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At least 433 records · Page 24Linked to original sources

PubMed1997

Human histidine-rich glycoprotein expressed in SF9 insect cells inhibits apatite formation.

Histidine-rich glycoprotein (HRG) is structurally related to the alpha2-HS glycoprotein/fetuin family of mammalian plasma proteins; both belong to the cystatin superfamily of proteins. We expressed recombinant human HRG and alpha2-HS in Sf9 insect cells for functional analysis. Recombinant HRG bound heparin and fibrinogen while alpha2-HS did not. Both proteins inhibited the formation of apatite, recombinant HRG (IC50 approximately 1 microM) with 2-fold lower molar activity than alpha2-HS (IC50 approximately 0.5 microM). The inhibition in vitro of apatite formation suggests a new function for plasma HRG protein, inhibition of phase separation in blood vessels.

Animals↗

PubMed2003

Bonelike apatite formation on ethylene-vinyl alcohol copolymer modified with silane coupling agent and calcium silicate solutions.

An ethylene-vinyl alcohol copolymer (EVOH) was treated with a silane coupling agent and calcium silicate solutions, and then soaked in a simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma. A smooth and uniform bonelike apatite layer was successfully formed on both the EVOH plate and the EVOH-knitted fibers in SBF within 2 days. Part of the structure of the resulting apatite-EVOH fiber composite was similar to that of natural bone. If this kind of composite can be fabricated into a three-dimensional structure similar to natural bone, the resultant composite is expected to exhibit both mechanical properties analogous to those of natural bone and bone-bonding ability. Hence, it has great potential as a bone substitute.

Apatites↗

PubMed2003

Bioactive sol-gel glasses with and without a hydroxycarbonate apatite layer as substrates for osteoblast cell adhesion and proliferation.

The biocompatibility of three sol-gel bioactive glasses with SiO(2) as the main constituent (75, 72.5 and 70 mol%), identical CaO content (25mol%), and without or with P(2)O(5) as third constituent (0, 2.5 and 5 mol%), have been analyzed (S75, S72.5P2.5, and S70P5 glasses). These studies were performed on both untreated glasses and on glasses coated with a hydroxycarbonate apatite (HCA) layer formed in vitro by soaking 7d in an acellular simulated body fluid. Cell attachment, spreading and proliferation were studied using neonatal rat calvaria osteoblasts. Cells attach to the three untreated glasses but show a higher efficiency on that with the higher phosphate content (S70P5). The formation of the HCA layer significantly enhances this process (1.7-fold). In all cases, attachment is followed by cell spreading on the surface of the materials, adopting the cells a flattened morphology and showing diverse anchoring cell projections. Mitotic activity has been detected on osteoblasts growing on the sol-gel glasses, being this process 2-4-fold higher when the apatite-like layer is already formed. Taking into account the results herein presented, these bioactive glasses can be considered biocompatible. In addition, their biocompatibility is greatly enhanced after induction of the formation of an HCA layer.

Animals↗

PubMed2004

Structural characterization of nano-sized calcium deficient apatite powders.

Nano-sized calcium-deficient apatitic (CDHA) crystals with Ca/P ratios from 1.5 to 1.67 were synthesized using wet chemical method and of needle-like shape with 5-10 nm in diameter and 40-50 nm in length was observed. The structural environment of the Ca atoms in all the CDHA nano-crystals has been investigated using EXAFS, XANES and EELS. The results reveal that a maximum Fourier transform amplitude occurs at the apatite with a Ca/P ratio of 1.67 and the structural disorder increase following the sequence of 1.67>1.5>1.6>1.55. A similar phenomenon is also observed in both K-edge XANES and L(2,3)-edge ELNES in the Ca atom. The structural analysis further demonstrates that different chemical and biological properties among these CDHA nano-crystals with Ca/P ratio from 1.5 to 1.67 are primarily due to the effect of stoichiometry and non-stoichiometry as compared to the structural order-disorder.

Apatites↗

PubMed1997

Heterogeneous iron-containing fluoridated apatites.

The iron-containing fluoridated hydroxyapatites Fe-FeFAp and FeF-FeAp were synthesized heterogeneously in the presence of ferrous ions at 80 degrees C and pH 7.4 in two different types of solution, i.e. fluoride-free solution during the initial half of the experimental period and fluoride-containing solution during the second half, in the latter of which the fluoride concentration was equivalent to that of fluorapatite. Another experiment was carried out under the opposite conditions. The total fluoride contents of both heterogeneous iron-containing fluoridated apatites were almost the same (0.83 +/- 0.01 and 0.89 +/- 0.02 mmol g-1, respectively). Their X-ray diffraction patterns were not significantly different. However, scanning electron microscopy showed that Fe-FeFAp was composed of clusters of rod-like crystals and FeF-FeAp of bundles of many thin needle-like crystals. Energy dispersive spectroscopy coupled with scanning electron microscopy estimated that the fluoride intensity of Fe-FeFAp was higher than that of FeF-FeAp. The apparent solubility of the former (Ca = 8.83 +/- 0.20, P = 4.27 +/- 0.13 mmol l-1) was less than that of the latter (Ca = 10.8 +/- 0.4, P = 5.56 +/- 0.09 mmol l-1) at 37 degrees C and pH 4.0. These results suggest that two different types of heterogeneous iron-containing fluoridated apatites may be formed.

Apatites↗

PubMed2003

Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions.

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K(d) values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons.

Adsorption↗

PubMed2003

Graft-preserving treatment for vascular graft infected with Staphylococcus aureus with antibiotic-releasing porous apatite ceramic in the rabbit.

OBJECTIVE: This study was undertaken to investigate whether infection of a vascular graft with Staphylococcus aureus can be treated in situ by applying antibiotic-loaded porous apatite ceramic, in a rabbit model. METHODS: Teicoplanin (TEIC) was loaded onto a beta-tricalcium phosphate (TCP) block, a type of porous apatite ceramic. The activity of TEIC released from the antibiotic-loaded TCP block was examined in vivo. A vascular graft was patched onto the abdominal aorta in 24 rabbits, and S aureus was applied directly on it. Seven days postoperatively, each rabbit underwent repeat laparotomy, and retroperitoneal abscess around the prosthetic vascular patch was debrided. Animals were divided into four groups of 6 rabbits each. In group 1 only debridement was carried out. In groups 2 and 3, solution containing 40 or 60 mg of TEIC, respectively, was applied to the prosthetic vascular patch. In group 4, an antibiotic-loaded TCP block (63 +/- 6.6 mg of TEIC) was placed around the graft. Three weeks after the second operation, the graft, the tissue around it, and arterial blood were collected and cultured. RESULTS: TEIC activity was maintained for 28 days in vivo. In group 1, bacterial cultures of the prosthetic vascular graft and the tissue around it were positive in 5 animals and negative in 1 animal (infection rate, 83%). In both groups 2 and 3, cultures were positive in 3 animals and negative in 3 animals (infection rate, 50%). In group 4, cultures were negative in all animals (infection rate, 0%). Blood cultures were negative in all animals. Infection rate in group 4 was significantly lower than that in group 1 (P =.03), and was also lower than that in groups 2 and 3, but the difference was not significant. CONCLUSIONS: Use of slow-release antibiotic loaded onto a TCP block, along with debridement, may control infection in vascular grafts in situ, averting the necessity to remove the graft.

Administration, Topical↗

PubMed2002

Bioinspired growth of crystalline carbonate apatite on biodegradable polymer substrata.

Mineralization in biological systems is a widespread, yet incompletely understood phenomenon involving complex interactions at the biomacromolecule-mineral nucleus interface. This study was aimed at understanding and controlling mineral formation in a poly(alpha-hydroxy ester) model system, to gain insight into biological mineralization processes and to develop biomaterials for orthopaedic tissue regeneration. We specifically hypothesized that providing a high surface density of anionic functional groups would enhance nucleation and growth of bonelike mineral following exposure to simulated body fluids (SBF). Polymer surface functionalization was achieved via hydrolysis of 85:15 poly(lactide-co-glycolide) (PLG) films. This treatment led to an increase in surface carboxylic acid and hydroxyl groups, resulting in a substantial increase in polymer surface energy from 42 to 49 dynes/cm2. Treated polymers exhibited a 3-fold increase in heterogeneous mineral grown and growth of a continuous mineral film on the polymer surface. The mineral grown on PLG surfaces is a carbonate apatite, the major mineral component of vertebrate bone tissue. Mineral crystal size and morphology were dependent on the solution characteristics but unaffected by the degree of surface prehydrolysis. The mechanism of heterogeneous carbonate apatite growth was examined via ion binding assays, which indicated that calcium binding is mediated independently by the presence of soluble phosphate counterions and surface functional groups. These findings indicate that poly(alpha-hydroxy ester) materials can be readily mineralized using a biomimetic process, and that the impetus for mineral nucleation in this system appears more complicated than the simple electrostatic interactions proposed in previous biomineralization theory.

Apatites↗

PubMed2006

On the kinetics of apatite growth on substrates under physiological conditions.

Derived from reaction kinetics, a simple but useful method, based on "apatite forming capacity" or AFC of solutions mimicking blood plasma, is proposed to decipher the rate of calcium phosphate mineralization. Apatite growth rate constants were calculated using this method for a model composite surface varying the volume fraction of synthetic hydroxyapatite (HA) in a polymer matrix. Previously reported data for mineralized surfaces on Ta, Ti, and its alloys are also analyzed similarly and compared. Utilizing the growth rate constant, the bioactivity of the materials was indexed in vitro. Complementarily, semiempirical quantum mechanical calculation (ZINDO method) showed that the interaction of cations with TRIS-hydroxymethyl aminomethane molecules in the solution is stronger than that with the polymer substrate considered, but weaker than hydrated Ti and TiO(2) surfaces. This analysis then quantifies for example the extent of polymer inertness and the "bioactivity" of alkali treated Ti. The growth rate constants for the model materials prepared in this work are explained on the basis of localized dissolution of HA, the amount of which simply increases with increasing volume fraction of HA in the composite.

Apatites↗

PubMed2004

Bonelike apatite formation on niobium metal treated in aqueous NaOH.

The essential condition for a biomaterial to bond to the living bone is the formation of a biologically active bonelike apatite on its surface. In the present work, it has been demonstrated that chemical treatment can be used to create a calcium phosphate (CaP) surface layer, which might provide the alkali treated Nb metal with bone-bonding capability. Soaking Nb samples in 0.5 M NaOH, at 25 degrees C for 24 h produced a nano-porous approximately 40 nm thick amorphous sodium niobate hydrogel layer on their surface. Immersion in a simulated body fluid (SBF) lead to the deposition of an amorphous calcium phosphate layer on the alkali treated Nb. The formation of calcium phosphate is assumed to be a result of the local pH increase caused by the cathodic reaction of oxygen reduction on the finely porous surface of the alkali-treated metal. The local rise in pH increased the ionic activity product of hydroxyapatite and lead to the precipitation of CaP from SBF that was already supersaturated with respect to the apatite. The formation of a similar CaP layer upon implantation of alkali treated Nb into the human body should promote the bonding of the implant to the surrounding bone. This bone bonding capability could make Nb metal an attractive material for hard tissue replacements.

Apatites↗

PubMed2003

Apatite formation on dental ceramics modified by a bioactive glass.

Restorative dental materials are considered biocompatible without exhibiting any bioactive behaviour. The aim of this study was the investigation of surface structure changes on conventional dental ceramics used in metal-ceramic restorations modified by a bioactive glass, after immersion in SBF for various time periods. Bioactive glass powder was mixed with porcelain powder with three different weight ratios: 1:1, 1:2, and 2:1. The two powders were mixed with porcelain modelling liquid and the mixture was transferred and spread on the surface of pre-fabricated ceramic disks. Coated ceramic specimens after being exposed to a specific thermal cycle as it is recommended for dental ceramics were soaked in Simulated Body Fluid (SBF) at 37 degrees C for various periods of time. After soaking, specimens were studied using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Results revealed the development of a non-stoichiometric, biological apatite layer on their surface after exposure in SBF for several time periods. The onset of apatite-layer formation is directly dependent on the amount of bioglass in the coating and its thickness reduces within the specimens of the same bioactive glass-porcelain proportion with time, reaching an average thickness of 15 microm at the longest immersion time, for all the specimens.

Apatites↗

PubMed2003

Local treatment of Dacron patch graft contaminated with Staphylococcus aureus with antibiotic-releasing porous apatite ceramic: an experimental study in the rabbit.

OBJECTIVE: The purpose of this study was to investigate whether or not infection of prosthetic vascular graft could be prevented with the placement of antibiotic-loaded porous apatite ceramic on the graft with bacterial contamination. METHODS: Teicoplanin as an antibiotic was loaded into a beta-tricalcium phosphate (TCP) block of porous apatite ceramic. The activity of teicoplanin released from teicoplanin-loaded TCP was examined for 40 days at 2-day intervals. In an in vivo study, the graft was patched in the abdominal aorta of a rabbit. Two different doses of Staphylococcus aureus were applied (n = 13). Teicoplanin-loaded TCP was placed around the graft infected with S aureus (n = 6). The graft, the tissue around it, and the arterial blood were collected and cultivated 4 weeks after operation. RESULTS: The activity of teicoplanin in the replaced saline solution was maintained for at least 40 days. Because graft infection was established in all rabbits with a dose of 2 x 10(7) colony forming units, this dose was used as the dose of S aureus in this study. Fifty-seven percent of the subjects died from the infection. When teicoplanin-loaded TCP was placed around the graft contaminated with S aureus, no rabbits died. Bacterial cultures of the graft and of tissues around it were negative in all rabbits killed 4 weeks after operation. This infection was prevented with teicoplanin-loaded TCP in all rabbits. CONCLUSION: Teicoplanin-loaded TCP may be useful in avoiding Dacron graft infection with S aureus in rabbits.

Animals↗

PubMed1996

The serum protein alpha2-HS glycoprotein/fetuin inhibits apatite formation in vitro and in mineralizing calvaria cells. A possible role in mineralization and calcium homeostasis.

We present data suggesting a function of alpha2-HS glycoproteins/fetuins in serum and in mineralization, namely interference with calcium salt precipitation. Fetuins occur in high serum concentration during fetal life. They accumulate in bones and teeth as a major fraction of noncollagenous bone proteins. The expression pattern in fetal mice confirms that fetuin is predominantly made in the liver and is accumulated in the mineralized matrix of bones. We arrived at a hypothesis on the molecular basis of fetuin function in bones using primary rat calvaria osteoblast cultures and salt precipitation assays. Our results indicate that fetuins inhibit apatite formation both in cell culture and in the test tube. This inhibitory effect is mediated by acidic amino acids clustering in cystatin-like domain D1. Fetuins account for roughly half of the capacity of serum to inhibit salt precipitation. We propose that fetuins inhibit phase separation in serum and modulate apatite formation during mineralization.

Animals↗

PubMed2003

Dentin matrix protein 1 immobilized on type I collagen fibrils facilitates apatite deposition in vitro.

During bone and dentin mineralization, the crystal nucleation and growth processes are considered to be matrix regulated. Osteoblasts and odontoblasts synthesize a polymeric collagenous matrix, which forms a template for apatite initiation and elongation. Coordinated and controlled reaction between type I collagen and bone/dentin-specific noncollagenous proteins are necessary for well defined biogenic crystal formation. However, the process by which collagen surfaces become mineralized is not understood. Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein expressed during the initial stages of mineralized matrix formation in bone and dentin. Here we show that DMP1 bound specifically to type I collagen, with the binding region located at the N-telopeptide region of type I collagen. Peptide mapping identified two acidic clusters in DMP1 responsible for interacting with type I collagen. The collagen binding property of these domains was further confirmed by site-directed mutagenesis. Transmission electron microscopy analyses have localized DMP1 in the gap region of the collagen fibrils. Fibrillogenesis assays further demonstrated that DMP1 accelerated the assembly of the collagen fibrils in vitro and also increased the diameter of the reconstituted collagen fibrils. In vitro mineralization studies in the presence of calcium and phosphate ions demonstrated apatite deposition only at the collagen-bound DMP1 sites. Thus specific binding of DMP1 and possibly other noncollagenous proteins on the collagen fibril might be a key step in collagen matrix organization and mineralization.

Amino Acid Sequence↗

PubMed2005

In vitro apatite formation on organic polymers modified with a silane coupling reagent.

Gamma-methacryloxypropyltrimethoxysilane (gamma-MPS) was grafted to high-density polyethylene, polyamide and silicone rubber substrates by the emulsion polymerization procedure in order to provide these organic polymers with in vitro apatite-forming ability. The contact angles towards distilled water of the gamma-MPS-grafted specimens were lower than those of the original organic polymer specimens, indicating that the grafted substrates were more hydrophilic. The in vitro apatite formation in a simulated body fluid (Kokubo solution) was confirmed for several of the gamma-MPS-grafted specimens.

Apatites↗

PubMed1975

Degrees of saturation with respect to apatites in parotid saliva at various ph values.

The purpose of the present work was to investigate the degrees of saturation with respect to hydroxyapatite and fluorapatite in saliva at various pH's. The data of ionic activities in parotid saliva were collected from the literature and the degrees of saturation with respect to hydroxyapatite and fluorapatite were calculated. It was found that parotid saliva was supersaturated with respect to both apatites above pH 5.5, unsaturated with respect to hydroxyapatite and concurrently supersaturated with respect to fluorapatite in the pH range 5.5-4.5, while it was unsaturated with respect to both apatities below pH 4.5. In the laboratory it has been found that when enamel is exposed to a liquid unsaturated with respect to hydroxyapatite and supersaturated with respect to fluorapatite, a caries-like lesion is developed. A liquid unsaturated with respect to both apatites leads to an erosion-like injury. It is concluded that the two chemical conditions leading to the two types of enamel lesions may both occur in the oral cavity.

Apatites↗

PubMed1977

Calcium fluoride formation on enamel and its influence on uptake of fluoride in the apatitic lattice.

Human dental enamel was exposed to a pH 4 buffer containing 150 parts/10(6) fluoride. It was found that due to the arising degrees of saturation with respect to calcium fluoride and apatites, surface enamel dissolved coincident with a formation of calcium fluoride. The calcium fluoride redissolved while it kept the liquid saturated with respect to this salt. During this second period, fluorapatite was formed while hydroxyapatite dissolved. Finally, all calcium fluoride was dissolved and the unreacted fluoride was taken up in the apatitic lattice. The results are discussed with reference to the conditions of the oral cavity and enamel solubility experiments.

Apatites↗

PubMed1981

X-ray diffraction patterns in human dentin, enamel and synthetic apatites related to Zn concentration.

The crystallization of human dentin and enamel containing different concentrations of Zn was studied using X-ray diffraction analysis. The concentrations of Ca, Mg, Mn, Fe, Zn, Cu, Co, Ni, Sr and Pb in the samples were determined by atomic absorption spectrophotometry. The concentration of F was assayed with a combination fluoride electrode. The increase of the Zn concentration (microgram/g) from 150 to 572 in dentin was found to intensify apatite reflections indicating changes parallel to c-axis. A slight increase parallel to a-axis (or better crystallization) of lattices was demonstrated in both dentin and enamel. The increase of Zn concentration from 164 microgram/g to 692 microgram/g in enamel weakened 002 and 112 reflections. The effect of Zn on the crystallinity of synthetic apatite prepared at 37 degrees C was of the same kind as its effect on the dentin.

Adolescent↗