Fluorine-substituted Hydroxyapatite Research Articles

Synthesis of boronized Ti6Al4V/FHA composites by microwave sintering for dental applications

Boronized Ti6Al4V/FHA composites were prepared by microwave sintering of mixed powders of Ti6Al4V, TiB2, and synthesized fluorine-substituted hydroxyapatite (FHA) with variable compositions at 1050 °C for 30 min. The unique “lens effect” of microwave facilitated the in-situ transformation of nanoscale TiB2 into TiB, serving as the reinforcing phase within the composites. Increasing the theoretical fluorine substitution percentage of FHA from 0% to 50% caused less thermal decomposition of hydroxyapatite during sintering, promoting densification and thereby mechanical properties of the composites. However, elevating the substitution percentage to 100% led to excessive grain growth and FHA agglomeration, deteriorating the composite mechanical performance. The boronized Ti6Al4V/FHA composite produced using FHA with the theoretical fluorine substitution of 50% exhibited the highest compressive strength (397.7 MPa), proper compressive modulus (10.65 GPa) and maximum microhardness (385.3 HV). Furthermore, it showed excellent hydrophilicity and good cell adhesion, confirming its superior bioactivity for dental applications.

Characterization, mechanical properties, corrosion behavior and bone-like apatite formation ability of fluorine substituted hydroxyapatite coating

Hydroxyapatite (HA) is a non-bioceramic commonly used in human implants in the form of coatings, which are limited in their application by mechanical and wear resistance properties, as well as biodegradability. In this study, fluorine substituted hydroxyapatite (FHA) coatings were prepared on Ti–6Al–4V surfaces by plasma spraying method using a mixture of calcium fluoride and hydroxyapatite powders. The prepared coatings were characterized by X-ray diffraction and fourier transform infrared (FTIR) spectroscopy at different levels of calcium fluoride (3 wt%, 6 wt%, 9 wt%, and 12 wt%). The biocompatibility of the coatings was evaluated by in vitro mineralization experiments. Experimental results showed that at 9 wt% of calcium fluoride, the prepared FHA coatings had better mechanical properties, with improved bond strength (28.2 MPa). The X-ray diffraction patterns of the coatings reflect the fluorine substitution during the spraying process and the 9FHA has the highest crystallinity according to the XRD analysis, which is closely related to the biological activity of the coating. In addition, Potentiodynamic polarisation showed that the sample coated with the 9FHA coating had the highest Ecorr and lowest Icorr, indicating the best corrosion resistance. The FHA coating exhibits faster apatite deposition in simulated body fluid, and the efficiency of apatite deposition increases with the increase of CaF2.

Novel mesoporous anionic substituted hydroxyapatite particles for multipurpose applications

The super-structured nanodimensional apatitic particles have been limited explored for therapeutic applications. Furthermore, ion substituted super-structured nanodimensional apatitic particles have been rarely attempted, which motivated the present investigation. In the present work, F− and Cl− substituted hydroxyapatite (HAP) prepared via a facile and economical one-pot hydrothermal route were characterized for their structural, morphological and bioactive properties. The F− and Cl− anions (1 wt%) were individually substituted in hierarchically assembled nanostructured apatitic (HANA) particles and produced fluorine substituted Hydroxyapatite (FHAP) and chlorine substituted Hydroxyapatite (ClHAP) HANA particles, respectively. Besides comprehensive characterization, particles were systematically tested for their in-vitro ionic dissolution and drug-carrying abilities. Both FHAP and ClHAP nanoparticles exhibited monolithic apatitic structure, novel spherical morphology having substituted elements, mesoporous large surface area, and pore-volume with high thermal stability. Furthermore, both particles exhibited superior in-vitro bioactivity ability. Besides it, both FHAP and ClHAP nanoparticles exhibited superior drug loading and sustained drug release characteristics. Thus, this study presented the potentials of novel particle shapes with superior bioactivity and drug-carrying abilities, making them suitable for multipurpose therapeutic applications, including tissue regeneration and drug-carrying agents.

Exceptional performance of gold supported on fluoridated hydroxyapatite catalysts in CO-cleanup of H2-rich stream: High activity and resistance under PEMFC operation conditions

Proton-exchange-membrane fuel cells (PEMFCs) appear to be the most promising solution for future automotive applications. Facing the lack of efficient hydrogen storage and transportation solutions, current research is focused on the development of on-board catalytic reformers. In this strategy, the purity of hydrogen stream is still an unresolved issue that needs to be addressed in order to avoid poisoning of the Pt electrodes of PEMFC.Here we report the extraordinary performance of gold supported on fluorine-substituted hydroxyapatite (HAP) catalysts in the CO preferential oxidation (COPROX) process. At 80 °C, the optimized catalyst (Au/F-(1)) proves to be highly active, selective (showing a CO conversion (XCO) of 100 % and selectivity towards CO2 production (SCO2) close to 62 %) and very resistant to deactivation, even in the presence of H2O (15 %) and CO2 (20 %). In addition, these results were obtained at relatively high weight hourly space velocity (WHSV: 60,000 cm3 g−1 h−1). It should be highlighted that our catalysts clearly outperform state-of-the-art gold catalysts. Our discovery introduces Au/F(x)-HAP catalysts as a viable solution for an effective elimination of CO to feed PEMFCs with CO-free hydrogen streams.

Formation of nanodimensional structures in precipitated hydroxyapatite by fluorine substitution

Hydroxyapatite Ca10(PO4)6(OH)2 is a bioactive compound, which is of great interest for medical application as a component of artificial bones and implants. The modification of its composition via anion and cation substitution can strongly affect its properties due to the formation of nanosized particles in the basic structure. In this work the influence of fluorine substitution of hydroxyl groups is examined. The powders of fluorine-substituted hydroxyapatite Ca10(PO4)6(OH)2−xFx (x = 1; 1.5; 2) were precipitated by chemical condensation from solutions. Such characteristics of powders as phase composition, morphology, particle size distribution, density, specific surface area have been studied. It was established that partial replacement of hydroxyl groups by fluorine leads to a decrease in the particle size to 10 nm. The degree of substitution affects the mechanical properties of synthesized powders and ceramics after annealing. A comparison of the particle size distribution in the initial samples and the distribution of grains in the sintered ceramics confirmed that the ceramics inherits the structure of the powders, which has a positive effect on its strength characteristics.

The antibacterial activity of an epoxy resin-based dental sealer containing bioactive glass, hydroxyapatite, and fluorohydroxyapatite nanoparticles against Enterococcus Faecalis and Streptococcus mitis

Objective(s): The present study aimed to investigate the antibacterial properties of a conventional epoxy-based dental sealer modified with synthesized bioactive glass (BG), hydroxyapatite (HA), and fluorine-substituted hydroxyapatite (FHA) nano-fillers. Materials and Methods: The synthesized nano-fillers were incorporated into the conventional epoxy-based dental seaer at the concentration of 10%. The antimicrobial properties of the unmodified sealers (controls) and modified seaers with BG, HA, and FHA nanoparticles (NPs) were evaluated based on biofilm formation and using the direct contact test (DCT) of Enterococcus faecalis and Streptococcus mitis. Data analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test at the significance level of 5%. Results: A significant reduction was observed in the biofilm formation and DCT of the microbial strains in the three modified groups compared to the unmodified conventional epoxy sealer (P<0.05). The addition of FHA NPs resulted in the most significant antibacterial effects against E. faecalis and S. mitis, as well as a statistically significant reduction compared to the unmodified and BG-modified groups (P≤0.001). Conclusion: According to the results of this preliminary study, nano-structured FHA, HA, and BG fillers incorporated into epoxy-based dental sealers could be potentially effective biomaterials for antibacterial approaches to root canal treatments.

Development of Novel Poly (ɛ-Caprolactone)/ Fluorine Substituted Hydroxyapatite Bilayer Coated 316L Ss for &lt;i&gt;In Vitro&lt;/i&gt; Corrosion Protection

A novel biocompatible fluorine substituted hydroxyapatite (F-HAp) / poly (ε-caprolactone) (PCL) bilayer coating on 316L SS with superior adhesion strength and admirable corrosion protection properties. PCL slurry was coated on 316L SS as a first layer using dip coating method followed by F-HAp coating as the second layer using electrodeposition method. The structural and functional group analysis of bilayer coatings were characterized by different analytical technique. Also, the mechanical properties of the bilayer coating showed higher adhesion strength than HAp and F-HAp coatings on 316L SS. The potentiodynamic polarization and electrochemical impedance spectroscopy results indicated that the admirable corrosion protection nature. The in vitro bioactivity test for coated 316L SS substrate was carried out by soaking it in the SBF solution, the induced apatite formation confirming the improved bioactivity of the specimen. Further, dissolution of metal ions was considerably reduced which was confirmed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The in vitro cell–material interaction of the bilayer coating was studied with human osteosarcoma MG63 cells for cell viability at 3, 7, 14 and 21 days of incubation and good biocompatibility was observed. The obtained results show that the F-HAp/PCL bilayer coating provides effective corrosion protection and enhanced bioactivity.

In-vitro bioactivity evaluation and physical properties of an epoxy-based dental sealer reinforced with synthesized fluorine-substituted hydroxyapatite, hydroxyapatite and bioactive glass nanofillers

The purpose of this study was to evaluate the physical properties and bioactivity potential of epoxy-based dental sealers modified with synthesized bioactive glass (BAG), hydroxyapatite (HA) and fluorine substituted hydroxyapatite (FHA) nanoparticles.The synthesized powders were incorporated at 10% and 20% into the epoxy-based dental sealer. The setting time, flow and solubility and microhardness of the modified and unmodified samples were examined. The bioactivity was evaluated using FESEM-EDX and elemental mapping, ATR-FTIR and XRD.The flow value of all of the experimental groups except the FHA modified samples, was greater than 20 mm. Concerning solubility, no specimens exhibited more than 1% weight loss. The solubility value of the FHA groups was statistically significant lower than other groups (p ≤ 0.001). The mean hardness values of all of the modified samples were significantly higher than the unmodified group (p ≤ 0.001).Regarding bioactivity, in vitro study revealed that after 3 days immersion in SBF a compact and continuous calcium phosphate layer formed on the surface of epoxy sealers containing BAG and HA nanoparticles.Based on these results, the addition of BAG and HA nanoparticles did not adversely alter the physical properties of epoxy sealers. Additionally, they improved the in vitro bioactivity of the epoxy sealer.

Surface modification of orthopedic implants by optimized fluorine-substituted hydroxyapatite coating: Enhancing corrosion behavior and cell function

Fluorine may only have negative effects on bone metabolism if the optimum concentration of fluorine would not be determined, especially in osteoporosis. In this study a nano-porous and uniform fluorhydroxyapatite (FA) coating in different concentration of fluorine could be deposited on the 316 L substrate with a thickness of 50 μm. Fluorine can have influence on cell proliferation, matrix production, ALP releasing, coating dissolution rate, bio activity, and corrosion resistivity. The dissolution rate of the coating evaluated by ICP and found with an increase in fluorine due to the elimination of CaO, Ca2+ releasing decreased. The results of SBF and MTT exhibited the fluorine within the apatite structure enhanced the growth of natural apatite and function of human osteoblast like cell (MG-63). Furthermore, cell density and attachment showed an enhancement while fluorine increased. Surprisingly the ALP activity test showed the mineralization ability of coating would be improved significantly in presence of fluorine. Furthermore potentiodynamic polarization showed with increasing fluorine, the current density decreased from 112 to 13 nA/cm2. Corrosion property of FA is higher because it is too stable but can also persuade to severe adverse effects like osteomalacia. According to the achieved results, 75% partially-substituted fluorine within apatite structure was introduced as a proper combination of biocompatibility while 100% substituted fluorine could be a better candidate in corrosion resistant performance.

Effect of fluorine substitution on sintering behaviour, mechanical and bioactivity of hydroxyapatite

Fluorine substituted hydroxyapatite (FAp) with different degree of fluorine (F) substitution, has been synthesized using hydrothermal synthesis method. In the present work, as synthesized powders were consolidated by sintering at 1200 °C in air for 1 h. The sintered specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) for phase analysis. Further, fluorine intake in the sintered specimens was evaluated using ion chromatography (IC). XRD peaks clearly showed biphasic nature of the sintered specimen. However, the sintered samples containing more than ∼60% fluorine substitution showed no β-tricalcium phosphate (β-TCP) phase formation. The IC results revealed that the degree of fluoridation decreased significantly in the sintered specimen compare to the respective as synthesized powders. The effect of actual fluorine content in the sintered specimens was further evaluated in terms of sinterability, surface energy, mechanical properties and in vitro cytocompatibility study. The surface energy of the sintered specimen decreased from 51.8 mN/m to 42.5 mN/m, in which degree of fluoridation varies from 0% to 110%. The in vitro cytocompatibility of the sintered specimen were carried out against mouse osteoblast cell line (MC3T3-E1). In vitro study showed that all the samples were nontoxic but cell proliferation for the samples containing more than 40% fluorine substitution became significantly low.

Influence of the atmosphere conditions in the structure, properties and solubility of fluorine-substituted hydroxyapatites

Abstract The influence of synthetic conditions in the composition and properties of chemically precipitated hydroxyapatite (HAp), fluorine-substituted HAp (xF-HAp) and fluorapatite (FAp) have been examined considering different atmospheres (nitrogen, air and carbon dioxide), temperatures (37 °C and 150 °C) and pressures (hydrothermal conditions). Results indicate that the synthetic conditions not only affect the fluorination degree but also have a pronounced effect on the carbonation degree, the crystallinity, the surface wettability and the thermal stability. Besides, the electrical polarization of HAp-based minerals mainly depends on the fluoride content, the formation of ordered channels of vacancies along the sintering and thermal polarization processes becoming more difficult with increasing fluorination degree. This limits the utilization of xF-HAp and FAp as electro-responsive scaffolds and electrocatalysts, as has been recently proposed for polarized HAp. Finally, the effects of the carbonation and the fluoridation degrees, the concentration fluoride anions supplied from an external source, and the pH on the solubility of HAp-based minerals have been examined. Observations indicate that, although strategies based on the substitution of HAp by xF-HAp or FAp have been proposed for coatings of dental implants, external fluoride anions inhibit the solubility more effectively than the fluorination of the own mineral matrix. Accordingly, HAp combined with an effective external supply of fluoride anions is more appropriated than xF-HAp and FAp for the fabrication of dental coatings.

Fluorine substituted nano hydroxyapatite: Synthesis, bio-activity and antibacterial response study

In the present investigation, nano hydroxyapatite (HAp) and fluorine substituted hydroxyapatite (FHAp) with varying fluorine concentrations have been successfully prepared by hydrothermal method. The as synthesized powders were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscope (HRTEM) and ion chromatography (IC) for fluorine content analysis. XRD results showed shifting of HAp peaks with increasing fluorine substitution and detected calcium fluoride (CaF2) phase in the synthesized powders where theoretically 100% or more OH ions substituted by F ions. The crystallinity of HAp powder gradually increased and cell volume decreased with fluorine substitution. HRTEM of the synthesized powders showed the nano rod like morphology. The IC was carried out to understand the degree fluoridation in the synthesized powder. The IC result of in vitro fluorine ion leaching showed that fluorine concentration in aqueous medium depends on the degree of fluoridation in the synthesized powder. The as synthesized powders were checked for antimicrobial activity by using both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. The powder having ~33% fluorine substitution showed bactericidal effect. The in vitro fluorine ion release study showed significantly high fluorine concentration in aqueous medium for the HAp powders having more than 50% fluorine substituted. The in vitro cell viability assay using mouse osteoblast cell line (MC3T3-E1) confirmed that the powders were non-cytotoxic.

Fabrication and Characterization of Carbon Nanotubes/Fluorhydroxyapatite Composites.

Hydroxyapatite (HA) ceramics have important biomedical applications as hard tissue replacements. However, the mechanical properties and chemical stability of HA ceramics in physiological environments need to be tailored for specific applications. To improve the mechanical properties of HA ceramics, carbon nanotubes (CNTs) are introduced into HA matrix materials by an in-situ chemical synthesis method. Meanwhile, fluorine is also incorporated into the HA structure to form fluorinesubstituted hydroxyapatite (FHA). A uniform distribution of CNTs and good interfacial bonding help to improve the hardness by 76.2% and fracture toughness by 74.5% compared to pure HA. Both the dissolution behavior and antibacterial activities of CNTs/FHA composites show close relativity with the fluorine content. Increasing the fluorine contents of CNTs/FHA composites increases their chemical stability and ability to inhibit Streptococcus mutans.

Influence of surface acid and base sites on the Guerbet coupling of ethanol to butanol over metal phosphate catalysts

Hydroxyapatite (HAP; Ca10(PO4)6(OH)2) is a well-recognized catalyst for the Guerbet coupling of ethanol to butanol. In an effort to explore the role of the anion components of the catalyst, steady-state, gas phase catalytic coupling of ethanol to butanol was investigated at 633K and atmospheric pressure over beta tricalcium phosphate (β-TCP; β-Ca3(PO4)2) and fluorine-substituted hydroxyapatite (FAP; Ca10(PO4)6F2). Both β-TCP and FAP catalysts were catalytically active for butanol formation, leading to ∼35% selectivity at low conversion, suggesting that the PO43− group contributes to the active acid-base site pair for butanol formation during ethanol coupling over HAP. Co-feeding water, a product of ethanol coupling, revealed weaker inhibition of the rate over HAP relative to MgO, confirming the potential negative influence of strong base sites on coupling catalysts. Catalytic reactions of ethanol over Mg3(PO4)2, β-TCP, and Sr3(PO4)2 catalysts demonstrated the importance of Lewis acidity of the metal phosphates on the reaction. Relatively strong Lewis acid sites on the Mg3(PO4)2 surface (Mg2+ cations) favored undesired ethanol dehydration to ethene (36% selectivity) and diethyl ether (52% selectivity) whereas the Sr3(PO4)2 catalyst predominantly catalyzed ethanol dehydrogenation to acetaldehyde (91% selectivity) at a rate significantly higher than that observed over the other catalysts. Evidently, the β-TCP exposes intermediate-strength Lewis acid sites provided by surface Ca2+ cations that enable the material to effectively convert ethanol to butanol with 35% selectivity.

Rod-shaped and fluorine-substituted hydroxyapatite free of molecular immunopotentiators stimulates anti-cancer immunity in vivo.

Herein, rod-shaped and fluorine-substituted hydroxyapatite nanoparticles (FHA) were synthesized using a facile hydrothermal method. The rod-shaped FHA significantly increased the cellular uptake of a model antigen by bone marrow dentritic cells in vitro, improved antigen presentation in vivo, stimulated immune-related cytokine secretion in vitro and ex vivo, and enhanced the anti-cancer immunity in vivo.

Synthesis of fluorine-substituted hydroxyapatite nanopowders for dental applications

Synthesis of fluorine-substituted hydroxyapatite nanopowders for dental applications

Tailored coating chemistry and interfacial properties for construction of bioactive ceramic coatings on magnesium biomaterial

Magnesium has the potential to replace materials currently used for medical implants, but its high corrosion rate limits its practical application. For the practical application purpose, a multilayer coating method that combined MgF2 layer and the sol–gel-synthesized hydroxyapatite (HA) layer on Mg substrate was proposed in this study to enhance corrosion resistance and biocompatibility. As characterized by SEM, TEM and electrochemical test, the MgF2 layer not only increases the interfacial stability during the coating process, but also provides a fluorine source that leads to the formation of low-solubility fluorine-substituted HA (FHA), resulting in excellent coating properties. The synthesized coatings were calcined at 400 and 500°C, respectively, to control their crystallinity and impurities. The results show that the corrosion resistance of the specimens calcined at 500°C was 11 times higher than that calcined at 400°C. MG63 cells cultured on the optimized HA/MgF2 coatings were more viable than other surface. Furthermore, the spreading behavior of the cells was significantly higher on the optimized HA/MgF2 coatings. These results suggest that the designed-multilayer process and optimized calcination temperature can effectively control the coating chemistry and interfacial properties, which improves biocompatibility and allows for orthopedic application.

Zirconia on the properties of pressureless sintered fluorohydroxyapatite/zirconia composites

In this study, fluorine-substituted hydroxyapatite (Ca10(PO4)6(OH)0·8F1·2; coded as HA06F) and yttria-stabilized zirconia (YTZP) were prepared by a sol-gel method to produce HA06F-YTZP composites with 5, 10, 15, 20, 40, and 60 wt% YTZP by pressureless sintering. Phase and microstructural analysis showed that the thermal stability of the HA06F matrices could be maintained when the YTZP content did not exceed 20 wt% and for sintering temperatures less than 1400 °C, while the YTZP phase retarded the densification of the composites if the zirconia content was over 20 wt%. High resolution TEM obervation revealed that the reaction between the HA06F phase and the zirconia phase was suppressed. Mechanical properties including the Knoop hardness, the Young’s modulus, and the fracture toughness of the HA06F-YTZP composites increased with the YTZP content until the optimal content of 20 wt%, while further increasing of the YTZP contents led to lower mechanical properties.

Crystalline nano-coatings of fluorine-substituted hydroxyapatite produced by magnetron sputtering with high plasma confinement

A radio-frequency magnetron sputtering technique operating in right-angle geometry (RAMS) with high plasma confinement was revised to produce thin films (15–570nm) of fluorine-substituted hydroxyapatite, FHA, adapted to be used as nano-coatings for biomedical implants. An electron temperature of Teff≈9.0eV and a plasma electron density of 1.2×1015m−3 assured the nucleation of an amorphous fluorine-substituted hydroxyapatite phase on Si and Ti surfaces. With the aid of a Langmuir probe, the RAMS plasma energy was tuned to control the coating stoichiometry and the ratio between the crystalline and amorphous phases. The energy delivered over time from the bombardment of ions and electrons transformed the amorphous calcium phosphate phase into crystalline fluorine-substituted hydroxyapatite. The crystalline films were obtained at room temperature. The partial substitution of OH− for F− in the HA structure was confirmed by X-ray diffraction using synchrotron radiation in grazing-incidence mode, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. High-resolution transmission electron microscopy carried out on cross-section film samples prepared by a focused ion beam (FIB) technique revealed that the film ultrastructure was composed of columnar crystals oriented perpendicularly to the substrate surface. The crystals were connected to the substrate surface by ordered nanolayers, indicating the existence of a continuous binding between the two materials. This work demonstrates that the RAMS technique is able to produce FHA nano-coatings with controlled chemical compositions and structures on metallic implants for clinical applications.

Controlled synthesis and enhanced luminescence of europium-doped fluorine-substituted hydroxyapatite nanoparticles

Europium-doped fluorine-substituted hydroxyapatite (Eu:FHAp) nanoparticles with different morphologies were synthesized by a simple hydrothermal method. The structure, composition, morphology, and luminescence of the products were investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. The prepared Eu:FHAp had a nanorod-like shape and their aspect ratios dropped when the pH of the solution was increased from 3.0 to 11.0. The luminescence intensity of the products increased significantly with increasing substitution of OH− with F−. The nanoparticles did not adversely affect the growth of hela cells, which indicates that they have potential applications as fluorescent cell labeling agents.