEGF and FA coatings in bone regeneration.

Effect of TiO2 addition on surface microstructure and bioactivity of fluorapatite coatings deposited using Nd:YAG laser

To study the effect of titania (TiO2) addition on the surface microstructure and bioactivity of fluorapatite coatings, fluorapatite was mixed with TiO2 in 1:0.5 (FA + 0.5TiO2), 1:0.8 (FA + 0.8TiO2), and 1:1 (FA + TiO2) ratios (wt%) and clad on Ti-6Al-4V substrates using an Nd:YAG laser system. The experimental results show that the penetration depth of the weld decreases with increasing TiO2 content. Moreover, the subgrain structure of the coating layer changes from a fine cellular-like structure to a cellular-dendrite-like structure as the amount of TiO2 increases. Consequently, as the proportion of TiO2 decreases (increase in fluorapatite content), the Ca/P ratio of the coating layer also decreases. The immersion of specimens into simulated body fluid resulted in the formation of individual apatite. With a lower Ca/P ratio before immersion, the growth of the apatite was faster and then the coating layer provided a better bioactivity. X-ray diffraction analysis results show that prior to simulated body fluid immersion, the coating layer in all three specimens was composed mainly of fluorapatite, CaTiO3, and Al2O3 phases. Following simulated body fluid immersion, a peak corresponding to hydroxycarbonated apatite appeared after 2 days in the FA + 0.5TiO2 and FA + 0.8TiO2 specimens and after 7 days in the FA + TiO2 specimen. Overall, the results show that although the bioactivity of the coating layer tended to decrease with increasing TiO2 content, in accordance with the above-mentioned ratios, the bioactivity of all three specimens remained generally good.

Surface Microstructure and Bioactivity of Hydroxyapatite and Fluorapatite Coatings Deposited on Ti-6AI-4V Substrates Using Nd-YAG Laser

Hydroxyapatite (HA) and fluorapatite (FA) coatings were deposited on Ti-6AI-4V substrates with an Nd-YAG laser and then immersed in simulated body fluid (SBF) for up to 21 days to evaluate their bioactivity. Prior to SBF immersion, the coating layer of the HA specimen had a coral-like structure, and was mainly composed of Ti, CaTiO_3, TiO_2, Al_2O_3, and Ca_2P_2O_7, whereas that of the FA specimen had a dense cellular-like structure, and was mainly composed of Ti, CaTiO_3, TiO_2, Al_2O_3, and residual FA. The Ca/P ratios of the HA and FA coating layers were 7.61 and 2.12, respectively. After 21 days of immersion in SBF, only a very small amount of precipitates, mainly consisting of CaCO_3 with some hydroxycarbonated apatite (HCA) and HA, formed on the HA coating layer, whose Ca/P ratio retained a high value of 6.34. In contrast, a dense accumulation of granulated precipitates, mainly consisting of HCA, formed on the FA coating layer after just 7 days of SBF immersion, with a corresponding Ca/P ratio of 1.63. The SBF immersion test shows that FA coatings produced via an Nd-YAG laser cladding technique on a Ti-6AI-4V substrate have better bioactivity than that of their HA counterparts.

The structural and bio-corrosion barrier performance of Mg-substituted fluorapatite coating on 316L stainless steel human body implant

In this study, Mg-substituted fluorapatite coatings were deposited on medical grade AISI 316L stainless steel via sol–gel dip coating method. Phase composition, crystallite size and degree of crystallinity of the obtained coatings were evaluated by X-ray diffraction (XRD) analysis. Fourier transform infrared (FTIR) spectroscopy was also used to evaluate functional groups of the obtained coatings. The surface morphology and cross-section of the final coatings were studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy was used to determine elemental chemical composition of the obtained coatings. In order to determine and compare the corrosion behavior of uncoated and Mg-substituted fluorapatite coated 316L stainless steel, electrochemical potentiodynamic polarization tests were performed in physiological solutions at 37±1°C. Moreover, the released metallic ions from uncoated and coated substrates were measured by inductively coupled plasma-optical emission spectrometry (ICP-OES) within 2 months of immersing in Ringer's solution at 36.5±1°C as an indication of biocompatibility. The results showed that fluoride and magnesium were successfully incorporated into apatite lattice structure and the prepared coatings were nanostructured with crystallinity of about 70%. Obtained coatings were totally crack-free and uniform and led to decrease in corrosion current densities of 316L stainless steel in physiological solutions. In addition, coated sample released much less ions such as Fe, Cr and Ni in physiological media. Therefore, it was concluded that Mg-substituted fluorapatite coatings could improve the corrosion resistance and biocompatibility of 316L stainless steel human body implants.

The stimulation of adipose-derived stem cell differentiation and mineralization by ordered rod-like fluorapatite coatings

In this study, the effect of ordered rod-like FA coatings of metal discs on adipose-derived stem cell (ASC)’s growth, differentiation and mineralization was studied in vitro; and their mineral inductive effects in vivo. After 3 and 7 days, the cell number on the metal surfaces was significantly higher than those on the ordered and disordered FA surfaces. However, after 4 weeks much greater amounts of mineral formation was induced on the two FA surfaces with and even without osteogenesis induction. The osteogenic profiles showed the up regulation of a set of pro-osteogenic transcripts and bone mineralization phenotypic markers when the ASCs were grown on FA surfaces compared to metal surfaces at 7 and 21 days. In addition to BMP and TGFβ signaling pathways, EGF and FGF pathways also appeared to be involved in ASC differentiation and mineralization. In vivo studies showed accelerated and enhanced mineralized tissue formation integrated within ordered FA coatings. After 5 weeks, over 80% of the ordered FA coating was integrated with a mineralized tissue layer covering the implants. Both the intrinsic properties of the FA crystals and the topography of the FA coating appeared to dominate the cell differentiation and mineralization process.

Biomimetic Synthesis of Fluorapatite Coating

In the present study, a simple method of regenerating microstructure of human tooth under near-physiological conditions (pH 7.0, 37 °C, 1 atm) was developed. Commercial gelatin was used as matrix materials in this method, which nucleated the formation of fluorapatite (FA) nanocrystals and regulated the growth of nanocrystals. As a result, the resulting thin FA coatings had been prepared on human tooth slices and sintered hydroxyapatite disks, which were in tight contact with the substrates. Besides, the morphologies of FA nanocrystals changed from acicular to hexagonal with the exchange cycle of gel increased. Electron dispersive spectrometer analysis indicated that some sodium and carbonate ions were incorporated into the FA crystal lattices and the calcium to phosphorus ratio was approximate 1.58. The mechanical properties of the resulting FA coating were investigated through nanoindentation system, which showed the similar hardness with dentin. In conclusion, this method demonstrated a potential application to repair tooth damage in dental clinics.

Investigation into microstructural properties of fluorapatite Nd-YAG laser clad coatings with PVA and WG binders

Biomedical implants are generally coated with a thin layer of hydroxyapatite (HA) using a plasma spraying or pulsed laser deposition method. However, the bonding strength between the coating layer and the substrate is relatively low. Moreover, the high temperature of the deposition process causes a structural instability of the HA, and therefore degrades its bioactivity and reduces the service life of the coating layer following implantation. Accordingly, the present study replaces HA with fluorapatite (FA) as the coating material, and examines the effects of two different binders, namely polyvinyl alcohol (PVA) and water glass (WG), on the properties of FA coatings deposited on Ti–6Al–4V substrates using an Nd-YAG laser cladding process. Scanning electron microscopy (SEM) observations reveal that the FA coating has a coral- and dendrite-like structure when mixed with the PVA binder, but a pure dendrite-like structure when mixed with the WG binder. In addition, the Ca/P value of the WG-based FA coating is significantly higher than that of the PVA-based coating. Fluorapatite, Al 2O 3, CaTiO 3 and Ca 3(PO 4) 2 phases are observed in both coating layers. However, the XRD analysis results indicate that the microstructure of the WG sample is dominated by Ca 3(PO 4) 2 phase while that of the PVA sample is dominated by FA. After soaking in SBF, it was observed that the specimen produced with PVA binder or less laser output power possessed a better apatite induction ability.

Electrodeposition of Fluorine‐Doped Calcium Phosphate Coatings onto Ti6Al4V Alloy—Chemical and Structural Characterization

The present study reports on the development of fluorapatite (FAP) coatings on Ti6Al4V substrate through an electrodeposition (ED) technique. Sodium fluoride (NaF) has been used as source for fluorine incorporation in the apatite structure. The surface morphology and chemical composition of the obtained coatings were characterized by scanning electron microscopy associated with X‐ray microanalysis (SEM‐EDXS). The phase composition of the coatings was determined through X‐ray diffraction and Raman micro‐spectroscopic techniques. The quantitative X‐ray microanalysis confirmed fluorine incorporation into the apatite structure during ED process on Ti6Al4V alloy. The results from the present investigation revealed that the quality of the FAP coating solely depends on the amount of fluorine precursor used during ED process.

Influence of fluorapatite on the properties of thermally sprayed hydroxyapatite coatings

Thermally sprayed hydroxyapatite has been the widely used on orthopaedic prosthesis to induce bone growth and facilitate bone attachment. However, hydroxyapatite has a greater affinity for the formation of an amorphous phase in the thermally sprayed coating that results in the release of excessive amount of mineral ions from the implant coating leading to a saturated environment in the immediate vicinity of the bone cells. Fluorapatite however is highly crystalline and offers the potential for lower mineral ion release by dissolution. Thus study investigates the influence of fluorapatite in a thermally sprayed hydroxyapatite coating. Mechanical blends of fluorapatite with hydroxyapatite were thermally sprayed, characterized with X-ray diffraction, SEM, FTIR, optical microscopy for microstructure, roughness and tested for solubility. Cathodoluminescence microscopy was used to examine the resorbed coating surface. Fluorapatite coatings crystallized more readily and produce a greater coating roughness. The roughness in fluorapatite coatings arises from less flattened droplets that show a tendency for finger formation. Addition of fluorapatite increases coating crystallinity. The use of slower resorbing fluorapatite produces less particle release which favors improved osseointegration. Less change in the surface topography during resorption can be used to an advantage to control the coating surface presented to cells and extra cellular matrix proteins.

Dissolution control and cellular responses of calcium phosphate coatings on zirconia porous scaffold.

Different types of calcium phosphates [hydroxyapatite (HA), fluorapatite (FA), tricalcium phosphate (TCP), and their composites (HA + FA, HA + TCP)] were coated on a zirconia (ZrO(2)) porous scaffold using a powder slurry method. The ZrO(2) porous scaffold was intended for a load-bearing implant, and the apatite layers were coated to improve osteoconductivity. The insertion of an FA intermediate layer between the coating layer and ZrO(2) scaffold effectively suppressed the reaction between the calcium phosphate and ZrO(2) and maintained the coating layer at the initial powder composition. The obtained coating layer, of a thickness of approximately 30 microm, was relatively microporous and firmly adherent to the ZrO(2) scaffold. Dissolution tests in physiological solution showed typical differences depending on the coating layers, with the dissolution rate increasing in the order TCP > HA + TCP > HA > HA + FA > FA. This result suggests the functional coating of the calcium phosphates in view of tailoring the solubility. Osteoblast-like cells, MG63 and HOS, responded similarly in terms of cell growth, morphology, and proliferation rate regardless of the coating types, indicating favorable and comparable cell viability. However, the alkaline phosphatase (ALP) activity of the cells on the pure HA and HA composite coatings (HA + FA and HA + TCP) expressed at higher levels compared to those on pure FA and pure TCP coatings for both MG63 and HOS cells, suggesting a selective cell activity depending on the coating types. All the calcium phosphate-coated-ZrO(2) scaffolds showed higher ALP levels compared to pure ZrO(2) scaffold.

A Radiological Follow-Up Study of Plasma Sprayed Fluorapatite (FA) Coatings

A Radiological Follow-Up Study of Plasma Sprayed Fluorapatite (FA) Coatings