Hexagonal HA Research Articles

Comparative structural refinement of nanocrystalline hydroxyapatite

An attempt was made to make a comparative structural refinement of nanocrystalline HA between the mechano-synthesis (MS), ultrasonic-assisted precipitation (UP), biogenic-based process (BP), and commercial grade (CG). Rietveld refinement of XRD patterns illustrated the main characteristic peaks of hexagonal HA. The anisotropic crystallite sizes were observed, where the smallest crystallite sizes of D〈001〉 (24.5 ± 3.1 nm) and D〈100〉 (17.7 ± 1.1 nm) were recorded in the 7h MS specimen. On the contrary, the highest D〈001〉/D〈100〉 ratio of 7.68 was achieved for the UP HA, showing HA crystals preferentially grew in the c-axis direction. The narrow particle size distribution of the 7h MS specimen, with an average diameter of 9 ± 2 nm, was smaller than the crystallite size estimated from the refined XRD pattern, indicating the single-crystal feature. Overall, MS HA holds great promise as an effective medical strategy for treating bone cavities.

Curcumin-loaded hydroxyapatite nanocomposite as a novel biocompatible shield for male Wistar rats from γ-irradiation hazard

Curcumin (CUR) is well known for its extraordinary benefits as an anti-cancer, anti-inflammatory, and wound healing agent. However, nano-formulation could maintain and regulate its pharmacological effect. Herein, we report the preparation of CUR/hydroxyapatite nanocomposite (CUR/HA NC) and its application in the protection of male Wistar rats from γ-irradiation carcinogenic consequences. TEM images of the nanocrystalline HA nanoparticles (NPs) had a rod-like form with average dimensions of 40±5 nm in length and 10 ± 5 nm in width. XRD analysis illustrated the formation of a single phase of hexagonal crystalline HA NPs. The presence of the CUR fingerprint is visible in its FTIR spectra of the CUR/HA NC. Biochemical analysis and histological examinations revealed that CUR/HA NC injection does not significantly affect non-irradiation rats compared to the control. However, when injected pre-irradiation, it controls the pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-6) GSH level, kidney, and liver functions as proved by biochemical histopathological and immunohistochemical findings. This research introduces a novel effective protection modality for the γ-irradiation hazard via biocompatible CUR/HA NC injection.

The effects of Fe3+ and Co2+ substitution in Ca10-x-yFexCoy(PO4)6(OH)2 hydroxyapatite nanoparticles: Magnetic, antibacterial, and improved drug release behavior

The mineral constituent of the bone contains non-stoichiometric hydroxyapatite with various substitutional ions. Iron (Fe) and cobalt (Co) are fundamental cofactors, which influence cell respiration and mitosis, respectively. In this study, undoped, Fe3+-, Co2+-, and dually-doped HA nanoparticles (NPs) were synthesized by the hydrothermal method. The Fe+CoCa+Fe+Co molar ratio was varied between 0.02 and 0.2. Samples were analyzed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), vibrating sample magnetometry (VSM), Fourier-transformed infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectroscopy (ICP-OES), and biological assessment. XRD results confirmed the formation of the hexagonal HA crystal structure. The crystallite size was reduced from 34.6 nm to 4.4 nm. Also, the c-axis dimension and the degree of crystallinity were reduced in all the doped samples. The FESEM results showed a change of morphology from rod-like in the undoped nHA into a sphere-like morphology in the doped-samples. With the addition of ferromagnetic dopant, the magnetic behavior of samples altered from diamagnetic to paramagnetic-like and ferromagnetic behavior. Bioactivity assessment indicated the formation of the HA particle on the surface of all synthesized materials. The antibacterial test demonstrated antibacterial activity against gram-negative (−) E. coli. Moreover, the antibiotic-impregnated samples had a synergistic effect on both gram (−), E. coli, as well as gram (+), S. aureus, bacteria. The MTT evaluation revealed the enhanced cell viability of osteoblast-like cells in the dually-doped NPs. Based on this survey, we can strongly emphasize the potential for bone bioactivity and antibacterial feature of these newly developed samples.

Bioactivity of Biphasic Calcium Phosphate Granules, the Control of a Needle-Like Apatite Layer Formation for Further Medical Device Developments.

Biphasic calcium phosphate (BCP) bioceramics (hydroxyapatite/tricalcium phosphate, or HA/TCP) for tissue engineering and drug delivery systems is a unique know-how. A mechanical mixture of HA and TCP does not lead to such bioactive ceramics. The wet elaboration conditions of calcium-deficient apatite (CDA) or CDHA, followed by sintering, converts it into TCP and HA. The dissolution precipitation of nano-sized needle-like crystals at the surface of BCP occurs on time at body temperature. Combining several technics of characterization [scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), Brunauer-Emmett-Teller method (BET), chemical analysis, x-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR)], we demonstrated an evolution on time of the HA/β-TCP. The current paper describes the crystallographic evolution of initial β-TCP rhombohedral crystallographic structure to microsized needle-like layer corresponding to apatitic TCP form. This phenomenon leads to an increase of the HA/TCP ratio, since hexagonal apatitic TCP is similar to hexagonal HA. However, the Ca/P ratio (reflecting the chemical composition HA/TCP) remains unchanged. Thus, the high reactivity of BCP involves dynamic evolution from rhombohedral to hexagonal structure, but not a chemical change. The dynamic process is reversible by calcination. These events are absolutely necessary for smart scaffolds in bone regeneration and orthobiology.

α-AgVO3 Decorated by Hydroxyapatite (Ca10(PO4)6(OH)2): Tuning Its Photoluminescence Emissions and Bactericidal Activity.

Defect-related luminescent materials have attracted interest because of their excellent optical properties and are considered as a less expensive and nontoxic alternative to commonly used lanthanide-based optical systems. These materials are fundamentally and technologically important for the next generation of full-color tunable light-emitting diodes as well as in the biomedical field. In this study, we report the preparation of α-silver vanadate (α-AgVO3, AV) decorated by hydroxyapatite (Ca10(PO4)6(OH)2, HA) with intense photoluminescence (PL) emissions at various HA/AV molar ratios (1:1-1:1/32) by a simple route based on chemical precipitation. The well-defined diffraction peaks observed by X-ray diffraction were all indexed to the monoclinic AV and hexagonal HA phases. Analysis of the results obtained by Fourier transform infrared spectroscopy reveals the presence of short-range structural order as deduced by the characteristic vibrational modes assigned to AV and HA systems. Characterization by scanning and transmission electron microscopies confirms the presence of AV and HA micro- and nanorods, respectively. UV-vis spectroscopy renders band gap energies of 5.80 eV for HA and in the range 2.59-2.65 eV for pure AV and HA/AV samples. The PL data reveal the presence of broad-band emission profiles, typical of defect-related optical centers in materials. Depending on the molar ratio, the emission can be completely tunable from the blue to red spectral regions; in addition, pure white color emission was obtained. On the basis of these results, we propose an order-disorder model induced by structural and interface defects to explain the PL emissions in the HA/AV system. Moreover, our results show that HA/AV composites have superior bactericidal activity against Staphylococcus aureus (methicillin-resistant and methicillin-susceptible) and can be used as a novel multifunctional material.

Cementing Line Configuration of Bioactive Engineered Zirconia Implants (<i>In Vivo</i> Histological Study)

Background: Osseointegration of dental implant is a challenging issue for those who need to restore a missing tooth, a matter that necessitates wide range of research on different implant manufacturing, modification and bioactive coating materials.Aim of the study: Investigation of cementing line configuration around osseointegrated engineered nano-porous zirconia implants coated with bioactive autologous HA, platelet rich plasma (PRP) and bovine HA (Bio-oss) coatings in rabbit model.Materials and methods: Zirconia implants (cylinders 3.7 mm x 8 mm) were milled and sintered according to manufacturer recommendations. Then all specimens were treated with selective infiltration etching (SIE) to produce a nano-porous surface. Implants were surgically placed bilaterally in the femur distal heads of 20 male line V Spain white rabbits. Implants were divided equally into 4 groups (n=10): group (A) control (non-coated), group (B) autologous HA coated, group (C) PRP coated and group (D) Bio-Oss coated implants. Specimens were characterized with x-ray diffraction (XRD) analysis and mercury porosimetery. Histological examination was performed after six weeks of peri-implant healing period.Results: XRD patterns revealed the detection of hexagonal HA and (Y-TZP) tetragonal crystal phases for the HA coated surfaces. Mercury porosimetery revealed a significant reduction in total porosity percent after application of bioactive coating materials. The histological picture of osseiointegration and cementing line continuity in association with both of autologous HA and PRP were outstanding and satisfactory followed by that of Bio-Oss and all coated implants showed a noticeable difference from that of the control specimens that were surrounded by unsupported cementing line adjacent to newly formed bone with low density.Conclusions: Engineering of zirconia implant surface with bioactive coatings either HA or PRP to enhance its biological activity could be considered as reliable method to provide satisfactory osseiointegration.

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca2+ size, it was assumed that the tantalum ions occupy either the Ca2+ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca2+ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900°C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca2P2O7) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO2 oxide). According to the TEM observations, the doped calcined powder at 900°C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5nm, respectively.

Effect of dopant loading on the structural features of silver-doped hydroxyapatite obtained by mechanochemical method

Abstract Silver-doped hydroxyapatite (Ag-doped HA) nanopowders were synthesized using calcium hydroxide (Ca(OH) 2 ), phosphorus pentoxide (P 2 O 5 ) and silver nitrate (AgNO 3 ) precursors, through a one-pot mechanochemical process. The influence of dopant content on the phase formation, structural properties and morphological features was examined. The results showed that the as-prepared powders were single-phase hexagonal HA in the absence of the dopant. With the addition of the dopant, a similar phase structure was achieved, however some changes were observed with regards to the peak position and broadening. With the increase of Ag substitution, some alterations in the structural features of the milled powders were observed, where the crystallite size, lattice strain and crystallinity degree were between 25 ± 18 and 33 ± 14 nm, between 0.486 ± 0.0.161 and 0.824 ± 0.477, and between ~ 83 and 93%, respectively. From the Fourier transformed infrared (FTIR) spectroscopy spectra, the location of the CO 3 -derived bands revealed that the replacement of PO 4 3− by CO 3 2− (B-type) was dominant in the Ag-doped HA nanopowders. This facile solid-state method is an alternative process for the preparation of bioceramic nanopowders.

Rapid synthesis and characterization of Zn substituted hydroxyapatite nanoparticles via a microwave-assisted hydrothermal method

Hydroxyapatite powders doped with Zn contents of 2, 4 and 6mol% were synthesized by microwave-assisted hydrothermal treatment. The ZnHA nanoparticles were characterized by X-ray diffraction, FTIR spectroscopy and transmission electron microscopy. Structural analyses conducted by Rietveld refinement indicated that Zn incorporation occurred at the Ca(II) sites of the hexagonal HA structure. However, the nominal Zn content selected did not react completely and therefore all the particles were deficient regarding the final amount of Zn in the HA structure. TEM observations confirmed that the ZnHA particles had a high crystallinity with a particle size varying between 29 and 67nm.

Surface characterization and biological properties of regular dentin, demineralized dentin, and deproteinized dentin.

Bone autografts are often used for reconstruction of bone defects; however, due to the limitations of autografts, researchers have been in search of bone substitutes. Dentin is of particular interest for this purpose due to high similarity to bone. This in vitro study sought to assess the surface characteristics and biological properties of dentin samples prepared with different treatments. This study was conducted on regular (RD), demineralized (DemD), and deproteinized (DepD) dentin samples. X-ray diffraction and Fourier transform infrared spectroscopy were used for surface characterization. Samples were immersed in simulated body fluid, and their bioactivity was evaluated under a scanning electron microscope. The methyl thiazol tetrazolium assay, scanning electron microscope analysis and quantitative real-time polymerase chain reaction were performed, respectively to assess viability/proliferation, adhesion/morphology and osteoblast differentiation of cultured human dental pulp stem cells on dentin powders. Of the three dentin samples, DepD showed the highest and RD showed the lowest rate of formation and deposition of hydroxyapatite crystals. Although, the difference in superficial apatite was not significant among samples, functional groups on the surface, however, were more distinct on DepD. At four weeks, hydroxyapatite deposits were noted as needle-shaped accumulations on DemD sample and numerous hexagonal HA deposit masses were seen, covering the surface of DepD. The methyl thiazol tetrazolium, scanning electron microscope, and quantitative real-time polymerase chain reaction analyses during the 10-day cell culture on dentin powders showed the highest cell adhesion and viability and rapid differentiation in DepD. Based on the parameters evaluated in this in vitro study, DepD showed high rate of formation/deposition of hydroxyapatite crystals and adhesion/viability/osteogenic differentiation of human dental pulp stem cells, which may support its osteoinductive/osteoconductive potential for bone regeneration.

Synthesis and antimicrobial activity of mesoporous hydroxylapatite/zinc oxide nanofibers

Abstract The aim of this study is to develop antimicrobial mesoporous hydroxylapatite/zinc oxide (meso-HA/ZnO) nanofibers from polyvinyl alcohol/hydroxylapatite/zinc acetate (PVA/HA/Zn(OAc)2) electrospun nanofibers by calcination process. The antibacterial activities of meso-HA/ZnO nanofibers towards Staphylococcus aureus (S. aureus, ATCC6538) and Escherichia coli (E. coli, 8099) were evaluated. The meso-HA/ZnO nanofibers were composed of hexagonal HA and wurtzite ZnO phases. The representative meso-HA/ZnO nanofibers with ZnO/HA ratio at 1:5 showed a wormhole-like shape, main pore diameter around 25 nm and specific surface area at 24.81 m2/g. The inhibition efficiency of meso-HA/ZnO nanofibers increased with the increase of ZnO/HA ratio, however, S. aureus was more sensitive to meso-HA/ZnO nanofibers than E. coli. The meso-HA/ZnO nanofibers with ZnO/HA ratio at 1:10 exhibited effective antibacterial activity towards S. aureus, whereas, the ZnO/HA ratio was raised up to 1:5 towards E. coli. The experimental results suggested that the meso-HA/ZnO nanofibers might have potential as an antimicrobial activity material in biomaterial applications.

Stability of the Dipolar (001) Surface of Hydroxyapatite

The features of the ferroelectric (proton ordered) hydroxyapatite HA (001) surface as derived from the P63 hexagonal HA bulk have been studied by periodic density functional calculations using the hybrid B3LYP functional and Gaussian basis set of polarized double-ζ quality. Geometry, surface energy, and electronic features of HA (001) slab models of thickness from 1 nm to almost 50 nm have been computed, by keeping under careful control numerical errors due to the very large system size. The present results reveal that the ferroelectric OH– alignment does not compromise the stability of the HA (001) surface up to the nanometric scale. Indeed, a slab thickness of 43 nm, containing 2640 atoms in the unit cell, exhibits a dipole moment across the slab of 0.73 D, a wide band gap of 7.60 eV, and a surface energy of 1.344 J·m–2. No sign of “metallization” occurs as for the classical macroscopic polar zinc- or oxygen-terminated ZnO (0001) surfaces, due to counterpolarization of the electronic density of the Ca2+ and PO43– moieties surrounding the monodimensional OH– polar arrays. These findings may be relevant to explain why, experimentally, HA nanocrystals orient along the main axis of the proto-collagen fibrils with their crystallographic c axis (perpendicular to the {001} crystal plane family).

X-Ray Peak Broadening and <i>In Vitro</i> Dissolution Studies of Thermally Stabilized Nanocrystalline Carbonated Hydroxyapatite

The present work aims to examine the effect of silicon substitution on thermal and in-vitro dissolution properties of carbonated hydroxyapatite. Hydroxyapatite [Ca10(PO4)6(OH)2, HA], carbonate substituted hydroxyapatite [Ca10(PO4)6-x(CO3)x(OH)2, x=1, 1CHA] and carbonate, silicate co-substituted hydroxyapatite [Ca10(PO4)6-x-y(CO3)x(SiO4)y(OH)2, x=1,y=1, 1C1SiHA] nanoparticles were prepared by microwave synthesis method under identical processing conditions. The XRD results of HA, 1CHA and 1C1SiHA correspond to the standard hexagonal HA (JCPDS 9-432). The crystallite size and lattice strain of the synthesized powder particles were estimated by Williamson-Hall isotropic strain model (W-H ISM) from powder X-ray diffraction data. The dislocation density was calculated by Williamson-Smallman formula. The functional groups present in the as-synthesized powder particles were analyzed by Fourier transform infrared (FT-IR) spectroscopy method. The size and the morphology were examined using a transmission electron microscope (TEM). The in-vitro dissolution behaviour of the synthesized powder particles was studied by ethylenediamine tetra-acetic acid (EDTA) titrimetric method. The W-H ISM results confirm that the prepared powder particles of HA, 1CHA and 1C1SiHA are nanocrystalline with an average crystallite size of 40 nm, 36 nm and 32 nm, respectively. Thus the crystallite size of hydroxyapatite was observed to be decreased gradually with increase in substitutions as indicated by the least size for the 1C1SiHA. In addition, the XRD results of powders annealed at 900 °C for 2 h show the improved thermal stability of 1C1SiHA compared to 1CHA. The TEM results show rod-like shaped morphology for HA, near rod-like with modified edge morphology and increased agglomeration for 1CHA and needle-like shaped morphology for 1C1SiHA powder particles. The in-vitro dissolution study results show a gradual increase in the solubility of HA with carbonate and carbonate-silicate co-substitutions. The calculated microstructural parameters, namely, crystallite size, root mean squared strain and dislocation density were correlated with in-vitro dissolution behaviour of hydroxyapatites.

Periodic B3LYP study of hydroxyapatite (001) surface modelled by thin layer slabs

The (001) surface of the hexagonal hydroxyapatite HA [Ca 10 (PO 4 ) 6 (OH) 2 , layer group P 3] is simulated with the slab approach by fully optimizing (cell size and internal coordinates) two models, respectively 6 A and 14 A thick, in a fully ab initio periodic approach. The B3LYP hybrid functional and a Gaussian basis set of polarized double zeta quality and pseudo potentials for Ca ions only have been adopted, as encoded in the CRYSTAL03 computer program. Both slab models are cut out of the optimized structure of the hexagonal HA bulk phase ( P 6 3 space group). Because the (001) surface derived from the hexagonal HA shows ferroelectricity due to the orientation of the OH groups, the convergence of the E surf with the slab thickness (until a thickness of about 60 A) has been studied at B3LYP level on slabs whose geometry has been optimized using the GULP program with a recently developed shell-ion model potential. Structural and electronic features are addressed and a comparison between results for the considered slabs is carried out with respect to the: i) surface energy, E surf ; ii) geometrical relaxation; iii) band gap, field across the slab and Mulliken analysis; iv) electrostatic features in close proximity of the surface; v) harmonic/anharmonic OH vibrational features. The same procedure has been adopted for non-ferroelectric slabs derived from the HA monoclinic phase (bulk belonging to the P 2 1 / b space group). E surf for hexagonal HA increases slightly, as a function of the slab thickness, from 1.080 J/m 2 (doublelayer) to 1.107 J/m 2 (nonalayer), showing that the OH ferroelectricity imparts an instability of ≈0.003 J/m 2 for each added layer (7 A thick). For the non-ferroelectric HA monoclinic phase, E surf converges to 1.337 J/m 2 within 1.0 −4 J/m 2 already for the doublelayer. It is shown that the OH ferroelectricity does not prevent the formation of a (001) slab of thickness of at least 10 nm, a fact relevant for technological applications. The HA doublelayer slab is suggested as a proper model of the HA (001) face to study adsorption processes relevant to understand the role of hydroxyapatite surface in biological processes.

Periodic ab initio study of structural and vibrational features of hexagonal hydroxyapatite Ca10(PO4)6(OH)2

Structural and vibrational features of hexagonal hydroxyapatite HA [Ca(10)(PO(4))(6)(OH)(2), space group P6(3)] are computed ab initio within a periodic approach using the CRYSTAL03 program and the B3LYP hybrid functional with a Gaussian-type basis set of polarized double zeta quality. Experimental lattice parameters and internal coordinates have been fully optimized and the final structure characterized by means of its band structure, density of states and Mulliken analysis. The full B3LYP harmonic vibrational spectrum of HA at Gamma point has also been computed and compares well with the available experimental IR and Raman data. Nevertheless, the presence of one negative frequency in the computed spectrum shows that, within the hexagonal symmetry imposed by the P6(3) group, the structure is a saddle point. This is at variance with the monoclinic structure (under P2(1)/b space group), which has been computed, with the same approach, to be a minimum of 17 kJ mol(-1) (per unit cell) more stable than the corresponding hexagonal HA structure.

Transmission electron microscopy investigation of pulsed-laser deposited hydroxylapatite thin films prepared by tripod and focused ion beam techniques

Hydroxylapatite-based ceramics are largely applied as coatings and thin films on metallic components of prostheses for inducing osteoblasts apposition and subsequent bone re-growth. We report for the first time the focused ion beam technique (FIB) as a milling method to prepare specimens for transmission electron microscopy investigations of HA thin films grown on metallic substrates. New FIB technique results were compared to those obtained by the thinning method of mechanical polishing with tripod. HA films were obtained by pulsed laser deposition on Si wafers and polished Ti–5Al–2.5Fe substrates coated with TiN buffer layers. A KrF* excimer laser ( λ=248 nm, τ FWHM≥20) was used for deposition. HA films were grown in vacuum (10 −4 Pa) on room temperature substrates, subsequently annealed at 550 °C in ambient air for 1 h. Processed structures were investigated by transmission electron microscopy (TEM), grazing incidence X-ray diffraction, selected area electron diffraction, and energy dispersive X-ray spectroscopy. We show that both tripod polishing and focused ion beam milling techniques well preserve the structural and chemical integrity of the thin layers, and their interfaces. Additionally, focused ion beam milling allows for preparation of long specimens (approx. 12 μm in our case). HA films were stoichiometric and had a nano-crystalline structure with an average grain size of 35 nm. Cross-section TEM patterns show a granular growth morphology of the films. Particulates trapped within the film were visualized. High resolution TEM analysis shows that the transition from cubic TiN to hexagonal HA is intermediated by a very thin amorphous calcium phosphate interlayer of ∼3–4 nm thickness.