Calcium Apatite Research Articles

Strontium hydroxyapatite and strontium carbonate as templates for the precipitation of calcium-phosphates in the absence and presence of fluoride

The heterogeneous precipitation of calcium-phosphates on calcium hydroxyapatite (Ca10(PO4)6(OH)2 or HAP) in the presence and absence of fluoride is important in the formation of bone and teeth, protection against tooth decay, dental and skeletal fluorosis and defluoridation of drinking water.Strontium hydroxyapatite (Sr10(PO4)6(OH)2 or SrHAP) and strontium carbonate (SrCO3) were used as calcium-free seed templates in precipitation experiments conducted with varying initial calcium-to-phosphate (Ca/P) or calcium-to-phosphate-to-fluoride (Ca/P/F) ratios. Suspensions of SrHAP or SrCO3 seed templates (which were calcium-limited for both templates and phosphate-limited in the case of SrCO3) were reacted at pH 7.3 (25°C) over 3 days. The resulting solids were examined with Scanning Transmission Electron Microscopy (STEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Near Edge Structure (XANES), and Extended X-ray Absorption Fine Structure spectroscopy (EXAFS).Calcium apatite was the predominant phase identified by all techniques independent of the added Ca/P ratios and of the presence of fluoride. It was not possible to make an unambiguous distinction between HAP and fluorapatite (Ca10(PO4)6F2, FAP). The apatite was calcium-deficient and probably contained some strontium.

Solid solution in the fluorapatite-chlorapatite binary system: High-precision crystal structure refinements of synthetic F-Cl apatite

Apatite sensu lato, Ca 10 (PO 4 ) 6 (F,OH,Cl) 2 , is the tenth most abundant mineral on Earth, and is fundamentally important in geological processes, biological processes, medicine, dentistry, agriculture, environmental remediation, and material science. The steric interactions among anions in the [0,0, z ] anion column in apatite make it impossible to predict the column anion arrangements in solid solutions among the three end-members. In this work we report the measured atomic arrangements of synthetic apatite in the F-Cl apatite binary with nominal composition Ca 10 (PO 4 ) 6 (F 1 Cl 1 ), synthesized in vacuum at high temperature to minimize both hydroxyl- and oxy-component of the apatite. Four crystals from the high-temperature synthesis batch were prepared to assess the homogeneity of the batch and the precision of the location of small portions of an atom in the apatite anion column by single-crystal X-ray diffraction techniques. Crystals were ground to spheres of 80 μm diameter, and full-spheres of Mo K α diffraction data were collected to θ = 33o, with average redundancies >16. Final R 1 values ranged from 0.0145 to 0.0158; the lattice parameters ranged from a = 9.5084(2)–9.5104(3), c = 6.8289(3)–6.8311(2) A. Based on this study, solid solution in P 6 3 / m apatites along the F-Cl join is attained by creation of an off-mirror fluorine site at (0,0,0.167), a position wherein the fluorine atom relaxes away from its normal position within the {00 l } mirror plane in P 6 3 / m apatites; that relaxation is coupled with relaxation of a chlorine atom at the adjacent mirror plane away from the off-mirror fluorine, allowing acceptable F-Cl distances in the anion column. There are a total of four partially occupied anion positions in the anion column, including two for fluorine [(0,0,1/4) and (0,0,0.167)] and two for chlorine [(0,0,0.086) and (0,0,0)]; the chlorine site at the origin was previously postulated but not observed in calcium apatite solid solutions.

Calcific periarthritis of the elbow presenting as acute tennis elbow

A 28-year-old woman presented with sudden acute lateral epicondylitis. There was no history of preceding trauma or repetitive use of the arm. Because of the acute onset and signs of acute inflammation, an X-ray was arranged. The X-ray showed a hyperdense calcified elongated globule distal to the lateral epicondyle. A diagnosis of calcific periarthritis (calcium apatite) of the elbow was made. Calcific periarthritis has rarely been reported as a cause of acute elbow pain.

Magnesium degradation products: Effects on tissue and human metabolism

Owing to their mechanical properties, metallic materials present a promising solution in the field of resorbable implants. The magnesium metabolism in humans differs depending on its introduction. The natural, oral administration of magnesium via, for example, food, essentially leads to an intracellular enrichment of Mg(2+) . In contrast, introducing magnesium-rich substances or implants into the tissue results in a different decomposition behavior. Here, exposing magnesium to artificial body electrolytes resulted in the formation of the following products: magnesium hydroxide, magnesium oxide, and magnesium chloride, as well as calcium and magnesium apatites. Moreover, it can be assumed that Mg(2+) , OH(-) ions, and gaseous hydrogen are also present and result from the reaction for magnesium in an aqueous environment. With the aid of physiological metabolic processes, the organism succeeds in either excreting the above mentioned products or integrating them into the natural metabolic process. Only a burst release of these products is to be considered a problem. A multitude of general tissue effects and responses from the Mg's degradation products is considered within this review, which is not targeting specific implant classes. Furthermore, common alloying elements of magnesium and their hazardous potential in vivo are taken into account.

High-pressure elastic behavior of Ca4La6(SiO4)6(OH)2 a synthetic rare-earth silicate apatite: a powder X-ray diffraction study up to 9.33 GPa

The compression behavior of a synthetic Ca4La6(SiO4)6(OH)2 has been investigated to about 9.33 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell. No phase transition has been observed within the pressure range investigated. The values of zero-pressure volume V0, K0, and \(K_{0}^{'}\) refined with a third-order Birch–Murnaghan equation of state are V0 = 579.2 ± 0.1 A3, K0 = 89 ± 2 GPa, and \(K_{0}^{'} = 10.9 \pm 0.8\). If \(K_{0}^{'}\) is fixed at 4, K0 is obtained as 110 ± 2 GPa. Analysis of axial compressible modulus shows that the a-axis (Ka0 = 79 ± 2 GPa) is more compressible than the c-axis (Kc0 = 121 ± 7 GPa). A comparison between the high-pressure elastic response of Ca4La6(SiO4)6(OH)2 and the iso-structural calcium apatites is made. The possible reasons of the different elastic behavior between Ca4La6(SiO4)6(OH)2 and calcium apatites are discussed.

Structural analysis by Rietveld refinement of calcium and lanthanum phosphosilicate apatites

Britholites with the general formula Ca10–xLnx(PO4)6–x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study showed that the stability of these compounds decreased as the substitution rate increased. The present work was an attempt to gain more information about the structural changes induced by the substitution, in order to understand the observed stability decrease. The samples were successfully synthesized as a single-phase apatite by a solid-state reaction between 1200 and 1400 °C. The structural refinement indicated that the La3+ ions preferentially occupied the 6(h) sites. A progressive shift of F− along the c-axis outside its ideal position occurred as a result of the substitution increase. This might be the cause of the observed stability decrease, especially as the energies of the La–O, La–F and Si–O bonds are higher than those of Ca–O, Ca–F and P–O. The distribution of La3+ between the two non-equivalent sites was confirmed by the charge distribution method.

AB0629 A critical appraisal of the competence of crystal identification by rheumatologists.

BackgroundThe gold standard for diagnosing crystal arthritis is aspiration of synovial fluid and subsequent polarized microscopy on the punctured fluid. However, various studies have shown a lack of consistency in...

Biphase CaO–P2O5 ceramic based on powder synthesized from calcium acetate and ammonium hydrophosphate

Biphase ceramic containing hydroxyapatite Ca10(PO4)6(OH)2 and -tricalcium phosphate -Ca3(PO4)2 has been obtained from a uniform nanocrystalline calcium phosphate powder with the structure of apatite, synthesized from water solutions of calcium apatite and ammonium hydrophosphate with molar ratio CaP = 1.5 at room temperature without pH regulation. After firing at 1100°C the material contained 75% -Ca3(PO4)2 and the grain size did not exceed 600 nm. It is suggested that the carbon formed in the interval 200 – 500°C, as a result of the carbonization of the organic components of synthesis adsorbed by particles of powder, be used as a physical barrier impeding intense mass transfer up to 800°C, which makes it possible to obtain an ultradisperse ceramic with grains smaller than 1 m.

Electrolytic one-pot synthesis of Group II nanohydroxyapatites

Several magnesium-doped calcium, calcium, strontium, and barium nanohydroxyapatites are synthesized using a saturated solution system (M2+/EDTA/PO43−) in a simple electrochemical cell. It was demonstrated that the nature of the precipitates does not depend on reaction time or subsequent treatments. Calcium apatite can be prepared from pH solution spanning 4.0–13.0 and current density from 50 to 260 mA cm−2. Interestingly, strontium and barium apatite synthesis strongly depends on the stability of the saturated solution and the nature of the counter ion in solution. In addition, preliminary kinetic studies indicate a zero-order reaction. FTIR, X-ray diffraction, thermogravimetric analysis, and TEM studies are also reported.

Tumoral Calcinosis Form of Hydroxyapatite Deposition Disease in Related Red-Bellied Short-Necked Turtles, Emydura subglobosa

Ten of 12 red-bellied short-necked turtles from a single clutch presented at 9 months of age with multiple white to tan nodules on their feet. Histologically, the nodules were composed of large periarticular deposits of mineralized crystalline material that extended into the joint spaces of interphalangeal joints and was surrounded by granulomatous inflammation and fibrosis. Crystallographic analysis determined the material to be apatite (calcium phosphate hydroxide) consistent with the tumoral calcinosis form of hydroxyapatite deposition disease (HADD). HADD has previously been described in aquatic turtles and rarely lizards and must be differentiated from gout in reptiles. A cause for the tumoral calcinosis lesions in these turtles could not be determined; however, based on previous reports in this species, a species-specific predilection, in conjunction with unknown environmental factors, is suspected. The use of the terms HADD, pseudogout (calcium pyrophosphate crystal deposition disease), and calcinosis circumscripta has been inconsistent, creating confusion in the literature.

A comparative study of various decalcification techniques

Study of fibrilar, cellular and sub cellular structures of mineralized tissues is only possible after the removal of the calcium apatite of these tissues by the process of demineralization. The present study aims to evaluate six commonly used demineralizing agents to identify the best decalcifying agent. The present study included six different decalcifying solutions: 10% formal nitric acid, 8% formal nitric acid, 10% formic acid, 8% formic acid, Perenyi's fluid and Ethylene Di-Amine Tetra Acetic Acid. eight samples of posterior mandible of rat were decalcified in each of the decalcifying solutions and subjected to chemical end-point test. Ehrlich's Hematoxylin stain was used. One way ANOVA was used for multiple group comparisons and Chi-square test was used for analyzing categorical data. P value of 0.05/less was set for statistical significance. Samples treated with EDTA showed the best overall histological impression and the tissue integrity were well preserved. Formal nitric of both the percentages 10 and 8% gave fairly good cellular detail and were rapid in their action. The final impression led to the proposition that EDTA was indeed the best decalcifying agent available. However, with time constraint, the use of formal nitric acid is advocated.

Crystallite Size—Is It a New Predictor for Renal Stone Burden?

To evaluate the importance of stone composition and crystallite size in the formation of ultimate stone burden. Crystallite is the smallest building block, which is unique in size and architecture for each type of stone component. Currently, the knowledge about the clinical importance of crystallite size is very limited. The results of quantitative X-ray diffraction phase analysis performed on 286 kidney stones extracted during endourological surgery or expelled spontaneously were retrospectively analyzed. Stone composition and crystallite size were determined and were compared to the burden occupying the pelvicalyceal system. A total of 286 renal stones were analyzed. Stones were low burden and high burden in 242 and 44 of cases, respectively. We observed statistically significant association of phosphates and urates with high-burden stones in contrast to oxalates, which formed mainly low-burden stones. Crystallite sizes were available for 179 stones. Large-sized crystallites of calcium oxalate monohydrate and hydroxyl apatite formed low-burden stones, whereas small-sized crystallites formed staghorn stones. Struvite and urates had a uniform average size of crystallites. Oxalate stones have statistically significant association with smaller stones, whereas high-burden calculi are significantly associated with urates and phosphates, especially the struvite type. The smaller the crystallite size is to start with, the larger will be the ultimate stone burden. This rule is followed by calcium oxalate monohydrate and Apatite minerals.

Amorphous Calcium Orthophosphates: Nature, Chemistry and Biomedical Applications

Amorphous calcium orthophosphates (ACPs) represent a unique class of biomedically relevant calcium or- thophosphate salts, having variable chemical but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. Normally, ACPs are the first solid phases, precipi- tated after a rapid mixing of aqueous solutions containing ions of Ca 2+ and PO4 3- ; however, other production techniques are known. Interestingly, but ACPs prepared by wet-chemical techniques were found to possess a relative constancy in their chemical composition over a relatively wide range of preparation conditions, which suggested the presence of a well-defined local structural unit, presumably, with the structure of Ca9(PO4)6 - so-called a Posner's cluster. However, the presence of similar clusters in ACPs produced by other techniques remains uncertain. All ACPs are thermodynamically unstable com- pounds and, unless stored in dry conditions or doped by stabilizers, spontaneously they tend to transform to crystalline cal- cium orthophosphates, mainly to calcium apatites. This solution instability of ACPs and their easy transformation to crys- talline phases are of a great biological relevance. Namely, the initiating role ACPs play in matrix vesicle biomineralization raises the importance of ACPs from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifi- cation. In addition, due to great chemical and structural similarities to the calcified tissues of mammals, as well as excellent biocompatibility and bioresorbability, all types of ACPs are very promising candidates to manufacture artificial bone grafts. In this review, current knowledge on occurrence, preparation, composition, structure, major properties and biomedical ap- plications of ACPs have been summarized. To assist the readers in looking for the specific details on ACPs, a great number of references have been collected and systematized.

Dissolution mechanism of calcium apatites in acids: A review of literature.

Eight dissolution models of calcium apatites (both fluorapatite and hydroxyapatite) in acids were drawn from the published literature, analyzed and discussed. Major limitations and drawbacks of the models were conversed in details. The models were shown to deal with different aspects of apatite dissolution phenomenon and none of them was able to describe the dissolution process in general. Therefore, an attempt to combine the findings obtained by different researchers was performed which resulted in creation of the general description of apatite dissolution in acids. For this purpose, eight dissolution models were assumed to complement each other and provide the correct description of the specific aspects of apatite dissolution. The general description considers all possible dissolution stages involved and points out to some missing and unclear phenomena to be experimentally studied and verified in future. This creates a new methodological approach to investigate reaction mechanisms based on sets of affine data, obtained by various research groups under dissimilar experimental conditions.

Evaluation of Compressive Strength of Eggshell Hydroxyapatite

This paper presents an in-vitro evaluation of compressive strength of a locally produced hydroxyapatite from eggshell. Hydroxyapatite (HA) is a mineral that naturally occur in form of calcium apatite with the formula Ca5 (PO4)3(OH) but it is usually written as Ca10(PO4)6(OH). Hydroxyapatite (HA) is an example of bioactive ceramics that most commonly used in the bone implantation, as coating on prostheses or as bone filling material. Eggshell waste is available in huge quantity from food processing, egg breaking and hatching industries. This material goes as waste products and leads to pollution since it is microbial action in the environment and it is simply burned as organic waste that releasing CO2. By utilizing this organic waste that has high content of calcium carbonate, the cost of high quality of calcium source for preparation of hydroxyapatite can be reduced. At the same time, recycling of eggshell can be done. Many methods have been introduced to convert the calcium carbonate of eggshell to hydroxyapatite. Hydrothermal method technique has been selected to convert the calcium carbonate obtained from the eggshell since the procedure to transform it is simple and straight forward. An addition, the material that been used is not so expensive as compared to other method. Mechanical properties such as compression strength will be done to compare the synthetic hydroxyapatite in the market and hydroxyapatite from the hen’s eggshell.

Surface mineralization of Ti6Al4V substrates with calcium apatites for the retention and local delivery of recombinant human bone morphogenetic protein-2

Titanium alloys are prevalently used as orthopedic prosthetics. Inadequate bone–implant interactions can lead to premature prosthetic loosening and implant failure. Local delivery of osteogenic therapeutics promoting osteointegration of the implant is an attractive strategy to address this clinical challenge. Given the affinity of calcium apatites for bone matrix proteins we hypothesize that titanium alloys surface mineralized with calcium apatites should be explored for the retention and local delivery of osteogenic recombinant human bone morphogenetic protein-2 (rhBMP-2). Using a heterogeneous surface nucleation and growth process driven by the gradual pH elevation of an acidic solution of hydroxyapatite via thermal decomposition of urea, Ti6Al4V substrates were surface mineralized with calcium apatite domains exhibiting good affinity for the substrate. The microstructures, size and surface coverage of the mineral domains as a function of the in vitro mineralization conditions were examined by light and scanning electron microscopy and the surface calcium ion content quantified. An optimal mineralization condition was identified to rapidly (<10 h) achieve surface mineral coverage far superior to those accomplished by week long incubation in simulated body fluids. In vitro retention–release profiles of rhBMP-2 from the mineralized and unmineralized Ti6Al4V, determined by an enzyme-linked immunosorbent assay, supported a higher degree of retention of rhBMP-2 on the mineralized substrate. The rhBMP-2 retained on the mineralized substrate after 24 h incubation in phosphate-buffered saline remained bioactive, as indicated by its ability to induce osteogenic transdifferentiation of C2C12 myoblasts attached to the substrate. This mineralization technique could also be applied to the surface mineralization of calcium apatites on dense tantalum and titanium and porous titanium substrates.

Matrix-Mediated Biomineralization in Marine Mollusks: A Combined Transmission Electron Microscopy and Focused Ion Beam Approach

The teeth of the marine mollusk Acanthopleura hirtosa are an excellent example of a complex, organic, matrix-mediated biomineral, with the fully mineralized teeth comprising layers of iron oxide and iron oxyhydroxide minerals around a calcium apatite core. To investigate the relationship between the various mineral layers and the organic matrix fibers on which they grew, sections have been prepared from specific features in the teeth at controlled orientations using focused ion beam processing. Compositional and microstructural details of heterophase interfaces, and the fate of the organic matrix fibers within the mineral layers, can then be analyzed by a range of transmission electron microscopy (TEM) techniques. Energy-filtered TEM highlights the interlocking nature of the various mineral phases, while high-angle annular dark-field scanning TEM imaging demonstrates that the organic matrix continues to exist in the fully mineralized teeth. These new insights into the structure of this complex biomaterial are an important step in understanding the relationship between its structural and physical properties and may help explain its high strength and crack-resistance behavior.

Spectroscopic study of explanted opacified hydrophilic acrylic intraocular lenses

To report a detailed spectroscopic analysis of explanted hydrophilic acrylic intraocular lenses (IOLs) that were removed because of postoperative opacification of the lens optic. Thirteen Hydroview H60M (Bausch & Lomb Surgical) IOLs were explanted from 13 different patients on average 56 months after phacoemulsification and IOL implantation. All patients had decreased visual acuity because of a fine granularity of the optical surface of the IOLs. The surface was investigated by gross, microscopic, histochemical and scanning electron microscopic analysis, and the elemental composition of the opacified IOLs was determined by X-ray fluorescence spectroscopy (XRF). The spectrograms were compared to three different originally packed and never-implanted hydrophilic acrylic IOLs. Light and scanning electron microscopy of the optical surface of explanted IOLs revealed multiple fine granular deposits varying in size and shape that were positive for alizarin red. XRF confirmed that the explanted IOLs contained not only the previously reported calcium and phosphorous (calcium apatite), chlorine, silicone, sodium, aluminum and magnesium but also iron, sulfur, potassium as well as lesser amounts of iodine, zinc, strontium and yttrium. This is the first spectroscopic analysis determining the content of more than 10 elements of explanted and originally packed never-implanted hydrophilic acrylic IOLs. The possible origin of the different elements obtained from the spectrograms and their implications are discussed.

Growth and characterization of Mg(OH) 2 film on magnesium alloy AZ31

Magnesium-based biomaterials have been proposed as potential candidates for biodegradable implant materials, such as bone screws, bone plates, intraluminal stents and so on. However, the poor corrosion resistance inhibits their applications in surgery. They collapse before the injured tissues are healed. In this paper, Mg(OH) 2 nonstructural film was synthesized on the substrate of AZ31 magnesium alloy by hydrothermal method with NaOH solution as mineralizer to reduce the corrosion rate of magnesium-based materials. The obtained films were characterized by XRD, SEM, and XPS. The results showed that a Mg(OH) 2 film with nanostructure surface can be synthesized by hydrothermal method. It was observed that the thickness of film increased with the holding time. Corrosion rates of the films were studied by immersing the samples in Hank's solution (37 °C). Surface deposits of samples with films soaked in Hank's solution for 31 days were investigated by XRD, SEM, EDS, XPS, and FTIR. It verified that the corrosion rate of the magnesium alloy with grown film was slowed down in the Hank's solution and the behavior of corrosion was inhibited effectively. Amorphous calcium apatite precursor was observed to deposit on the surface of the film during corrosion experiments in Hank's solution. And the tape test revealed a strong adhesion between the film and the substrate.

Fat malabsorption and increased intestinal oxalate absorption are common after roux-en-Y gastric bypass surgery

Hyperoxaluria and increased calcium oxalate stone formation occur after Roux-en-Y gastric bypass (RYGB) surgery for morbid obesity. The etiology of this hyperoxaluria is unknown. We hypothesized that after bariatric surgery, intestinal hyperabsorption of oxalate contributes to increases in plasma oxalate and urinary calcium oxalate supersaturation. We prospectively examined oxalate metabolism in 11 morbidly obese subjects before and 6 and 12 months after RYGB (n = 9) and biliopancreatic diversion-duodenal switch (BPD-DS) (n = 2). We measured 24-hour urinary supersaturations for calcium oxalate, apatite, brushite, uric acid, and sodium urate; fasting plasma oxalate; 72-hour fecal fat; and increases in urine oxalate following an oral oxalate load. Six and 12 months after RYGB, plasma oxalate and urine calcium oxalate supersaturation increased significantly compared with similar measurements obtained before surgery (all P ≤ .02). Fecal fat excretion at 6 and 12 months was increased (P = .026 and .055, 0 vs 6 and 12 months). An increase in urine oxalate excretion after an oral dose of oxalate was observed at 6 and 12 months (all P ≤ .02). Therefore, after bariatric surgery, increases in fecal fat excretion, urinary oxalate excretion after an oral oxalate load, plasma oxalate, and urinary calcium oxalate supersaturation values were observed. Enteric hyperoxaluria is often present in patients after the operations of RYGB and BPD-DS that utilize an element of intestinal malabsorption as a mechanism for weight loss.