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PubMed2000

In vitro apatite induction by phosphophoryn immobilized on modified collagen fibrils.

Noncollagenous phosphoproteins that interact with type I collagen are thought to nucleate the mineral phase to collagen network of mineralized tissues. Previously, we found that phosphophoryn cross-linked to type I collagen was an effective nucleator of apatite. Here, we investigated the potential role of collagen telopeptide structure on this nucleation. We used pepsin and sodium borohydride (NaBH4) to modify the telopeptide region and reducible cross-links in the collagen fibrils and determined the effect on mineral induction by phosphophoryn cross-linked to it. The amount of phosphophoryn cross-linked to NaBH4-reduced collagen fibrils was higher than that to intact (unmodified) collagen fibrils. However, the amount of phosphophoryn cross-linked to collagen that lacked the telopeptides (atelocollagen) was 25% of that cross-linked to intact collagen fibrils. Each preparation was incubated at 37 degrees C in metastable calcium phosphate solutions that did not spontaneously precipitate. Apatite was induced by phosphophoryn cross-linked to intact collagen fibrils at 15.0 h whereas phosphophoryn cross-linked to reduced collagen fibrils induced apatite formation after 10.9 h. Enough phosphophoryn was cross-linked to atelocollagen to induce mineral formation, but it did not. The failure of the phosphophoryn-atelocollagen complex to nucleate mineral might have been caused by a cross-linking pattern in the helical portion of the collagen molecule that did not promote the growth of the calcium-phosphate clusters into nuclei. The present study indicates that the telopeptide domains of type I collagen play a role in the interaction with phosphophoryn, which is critical for the nucleation process.

Animals↗

PubMed1998

General principle of ordered apatitic crystal formation in enamel and collagen rich hard tissues.

The biomineralization processes in different hard tissues like enamel, circumpulpal dentine, epiphyseal growth plates were analyzed morphologically and ultrastructurally by an energy filtering transmission electron microscope. In the primary stage of crystal formation Ca- and phosphate-ions accumulate at charged sites, "active sites", along the fiber matrix-molecules of the extracellular matrix. After exceeding the critical radius for nucleation, crystal nuclei appear that develop to "chains" of stable nanometer-sized paracrystalline particles. In the latest studies of small area electron diffraction it was found that in the earliest stage of crystal formation these mineral chains show a parallel orientation in the direction of the c-axis of apatite. This was supported by a texture of the 002 reflection in the corresponding diffraction patterns. Since apatite is bipolar in this direction crystal growth would be in like manner in both directions. Thus the center-to-center distances between nucleating sites along the matrix macromolecules show with the chains of nanometer islands the same process of biomineralization in the different mineralizing hard tissue systems. This way of crystal formation might be a general principle of apatitic biomineralization.

Animals↗

PubMed1978

Structural role of bone apatite in human femoral compacta.

Tensile and compressive strength of human femoral compacta have been shown to be related (P is greater than 0.005) to the average bone apatite crystallite length (D002) as determined by X-ray diffraction line breadth measurement. However, statistical variance of crystallite length was not sufficient to explain observed differences in mechanical properties, these differences being primarily due to variation in mineral density. Average bone apatite crystallite length was not found to change significantly with biological age (P=0.30) over the range 3 1/2 to 87 years. It is concluded that increased bone apatite crystallite length is detrimental to the structural role of the skeleton but that this is not a major factor in determining fracture incidence in the elderly.

Adolescent↗

PubMed1998

Dentinal tubule occlusion with lanthanum fluoride and powdered apatite glass ceramics in vitro.

To simulate hypersensitive dentin, the smear layer and dentinal plugs of bovine root dentin specimens were removed by immersion in 10% phosphoric acid, polishing with hydroxyapatite particles, and ultrasonic cleansing. The fluoride-tannic acid-lanthanum-apatite (FTLA) group was treated with acidulated phosphate fluoride (APF) containing tannic acid followed by rubbing with a paste of lanthanum chloride (LaCl3) and powdered apatite glass ceramics. The treated specimens were immersed in a remineralizing solution that mimics saliva for 6 weeks. The SEM observations revealed that the treated surfaces of the FTLA group were completely covered with fine spherical compounds and the dentinal tubules were occluded with plugs to a depth of about 3 microns. Fluoride and lanthanum were detected to a depth of over 20 microns by EPMA observation. After the remineralization, the surface of FTLA-treated specimen did not have any opened tubules and showed a remarkable increase in the number of fine spherical deposits in the dentinal tubules. These results suggest that the reaction products produced by sequential treatment with acidic fluoride and LaCl3 and powdered apatite glass ceramics are able to effectively occlude dentinal tubules.

Acidulated Phosphate Fluoride↗

PubMed2003

[Investigation of biocompatibility of the apatite cement].

The results of experimental studies of biocompatibility of the apatite cement, implanted in the muscular tissue of rats and bone tissue of rabbits were presented in this study. Investigations of the local reactions of the muscular tissue were carried out on 18 rats of Wistar type by implanting samples from the apatite cement in the dorsal muscles. Macroscopic and microscopic investigations were carried out 7, 14, 30, 180, 270 days after the implantation. Investigations of local reactions of bone tissue were carried out on 12 rabbits of New Zealand breed. By implanting the tested material into the femoral bone in the region of trochanter. Sections of the animals were made 1, 3, 6, and 9 months after the surgery. In the early period active inflammatory process was seen in the muscles in the direct vicinity of the implant and then it disappeared leading to formation of a thin fibrous connective tissue capsule. Histological investigations made of bone tissue later showed, formation of young tissue with small focuses of fibrous connective tissue. In the carried out investigations it was shown that the apatite cement is characterized with a high degree of biocompatibility and osteoinductive activity.

Animals↗

PubMed2004

[The effect of a simulated inflammation procedure in simulated body fluid on bone-like apatite formation on porous HA/beta-TCP bioceramics].

The formation of bone-like apatite on porous HA/beta-TCP bioceramics in dynamic simulated body fluid (SBF) undergoing a simulated inflammation procedure (pH = 6.5) was investigated in order to study the mechanism of osteoinduction and build a new method to choose biomaterials with better bioactivity. The results showed that the surface of porous HA/beta-TCP bioceramics which underwent a simulated inflammation procedure in dynamic SBF was more smooth. The light acidity in the simulated inflammation procedure would dissolve the fine grains and the parts possessing smaller curvature radius on the surface of porous HA/beta-TCP bioceramics, which would reduce the bioceramics solubility. Followed in normal SBF (pH = 7.4), the amount of bone-like apatite formed on the porous HA/beta-TCP bioceramics was less than that of porous HA/beta-TCP bioceramics incubation in normal SBF all along. The results also showed that the amount of bone-like apatite formed on the porous HA/beta-TCP bioceramics sintered by a microwave plasma was more than that of porous HA/beta-TCP bioceramics sintered by a conventional furnace.

Apatites↗

PubMed2006

[Chemical stabilization technology in treating with flyash using apatite].

Toxicity leaching characteristics and chemical compositions of sample flyash collected from municipal solid waste incinerator was analyzed, it was clear that different heavy metals were contained in flyash and the heavy metal leaching concentration for Pb, Zn, Cd was 11.8, 164.9 and 31.2 mg/L respectively which was much higher than that in Hazardous Waste Toxicity Leaching Standards. A new kind of inorganic chemical agent apatite was chosen to treat with this kind of incineration flyash, the results indicate that the heavy metals (not including Cd in some samples) in the treated flyash using apatite at dosage 7% can reach the landfilling standards for hazardous waste, and the treated flyash can have better stabilization when the size of apatite was 74 microm, and the heavy metal leaching concentration of the treated flyash keep stable at a curing time of 1 day, and it can keep stabilization with a broader pH value of 3 to 11. Thus the risk of secondary pollution for the treated flyash was reduced dramatically when the environment conditions change.

Apatites↗

PubMed1989

Solution-mediated transformation of octacalcium phosphate (OCP) to apatite.

OCP crystals were hydrolyzed in solutions containing Ca2+, Mg2+, HPO4(2-), CO3(2-), F-, citrate or P2O7 ions. Products of hydrolysis were analyzed using scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy and x-ray diffraction. Results demonstrated that the OCP to Apatite (AP) transformation is influenced by: (1) types of ions in solution: inhibited by Mg2+, citrate or P2O7(4-); facilitated by F-, CO3(2-), HPO4(2-) or Ca2+ ions; (2) ionic concentrations; (3) solution pH; (4) OCP crystal size. SEM showed needle-like micro-crystals on the surfaces and ends of OCP macrocrystals. TEM showed side-to-side and end-to-end arrangements and presence of central defects in the apatite crystals. IR spectra showed the incorporation of CO3, or HPO4, the HPO4 incorporation being least from F-containing solutions. These results suggest that OCP to AP transformation occurred by the process of dissolution of OCP and subsequent precipitation of Ca-deficient apatites, incorporating CO3(2-), HPO4(2-) or F- present in solution. These results indicate that the observed stability of OCP in pathological calcifications may be due to the presence of Mg2+, citrate and/or P2O7(4-) and/or low levels of CO3(2-), F-, Ca2+, HPO4(2-) ions in the biological fluids.

Apatites↗

PubMed1978

[Experimental silicosis. Evaluation of the silicogenic properties of apatites and phosphorites].

White rats were intratracheally injected with 50 mg of apatite or phosphorite dust. The animals were killed 3, 6 and 10 months after the injection. Fibrogenic properties were evaluated on the basis of biochemical and histopathological studies. It was found that the dusts under examination after 3 months of experiment induced a statistically significant increase of wet and dry lungs weight, of hydroxyproline and lipids content in the lungs, and intrathroacic lymph nodes as compared with the control group. After 3 and 10 months, a further but statistically insignificant increase of hydroxyproline content in lungs and of wet lung weight was observed, as compared with animals in the 3--months experiment. The obtained values of fibrogenic action indices for apatite and phosphorite dusts were quite similar to the values obtained in animals injected with inert dust of titanium dioxide. They were 4--5 times lower than the indices obtained after administrating the river sand--a dust of strong fibrogenic properties. Histopathological studies primarily revealed inflammatory changes in bronchial and peribronchial tissue, and focal emphysematous changes, whereas no features of a progressive development of fibrous changes in lungs. The MAC values of 6 mg/m3 for phosphorite dust of 8 mg/m3 for apatite dust--were suggested.

Animals↗

PubMed1993

Pressure sintering of apatite-collagen composite.

Preparation of a composite consisting of apatite and collagen was attempted. Starting from an aqueous solution of collagen, phosphoric acid, and calcium hydroxide suspension, an apatite (90wt%)-collagen (10wt%) composite of 1.75 g/ml in apparent density, with 2 GPa in Young's modulus, and 6.5 MPa in compression strength was synthesized at 40 degrees C, 200 MPa, successfully. It was found that the presence of liquid water in the system was essential for the sintering of the composite under high pressures. Without liquid water, the specimen that was pressure treated and brought in atmospheric pressure, broke into small pieces due to residual strain. The prepared composite could be cut by a razor blade, and was stable against immersion in water. The mean size of the apatite crystals in the composite was 10 nm in width and 40 nm in length.

Apatites↗

PubMed1996

Characterization of apatite layer formation on P2O5-CaO, P2O5-CaO-Na2O, and P2O5-CaO-Na2O-Al2O3 glass hydroxyapatite composites.

P2O5-based glass hydroxyapatite (HA) composites denoted HA-2 oxide, HA-3 oxide, and HA-4-oxide, were immersed in Hank's balanced salt solution for a period of 1, 2, 3, and 4 weeks at 37 degrees C in nonagitated condition for in vitro evaluation. A surface layer was precipitated on the composites that was analyzed using scanning electron microscopy (SEM), X-ray photoelecton spectroscopy, and thin film X-ray diffractometry (TF-XRD). SEM micrographs showed complete coverage of the composite surface by crystallites after immersion of 1 week in the solution, which grew thicker with respect to immersion time. The binding energies measured by XPS indicated apatite formation and the presence of carbonate on the composite surface, showing the newly formed layer was a carbonated apatite. Confirmation of the formed apatite layer was obtained by TF-XRD.

Glass↗

PubMed1999

Influence of P2O5 on crystallinity of apatite formed in vitro on surface of bioactive glasses.

Two sol-gel glasses with 80 mol % SiO2 were prepared in the system SiO2-CaO-P2O5; the first one had 3 mol% P2O5 in its composition, and the second one was P2O5 free. The in vitro behavior of glasses was studied by soaking them in simulated body fluid for 7 days at 37 degrees C. After the in vitro test, the study by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, electron diffraction, and transmission electron microscopy showed an apatite-like layer had formed on the surface of both glasses. However, for identical soaking time, the apatite crystals formed on the surface of the glass containing P2O5 in the composition were larger. Therefore, the presence of P2O5 in the sol-gel glass composition promotes the crystal growth of the apatite.

Ceramics↗

PubMed1988

Crystallographic structure and surface morphology of sintered carbonated apatites.

Densely sintered synthetic hydroxyapatite (HA) is used as an implant material because of its excellent tissue biocompatibility. In order to maximize the biological potential of this calcium phosphate, we have investigated the incorporation of carbonate into HA to make a material which more closely resembles the mineral found in bones and teeth. The aim of the present study was to determine the conditions under which sintered carbonated apatites of specific carbonate content could be produced. The apatites were prepared by heating compressed pellets of precipitated carbonated apatite under a carbon dioxide/steam or nitrogen/steam atmosphere between 825 and 1050 degrees C. The products were analyzed chemically and the surfaces examined by x-ray diffraction, infrared spectroscopy, reflected light microscopy, and scanning electron microscopy. The results showed that carbonate loss during sintering could be reliably predicted, making it possible to produce materials with specific carbonate content, and with specific physical and chemical composition.

Carbonates↗

PubMed1994

The role of hydrated silica, titania, and alumina in inducing apatite on implants.

Pure soluble silica prepared by a sol-gel method induced bone-like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel-derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bone-bonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel-derived silica and titania are important for hydroxyapatite induction. material which possesses and/or develops both a negatively charged surface and abundant OH groups in a physiologically-related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone-bonding biomaterials.

Aluminum Oxide↗

PubMed2004

Ultrastructural comparison of dissolution and apatite precipitation on hydroxyapatite and silicon-substituted hydroxyapatite in vitro and in vivo.

Recent histological studies have demonstrated that the substitution of silicate ions into hydroxyapatite (HA) significantly increases the rate of bone apposition to HA implants. The enhanced bioactivity of silicon-substituted HA (Si-HA) over pure HA has been attributed to the effect of silicate ions in accelerating dissolution. In the present study, high-resolution transmission electron microscopy (HR-TEM) was employed to compare dissolution of HA and Si-HA in an acellular simulated body fluid (SBF) to dissolution in an in vivo model. HR-TEM observations confirmed a difference in morphology of apatite precipitates in vivo and in SBF: apatite deposits were platelike in vivo and nodular in SBF. Compositional mapping suggested that preferential dissolution of silicon from the implant promotes the nucleation of carbonate apatite around the implant. The in vivo findings illustrated an absence of dissolution at the bone-HA or Si-HA interface, whereas dissolution was extensive from within the implant. The amount of dissolution in acellular SBF was similar to dissolution from within the implant, although the site at which the dissolution nucleates was different: dissolution predominates at the crystallite surfaces in SBF, whereas grain boundary dissolution predominates in vivo. These findings suggest that proteins in the in vivo milieu modify the processes of dissolution from the implant.

Biocompatible Materials↗

PubMed1976

An X-ray diffraction investigation of age-related changes in the crystal structure of bone apatite.

Evidence relating to the existence of crystalline bone mineral in vivo is considered, and bone apatite crystal structure investigated using an x-ray powder diffraction technique. Specimens of femoral compacta excised post-mortem from male and female subjects ranging from 3 1/2 years to 87 years of age have been studied. Values of the ratio c/a of bone apatite crystal cell axes for females are significantly higher (p less than 0.05) than for males. Moreover, significant change of c/a with age is observed for males (p = 0.0005) but not for females (p = 0.30). Differences in c/a are interpreted as indicating substitution of constituent ions in the bone apatite crystals.

Adolescent↗

PubMed1977

An x-ray study of the paracrystalline nature of bone apatite.

X-ray diffraction from oriented bone sections show that the crystalline apatite content of untreated mature cortical bovine bone has, in fact, a paracrystalline structure (i.e., no long range order). There is anisotropy in both lattice distortions and the sizes of the coherently diffracting domains. The paracrystalline mean distance fluctuations (g) were found to be 1.5 (+/- 0.1)% and 2.9 (+/- 0.2)% for the basal and prism planes respectively, the corresponding paracrystalline sizes being 220 (+/- 20) and 70 (+/- 10) A. The paracrystalline structure became more ordered above 600 degrees C, suggesting the association of hydroxyl and possibly carbonate and other ions with the paracrystalline structure. The paracrystalline model for bone apatite helps explain anomalies between X-ray and electron microscope measurements of crystal size and also more of the biological functions of the crystalline apatite.

Animals↗

PubMed1989

Insolubilization of apatite-collagen composites by UV irradiation.

The physico-chemical properties and biocompatibility of insolubilized apatite-collagen composites were examined. A carbonate-containing hydroxyapatite with chemical composition and crystallinity similar to that of bone was synthesized at pH 7.4 and 60 degrees C. The apatite powder was mixed with collagen solution, whose antigenicity had been removed by enzymatic treatment and formed into apatite-collagen pellets. After insolubilization by UV irradiation for 4 h, the composites showed remarkably reduced disintegration and showed good biocompatibility when implanted into rat abdomen.

Animals↗