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The hydroxyapatite (HA) coating doped with multiple ions has attracted much attention due to its potential to impart various functions (antibacterial and osteogenic activity, etc.) to plastic surgery and dental implants. In this work, novel nano fluorohydroxyapatite (FHA) coatings substituted simultaneously with Sr2+ and Ag+ (SrAgFHA) were designed and successfully synthesized by one-step electrodeposition. Ag was used to impart antibacterial ability to SrAgFHA, and Sr can balance the potential cytotoxicity of Ag, thereby improving the cell compatibility of the composite coating. The SrAgFHA coating was consisted of closely aggregated/fused hexagonal columnar nanorods of ~100–150 nm. The nano-coating has higher corrosion resistance than FHA coating and uncoated Ti. Due to the doping of F, SrAgFHA nanorods have a complete single crystal structure and exhibit low degradability, which can ensure the long-term and slow release of Sr2+ and Ag+ ions. This nanorod coating with a low roughness and zeta potential was superhydrophobic and displayed good in vitro bioactivities, such as excellent apatite forming ability, which proves the osteoconductive nature. The results of electrochemical impedance spectroscopy confirmed that by electrodepositing the SrAgFHA coating on the Ti surface, the corrosion resistance was significantly improved. SrAgFHA coating has the best antibacterial effect and osteogenesis ability, for example, the broad-spectrum antibacterial effect on E. coli and S. aureus is 96.5 and 96.8%, respectively, and it can induce osteoblast adhesion, proliferation and differentiation. The rabbit bone defect experiment showed that a large amount of new bone was formed around the SrAgFHA coated implant, and its early bone integration ability was the strongest. In summary, SrAgFHA strikes a balance between superior corrosion resistance, cytocompatibility and excellent antibacterial properties. The multi-element co-doped HA coating has huge clinical application potential in anti-infective repair. [ABSTRACT FROM AUTHOR]

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. Image 1 • The full ranges of fluorhydroxyapatite were synthesized by substitution of OH- with F- within the HA structure. • Measuring of FA coating dissolution rate by dissolved Ca, P ions versus fluorine concentration within the apatite structure. • Better biocompatibility and corrosion performance were obtained by 75% partially and 100% substituted fluorine, respectively. [ABSTRACT FROM AUTHOR]

Calcium phosphate biomaterials can be classified as polycrystalline ceramics. Hydroxyapatite is one kind of calcium phosphate biomaterials which is also a mineral component in hard tissue, especially dental and bones. Hydroxyapatite has low chemical stability at high temperatures and low durability in an acidic environment. On the other hand, fluorhydroxyapatite has good chemical stability at high temperatures as well as the nature of its bioactivity. Fluorhydroxyapatite is made by adding F to replace some OH functional groups in hydroxyapatite. In this research, fluorhydroxyapatite was synthesized through precipitation method and microwave assistant with sintering temperatures of 600°C, 800°C, and 1000°C. Based on the characterization using an x-ray diffractometer, the results showed that at 1000°C sintering temperature, the samples have a higher intensity of fluorapatite and fewer impurities than other samples sintered at 800°C and 600°C. Fourier Transform Infra-Red (FTIR) analysis shows that similar functional groups appeared in the samples with all sintering temperatures. Conductivity evaluation shows that the conductivity values of the samples were inversely proportional to the sintering temperatures. The morphology of the samples not so clearly seen due to agglomeration, but it can be observed that fluorhydroxyapatite is flat-shaped needle-like or rod-shaped. [ABSTRACT FROM AUTHOR]

The objective of this research was to study the degradation and biological characteristics of the three-dimensional porous composite scaffold made of poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite microsphere using sintering method for potential bone tissue engineering. Our previous experimental results demonstrated that poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite composite scaffold with a ratio of 4:1 sintered at 90ºC for 2 h has the greatest mechanical properties and a proper pore structure for bone repair applications. The weight loss percentage of both poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite and poly(lactic-co-glycolic acid) scaffolds demonstrated a monotonic trend with increasing degradation time, that is, the incorporation of nano-fluorhydroxyapatite into polymeric scaffold could lead to weight loss in comparison with that of pure poly(lactic-co-glycolic acid). The pH change for composite scaffolds showed that there was a slight decrease until 2 weeks after immersion in simulated body fluid, followed by a significant increase in the pH of simulated body fluid without a scaffold at the end of immersion time. The mechanical properties of composite scaffold were higher than that of poly(lactic-co-glycolic acid) scaffold at total time of incubation in simulated body fluid; however, it should be noted that the incorporation of nano-fluorhydroxyapatite into composite scaffold leads to decline in the relatively significant mechanical strength and modulus during hydrolytic degradation. In addition, MTT assay and alkaline phosphatase activity results defined that a general trend of increasing cell viability was seen for poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite scaffold sintered by time when compared to control group. Eventually, experimental results exhibited poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite microsphere-sintered scaffold is a promising scaffold for bone repair. [ABSTRACT FROM AUTHOR]

Introduction: Bone tissue engineering proposes a suitable way to regenerate lost bones. Different materials have been considered for use in bone tissue engineering. Hydroxyapatite (HA) is a significant success of bioceramics as a bone tissue repairing biomaterial. Among different bioceramic materials, recent interest has been risen on fluorinated hydroxyapatites, (FHA, Ca 10 (PO 4 ) 6 F x (OH) 2−x ). Fluorine ions can promote apatite formation and improve the stability of HA in the biological environments. Therefore, they have been developed for bone tissue engineering. The aim of this study was to synthesize and characterize the FHA nanopowder via mechanochemical (MC) methods. Materials and Methods: Natural hydroxyapatite (NHA) 95.7 wt.% and calcium fluoride (CaF 2 ) powder 4.3 wt.% were used for synthesis of FHA. MC reaction was performed in the planetary milling balls using a porcelain cup and alumina balls. Ratio of balls to reactant materials was 15:1 at 400 rpm rotation speed. The structures of the powdered particles formed at different milling times were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: Fabrication of FHA from natural sources like bovine bone achieved after 8 h ball milling with pure nanopowder. Conclusion: F− ion enhances the crystallization and mechanical properties of HA in formation of bone. The produced FHA was in nano-scale, and its crystal size was about 80-90 nm with sphere distribution in shape and size. FHA powder is a suitable biomaterial for bone tissue engineering.

A novel graphene oxide-based fluorhydroxyapatite (GO/FHA) composite is prepared using an in situ chemical synthesis method. The mechanical properties, chemical stability, in vitro bioactivity, and antibacterial properties of the as-synthesized GO/FHA composites with different GO amounts are reported. The result shows that the mechanical properties of the composites are strongly dependent on the adding amount of GO. The result of chemical stability indicates that the substitution of fluorine (F) into the hydroxyapatite (HA) crystal has a positive effect on the dissolution resistance. The in vitro bioactivity assessment shows that the osteoblast proliferation and differentiation ability on GO/FHA composites are improved. [ABSTRACT FROM AUTHOR]

Poor mechanical properties and a relatively low stability in physiological environments have significantly limited hydroxyapatite (HA) for many practical implant applications. In this study, we developed a reduced graphene oxide/fluorhydroxyapatite (rGO/FHA) biocomposite with enhanced mechanical properties, dissolution resistance, biocompatibility and antibacterial activity. rGO and fluorine (F) are simultaneously incorporated into HA to form the rGO/FHA composite by an in situ chemical synthesis method and spark plasma sintering technology. The uniform distribution of rGO and the good interfacial bonding help to improve the hardness by 86% and the fracture toughness by 137%. The chemical stability of the rGO/FHA composite is evaluated by determining the Ca 2+ ion release. The result indicates that the substitution of F − ions into the HA structure has a positive effect on the dissolution resistance of HA. The in vitro bioactivity assessment shows that the osteoblast adhesion and proliferation ability on the rGO/FHA composite are improved. In addition, a higher alkaline phosphate activity is also detected in cells cultured on the rGO/FHA composite. More importantly, it is observed that the rGO/FHA composite can effectively inhibit the adhesion and proliferation of Streptococcus mutans . These findings suggest that the rGO/FHA biocomposite would be highly useful as a dental implant material. [ABSTRACT FROM AUTHOR]

Objectives: Dentin hypersensitivity (DH) is a prevalent problem. This study aimed to formulate a paste using fluorhydroxyapatite (FA) crystals dispersed in different carriers to treat DH. The ability to occlude patent dentinal tubules and to release ions was investigated. Materials and methods: Twenty percent FA/sodium alginate, 40 % FA/poly(hydroxyethyl methacylate(HEMA)), and 40 % FA/poly(DMA-co-MEA) were applied to etched dentin samples and examined with scanning electron microscopy (SEM) to determine the degree of tubule occlusion. Fluoride electrode was used to measure F release and spectroscopy to evaluate Ca and PO release. The cytotoxicity of the synthesized poly(DMA-co-MEA) gel was tested. Kruskall-Wallis test was used to test the differences in ion release between the groups. Results: FA/poly(DMA-co-MEA) paste obstructed up to 80 % of the dentinal tubules, while the coverage was up to 70 % for FA/poly(HEMA) and less than 50 % for FA/sodium alginate. Fluoride and Ca release was the highest for FA/P(HEMA), 7.2 ± 0.7 and 139.8 ± 32.5 ppm, respectively. The highest concentration of PO was 46.2 ± 16.4 ppm for FA/Sodium alginate. No statistical significance was found. Conclusions: FA/Poly(DMA-co-MEA) and FA/poly(HEMA) pastes may offer immediate short-term relief of DH because of their ability to occlude the tubules and adhere to wet dentin surfaces. The release of the F, Ca, and PO ions may offer long-term relief by forming a mineral barrier both within the dentinal tubules and on the dentin surface. Clinical significance: The tested materials may offer a long-term treatment for DH. [ABSTRACT FROM AUTHOR]

Introduction: Bone tissue engineering proposes a suitable way to regenerate lost bones. Different materials have been considered for use in bone tissue engineering. Hydroxyapatite (HA) is a significant success of bioceramics as a bone tissue repairing biomaterial. Among different bioceramic materials, recent interest has been risen on fluorinated hydroxyapatites, (FHA, Ca10(PO4)6Fx(OH)2-x). Fluorine ions can promote apatite formation and improve the stability of HA in the biological environments. Therefore, they have been developed for bone tissue engineering. The aim of this study was to synthesize and characterize the FHA nanopowder via mechanochemical (MC) methods. Materials and Methods: Natural hydroxyapatite (NHA) 95.7 wt.% and calcium fluoride (CaF2) powder 4.3 wt.% were used for synthesis of FHA. MC reaction was performed in the planetary milling balls using a porcelain cup and alumina balls. Ratio of balls to reactant materials was 15:1 at 400 rpm rotation speed. The structures of the powdered particles formed at different milling times were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: Fabrication of FHA from natural sources like bovine bone achieved after 8 h ball milling with pure nanopowder. Conclusion: F- ion enhances the crystallization and mechanical properties of HA in formation of bone. The produced FHA was in nano-scale, and its crystal size was about 80-90 nm with sphere distribution in shape and size. FHA powder is a suitable biomaterial for bone tissue engineering. [ABSTRACT FROM AUTHOR]

Fluorhydroxyapatite/strontium-substituted hydroxyapatite (FHA/SrHA) biphasic coatings with F and Sr elements incorporated simultaneously into one coating layer were prepared on titanium substrate via colloidal sol-gel method. The bioactivity of the as-prepared FHA/SrHA biphasic coatings was evaluated in vitro by immersion in simulated body fluid (SBF). All the biphasic coatings exhibited great ability to induce apatite precipitation on their surfaces. In vitro cell responses were evaluated using osteoblast-like MG63 cells in terms of cell proliferation and differentiation (alkaline phosphatase activity and osteocalcin level). The biphasic coatings show significantly positive effects on the viability and functional activity of osteoblastic cells with clear evidence that an optimum SrHA amount dose exists, indicating that the coexistence of FHA and SrHA had a synergistic stimulatory effect. This finding suggests the potential use of this colloidal sol-gel derived FHA/SrHA biphasic coatings for hard tissue applications. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 621-627, 2014. [ABSTRACT FROM AUTHOR]

Abstract: In this study, several fluorine-substituted hydroxyapatite ceramics with the general chemical formula Ca5(PO4)3(OH)1− x F x (0≤ x ≤1), where x =0.0 (hydroxyapatite; HA), x =0.68 (fluorhydroxyapatite; FHA) and x =0.97 (fluorapatite; FA) were prepared. The powders were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infra-red (FTIR), X-ray diffraction (XRD), F-selective electrode, atomic absorption spectroscopy (AAS) and EDTA titration analyses. The powders were uniaxially pressed and were formed as a disc shape. Subsequently, sinterability and thermal stability of synthesized powders were compared together. Also the effect simultaneously of fluoride content and temperature were examined on the lattice parameters and crystallites size of the obtained powders. Mechanical properties including hardness, elastic modulus and fracture toughness were measured using indentation. The in vitro dissolution studies of the samples were carried out at osteoclastic resorption conditions. Finally, the biocompatibility and cytotoxicity of the samples were carried out using osteoblast-like cells and L929 cell line, respectively. The obtained results showed that the thermal stability substantially is increased with increase incorporated fluoride into HA structure. Also it was found that the fluoride reduced the lattice parameters and crystallites size of HA. Finally, the in vitro dissolution studies results suggest that the fluoride substitutions in HA offer the ability to prepare HAs with different degrees of solubility. [Copyright &y& Elsevier]

Abstract: Fluorhydroxyapatite coatings were prepared on the surface of carbon/carbon composites using the combined action of ultrasonic-electrodeposition and ion exchange. The morphology, structure and composition of the prepared coatings after ion exchange were investigated by scanning electron microscopy, X-ray energy spectrum analysis, infrared spectroscopy and X-ray diffraction. Results show that the crystallinity of the coating as well as the intensity of the diffraction peaks (112) and (300) of hydroxyapatite increased, whereas the intensity of the diffraction peaks of tricalcium phosphate decreased. The small lamellar crystals were converted into large ones. The fluorine content in the coating was 4.59%. The bonding strength between the coating and the carbon/carbon matrix increased slightly after immersion, reaching 4.12 MPa. The mechanism of the ion exchange during which hydroxyapatite turned into fluorhydroxyapatite is discussed. [Copyright &y& Elsevier]

This study is aimed at the development of a method to fabricate porous spherical hydroxyapatite (HA)—fluorapatite (FA) granules. The method to produce porous granules is based on liquid immiscibility effect. A suspension of HA–FA powder mixtures in aqueous solution of gelatin and oil as a dispersion media were used. By stirring the mixtures of these immiscible liquids, granules of 50–200 μm diameter can easily be produced. The granules were characterized with respect to their microstructure, phase composition and specific area. In vitro testing of human plasma protein adsorption onto the granules of HA and fluorhydroxyapatite were performed. No kind of difference in the dynamic protein adsorption between pure HA and the HA up to 10 wt% FA materials has been revealed. [Copyright &y& Elsevier]

The kinetics of seeded crystal growth of calcium apatites were studied in dilute supersaturated solutions at various levels of fluoride concentrations. Initial precipitation rates were enhanced by fluoride concentrations higher than 0.05 ppm. The analytical results are consistent with the precipitation of fluoridated hydroxyapatites, CaF-(OH)(PO), FHA. The degree of fluoridation, X, appears to be determined by the activity of HF in solution, which varies for the various initial fluoride levels but remains fairly constant during precipitation. Thus the composition of the precipitating phase was the same for a given solution whether 25 or 10 mg of hydroxyapatite was added as seeds. All the experimental results are consistent with the BCF theory, which relates the mean linear rate of growth, R, to the supersaturation, DS, by the expression R=CT(DS-1)1n(DS)tanh(C/T 1n DS), in which DS is the supersaturation defined by mean molar activities with respect to the precipitating FHA, T the absolute temperature, and C and C are constants calculated from the experimental results. Consequently, the crystal growth appears to take place in surface kinks and to be controlled by surface diffusion. Since crystal growth in most biological systems takes place at fluoride concentrations within the experimental range used, it seems probable that it occurs along the model advanced in the present investigation. [ABSTRACT FROM AUTHOR]

The effect of fluoride derived from fluorhydroxyapatite (FHAp) minerals on bacterial glycolysis under aerobic and strictly anaerobic conditions was studied to validate the claims that this mineral could be used as a reservoir of fluoride in plaque. To isolate the direct effect of fluoride on bacterial glycolysis from that of an indirect pH-buffering effect of hydroxyl or phosphate ions which are also dissolved from the mineral, we equalized the pH-fall time course of reactions by manually adding KOH or HCI. This ensured that pH effects on glycolysis were minimized. Under controlled pH-fall and strictly anaerobic conditions, fluoride derived from the dissolution of FHAp containing more than 30,100 ppm fluoride (i.e., when the substitution of OH by F in the mineral was greater than 80%) had a direct inhibitory effect on lactic acid production in Streptococcus mutans. Under free pH-fall and strictly anaerobic conditions, increasing amounts of fluoride in FHAp (starting as low as 2000 ppm fluoride), appeared to have a pronounced indirect inhibitory effect on lactic acid production. This was probably mediated through a reducing pH buffer effect of the mineral. Even in the presence of high-fluoride FHAp, only 0.01 to 0.025 mmol/L fluoride was found in the reaction mixtures, a probable result of non-stoichiometric dissolution of FHAp. In spite of such low levels of fluoride, marked inhibitory effects on bacterial glycolysis were demonstrated. The results of this study suggest that high- fluoride FHAp may serve as a reservoir of fluoride for the inhibition of anaerobic acid production by S. mutans. [ABSTRACT FROM AUTHOR]

This work shows that mechanochemical synthesis allows the obtaining of hydroxyapatite in which fluorine ions replace hydroxyl ions either partially or completely after 30 ​min of synthesis. The crystal structure of the materials obtained and their thermal stability when heated in the air were studied. It has been shown that the fluorine ions in the hexagonal channel of hydroxyapatite hinders diffusion of hydroxide ions at high temperatures, which leads to increased thermal stability of the apatite. Image 1 • A new approach to the synthesis of F-substituted apatites is proposed. • Dry mechanochemical method allows reducing the synthesis time down to 30 ​min. • The product of synthesis is single-phase with an average crystallite size of 25 ​nm. • Partially and fully substituted F-apatites are stable up to 1400C. [ABSTRACT FROM AUTHOR]

Background: Poor mechanical properties, undesirable fast dissolution rate, and lack of antibacterial activity limit the application of hydroxyapatite (HA) as an implant coating material. To overcome these limitations, a hybrid coating of Ag + -substituted fluorhydroxyapatite and titania nanotube (TNT) was prepared., Methods: The incorporation of silver into the HA-TiO 2 hybrid coating improves its antimicrobial properties. The addition of F as a second binary element increases the structural stability of the coating. The TNT/F-and-Ag-substituted HA (FAgHA) bilayer coating on the Ti substrate was confirmed by X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS)., Results: The results indicate that the FAgHA/TNT nanocomposite coating has a dense and uniform morphology with a nano-rod-like structure. The solubility measurement result shows that the substitution of F - ions into the AgHA structure has a positive effect on the dissolution resistance of HA. The adhesion strength of FAgHA/TNT has significantly increased because of the interlocking of the roughened surface with nano-rod-like particles that entered into the voids of the TiO 2 nanotubes. Compared with that of the bare Ti, the corrosion current density of FAgHA/TNT-coated Ti substrate decreased from 3.71 to 0.18 μA, and its corrosion resistance increased by almost two orders of magnitude. Moreover, despite pure HA, the FAgHA killed all viable Staphylococcus aureus after 24 hours of incubation. Although the fabricated FAgHA/TNT coating is hydrophobic, it induced deposition of the typical spherical apatite when immersed in a simulated body fluid (SBF); the osteoblasts spread very well on the surface of the coating. In addition, in vitro cell culture tests demonstrated cell viability and alkaline phosphatase (ALP) similar to pure HA, which indicated good cytocompatibility. Interestingly, compared with bare Ti, FAgHA/TNT-coated Ti surface was innocent for cell vitality and even more beneficial for cell osteogenesis in vitro., Conclusion: Enhancing the osseointegration and preventing infection in implants, the FAgHA/TNT-coated Ti makes implants more successful., Competing Interests: Disclosure The authors report no conflicts of interest in this work.