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At least 595 records · Page 33Linked to original sources

PubMed2002

Bone growth in biomimetic apatite coated porous Polyactive 1000PEGT70PBT30 implants.

We recently, developed a simple one-day one-step incubation method to obtain bone-like apatite coating on flexible and biodegradable Polyactive 1000PEGT70PBT30. The present study reports a preliminary biological evaluation on the coated polymer after implantation in rabbit femurs. The porous cylindrical implants were produced from a block fabricated by injection molding and salt leaching. This technique provided the block necessary mechanical integrity to make small cylinders (diameter 3.5 x 5 mm2) that were suitable for implantation in rabbits. The coating continuously covered the surface of the polymer, preserving the porous architecture of outer contour of the cylinders. Two defects with a diameter of 3.5 or 4 mm were drilled in the proximal and distal part of femur diaphysis. The implants were inserted as press-fit or undersized into the cortex as well as in the marrow cavity. The polymer swelled after implantation due to hydration, leading to a tight contact with the surrounding bone in both defects. The adherence of the coating on the polymer proved to be sufficient to endure a steam sterilization process as well as the 15% swelling of the polymer in vivo. The coated Polyactive 1000PEGT70PBT30 has a good osteoconductive property, as manifested by abundant bone growth into marrow cavity along the implant surface during 4-week implantation. A favorable bioactive effect of the coating with an intimate bone contact and extensive bone bonding with this polymer was qualitatively confirmed. Concerning the bone ingrowth into the porous implant in the defect of 4 mm diameter, only marginal bone formation was observed up to 8 weeks with a maximal penetration depth of about 1 mm. The pore interconnectivity is important not only for producing a coating inside the porous structure but also for bone ingrowth into this biodegradable material. This preliminary study provided promising evidence for a further study using a bigger animal model.

Animals↗

PubMed2003

Calcium-deficient apatite: influence of granule size and consolidation mode on release and in vitro activity of vancomycin.

The use of dynamic compaction and isostatic compression to consolidate calcium phosphate powder loaded with a therapeutic agent avoids a sintering step that could destroy the drug. The present study applied these consolidation methods to vancomycin-loaded calcium-deficient apatite powder, using three granulometric fractions (40-80, 80-200 and 200-500 micrometer). In vitro release profiles were determined via an original system derived from low-pressure liquid chromatography. The biological activity of vancomycin was measured by an in vitro standardized bacteriologic assay, which showed that the drug is completely active after association with calcium phosphate. Regardless of the consolidation method and granulometric fraction used, release profiles were not significantly different and therefore adaptable to injectable suspensions.

Anti-Bacterial Agents↗

PubMed2003

Apatite-forming ability and mechanical properties of CaO-free poly(tetramethylene oxide) (PTMO)-TiO2 hybrids treated with hot water.

Poly(tetramethylene oxide) (PTMO)-TiO(2) hybrids were prepared by a sol-gel method from triethoxysilane-functionalized PTMO (Si-PTMO) and tetraisopropyltitanate with weight ratios of 30/70, 40/60 and 50/50 (hybrids PT30, PT40 and PT50, respectively), and subsequently subjected to a hot-water treatment at 95 degrees C for 2 d. All the obtained hybrids were amorphous before the hot-water treatment, and precipitated nanosized anatase after the hot-water treatment. The amount of precipitated anatase increased with decreasing PTMO content. Apatite was not formed on the surfaces of the hybrids in a simulated body fluid before the hot-water treatment, but was formed after the hot-water treatment, and its amount increased with decreasing PTMO content. Hybrid PT40 showed strength and Young's modulus analogous to those of human cancellous bones, and high ductility after the hot-water treatment. This kind of hybrid is expected to be useful as a new type of bone-repairing material.

Apatites↗

PubMed1997

Nano-apatite/polymer composites: mechanical and physicochemical characteristics.

Hydrothermally synthesized acicular nano-apatite (Nap) was used as filler to make composites with a polyethylene glycol/poly(butylene terephthalate) (PEG/PBT) block copolymer (Polyactive 70:30). The Nap had a particle diameter of 9-25 nm and a length of 80-200 nm. The mechanical properties and the physiochemical characteristics of the composites, such as Young's modulus, swelling degree in water and the calcification behaviour, have been determined. It was found that Nap had a strong ability to promote the calcification of composites when incorporated into Polyactive 70:30, while poly(acrylic acid) (PAA) coating of Nap had an adverse effect on the calcification of composites, presumably due to the formation of complexes between PAA and PEG segments. Nap had a prominent stiffening effect for Polyactive 70:30 in the dry state, but had a poor stiffening effect for composites in an aqueous environment due to the hygroscopic nature and/or the formation of aggregates. PAA coating on Nap had almost no additional effect on the mechanical properties of composites either in the dry state or in an aqueous environment. To reinforce the polymer by Nap, achieving a more homogeneous dispersion of Nap in the polymer matrix and surface modifications to render the powders less hygroscopic appear to be necessary.

Acrylic Resins↗

PubMed1999

Apatite formation on PDMS-modified CaO-SiO2-TiO2 hybrids prepared by sol-gel process.

Dense and homogeneous monolithics of polydimethylsiloxane (PDMS)-modified CaO-SiO2-TiO2 hybrids were successfully synthesized by sol-gel process. They were assumed to be composed of a silica and titania network incorporated with PDMS and the calcium ion ionically bonded to the network. Among them, the hybrids containing relatively larger amounts of the calcium in their surfaces formed an apatite on their surfaces within only 1 or 0.5 day in a simulated body fluid with ion concentrations nearly equal to those of human flood plasma. This indicates that they are highly bioactive. Organic-inorganic hybrids synthesized by a sol-gel process usually exhibit high ductility, low elastic modulus and high mechanical strength. The present hybrids are, therefore, expected to be useful as a new kind of bone-repairing material, because of their high bioactivity and unique mechanical properties.

Apatites↗

PubMed2000

Preparation and characterisation of monoclinic hydroxyapatite and its precipitated carbonate apatite intermediate.

Five 100 g batches of a carbonate apatite (the intermediate) were produced by heating an aqueous slurry of CaCO3 and CaHPO4 with an overall Ca/P mole ratio of 5/3 with vigorous stirring. Each intermediate produced by boiling off water was heated in vacuum at 1100 degrees C to remove carbonate, then steamed at 900 degrees C to ensure complete hydroxylation. Comparison of calculated and observed X-ray diffraction patterns showed final products containing 50-100 wt% monoclinic hydroxyapatite (remainder hexagonal). Rietveld refinements in P6(3)/m gave structures similar to several hydroxyapatite standards, including NIST SRM 2910, although there was no evidence from X-ray diffraction that the latter was in the monoclinic form. Refinements from standards and final products were slightly different from published single crystal data for Holly Springs hydroxyapatite. This is attributed to known impurities in mineral hydroxyapatite and indicates that parameters from the Rietveld refinements are closer to the true values for pure hydroxyapatite. Rietveld refinements for intermediates showed small, but significant differences from the final product, the largest being in O1x, O2x and O(H)z. All P-O bond lengths were shorter than in the final product, resulting in a 3.2% lower PO4 tetrahedron volume. The occupancies of P and Ca(2) were reduced. These differences are attributed to partial replacement of PO4(3) by CO3(2-) ions.

Apatites↗

PubMed2000

Gamma dose response of synthetic A-type carbonated apatite in comparison with the response of tooth enamel.

Synthetic A-type carbonated apatite samples were irradiated at room temperature with 60Co gamma rays. Their ESR spectra consist of the lines of CO2- and CO3- radicals of orthorhombic and axial symmetry. The measurements carried out immediately after sample irradiation showed that CO2- species are produced by decomposition of CO3- radicals. Intensity of the CO2- lines in the synthetic and enamel samples increases during the first 400 and 200 h after irradiation, respectively. The dependence of the EPR signal on the dose varies with carbonate content of the sample. The dose response curve for tooth enamel is steeper for the synthetic material.

Apatites↗

PubMed2001

Fourier transform infrared microspectroscopic investigation of the maturation of nonstoichiometric apatites in mineralized tissues: a horse dentin study.

Fourier transform infrared microspectroscopy (FTIRM) was used to study carbonated apatite/collagen interactions and maturation in horse secondary dentin. Unlike human dentin, this model contains no peritubular material around the odontoblastic processes and is thus quite similar to bone in composition, but not subject to tissue turnover. Crystals close to the mineralization front were very immature, showing high HPO(4) and very low CO(3) levels. Carbonate ions were located essentially in very labile, reactive environments, probably on the crystal surface. Removal of some of the HPO(4) ions from crystals during maturation was linked to an increase in total carbonate content. The CO(3) ions in labile environments decreased, probably after incorporation into more organized regions of the lattice. However, this increase of total carbonate content was associated with greater mineral crystallinity, confirming findings in other studies of synthetic apatite maturation in vitro. The good correlation between these results and those of in vitro experiments suggests that crystal maturation is essentially due to physicochemical processes and that the organic matrix controls only crystal size, multiplication, and/or organization.

Animals↗

PubMed2002

Unique alignment and texture of biological apatite crystallites in typical calcified tissues analyzed by microbeam X-ray diffractometer system.

Preferential orientation of biological apatite (Ap) crystallites in typical calcified tissues of rabbit ulna, rabbit skull, and monkey dentulous mandible was investigated using a microbeam X-ray diffractometer, with a beam spot of 100 microm in diameter, to clarify relationship between the Ap orientation and mechanical function. Preferential alignment of the c-axis of the biological Ap was evaluated by the relative intensity between (002) and (310) diffraction peaks. Preferential alignment of biological Ap in each calcified tissue varied depending on the shape and stress condition in vivo; that is, the c-axes of biological Ap in the rabbit ulna and the rabbit skull bone were preferentially observed as a one-dimensional orientation along the longitudinal axis and a two-dimensional orientation along the surface, respectively. Precise analysis of the preferential alignment along the skull surface showed an elliptical distribution of the c-axis of biological Ap elongating along the suture inside the skull surface of both lamina exterior and interior. The c-axis of biological Ap in a monkey dentulous mandible basically aligned along the mesiodistal direction in the flat bone, but this alignment changed along the normal direction to the flat bone surface parallel to the biting direction near the tooth, due to the force of mastication. It was concluded that the microscale measurement of biological Ap texture is one of the useful new methods for evaluating mechanical function and stress distribution in vivo in calcified tissues.

Animals↗

PubMed2004

In vivo absorption of porous apatite- and wollastonite-containing glass-ceramic.

The behavior of porous apatite- and wollastonite-containing glass-ceramic (AW) in the bone marrow cavity was investigated. Cylinders of porous AW (4 mm in diameter and 20 mm long, mean porosity of 70% and mean pore diameter of 200 microm) were implanted into the bone marrow cavity of rabbit femurs, and analyzed by chronological radiograms and by scanning electron microscopy one, three, six, and 12 months later. The pores of porous AW are interconnected and homogeneously distributed, and its compressive strength is nearly equal to that of human cancellous bone. Bone formed in the pores at the center of the material by one month and bonded to the material directly. The volume of newly formed bone in the material pores reached a peak at three months, and decreased gradually after six months. The trabecular structures of AW were gradually remodeled by newly formed bone, while AW-bone bonding was maintained during bone remodeling and material absorption. AW was absorbed continuously, and at six and 12 months the residual material corresponded to about 64 and 30% of the starting material, respectively. Porous AW may therefore be useful as an absorbable bone substitute.

Absorbable Implants↗

PubMed2001

Ultrastructural analysis of structural framework in dental plaque developing on synthetic carbonate apatite applied to human tooth surfaces.

This study focused on determining the structural framework by oral microbiota in supragingival plaque on a carbonate apatite film applied to human tooth surfaces. The sequential phases of plaque formation over a 3-wk period were found to be equivalent to those previously reported for natural tooth surfaces. Scanning electron microscopy of specimens prepared by vertical sectioning demonstrated the organization of two types of framework between certain genera of initial and secondary colonizers in the pre- and post-organization phases, respectively. The initial colonizers in the pre-organization phase were of a coccoid type, while colonizers in the post-organization phase were of a bacillary type. Secondary colonizers, filamentous cells, were common to both frameworks. Transmission electron microscopy using freeze-substitution and immunohistochemistry demonstrated two types of coaggregation, fibril- and saliva-mediated modes, among the plaque microbiota. Coaggregation between microbiota, which organized the framework, showed a tendency to occur in the fibril-mediated mode, and the filamentous secondary colonizers were characterized by inducing multigeneric coaggregation. The present findings indicate that a structural framework and specific cells to form this framework are essential for plaque formation.

Adult↗

PubMed1995

Rapidly forming apatitic mineral in an osteoblastic cell line (UMR 106-01 BSP).

This study evaluated a rapid biomineralization phenomenon exhibited by an osteoblastic cell line, UMR 106-01 BSP, when treated with either organic phosphates [beta-glycerophosphate (beta-GP), Ser-P, or Thr-P], inorganic phosphate (P(i)), or calcium. In a dose-dependent manner, these agents (2-10 mM) stimulated confluent cultures to deposit mineral in the cell layer (ED50 of approximately 4.6 mM for beta-GP (30 +/- 2 nmol Ca2+/microgram DNA) and approximately 3.8 mM (29 +/- 2 nmol Ca2+/microgram DNA) for P(i)) with a plateau in mineral formation by 20 h (ET50 approximately 12-15 h). beta-GP or P(i) treatment yielded mineral crystals having an x-ray diffraction pattern similar to normal human bone. Alizarin red-S histology demonstrated calcium mineral deposition in the extracellular matrix and what appeared to be intracellular paranuclear staining. Electron microscopy revealed small, needle-like crystals associated with fibrillar, extracellular matrix deposits and intracellular spherical structures. Mineral formation was inhibited by levamisole (ED50 approximately 250 microM), pyrophosphate (ED50 approximately 1-10 microM), actinomycin C1 (500 ng/ml), cycloheximide (50 micrograms/ml), or brefeldin A (1 microgram/ml). These results indicate that UMR 106-01 BSP cells form a bio-apatitic mineralized matrix upon addition of supplemental phosphate. This process involves alkaline phosphatase activity, ongoing RNA and protein synthesis, as well as Golgi-mediated processing and secretion.

Alkaline Phosphatase↗

PubMed2004

Bone acidic glycoprotein-75 delineates the extracellular sites of future bone sialoprotein accumulation and apatite nucleation in osteoblastic cultures.

Addition of an organophosphate source to UMR osteoblastic cultures activates a mineralization program in which BSP localizes to extracellular matrix sites where hydroxyapatite crystals are subsequently nucleated. This study identifies for the first time novel extracellular spherical structures, termed biomineralization foci (BMF), containing bone acidic glycoprotein-75 (BAG-75), bone sialoprotein (BSP), and alkaline phosphatase that are the exclusive sites of initial nucleation of hydroxyapatite crystals in the UMR model. Importantly, in the absence of added phosphate, UMR cultures after reaching confluency contain two size populations of morphologically identifiable BMF precursors enriched in BAG-75 (15-25 and 150-250 microm in diameter). The shape and size of the smaller population are similar to structures assembled in vitro through self-association of purified BAG-75 protein. After organophosphate addition, BSP accumulates within these BAG-75-containing BMF precursors, with hydroxyapatite crystal nucleation occurring subsequently. In summary, BAG-75 is the earliest detectable biomarker that accurately predicts the extracellular sites of de novo biomineralization in UMR cultures. We hypothesize that BAG-75 may perform a key structural role in the assembly of BMF precursors and the recruitment of other proteins such as alkaline phosphatase and BSP. Furthermore, we propose a hypothetical mechanism in which BAG-75 and BSP function actively in nucleation of apatite within BMF.

Alkaline Phosphatase↗

PubMed1960

Electron microscopic observations on the three-dimensional morphology of apatite crystallites of human dentine and bone.

In sections of human dentine (carious and sound) and bone examined with the electron microscope, apatite crystallites were seen to present long thin profiles somewhat suggestive of a cylindrical shape, broad profiles indicative of a plate-like shape, and profiles intermediate between these two extremes. With a special stereoscopic specimen holder allowing the specimen to be tilted through an angle of 30 degrees it was possible to record images of two profiles of the same crystallite from different angles and thus gain information concerning the 3-dimensional morphology of crystallites showing a thin profile. In all fields so examined, the thin-profile crystallites that were properly oriented with respect to the axis of tilt exhibited a different width dimension in each of the two micrographs. From this it is concluded that the thin profiles actually represented edge views of plate-like crystallites.

Apatites↗

PubMed2003

Ex vivo mechanical evaluation of carbonate apatite-collagen-grafted porous poly-L-lactic acid membrane in rabbit calvarial bone.

Appropriate mechanical recovery is an important parameter in successful restoration of skeletal defects. Carbonate apatite and type I atelocollagen mixture (CAp) was grafted on a porous poly-L-lactic acid (PLLA) membrane to produce a CAp bilayered PLLA membrane (CAp+PLLA). After implantation, regional mechanical change in the membrane was investigated in rabbit calvarial bone defects. Dynamic viscoelasticity and elastic modulus of the implanted specimen were measured after 2, 4, 8, 12, 16, 26, and 52 weeks. The modulus of the peripheral part was higher than that of the central part of the implanted area, whereas the central part demonstrated a gradual increase. This phenomenon indicates that regeneration initially occurs from the periphery of the calvarial bone. After 26 weeks, stiffness of the central part became similar to that of the periphery in the CAp+PLLA-implanted area. According to this result, measuring viscoelasticity of an implanted biodegradable material would be a useful method to determine degrees of regeneration and replacement of an implanted region.

Analysis of Variance↗

PubMed1984

Apatite associated destructive arthritis.

Twelve patients, 11 women and one man, aged 66-83, with a distinctive type of destructive arthropathy are described. The principal joints affected were the shoulders (ten) and knees (seven). Clinical features included pain on use, large cool effusions, instability and rapid progression. Radiographs showed attrition of bone and cartilage with a paucity of reparative changes. Synovial fluids were viscous, with low cell counts, and stained positively for the presence of apatite-containing particles. Extensive calcific material was seen in the synovium of the four patients biopsied, and on the radiographs in seven. Most patients had some associated or preceding joint disorder. The literature on similar cases is reviewed, and the possible role of crystals and other aetiological factors is discussed. It is suggested that a characteristic form of large-joint atrophy can occur in elderly patients at a number of joint sites and in several different clinical settings.

Aged↗

PubMed2004

New method of pediatric cranioplasty for skull defect utilizing polylactic acid absorbable plates and carbonated apatite bone cement.

Cranial defect repair in the pediatric population requires a variety of special considerations. The pediatric skull has a dynamic nature that prohibits the use of rigid fixation, which is commonly applied in the adult population. A technique using a combination of polylactic acid plates and carbonated apatite bone cement has been devised by our group. Skull defects of varying sizes were repaired in 34 pediatric patients. Patients were examined on postoperative day 3 and at 3 months via three-dimensional computed tomography scans. Patients have been followed up to 60 months after surgery without complications or failures to date. This method benefits the pediatric patients undergoing cranioplasty by minimizing the insertion of long-term foreign bodies and allows the possibility for transformation of this construct into viable tissue.

Absorbable Implants↗

PubMed1992

Interactions between acidic matrix macromolecules and calcium phosphate ester crystals: relevance to carbonate apatite formation in biomineralization.

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Earlier studies on the interactions between acidic macromolecules and carboxylate- and carbonate-containing crystals showed that the proteins recognize a specific stereochemical motif on the interacting plane. Here we show that a similar stereochemical motif is recognized by acidic mollusc shell macromolecules interacting with four different organic calcium phosphate-containing crystals. In addition, an acidic protein from vertebrate tooth dentin was also observed to recognize a similar structural motif in one of the crystals. The characteristic motif recognized is composed of rows of calcium ions and phosphates arranged in a plane defined by two free oxygens and a phosphorus atom emerging perpendicular to the affected face. These observations may have a direct bearing on the manner in which control over crystal growth is exerted on carbonate apatite crystals commonly found in vertebrate tissues.

Animals↗