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PubMed2000

Inhibition of apatite formation by vitronectin.

This study investigated the concentration-dependent effect of vitronectin (VN), a glycoprotein of the bone matrix, on apatite formation and growth. Precipitation trials in metastable solution and in a pH-controlled solution system showed an inhibition of apatite microcrystal formation by VN. In the presence of biphasic calcium-phosphate ceramic, transmission electron microscopy showed a reduction of precipitated microcrystal size: precipitates were significantly smaller than in ionic simulated body fluid without proteins or in the presence of type I collagen as a negative control. Moreover, the size of the precipitated microcrystals was reduced in a dose-dependent manner. Two indirect methods showed that calcium-phosphate precipitation was inhibited by VN. It would appear that VN prevents apatite formation by inhibiting the growth of apatite crystals rather than by secondary nucleation, as in the case of osteopontin, a bone-specific protein.

Apatites↗

PubMed1993

Factors affecting the transformation of octacalcium phosphate to apatite in vitro.

A fresh octacalcium phosphate (OCP) precipitate without drying and three kinds of dried OCP powders were soaked for 3 weeks in 11 kinds of physiological solutions consisting of different combinations of Ca2+, Mg2+, K+, Na+, HCO3-, HPO4(2-), F-, albumin, collagen and alkaline phosphatase, in three different pH values and at three different temperatures. X-ray diffraction study showed that most of the OCP had been transformed to apatite with low crystallinity after soaking in the solutions without Mg2+. The IR absorption spectra revealed that CO3 was incorporated in the apatite formed from OCP in the solution without Mg2+, whereas OCP changed little after soaking in the solution containing Mg2+. These results suggest that the presence of Mg2+ in the solution is one of the most effective means of inhibiting the transformation of OCP to apatite by interrupting the precipitation process of apatite.

Analysis of Variance↗

PubMed2002

[Effects of simulated body fluid flowing rate on bone-like apatite formation on porous calcium phosphate ceramics].

Objective. Bone-like apatite formation on the surface of calcium phosphate ceramics was believed to be the necessary step that new bone grows on the ceramics and to be relative to the osteoinductivity of the material. This study aimed at investigating the influence of the flow rate of simulated body fluid (SBF) (2 ml/min) in skeletal muscle upon the formation of bone-like apatite on porous calcium phosphate ceramics. Method. The dynamic condition was realized by controlling the SBF flowing in/out of the sample chamber of 100 ml. The flow rate of 2 ml/min is close to that in human muscle environment. The pH and inorganic ionic composition of SBF are close to those of human body fluid. Result. Bone-like apatite formation was relatively easier to occur in static SBF than in dynamic SBF. Experiment with flowing SBF (dynamic SBF) is better in mimicking the living body fluid than static SBF. Conclusion. The results from dynamic SBF may more truly show the relation between apatite layer formation and osteoinduction in biomaterials than that from in vitro experiments before.

Apatites↗

PubMed1992

Crystallographic and chemical properties of Mg-containing apatites before and after suspension in solutions.

Mg-containing synthetic apatites were prepared and then incubated in unbuffered 0.9% NaCl solution and in buffered 0.1 M CH3COOK solution (pH 7.4) at 37 degrees C to examine the changes in their crystallographic and chemical properties after suspension in these solutions. After one month of incubation, the magnesium (Mg) content in the samples decreased greatly, especially in samples with higher Mg content. The a and c axis dimensions of the samples changed with the decrease of Mg content. On the other hand, Mg concentrations in both solutions increased more than the Ca concentrations. Mg-substituted beta-tricalcium phosphate (beta-TCP), or whitlockite, formed from solutions with high Mg concentration. These results show that Mg-containing apatites dissolve to a greater extent than Mg-free apatites with the subsequent reprecipitation of Mg-poor apatites. In addition, the high Mg/Ca in solution favoured the reprecipitation of Mg-containing beta-TCP.

Apatites↗

PubMed2004

Fabrication of synthetic apatites by solid-state reactions.

The paper presents a method of producing synthetic Hydroxyapatite (HA) Ca10(PO4)6(OH)2 and other apatites for biological use by solid-state reaction. The solid-state reaction involves mix-grinding dry powders of beta-tricalcium phosphate powder (TCP) and either calcium hydroxide (Ca(OH)2) or calcium carbonate (CaCO3) or combination thereof, from pure commercial chemicals or derived from natural limestone or from seashells, of total calcium/phosphorus molar ratio between 1.5 to 2.0, to particle size of less than 10 microns, and firing the resultant powder to temperature between 600 degrees C - 1250 degrees C in atmosphere or in controlled atmospheric condition. The resultant apatites formed were characterised using XRD, SEM-EDX and FTIR. The presented reaction process was found to be much simpler compared to conventional methods of producing synthetic apatites since it involves only dry mix-grinding of the reactants before firing at high temperatures based on the required levels of purity. It can also produce synthetic apatites with good reproducibility in a shorter time. Thus the presented method has a great industrial value.

Apatites↗

PubMed1988

Comparison of the compression strength of human vertebral bodies with the mass and density of apatite: a study by 31P NMR spectroscopy.

The force needed to fracture individual human thoracic and lumbar vertebral bodies is compared with the mass and density of apatite. 31P NMR spectrometry was used to quantify the apatite, because it permits the mineral content of bone to be determined noninvasively with minimal nonspecific interference from the organic matrix or from variations in composition of the marrow. Experiments were performed with bones of similar structure and function from a single individual with no history of trabecular fractures, to compensate for the effects of the other variables that affect bone strength. The coefficient of correlation between compression strength and the volume density (i.e., g/cm3) of apatite was 0.95. The correlation of strength with the mass (i.e., grams) of apatite in a vertebral body also was reasonably good, r = 0.82, but correlations with areal density (i.e., g/cm2) and linear density (i.e., g/cm) were much poorer.

Apatites↗

PubMed1986

[The place of apatite in rheumatic diseases. Study of 25 cases by x-ray microanalysis and scanning electron microscopy].

The importance of "apatite deposition disease" among the arthropathies has been recognized for some years: it is well known that X-ray microanalysis (XRMA) is an efficient method of determining the elemental constitution of microcrystalline deposits obtained from synovial fluids or from tendon washing solutions during examination in scanning electron microscopy. In all 25 patients studied (11 intraarticular and 14 extraarticular samples), alizarine red S staining was positive and XRMA confirmed the diagnosis of apatite deposition by determination of the phosphorus/calcium (P/Ca) ratio in the deposits. In the 25 patients the mean values obtained for the P/Ca ratios were situated between 0.362 and 0.450, with a general mean value of 0.411, i.e. a ratio clearly lower than the P/Ca ratio of pure hydroxyapatite specimens (0.438) measured in identical conditions. This apparent discrepancy seems to be related to the probable presence of carbonated apatites. The study confirmed the presence of apatite microcrystals in intra- and extraarticular location; in the first condition, these were generally found in patients with severe destructive arthrosis, whereas in the second condition the calcifications derived from supraspinatus tendons.

Adult↗

PubMed1985

The structure of bone apatite surfaces.

This is a review of the surface chemistry of bone mineral and its synthetic counterpart hydroxyapatite. Small-angle x-ray scattering and low-temperature nitrogen adsorption measurements show bone mineral surfaces range from 100 to 200 m2/g. The heats of adsorption of small molecules on bone and apatite surfaces show that these materials have polarizing surfaces which form strong bonds with polar and polarizable molecules. Water is hydrogen bonded to these surfaces with energies ranging from 23 Kcal/mol, for low coverage, to 11 Kcal/mol after two full layers; the latter value shows that after two monolayers the water is bonded as strongly to the solution as it is to the apatite surface. Stearic acid in cyclohexane adsorbs on bone and apatite surfaces in a closed-packed manner with the straight-chain molecules in parallel array with the end carboxyl groups hydrogen bonded to surface electronegative ions. Synthetic hydroxyapatite has long been used in chromatography because of the bonding capacity apatite surface has for certain proteins and polynucleotides. The metabolic interplay between bone mineral and the body results from the high magnitude and high reactivity of the mineral surface.

Adsorption↗

PubMed2004

A novel covalently crosslinked gel of alginate and silane with the ability to form bone-like apatite.

Hybrids consisting of bone-like apatite and biodegradable polymers are attractive materials for bone repair. We have shown that an alginate gel crosslinked covalently with ethylenediamine (EDA) enhances the repair of skin and nerves. In this study, we report a novel method for fabrication of an apatite-alginate nanohybrid using a simulated body fluid (SBF). Alginate was reacted with 3-aminopropyltriethoxysilane (APES), which gives silanol groups after hydrolysis, and/or EDA, by dehydration condensation using water-soluble carbodiimide to form gels. Modification of alginate with APES alone also gave a gel, because the alginate could be crosslinked by dehydration of silanol groups derived from APES. The gels obtained were soaked in a 1 mol/L CaCl2 solution and subsequently soaked in SBF. Apatite was formed on and inside the alginate gels modified with APES, whereas it was not formed on the gels without APES. Modification of alginate with silanol groups induced not only gel formation but also the apatite-forming ability on and inside the alginate gel in SBF. Consequently, a hydroxyapatite-alginate hybrid can be produced by modification of alginate with silanol groups and subsequent soaking in CaCl2 solution and SBF. Such a material is expected to be useful in bone repair.

Alginates↗

PubMed1997

Surface Reactions of Apatite Dissolution

New experimental data about surface processes of interaction between natural apatite and phosphoric acid solutions were obtained by scanning electron microscopy, Auger electron spectroscopy, and IR reflection spectroscopy. The interaction was found to occur nonstoichiometrically (incongruently) on the very thin surface layer of apatite. The experimental data obtained were compared and extended with results taken from literature. The following sequence of ionic detachment from the surface of apatite to a solution was suggested: first fluorine for fluorapatite or hydroxyl for hydroxyapatite, next calcium, and afterward phosphate. A new chemical mechanism of apatite dissolution was proposed as a result. The mechanism for the first time described the surface irregularity of the dissolution process at the nanolevel. A comparison between this new dissolution mechanism and earlier mechanisms described in the literature was made.

Journal Article↗

PubMed1994

Formation of a bone apatite-like layer on the surface of porous hydroxyapatite ceramics.

Phosphoric acid solution was used to react with commercial hydroxyapatite (HA) powders to demonstrate the possibility of converting HA to non-stoichiometric apatite and thus to treat porous HA ceramics, to form a thin bone-apatite like layer on the HA ceramic surface. Such a carbonate-containing non-stoichiometric apatite "bioceramic" would be more efficient in bone bonding or bone formation, due to its analogy to natural bone apatite.

Bone and Bones↗

PubMed1995

Crystallographic properties of heterogeneous Mg-containing fluoridated apatites synthesized with a two-step supply system.

Mg-containing fluoridated hydroxyapatites (Mg-MgFAp and MgF-MgAp) were synthesized heterogeneously with two different modes of fluoride supply. The expanded (300) reflections of the X-ray diffraction of both apatites were broader than and different from those of the mechanical mixture of the homogeneous apatites (MgAp and MgFAp). Scanning electron microscopy (SEM) showed that the crystal size and shape of Mg-MgFAp and MgF-MgAp were different. Energy dispersive spectroscopy (EDS) indicated that the fluoride intensity of Mg-MgFAp synthesized with the fluoride supply in the latter half of the experimental period was higher than that of MgF-MgAp. The apparent solubility of Mg-MgFAp was lower than that of MgF-MgAp. These results suggested that two different types of Mg-containing fluoridated hydroxyapatites might be formed: surface fluoride-rich apatites (Mg-MgFAp) and inner fluoride-rich apatites (MgF-MgAp).

Crystallography↗

PubMed2005

Ultrastructural observation of single-crystal apatite fibres.

Hydroxyapatite (HAp) has been widely used as a biomaterial for substituting human hard tissues such as bone. By altering the morphology of HAp crystals, novel properties may be produced by controlling the orientation of the crystal planes. Apatite fibres were successfully synthesized by precipitation from aqueous solutions containing Ca(NO(3))(2), (NH(4))(2)HPO(4), urea and HNO(3). The products were composed of carbonate-containing apatite fibres with preferred orientation along the {h00} planes. Examination of individual fibres using transmission electron microscopy showed that the as-synthesized apatite fibres were highly strained single crystals with the c-axis orientation parallel to the long axis of the fibre. The crushed fibres consisted of domains that were preferentially oriented with the c-axis parallel to the long axis of the fibres. When the apatite fibres were heated to 800, 1000 and 1200 degrees C for 1h, the domains were removed and grain boundaries, dislocations and voids were formed.

Biocompatible Materials↗

PubMed2005

Fluoridated apatite coatings on titanium obtained by electron-beam deposition.

In this report, a series of fluoridated apatite coatings were obtained by the electron-beam deposition method. The fluoridation of the apatite was aimed to improve the stability of the coating and elicit the fluorine effect, which is useful in the dental restoration area. Apatites fluoridated at different levels were used as initial evaporants for the coatings. The as-deposited coatings were amorphous, but after heat treatment at 500 degrees C for 1 h, the coatings crystallized well to an apatite phase without forming any cracks. The adhesion strengths of the as-deposited coatings were about 40 MPa. After heat treatment at 500 degrees C, the strengths of the pure HA and FA coatings decreased to about 20 MPa, however, the partially fluoridated coatings maintained their initial strength. The dissolution rate of the fluoridated coatings was lower than that of the pure HA coating, and the rate was the lowest in the coatings with 25% and 50% fluorine substitutions. The osteoblast-like cells responded to the coatings in a similar manner to the dissolution behavior. The cells on the fluoridated coatings showed a lower (p < 0.05) proliferation level compared to those on the pure HA coating. The alkaline phosphatase activity of the cells was slightly lower than that on the pure HA coating, but this difference was not statistically significant.

Absorbable Implants↗

PubMed2001

Affinity binding phenomena of DNA onto apatite crystals.

The effect of DNA on the crystal growth of hydroxyapatite (HAp) and its morphology was examined. X-ray diffraction patterns of DNA-containing apatites showed typical apatitic features. However, crystal growth was greatly inhibited in the presence of DNA during synthesis; particularly, the crystallinity in the a-axis direction decreased dramatically at low concentrations of DNA. The a- and c-axis dimensions of each precipitate were almost the same, which implies that DNA molecules affect only the crystal surface. CHN analysis clearly showed the presence of these elements, which increased with an increase in DNA concentration in the solution. Scanning electron micrographs of the precipitates formed in the presence of DNA showed typical needle-like crystals, with a decreased crystal size, especially width. Infrared absorption spectroscopy of the DNA-containing apatites showed that the 1630-1700 cm(-1) absorption band due to C=C and C=N stretching increased with an increase in DNA concentration during precipitation. The ESCA spectrum of HAp(DNA 1.0) shows N 1s and C 1s peaks that are absent and weak, respectively in HAp. 31P NMR spectroscopy revealed a weak peak at the base of the 31P peak from the PO4(3-) ions in the HAp crystals. This weak 31P peak had a small positive shift from the position found in native DNA which may be due to the phosphate backbone of adsorbed DNA. The apparent solubility of the HAps increased with an increase in DNA concentration. These results suggest that there is an affinity binding between apatite crystal and DNA molecules.

Animals↗

PubMed2000

Electron spin resonance (ESR) studies of CO2- radicals in irradiated A and B-type carbonate-containing apatites

ESR spectra of irradiated carbonate-containing hydroxyapatites are complex and strongly dependent on the method of preparation of these materials. This paper describes results of our studies of the ESR spectra of irradiated A- and B-type carbonated hydroxyapatites. The most intense and stable lines in these spectra are attributed to CO2- radicals. The ESR spectrum of A-type carbonated apatite can be predominantly due to either axial or orthorhombic CO2- species, depending on whether the apatite was cooled in or without a CO2 flow. The B-type carbonated apatite has an ESR spectrum composed basically of signals from isotropic and orthorhombic CO2- species. These signals are different in intensity, line width, and g-factor for samples heated for 3 h at 200, 400 and 600 degrees C. The effect of the method of preparation of the A- and B-type carbonated apatites on the ESR spectra and the application of these materials to the ESR dating and dosimetry are discussed.

Journal Article↗

PubMed1998

Apatite formation on silica gel in simulated body fluid: effects of structural modification with solvent-exchange.

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bone-like apatite on their surfaces. It has been shown that even a pure silica gel forms the bone-like apatite on its surface in a simulated body fluid. In the present study, pore structure of silica gels prepared by hydrolysis and polycondensation of tetraethoxysilane in an aqueous solution containing polyethylene glycol was modified by 1M HNO3, and 0.1M and 1M NH4OH solution treatments. The three kinds of resultant gels all contained large amounts of silanol groups and trisiloxane rings, but differ greatly in pore structure of nanometre pore size. Irrespective of these differences, all the gels formed the bone-like apatite on their surface in the simulated body fluid. It was speculated that a certain type of structural unit of silanol groups, which is easily formed in the presence of the polyethylene glycol, is effective for the apatite formation.

Journal Article↗

PubMed1998

Effect of fluoride on apatite formation from Ca4(PO4)2O in 0.1 mol L(-1) KH2PO4.

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) was investigated in 0.1 mol l(-1)KH2PO4 containing 0-83 mol l(-1) KF. Characterization of the final apatite phase formed by the hydrolysis was made with X-ray diffraction and SEM. The initial pH was between 4.5 and 5.4, depending on the solutions, and the pH rapidly increased and was kept constant between 7.3 and 6.5. An increase in KF concentration tended to lower the pH in the final stage of hydrolysis. The calcium concentration was considerably lower than the phosphorus concentration throughout the reaction. The fluoride concentration decreased shortly after the start of hydrolysis. The hydrolysis of TTCP in 0.1 mol l(-1) KH2PO4 proceeded to form hydroxyapatite via DCPD when the KF concentration was low. The hydrolysis product was a calcium-deficient non-stoichiometric hydroxyapatite with a Ca/P ratio of about 1.5. With an increase in the KF concentration in the 0.1 mol l(-1) KH2PO4 solution, TTCP directly transformed into hydroxyapatite containing F- ions or fluorapatite and with improved crystallinity. The addition of fluoride in the solution initially accelerated the formation of apatite. However, the layer of newly formed apatite adhering to the TTCP particles retarded TTCP dissolution; as a result, hydrolysis was delayed. IR analysis showed that the apatite phase contained HPO2-4 ions in the structure. The formula for the hydrolysis product of TTCP in the presence of fluoride can be expressed as follows: Ca10-x(HPO4)x(PO4)10-x(OH)2-x-yFy.

Journal Article↗