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At least 991 records · Page 55Linked to original sources
PubMed2005

Highly-ordered layered organo-mineral materials prepared via reactions of n-alkylphosphonic acids with apatite.

This work describes a novel class of layered organo-mineral materials manufactured via a single-step solution-phase reaction of n-alkylphosphonic acids (CnH(2n+1)P(O)(OH)2) with calcium hydroxyapatite mineral (CaHAP). TEM, SAXS, WAXS, FTIR, and Vapor Phase Adsorption data suggest that these alkyl-CaHAP materials present a surface-modified CaHAP matrix coated with ordered layers of calcium alkylphosphonates that are strongly adhered to the surface. Interlayer spacing increases from 1.47 (C3-CaHAP) to 4.77 nm (C18-CaHAP). According to FTIR, ordering of alkyl chains improves with the alkyl chain length. The organic loads in these alkyl-CaHAP can be controlled over a wide range (up to approximately 60%) by varying alkyl chain and the concentration of alkylphosphonic acids in the solution.

Journal Article↗
PubMed1999

Improved liquid chromatographic separation of different proteins by designing functional surfaces of cattle bone-originated apatite.

Spherical particles of cattle bone-originated hydroxyapatite (r-HAp) were prepared by dissolution-precipitation, spray-drying using a two fluid-nozzle apparatus, and subsequent heat treatment. The product had effective pore structures for liquid chromatographic separation of albumin, myoglobin, ribonuclease, lysozyme and cytochrome c. The activated surfaces of the r-HAp particles were easily prepared with desired proportions of P- and C-sites and appropriate acid-basic strength for selective protein adsorption by optimizing the synthesis conditions. Liquid chromatography columns packed with the particles exhibited high resolution and durability in protein separation, reflecting stable distribution of pore size.

Animals↗
PubMed1998

Biocompatibility of two apatite cements.

Biocompatibility and osteogenic potential of two calcium phosphate cements (G-5 and G-6) and Super-EBA were investigated by subcutaneous and intraosseous implantation in 90 rats. Reactions were studied microscopically at 15, 30, and 60 days after implantation. Super-EBA was well tolerated by both soft and hard tissues. G-5 was highly biocompatible with resorption and bone replacement at intraosseous implantation sites. G-6 promoted moderate inflammation and a foreign body giant cell response over the 60-day study period. None of the materials elicited osteogenesis or dystrophic calcification at the subcutaneous implantation sites.

Animals↗
PubMed2002

Calcium phosphate apatites with variable Ca/P atomic ratio III. Mechanical properties and degradation in solution of hot pressed ceramics.

Calcium deficient hydroxyapatite powders Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) (0 < or = x < or = 1) were hot pressed to produce dense hydroxyapatite-tricalcium phosphate (HAP/TCP) biphasic materials. Ceramics hot pressed at 1000 degrees C were composed of an homogeneous distribution of the HAP and beta-TCP grains with an average size of 0.2 microm. Grain growth was observed for TCP loading > 70 wt%. The strength exhibited a maximum of sigma(f) = 150 MPa for 90/10 (w/w) HAP/TCP and it dropped for smaller and greater amounts of TCP. This value was twice that of pure HAP. When placed in Ringer's solution, only the surface of biphasic compounds was degraded after 60 days of immersion with a preferential etching of the TCP phase. After hot pressing at 1200 degrees C, grain growth was observed and the mechanical properties were decreased. This was explained by the allotropic transformation alpha/beta of TCP.

Biocompatible Materials↗
PubMed1998

Limited compliance of some apatitic calcium phosphate bone cements with clinical requirements.

Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time and the ultimate compressive strength. Two cements were tested. Biocement H was made of a powder containing alpha-tertiary calcium phosphate and precipitated hydroxyapatite. Biocement F was made of a powder containing, in addition, some monetite. The liquid/powder (L/P) ratio was varied over the range 0.30-0.40 ml g(-1), whereas the accelerator concentration in the liquid was varied from 0%-4% Na2HPO4 in water. For Biocement H there was no combination L/P ratio and % Na2HPO4 for which all clinical requirements were satisfied. However, Biocement F had a certain area where this was the case. Therefore, it is expected that Biocement F can be applied in clinical situations such as orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, even when early contact with blood is inevitable.

Journal Article↗
PubMed1997

Infrared and Raman microspectrometry study of fluor-fluor-hydroxy and hydroxy-apatite powders.

Visible Raman and infrared microspectrometry studies performed on fluorapatite and hydroxyapatite powders have shown similar results. Small modifications of the nu2 and nu4 PO(3-)4 tetrahedra bending modes are observed. A small frequency shift of the nu1 mode and modifications on the nu3 mode region accompanied with a simplification of the hydroxyapatite and fluorapatite respective spectra from seven to four bands were observed. A broad and weak band which could be attributed to the Ca-F bond is detected at 311 cm(-1) on the Raman fluorapatite spectra. The phosphate vibration modes are little disturbed by fluoride substitution. This could indicate that phosphate groups interact strongly between themselves and weakly with substituted atoms (i.e. hydroxyle and fluoride atoms). Whatever crystallographic model is considered, the number of bands observed is always lower than the number of calculated ones, even for hydroxyapatite, whose symmetry is lower than that of fluorapatite.

Journal Article↗
PubMed1997

Treatments to induce the nucleation and growth of apatite-like layers on polymeric surfaces and foams.

In this work, a bioactive glass is used as a percusor of calcium-phosphate (Ca-P) film deposition onto several polymer-based materials. Both bioinert (high molecular weight polyethylene, HMWPE), and biodegradable (corn starch-based blends, SEVA-C) polymers, unreinforced or reinforced with hydroxylapatite (HA), were coated by the very simple proposed route. Also polyurethane (PU) foams, with an open-cell structure, were mineralized by the proposed method. In fact, it was possible to induce the growth of the Ca-P films not only at the surface, but also in the bulk of the PU foam. These cellular materials are intended for cancellous bone replacement applications. The morphology of the formed films was strongly dependent on the used substrate, its polar character, and on the presence of HA in its composition, as observed by SEM. Nevertheless, a well defined needly like structure was observed in all samples at high magnifications. The Ca:P ratios of the films were between 1.5 and 1.7, i.e. in the range of tricalcium phosphate-hydroxylapatite. Raman spectroscopy and thin-film x-ray diffraction (XRD) evidenced the formation of mostly amorphous calcium-phosphate films. After scraping the coating from the polymer surface and heat-treating the resulting powder at 1000 degrees C for 1 h, HA and beta-tricalcium phosphate (TCP) typical peaks were found on XRD patterns.

Journal Article↗
PubMed2003

Encapsulation of apatite particles for improvement in bone regeneration.

The layering of fluorapatite on hydroxyapatite bodies provides a means of decreasing the solubility of hydroxyapatite, providing fluoride for possible stimulation of bone formation and delaying the release of calcium and phosphate from the more soluble hydroxyapatite. The purpose of this work was to encapsulate hydroxyapatite particles with fluorapatite spanning a thickness more than several crystallites deep. A three-step procedure was employed. Hydroxyapatite powder was immersed in an electrolyte solution until an equilibrium was established between the solid and the dissolved calcium at pH 4.67 and 37 degrees C. Equilibrium was determined by measurement of dissolved calcium with a calcium-specific ion-specific electrode. A 5x10(-2) M ammonium fluoride added to the suspension resulted in a rapid decrease of both calcium and fluoride in the solution. Analysis with X-ray diffraction indicated that a fluoride rich layer containing calcium fluoride deposited onto the particle surface. Scanning electron microscopy revealed submicron spherical precipitate clusters on the hydroxyapatite particles. These clusters transformed to fluorapatite by soaking in a 0.1 M K(2)HPO(4) solution at pH 8 and 70 degrees C. A total time of 10 h was necessary for complete transformation of CaF(2) into fluorapatite.

Journal Article↗
PubMed1996

The biocompatibility (cell culture and histologic study) of hydroxy-apatite-coated implants created by ion beam dynamic mixing.

Titanium implants were coated with hydroxyapatite by using a method of ion beam dynamic mixing. Coated and noncoated plates of titanium were placed in a growth medium with fibroblast cells. Implant screws, coated and noncoated, were inserted in rabbit bones and the animals were euthanized after 7, 27, and 122 days, respectively. The results from the cell culture test showed no visible difference between the specimens. Histologic examination of implant specimens indicated more new bone activity against coated screws at 27 days, and that was more pronounced at 127 days. Although the amount of new bone formation was not significantly different, certain signs of favourable new bone formation could be seen in contact with coated implants compared to the noncoated controls.

Animals↗
PubMed2003

Nucleation of apatite crystals in vitro by self-assembled dentin matrix protein 1.

Bones and teeth are biocomposites that require controlled mineral deposition during their self-assembly to form tissues with unique mechanical properties. Acidic extracellular matrix proteins play a pivotal role during biomineral formation. However, the mechanisms of protein-mediated mineral initiation are far from understood. Here we report that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate the formation of hydroxyapatite in vitro in a multistep process that begins by DMP1 binding calcium ions and initiating mineral deposition. The nucleated amorphous calcium phosphate precipitates ripen and nanocrystals form. Subsequently, these expand and coalesce into microscale crystals elongated in the c-axis direction. Characterization of the functional domains in DMP1 demonstrated that intermolecular assembly of acidic clusters into a beta-sheet template was essential for the observed mineral nucleation. Protein-mediated initiation of nanocrystals, as discussed here, might provide a new methodology for constructing nanoscale composites by self-assembly of polypeptides with tailor-made peptide sequences.

Biomimetic Materials↗
PubMed1978

[Bone mineral estimation (Hydroxyl apatite equivalent) by direct measurement of photo absorption in the upper extremity (phalanges, radius and ulna) (author's transl)].

The x-ray source of the apparatus developed by the authors for bone mineral estimations consists of a small anode tube with a silver anode. The value of the procedure has been tested by in vitro and in vivo experiments. The in vitro measurements were carried out on a bone reference system consisting of a model bone (Reiss) as well as on a macerated tibia embedded in a resin (Heuck). The results were compared with the values obtained by Rassow. It has been shown that the artificial resin is of only limited value as a connective tissue equivalent. The method of mineral estimation using phalanges is described and its reproducibility was tested on 17 parameters. The absorption coefficient of the spongiosa proved to be particularly critical. Finally, measurements, using the forearm, by Cameron's method are discussed briefly.

Absorption↗
PubMedDate not supplied

A new improved biodegradable tracheal prosthesis using hydroxy apatite and carbon fiber.

A new biodegradable tracheal prosthesis was developed using hydroxyapatite rings as the artificial tracheal cartilage, a carbon fiber tube as the tracheal tube; it was then implanted into the cervical trachea in dogs. Morphologic examination revealed that the hydroxyapatite ring was anchored firmly to the tracheal cartilage by ingrowth of cartilaginous tissue into the macropores of the hydroxyapatite.

Animals↗
PubMed2004

Active domains of salivary statherin on apatitic surfaces for binding to Fusobacterium nucleatum cells.

Fusobacterium nucleatum can bind to saliva-coated tooth surfaces. However, the nature of the domains of salivary protein that interact with F. nucleatum remains unclear. The ability of individual proteins in human submandibular-sublingual saliva (HSMSL) to bind F. nucleatum cells was examined by dot blot assay; statherin displayed the strongest binding activity. Statherin binding sites were determined based on binding of (125)I-labelled F. nucleatum to statherin-coated hydroxyapatite (sHAP) beads via inhibition assays using synthetic analogous peptide fragments of whole statherin. Analogous peptides corresponding to residues 19-26 and 32-39 of statherin inhibited binding by 77 % and 68 %, respectively. Synthetic peptides were also prepared by serial deletions of individual residues from N- and C-termini of the peptides GPYQPVPE (aa 19-26) and QPYQPQYQ (aa 32-39). The inhibitory effects of peptides YQPVPE (aa 21-26) and PYQPQYQ (aa 33-39) were very similar to those of GPYQPVPE and QPYQPQYQ, respectively. However, additional deletion of residues resulted in significant reduction of the inhibitory effect. Alanine-scan analysis of YQPVPE revealed that all tested peptides retained inhibitory activity; only YAPVPE exhibited significantly decreased inhibitory activity. These findings suggest that YQPVPE and PYQPQYQ may represent the minimal active segments of statherin for binding to F. nucleatum; moreover, Gln may be a key amino acid in the active segment.

Amino Acid Sequence↗