Crystallite Size Of Hydroxyapatite Research Articles

Enamel proteins mitigate mechanical and structural degradations in mature human enamel during acid attack

A hydrazine deproteination process was used to investigate the role of enamel proteins in the acid erosion of mature human dental enamel. Bright field high resolution transmission electron micrographs and x-ray diffraction analysis show no crystallographic changes after the hydrazine treatment with similar nanoscale hydroxyapatite crystallite size and orientation for sound and de-proteinated enamel. However, the presence of enamel proteins reduces the erosion depth, the loss of hardness and the loss of structural order in enamel, following exposure to citric acid. Nanoindentation creep is larger for sound enamel than for deproteinated enamel but it reduces in sound enamel after acid attack. These novel results are consistent with calcium ion-mediated visco-elasticty in enamel matrix proteins as described previously for nacre, bone and dental proteins. They are also in good agreement with a previous double layer force spectroscopy study by the authors which found that the proteins electrochemically buffer enamel against acid attack. Finally, this suggests that acid attack, and more specifically dental erosion, is influenced by ionic permeation through the enamel layer and that it is mitigated by the enamel protein matrix.

Structural characterization of nanostructured hydroxyapatite–iron oxide composites

Nanostructured hydroxyapatite (HA)–iron oxide composites obtained by a wet-chemical method through co-precipitation were investigated with respect to the changes induced in the samples structure by progressive addition of iron, by thermal treatments carried out at 450°C, 550°C and 700°C, and by incubation in simulated body fluid. The structural changes were analyzed by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and magic angle spinning nuclear magnetic resonance (MAS-NMR). After heat treatments, crystalline HA was developed in all samples, even in larger amount in those with iron, showing that iron acts as a catalyzer for HA development. The MAS-NMR results show as well that only a part of the iron atoms are uniformly incorporated in the HA structure by replacing calcium. EPR results support that an important part of iron atoms are disposed in regions rich in iron that behave like superparamagnetic or magnetic particles distributed in HA matrix. The analyses carried out on 550°C treated samples, after three days of immersion in SBF, point out a decrease of HA crystallite size and the appearance on particles surface of a new amorphous calcium phosphate layer.

Characterization of silicon-substituted hydroxyapatite powders synthesized by a wet precipitation method

The preparation of nano sized silicated hydroxyapatite Ca10(PO4)6-x(SiO4)x(OH)2-x (Si-HA) with three different silicon concentrations were investigated using a wet precipitation method. The effects of the Si substitution on crystallite size, lattice parameters and fraction of crystalline phase of the powders were discussed. The crystalline phase, chemical composition,and crystallite size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma and transmission electron microscopy. The crystallite size and fraction of crystalline phase decreases with increase in silicon content and particle morphology spheroidal for pure hydroxyapatite changes to elongated ellipsoidalcrystals while silicon substitution increases. FTIR analysis reveals, the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group by silicate in the Si-HA structure results an increase in the lattice parameters in both a-axis and c-axis of the unit cell.

Synthesis of calcium phosphate-based composite nanopowders by mechanochemical process and subsequent thermal treatment

One-step mechanochemical process followed by thermal treatment has been used to produce calcium phosphate-based composite nanopowders. Effects of milling and subsequent heat treatment on the phase transition as well as structural features were investigated. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The results revealed that the dominant phases after mechanical activation were hydroxyapatite, anatase (TiO2), and periclase (MgO), while after thermal annealing process at 700°C hydroxyapatite along with geikielite (MgTiO3) and periclase (MgO) were the major phases. In addition, decomposition of hydroxyapatite to tricalcium phosphate (β-TCP) occurred after heat treatment in the range 900–1100°C which resulted in the formation of tricalcium phosphate-based composite nanopowders. Evaluation of structural features of the samples calculated by X-ray diffraction profiles analysis indicated that the average crystallite size of hydroxyapatite after 10h of milling and subsequent heat treatment at 700°C were about 21 and 34nm, respectively. TEM and SEM studies exhibited that the considerable morphological changes at temperatures ≥900°C had to be ascribed not only to grain growth, but also for the transformation of hydroxyapatite to β-TCP.

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.

Enhanced bioactivity and biocompatibility of nanostructured hydroxyapatite coating by hydrothermal annealing

The crystallinity of hydroxyapatite (HA) coatings prepared by aerosol deposition may be increased by heating in air or low-temperature hydrothermal processing. From the X-ray diffraction and Fourier transform infrared spectroscopy results, it was revealed that the crystallinity of the HA coatings significantly increased after the post-annealing. Transmission electron microscopy showed that the conventional furnace heating induced the substantial growth of the HA crystallites, whereas the hydrothermal treatment did not bring about any remarkable change in the HA crystallite size, which remained below 20 nm. The bioactivity of the HA coatings was estimated by the acellular simulated body fluid immersion test. After immersion for 7 days, newly-precipitated apatite crystals were only observed on the surfaces of the samples hydrothermally treated at 170 and 190 °C. In addition, the alkaline phosphatase activity of MC3T3-E1 preosteoblast cells cultured on the hydrothermally treated samples was significantly higher than those on the as-deposited coating and conventional furnace heated samples. The enhanced bioactivity and excellent biological in vitro cellular response of the hydrothermally treated samples were attributed to their nanostructured nature and high degree of crystallinity.

Fibrous growth of strontium substituted hydroxyapatite and its drug release

The effect of strontium on the crystallization of helical ribbon of hydroxyapatite (HAp) was investigated by single diffusion technique in silica gel matrix at 27°C and physiological pH. Fibers of HAp were obtained on addition of strontium. The length of the HAp fibers, were found to decrease as the strontium substitution increases. The presence of strontium ion increased the crystallinity as well as crystallite size of HAp. The strontium substituted HAp (Sr-HAp) has similar stoichiometry to that of biological apatite. Sr-HAp was found to have increased surface area (35%) compared to control. Further, strontium substitution leads to an enhancement of in vitro bioactivity. The cumulative in-vitro amoxicillin drug release in phosphate buffer solution (PBS, pH 7.2) showed a prolonged release profile for Sr-HAp.

A novel, low temperature method for the preparation of ß-TCP/HAP biphasic nanostructured ceramic scaffold from natural cancellous bone

In this study, a novel method was used to synthesize ß-TCP/HAP biphasic ceramic scaffold from natural cancellous bone. Bovine bone was calcined to remove the organic content. The remaining material was then soaked in P 2O 5 solution for different periods. P ions were doped into cancellous bone and reacted with hydroxyapatite (HAP) to produce ß-tricalcium phosphate (ß-TCP) at room temperature without any subsequent high-temperature heat treatment. By increasing the soaking time, the crystalline phase composition of the calcined bone gradually changed from HAP into a HAP/ß-TCP biphasic structure with different HAP/TCP ratios. The crystallite size of HAP and ß-TCP was smaller than 100 nm.

Effect of Polymeric Milling Media on the Mechanosynthesis and Structural Properties of Nanocrystalline Hydroxyapatite

Mechanochemical process in polymeric vials has been carried out successfully to produce nanocrystalline hydroxyapatite (HAp) through two different reactions R1 and R2. Morphological properties and structural evaluation of obtained materials are studied by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The obtained data show that the increase in milling time leads the increasing in lattice strain and decreasing in crystallite size. The average crystallite size of HAp is below 20 and 23 nm for R1 and R2 reactions, respectively. Based on XRD patterns and SEM/TEM micrographs, the possible formation mechanism of nanocrystalline hydroxyapatite by mechanochemical process in polymeric milling media is confirmed. Final results indicate that the nanocrystalline hydroxyapatite with low chemically stable contaminations and suitable morphology can be produced in Polyamide6 vials similar to stainless steel vials, therefore it seems that using polymeric vials could lead to a new way for the mass production of nanocrystalline hydroxyapatite with high performance, low contamination and cost and also suitable morphology.

Synthesis and characterization of mesoporous CaO–MO–SiO2–P2O5 (M = Mg, Zn, Cu) bioactive glasses/composites

Mesoporous CaO–MO–SiO2–P2O5 (M = Mg, Zn, Cu) bioactive glasses/composites have been prepared by a one-pot synthesis route of simultaneous evaporation-induced self-assembly of Ca, P, Si and M sources. The effects of the substitution of CaO by MO in the mesoporous bioactive glasses/composites on the mesoporous structure and hydroxyapatite (HA)-forming ability were studied. The amorphous silicate can be detected on all the mesoporous CaO–MO–SiO2–P2O5 (M = Mg, Zn, Cu) bioactive glasses/composites, and Zn2SiO4 and CuO can be clearly detected on bioactive glass with high Zn contents and all of the Cu-containing bioactive glasses/composites, respectively. The MgO-substituted bioactive glasses/composites show the highest surface area among all MO-containing glasses/composites and the presence of crystallized phases of Zn2SiO4 and CuO in the ZnO- and CuO-containing bioactive glasses/composites lead to the decreased surface area and pore volume. The substitution of Ca with Mg, Zn or Cu inhibits the formation of HA deposition on the surface of the mesoporous bioactive glasses/composites, especially at high MO contents. The presence of MgO, ZnO and CuO slowed down the deposition rate of HA following a sequence of Cu < Mg < Zn. Therefore, the HA crystallite size and morphology can be easily tuned by the incorporation of Mg, Zn and Cu, which facilitates the wide application of the mesoporous bioactive glasses/composites.

THERMAL ALTERATIONS IN ARCHAEOLOGICAL BONES*

Archaeological bones, found close to Mexico City (Tlatelcomila), with alterations due to probable thermal exposure attributed to a possible case of cannibalism, have been characterized by XRD, SAXS and SEM. It is shown how these non‐destructive techniques, which are not conventionally used in archaeological research, may provide useful information. The deterioration degree of the bone structure is quantified through parameters such as gyration radius or fractal dimension. As some of the reported modifications could be attributed to diagenesis, a discussion is presented in terms of bone crystallinity and ionic exchange. Furthermore, the hydroxyapatite crystallite size increased depending on colour: this feature is not explained by diagenesis—it can only be attributed to temperature. We conclude that the samples were thermally treated. Indeed, thermal treatment alters the structure and morphology of bone at a very fine level (microscopic and nanometric), while morphology follows the structural modifications. It is determined that the studied human bones were treated at three different temperatures close to 100, 250 and 600°C. Therefore, they were either boiled (barbacoa) or grilled.

Characterization of hydroxyapatite/titania composite coatings codeposited by a hydrothermal–electrochemical method on titanium

Hydroxyapatite (HA)/titania (TiO2) composite coatings were successfully prepared in an electrolyte solution contain Ca2+ and H2PO4− ions with added TiO2 particles, between 100 °C and 200 °C in an autoclave through a hydrothermal–electrochemical codeposited method under galvanostatic conditions. The effect of TiO2 additions on the phase composition, microstructure, thermal stability, corrosion behavior and the bonding strength of the HA/TiO2 composite coatings were studied. The results show that the crystallinity of HA in HA/TiO2 composite coatings increased continuously with the electrolyte temperature and became close to stoichiometric HA. The n(Ca)/n(P) ratio for coatings prepared at 200 °C is about 1.67 in accordance with stoichiometric HA. TiO2 particles were imbedded uniformly between HA crystals and the addition of TiO2 reduced the HA crystallite size. After heating at 800 °C, HA in the HA/TiO2 composite coating partially decomposes into β-tri-calcium phosphate (β-TCP) due to the incorporation of TiO2. After heating at 1200 °C, HA tended to react with TiO2 to form CaTiO3, and β-TCP converted to α-tri-calcium phosphate (α-TCP), anatase TiO2 transformed to rutile TiO2. The bonding strength of the HA/TiO2 composite coatings increased with the addition of TiO2, and the bonding strength of the TiO2 reinforced HA increased with increases TiO2 content in the coatings.

Hydoxyapatite/titanium composite coating prepared by hydrothermal–electrochemical technique

To improve the bonding strength of HA coating, hydroxyapatite(HA)/titanium(Ti) composite coatings were successfully prepared by modifying hydrothermal–electrochemical (HTEC) technique. The effect of Ti additions on the phase composition, microstructure, thermal stability and the bonding strength of the HA/Ti composite coatings was studied. The results show that HA and Ti particles are relatively well distributed in the coating, and the addition of Ti reduces the HA crystallite size. The bonding strength of HA/Ti composite coatings increases with addition of Ti, and the bonding strength of the Ti reinforced HA increases with increase of Ti content in the coatings. The bioactivity of HA/Ti composite coating was investigated by immersion of coating in simulated body fluid (SBF). A bone-like apatite layer form on the coating surface after 7 days of soaking in SBF, indicating good bioactivity for HA/Ti composite coating.

Optical and electrical properties of barium titanate-hydroxyapatite composite screen-printed thick films

In this paper we will study the effect of the presence of hydroxyapatite (HA—Ca 10(PO 4) 6(OH) 2) on the dielectric permittivity and losses of the barium titanate (BTO—BaTiO 3) thick films. These films were prepared in two layers geometry using the screen printing technique on Al 2O 3 substrates. Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) used in the films. We also look for the effect of the grain size of the BTO and HA on the final properties of the film. The samples were studied using X-ray diffraction, scanning electron microscopy (SEM), Raman and infrared spectroscopies, dielectric permittivity and losses measurements. The study of the dielectric permittivity and losses was done in the radio-frequency range (100 Hz–10 MHz). The role played by the firing process in the film preparation and the crystallite size of HA and BTO on the dielectric constant and structural properties of the films are discussed.

Hydroxyapatite Nano Sol Prepared via A Mechanochemical Route

Well-dispersed sol with crystalline hydroxyapatite (HAp) was obtained directly by milling a mixture comprising Ca(OH)2, an aqueous solution of H3PO4 and a dispersant, an ammonium salt of polyacrylic acid. The average crystallite size of HAp was below 20 nm. Ca/P molar ratio of the product was 1.51 ± 0.04, i.e. Ca deficient from stoichiometric HAp. Minimum apparent viscosity was attained at a dispersant concentration 0.92wt% of sol. An as-milled sol was diluted by a factor 10–2.61 solid wt% to give a Newtonian fluid of 2 mPa s. From the diluted sol, we obtained a few μm thick dense film of HAp by dip coating on the slide glass precoated by chitosan.

Adsorption Characteristics of Albumin and Lysozyme on Heat-Treated Hydroxyapatite

Adsorption characteristics of bovine serum albumin (BSA) and lysozyme prepared from egg white (LSZ) were investigated on hydroxyapatite (HAp) powders which were prepared in a stream of water vapor and in air at the heating temperatures of 673-1473K. The BSA or LSZ adsorption isotherm obtained on these HAp's in phosphate buffer solutions satisfied Langmuir's equation, regardless of the kind of gas atmosphere for the HAp heat treatment. The saturated amount of adsorption per surface area (designated by ASA (B) for BSA and ASA (L) for LSZ) and the heat of adsorption (QB for BSA and QL for LSZ) increased and decreased, respectively, with gradual increase in the crystallite size of HAp at 673-1073K (region I). At 1073-1473K (region II), ASA (B) and ASA (L) appreciably increased, whereas QB and QL were gradually reduced due to the transforming morphology of HAp particles as well as grain growth. ASA (L) became about fourfold larger than ASA (B), and QL became 10-30% higher than QB in the two regions, indicating that the adsorption ability of LSZ on the P-sites of HAp is stronger than that of BSA on the C-sites of HAp. The increase of HAp heating temperature can effectively enhance the growth of crystallite size and the transformation of microstructure, so that the total numbers of C- and P-sites increase and both the basic strength of the C-sites and acid strength of the P-sites are reduced. The ratios of the numbers of the two sites (P/C) were kept almost constant at 4.34±0.01 in region I and gradually increased from 4.34 to 4.75 in region II.

Effect of short-term hypomagnesemia on the chemical and mechanical properties of rat bone.

Magnesium is known to have an essential role in determining the properties of bone, but the way in which Mg exerts its actions remains unclear. Although long-term Mg deficiency is known to produce osteopenia, the effects of short-term Mg deficiency have not been established. To test the hypothesis that Mg deficiency results in an altered pattern of initial mineralization and concomitant altered bone properties, the radiographic, histologic, chemical, and mechanical properties of the bones of rats given a Mg-deficient diet were compared to those of rats pair-fed the same diet supplemented with Mg. Short-term Mg-deficiency in the diet of growing rats produced a significant decrease in both the trabecular bone volume and the mineral content of the newly formed metaphysis, a significant increase in the Ca:P ratio, and a slight, but significant increase in hydroxyapatite crystallite size and/or perfection in the metaphysis. Comparable, but not significant, trends were found in the diaphyses. Metaphyseal bone osteocalcin levels were reduced in the Mg-deficient rats and lipid was more easily extracted from their bones. No detectable alterations in radiographic microstructure were noted. Mechanically, a significant decrease in the maximum three-point bend strength of the femurs of Mg-deficient rats was observed. These data support the hypothesis that short-term Mg deficiency affects the pattern of bone mineral formation.

Determination of hydroxyapatite crystallite size in human dental enamel by dark-field electron microscopy.

Ion-thinned longitudinal sections of a third molar were observed by bright- and dark-field electron microscopy. In bright field, the hydroxyapatite crystallites in enamel appeared as long rods, but, when observed in dark field, the crystallites were rectangular, with a mean length of 321 A.

Crystal chemistry of bone mineral.

Crystal chemistry of bone mineral.