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PubMed2005

Microsphere of apatite-gelatin nanocomposite as bone regenerative filler.

In this study, we developed novel microspheres comprised of an apatite-gelatin nanocomposite. This microsphere formulation is considered to be useful as a bone regenerative filler, either directly or combined with polymeric matrices. Using the water-in-oil emulsion technique, the apatite-gelatin viscous nanocomposite solution was successfully formulated into microspheres with an average diameter of approximately 110 microm. The microspheres were composed of apatite nanocrystallines precipitated within the gelatin matrix, revealing a typical nanocomposite internal structure. This nanocomposite structure contrasted markedly with that of the conventional composite microspheres which were obtained by directly mixing gelatin with apatite powder. Initial cellular assays showed that the microspheres maintained the adhesion and proliferation of the osteoblastic cells, suggesting the usefulness of the apatite-gelatin nanocomposite microspheres in the bone regeneration field.

Apatites↗

PubMed1991

Histologic findings of apatite-titanium complex dental implants in the jaws of dogs.

This study concerns the histologic examination of apatite-titanium complex dental implants (two-piece, cylindrical type) in dogs. There was no plaque control. One to 3 months after implantation, the surface of the apatite root was directly bound to newly formed, woven bone. Seven-and-a-half months to 1 year after implantation, the apatite root was directly bound to the newly formed lamellar bone, which provided strong bone bonding (apatite-bone bonding). There appear to be two types of mechanisms for the resorption of apatite ceramics: first, cellular-type resorption by both multinuclear and mononuclear macrophages; and second, a noncellular, fluid mechanism (dissolution). The gingival sulcus around implants and downward growth of the epithelial cells could be observed in almost all of the implants. There was no cellular inflammation in the tissue around the implants, in the nasal cavity, or in the maxillary sinus. From this study we concluded that clinical application of this dental implant system would be practical.

Animals↗

PubMed1987

Comparison of calcium phosphate glass ceramics with apatite ceramics implanted in bone. An interface study--II.

In order to study bone tissue interaction on calcium phosphate glass ceramics and on apatite ceramics, cylinders of standard size were implanted in the tibiae of rabbits. The materials were evaluated by radiography, light microscopy and microradiography. Apatite ceramics gave rise to a very close contact with new bone. Glass with an apatite surface evoked bone growth similar to that for apatite ceramics but with a loose contact while glass without an apatite surface gave rise to porous remodelling of new bone without close contact to the implant.

Animals↗

PubMed1989

A comparative electron microscopic study of apatite crystals in collagen fibrils of rat bone, dentin and calcified turkey leg tendons.

Crystal-collagen relationships in calcified turkey leg tendons and cortical bone and dentin of the rat were studied by bright field and selected-area dark field electron microscopy. The latter imaging technique enables the specific and direct visualization of apatite crystal sizes and their crystallographic orientations within collagen fibrils. Cortical bone possessed the longest mean c-axial length (170 +/- 50 A), then the tendon (142 +/- 43 A) and the smallest was dentin (110 +/- 30 A). Crystallographic orientations of apatite were found to alternate between a,b- and c-axial planes along the axial period of longitudinally sectioned collagen. This distribution of apatite may reflect a crystal alignment with collagen molecules as they spiral in superhelical fashion along the long axis of the collagen fibril. Apatite crystals were localized within both the gap and overlap zones of collagen fibrils even at very early stages of mineralization. The relative amounts of mineral within single collagen periods were determined as a function of electron absorbency. In the tendon at the onset of mineralization 80% of the mineral was located in the gap zone and 20% in the overlap zone; with further mineralization these relative amounts changed to 55% in the gap zone and 45% in the overlap zone. This 55/45% ratio observed in the heavily mineralized tendon was also observed in both cortical bone and dentin. The implications of these findings are discussed in view of collagen molecular ordering and the spread of apatite along collagen fibrils.

Animals↗

PubMed2005

Photoluminescence of annealed biomimetic apatites.

Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid. The development of the crystal phases was monitored by X-ray diffractometry in addition to Fourier-transform infrared spectroscopy. The microstructure of the biomimetic apatites and phase composition was analysed using scanning and transmission electron microscopy as well as attached energy dispersive X-ray spectrometry. The samples were annealed in air yielding in an inherent luminescence of the biomimetic apatite up to temperatures of 600 degrees C. The photo-induced emission spectra were recorded in the range from 400 to 750 nm at excitation wavelengths ranging 310-450 nm. A blue (437 nm) and a green (561 nm) emission were found between 200 and 600 degrees C visually appearing white. Photoluminescence of annealed biomimetic apatites might be of interest for histological probing and monitoring of bone re-modelling. The results are discussed in terms of chemical and crystallographic changes in the calcium phosphate layer during heat treatment.

Apatites↗

PubMed2005

Control of apatite crystal growth in a fluoride containing amelogenin-rich matrix.

To study how crystal growth in dental enamel is controlled by the components of the extracellular matrix, we investigated the functional roles of amelogenins and fluoride ions in apatite formation occurring through an octacalcium phosphate (OCP)-precursor pathway. Using a cation selective membrane system as a model of tooth enamel formation, we evaluated the resulting mineral habit grown in native porcine amelogenins and fluoride ions. In the absence of amelogenin and in the presence of 1 or 2 ppm F, we obtained OCP + apatite and apatite, respectively. Without amelogenins, the crystals were hexagonal prisms and cones with diameters of approximately 100-200 nm. In the presence of 10% amelogenins and in the absence of fluoride, rod-like OCP with a diameter of 35 nm were obtained. Remarkably, a combination of amelogenin and fluoride created the formation of rod-like apatite crystals with dimensions similar to the former crystals. These observations indicate a cooperative role of amelogenin and fluoride in the regulation of habit, size orientation and phase of the calcium-phosphate crystals, resulting in the formation of fine rod-like apatite whose habit and orientation were similar to that of authentic tooth enamel crystals. The significant modulating effect of the amelogenin matrix combined with fluoride ions suggests the potential for this artificial system to contribute to the engineering of novel enamel-like biomaterials in vitro.

Amelogenin↗

PubMed2005

In vitro apatite formation and its growth kinetics on hydroxyapatite/polyetheretherketone biocomposites.

The formation of biologically equivalent carbonate-containing apatite on the surface of synthetic hydroxyapatite (HA) is an important step leading to good bone healing. In this study, HA-reinforced polyetheretherketone (PEEK) composites were prepared by homogeneous mixing of HA and PEEK powders, compaction, and pressureless sintering. The bioactivity of HA/PEEK composite with 10, 20, 30 and 40 vol% HA was evaluated by immersing the composite disks in the simulated body fluid (SBF) for up to 4 weeks. The surface of composite with 40 vol% HA was covered by a layer of bone-like apatite just after 3 days of immersion, while 10 vol% HA was covered only after 28 days. This apatite layer was characterized by SEM, thin film X-ray diffractometer, attenuated total reflectance-Fourier transform infrared spectrometer (FTIR)/FTIR. Introducing a concept called apatite-forming capacity of SBF, growth kinetics of the apatite layer on the surface of the composite disks was carried out. The growth rate constant increased with HA volume fraction of the composite, suggesting that the bioactivity of the HA/PEEK composite increases with increasing HA volume fraction in the composite.

Apatites↗

PubMed2005

Nucleation of biomimetic apatite in synthetic body fluids: dense and porous scaffold development.

The effectiveness of synthetic body fluids (SBF) as biomimetic sources to synthesize carbonated hydroxyapatite (CHA) powder similar to the biological inorganic phase, in terms of composition and microstructure, was investigated. CHA apatite powders were prepared following two widely experimented routes: (1) calcium nitrate tetrahydrate and diammonium hydrogen phosphate and (2) calcium hydroxide and ortophosphoric acid, but using SBF as synthesis medium instead of pure water. The characteristics of the as-prepared powders were compared, also with the features of apatite powders synthesized via pure water-based classical methods. The powder thermal resistance and behaviour during densification were studied together with the mechanical properties of the dense samples. The sponge impregnation process was used to prepare porous samples having morphological and mechanical characteristics suitable for bone substitution. Using this novel synthesis was it possible to prepare nanosized (approximately equal to 20 nm), pure, carbonate apatite powder containing Mg, Na, K ions, with morphological and compositional features mimicking natural apatite and with improved thermal properties. After sintering at 1250 degrees C the carbonate-free apatite porous samples showed a surprising, high compressive strength together with a biomimetic morphology.

Apatites↗

PubMed2005

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid.

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

Apatites↗

PubMed2006

Spontaneous growth of a laminin-apatite nano-composite in a metastable calcium phosphate solution.

We have previously reported that a laminin-apatite composite layer is formed on an ethylene-vinyl alcohol copolymer (EVOH) in a laminin-containing calcium phosphate (LCP) solution. In this work, the stability of the LCP solution and growth process of the laminin-apatite composite layer have been investigated. Dynamic light scattering technique revealed that the LCP solution was stable for periods as long as 24 h; it did not induce homogeneous precipitation of laminin or calcium phosphates in the solution. Analysis of the EVOH surface and the LCP solution showed that the laminin-apatite composite layer was formed via coprecipitation of laminin and apatite on the EVOH plate, i.e., spontaneous growing of apatite and simultaneous immobilization of laminin molecules or laminin-calcium phosphate nano-complexes onto its surface. Transmission electron microscopy also revealed that the laminin molecules in the resulting composite layer were not localized or aggregated, but were dispersed on a nano-scale in the entire layer. Because of this nano-composite structure, a large number of laminin molecules were stably immobilized on the EVOH plate. This may be responsible for the excellent cell adhesion properties of this type of composite material.

Animals↗

PubMed1983

A high-resolution electron microscope study of synthetic and biological carbonated apatites.

A series of synthetic carbonated apatites and human dental enamels characterized by chemical analysis, infrared spectroscopy, and X-ray diffraction was studied using high-resolution transmission electron microscopy. Steps on the surfaces of apatite crystals, often only a few unit cells high and occasionally one unit cell high, were observed by their Fresnel diffraction contrast. Highly substituted synthetic carbonated apatites appeared to have more irregular and finer-textured surface features than materials with less carbonate substitution. The surface features of enamel apatite crystal were also irregular, but surface steps were less frequently aligned in crystallographic directions. Complex strain fields due to radiation damage centers were observed in some crystals and the fine structure of dislocations and grain boundaries in synthetic apatites was resolved at high magnification. Experimental lattice-image contrasts, in favorable circumstances, could be matched to computer-simulated images and were found to contain detail at near atomic resolution, around 2.0-2.5 A.

Adult↗

PubMed1994

Evaluation of an apatite cement as a root end filling material.

A self-setting apatite cement, EBA cement, and amalgam with varnish were tested for root end sealing ability using a fluid filtration and dye technique. Single-rooted human teeth were prepared in vitro to receive root end fillings. Experimental groups were amalgam with two layers of varnish, EBA cement with dry cavity, EBA cement within a wet cavity, apatite cement within a dry cavity, and apatite cement within a wet cavity. Fluid filtration measurements were made at 6, 24, and 7 days, and 1 and 3 months. Each specimen was also subjected to a dye leakage test using Procion Green dye at 3 months. Results indicated that apatite cement provided a comparable seal to amalgam and EBA cement. This finding, in conjunction with its excellent biocompatibility, suggests that apatite cement is an acceptable alternative to present-day root end filling materials.

Aluminum Oxide↗

PubMed2001

Preparation of porous composite implant materials by in situ polymerization of porous apatite containing epsilon-caprolactone or methyl methacrylate.

Biodegradable and biostable composite foams were formed from porous apatite cement infiltrated with epsilon-caprolactone (CL) or methylmethacrylate (MMA) using a high over vacuum. For CL composites in situ polymerization was induced using trace water as an initiator and heating at 120 degrees C for up to 10 days or at 80 degrees C for 60 days. MMA composites were polymerized using AIBN initiator at 70 degrees C for 8 h. CL preparations gave composites with a polycaprolactone (PCL) number average of molecular weight (Mn) up to the maximum of 7.1 x 10(3) g/mol after 10 days and 16.8 x 10(3) g/mol after 60 days. The PCL and PMMA contents were close to 50 and 40 wt%, respectively, polymer was present as a thin coating on the apatite crystal plates and was evenly distributed throughout the samples. Re-evacuation of apatite saturated with monomer during preparation ensured that the upwards of 200 nm microchannels within the apatite cement were largely free of polymer, and the overall macroporous structure of the apatite foams was partly retained. Maximum compressive strengths increased from 9 MPa to 37 and 64 MPa for PCL and PMMA composites, respectively. The water drop contact angle of the PCL composite was 64 degrees, and therefore suitable for cell attachment. PMMA composite surfaces were more hydrophobic. Composites were subjected to corona discharge to induce suitable moderate hydrophilicity at the surface.

Apatites↗

PubMed2001

Biomimetic apatite formation on polyethylene photografted with vinyltrimethoxysilane and hydrolyzed.

A photografting technique to produce functional groups of silanol able to induce apatite nucleation was attempted on polyethylene substrate for biomimetic formation of bone-mineral-like apatite layer on its surface. The polyethylene surface was subjected to vapor-phase photografting of vinyltrimethoxysilane and subsequently to hydrolysis. The photografting formed methoxysilyl groups on the polyethylene substrate, which was changed into silanol groups successively by the hydrolysis in a hydrochloric solution. The polyethylene modified in this way formed a dense and homogeneous bone-mineral-like apatite layer in a solution with ion concentrations 1.5 times that of human blood plasma. This result indicates that the biomimetic process in combination with a polymeric grafting technique might provide a homogeneous bone-mineral-like apatite coating even on polymer fibers to be woven into an apatite-polymer composite with three-dimensional structure analogous to that of natural bone.

Apatites↗

PubMed2002

Interaction of calcium and phosphate in apatite coating on titanium with serum albumin.

A Ca-deficient carbonate apatite coating on titanium was prepared by pre-calcifying titanium in a saturated Ca(OH)2 solution and then immersing in a supersaturated calcium phosphate solution. The interaction of the protein with the apatite coating on titanium was investigated by scanning electron microscopy with X-ray energy dispersion spectroscopy. X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. During immersion of the coating in bovine serum albumin (BSA) solution, accompanied by an adsorption of BSA onto the coating, calcium and phosphate ions dissolved and reprecipitated, resulting in the formation of the coating containing BSA from the surface to subsurface layers. The adsorption modified the structure and morphology of the apatite coating on titanium and changed the protein configuration. It was also found that the protein chemically adsorbed onto surfaces containing calcium or phosphorus, showed that both Ca and P on the apatite coating were the binding sites with protein. The BSA adsorption onto the coating involved several elements and groups. In this process. Ca played an essential role, and the interaction of Ca on the apatite coating with the protein stimulated the bond of the protein at P sites.

Animals↗

PubMed2003

Nucleation and growth of apatite on chemically treated titanium alloy: an electrochemical impedance spectroscopy study.

Bone-like apatite formed on the surface of Ti6Al4V pretreated with NaOH solution after having been immersed in simulated body fluid (SBF), while no apatite formed on the surface of untreated Ti6Al4V. In the present study, electrochemical impedance spectroscopy (EIS) measurement was used to investigate the nucleation and growth of apatite on chemically treated Ti6Al4V immersed in the SBF solution, and the difference between the behaviors of treated and untreated Ti6Al4V. Appropriate equivalent circuit models were constructed to describe the nucleation and growth of apatite, and thin oxide film formed on the surface of untreated Ti6Al4V. It was found that EIS is a useful method for investigating the nucleation and growth of bone-like apatite on Ti6Al4V pretreated with NaOH solution.

Alloys↗

PubMed1999

Sol-gel modification of silicone to induce apatite-forming ability.

Silicones formed with silanol groups on their surfaces were prepared by partial hydrolysis and polycondensation of tetraethoxysilane (TEOS) dispersed in silicones in molecular scale. Although the silanol-modified silicones thus prepared formed no apatite in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma within 21 d, they formed a bone-like apatite layer in situ on their surfaces in a solution (1.5 SBF) with ion concentrations 1.5 times the SBF within 7 d. This indicates that the silanol groups formed on the silicones by the present method can induce the apatite nucleation in 1.5 SBF and hence, apatite-coated silicones can be fabricated by a biomimetic process. Apatite-silicone composites thus prepared could exhibit mechanical properties analogous to the natural bone as well as bioactivity.

Apatites↗

PubMed2003

Molecular-scale characterization of uranium sorption by bone apatite materials for a permeable reactive barrier demonstration.

Uranium binding to bone charcoal and bone meal apatite materials was investigated using U L(III)-edge EXAFS spectroscopy and synchrotron source XRD measurements of laboratory batch preparations in the absence and presence of dissolved carbonate. Pelletized bone char apatite recovered from a permeable reactive barrier (PRB) at Fry Canyon, UT, was also studied. EXAFS analyses indicate that U(VI) sorption in the absence of dissolved carbonate occurred by surface complexation of U(VI) for sorbed concentrations < or = 5500 microg U(VI)/g for all materials with the exception of crushed bone char pellets. Either a split or a disordered equatorial oxygen shell was observed, consistent with complexation of uranyl by the apatite surface. A second shell of atoms at a distance of 2.9 A was required to fit the spectra of samples prepared in the presence of dissolved carbonate (4.8 mM total) and is interpreted as formation of ternary carbonate complexes with sorbed U(VI). A U-P distance at 3.5-3.6 A was found for most samples under conditions where uranyl phosphate phases did not form, which is consistent with monodentate coordination of uranyl by phosphate groups in the apatite surface. At sorbed concentrations > or = 5500 microg U(VI)/g in the absence of dissolved carbonate, formation of the uranyl phosphate solid phase, chernikovite, was observed. The presence of dissolved carbonate (4.8 mM total) suppressed the formation of chernikovite, which was not detected even with sorbed U(VI) up to 12,300 microg U(VI)/g in batch samples of bone meal, bone charcoal, and reagent-grade hydroxyapatite. EXAFS spectra of bone char samples recovered from the Fry Canyon PRB were comparable to laboratory samples in the presence of dissolved carbonate where U(VI) sorption occurred by surface complexation. Our findings demonstrate that uranium uptake by bone apatite will probably occur by surface complexation instead of precipitation of uranyl phosphate phases under the groundwater conditions found at many U-contaminated sites.

Apatites↗