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PubMed2005

Formation of apatitic calcium phosphates in a Na-K-phosphate solution of pH 7.4.

Poorly crystalline, apatitic calcium phosphate powders have been synthesized by slowly adding a Na- and K-containing reference phosphate solution with a pH value of 7.4 to an aqueous calcium nitrate solution at 37 degrees C. Nano-particulated apatitic powders obtained were shown to contain small amounts of Na and K, which render them more similar in chemical composition to that of the bone mineral. Precipitated and dried powders were found to exhibit self-hardening cement properties when kneaded in a mortar with a sodium citrate- and sodium phosphate-containing starter solution. The same phosphate solution used in powder synthesis was found to be able to partially convert natural, white and translucent marble pieces of calcite (CaCO3) into calcium-deficient hydroxyapatite upon aging the samples in that solution for 3 days at 60 degrees C. Sample characterization was performed by using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, inductively-coupled plasma atomic emission spectroscopy, and simultaneous thermogravimetry and differential thermal analysis.

Apatites↗

PubMed2007

A novel bioactive porous bredigite (Ca7MgSi4O16) scaffold with biomimetic apatite layer for bone tissue engineering.

The aim of this study was to develop a novel bioactive, degradable and cytocompatible bredigite (Ca(7)MgSi(4)O(16)) scaffold with biomimetic apatite layer for bone tissue engineering. Porous bredigite scaffolds were prepared using polymer sponge method. The bredigite scaffolds with biomimetic apatite layer (BTAP) were obtained by soaking bredigite scaffolds in simulated body fluid (SBF) for 10 days. The porosity and in vitro degradability of BTAP scaffolds were investigated. In addition, osteoblast-like cell morphology, proliferation and differentiation on BTAP scaffolds were evaluated and compared with beta-tricalcium phosphate (beta-TCP) scaffolds. The results showed that BTAP scaffolds possessed 90% of porosity. The degradation of BTAP scaffolds was comparable to that of beta-TCP scaffolds. Cells on BTAP scaffolds spread well and presented a higher proliferation rate and differentiation level as compared with those on beta-TCP scaffolds. Our results indicated that BTAP scaffolds were degradable and possessed the function to enhance cell proliferation and differentiation, and might be used as bone tissue engineering materials.

Absorbable Implants↗

PubMed2006

Bone-like apatite coating on Mg-PSZ/Al2O3 composites using bioactive systems.

A biomimetic method was used to promote bioactivity on zirconia/alumina composites. The composites were composed of 80 vol% Mg-PSZ and 20 vol% Al2O3. Samples of these bioinert materials were immersed in simulated body fluid (SBF) for 7 days on either a bed of wollastonite ceramics or bioactive glass. After those 7 days, the samples were immersed in a more concentrated solution (1.4 SBF) for 14 days. Experiments were also performed without using a bioactive system during the first stage of immersion. A bone-like apatite layer was formed on the surface of all the materials tested, using wollastonite the bioactive layer was thicker and its morphology was close to that observed on the existing bioactive systems. A thinner apatite layer consisting of small agglomerates was obtained using bioactive glass. The thickness of the ceramic layers was within the range of 15 to 30 microm.

Alloys↗

PubMed1992

Effects of non-collagenous proteins on the formation of apatite in calcium beta-glycerophosphate solutions.

The effects of the non-collagenous proteins; osteonectin, bone Gla protein and dentine phosphoprotein, on the formation of apatite were studied in calcium beta-glycerophosphate solutions containing catalytic amounts of alkaline phosphatase under physiological conditions. In the system used, calcium phosphate precipitates de novo at levels of supersaturation precisely determined through the enzymatic hydrolysis of beta-glycerophosphate. At 1.7 mM of calcium beta-glycerophosphate, calcium phosphate precipitated when inorganic phosphate accumulated to about 1.4 mM. In the presence of the proteins, however, a greater accumulation of inorganic phosphate was needed for calcium phosphate to precipitate, suggesting that a higher degree of supersaturation, though still a slight undersaturation with respect to dicalcium phosphate dihydrate, is required for calcium phosphate to precipitate in the presence of the proteins. At the same protein (micrograms/ml) concentration, dentine phosphoprotein was approximately four times as effective as bone Gla protein, which was about twice as effective as osteonectin in delaying precipitation. The proteins also retarded subsequent crystal growth, with apatite formed in the presence of the more inhibitory proteins having the smallest crystals, especially in width.

Alkaline Phosphatase↗

PubMed1992

Dimensional accuracy of castable apatite ceramic crowns: the influence of heat treatment on dimensional changes and distortion of crowns.

Castable apatite ceramic crowns are subjected to heat treatment during crystallizing and during coloring after casting. The dimensional accuracy of the heat-treated crowns was investigated with respect to its influence on dimensional changes in castable apatite ceramic crowns and on distortion of the interior of the crowns, using two investment techniques and a three-coordinate measuring machine. Dimensional changes were not influenced by the number of coloring firings. Distortion of the interior of crowns was slightly outward at the gingival plane. Shrinkage because of crystallizing was approximately 20 microns and the shrinkage of the gingival plane was equal to that of the occlusal plane.

Apatites↗

PubMed1985

Cervical laminoplasty using apatite beads as implants. Experiences in 31 patients with compressive myelopathy due to developmental canal stenosis.

Cervical laminoplasty was performed in 31 patients with compressive myelopathy due to developmental stenosis of the spinal canal, using apatite beads as implants. Bilateral foraminotomies were performed at C-5-C-8 levels in an attempt at preventing aggravation of radicular symptoms. Laminae of C-3 through C-7 (or T-1) were removed en bloc and then replaced maintaining an increased anteroposterior diameter of the bony canal by means of insertion of apatite beads between the cut surfaces of the laminae. The literature on posterior decompression for cervical canal stenosis is reviewed, and the advantage of the present method is briefly discussed.

Adult↗

PubMed1990

Quantitative study on osteoconduction of apatite-wollastonite containing glass ceramic granules, hydroxyapatite granules, and alumina granules.

The osteoconductive potential of apatite-wollastonite containing glass ceramic (A-W.GC), hydroxyapatite (HA), and alumina (AL) was quantitatively evaluated by implanting them as granules into rat tibiae. The amount of mature bone formed in contact with the ceramics varied depending on the ceramic materials; it reached a plateau earliest in A-W.GC and latest in AL. The bone mass at the interface showed the same results. The osteoconductive potential was suggested to be higher in bioactive ceramics than in bioinert ceramics, and to be related to the formation rate of the surface apatite layer of the bioactive ceramics.

Aluminum Oxide↗

PubMed1992

Influence of substituting B2O3 for CaF2 on the bonding behaviour to bone of glass-ceramics containing apatite and wollastonite.

Glass-ceramics containing crystalline oxy-fluoroapatite (Ca10(PO4)6(O,F2)) and wollastonite (CaSiO3) (designated AWGC) are reported to have a fairly high mechanical strength as well as the capability of forming a chemical bond with bone tissue. The chemical composition is MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, and CaF2 0.5 in weight ratio. In this study the influence of substituting B2O3 for CaF2 on the bonding behaviour of glass-ceramics containing apatite and wollastonite to bone tissue was investigated. Two kinds of glass-ceramics containing apatite and wollastonite were prepared. CaF2 0.5 was replaced with B2O3 at 0.5 and 2.0 in weight ratio (designated AWGC-0.5B and AWGC-2.0B). Rectangular ceramic plates (15 x 10 x 2 mm, abraded with No. 2000 alumina powder) were implanted into a rabbit tibia. The failure load, when an implant detached from the bone, or the bone itself broke, was measured. The failure load of AWGC-0.5B was 8.00 +/- 1.82 kg at 10 weeks after implantation and 8.16 +/- 1.36 kg at 25 weeks after implantation. The failure load of AWGC-2B was 8.08 +/- 1.70 kg at 10 weeks after implantation and 9.92 +/- 2.46 kg at 25 weeks after implantation. None of the loads for the two kinds of glass-ceramics decreased as time passed. Giemsa surface staining and contact microradiography revealed direct bonding between glass-ceramics and bone. SEM-EPMA showed a calcium-phosphorus rich layer (reaction zone) at the interface of ceramics and bone tissue. The thickness of the reaction zone was 10 to -15 microns and did not increase as time passed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

Surface chemistry of enamel apatite during maturation in relation to pH: implications for protein removal and crystal growth.

Apatite crystal growth rate and morphology in mineralized tissues are considered to be controlled by surface interaction with extracellular matrix proteins. During enamel maturation where protein is finally removed from crystal surfaces to permit massive crystal growth, pH oscillates between approximately 5.8 and approximately 7.2. With this in mind, a study of enamel apatite surface chemistry in terms of local environmental pH was undertaken. Using atomic force microscopy adhesion force measurements were made between hydroxylated or carboxylated cantilever tips and maturation stage crystals between pH 2 and 10. Adhesion force increased from pH 10 to a maximum at pH 6.6 presumably due to increased hydrogen bonding due to replacement of surface cations (Na, Ca, Mg) with protons and/or protonation of phosphate per se. Below pH 6.6 adhesion force decreased and became very variable indicating that the surface had become unstable probably due to removal of fully protonated phosphate from the surface by adherence to the cantilever tip. Frictional force measurements also revealed 2-3, approximately 30 nm diameter high friction domains in bands across the crystal long axis. Their location mirrored the binding pattern of similarly sized amelogenin aggregates seen in vitro. The data suggests that specific protein binding sites may exist on crystal surfaces and may be released at lower pH by protonation which would lower cationic charge on both crystal surface and ionic charge on the protein. Instability of the crystal surface could also play a role.

Animals↗

PubMed2004

Rietveld structure refinement of precipitated carbonate apatite using neutron diffraction data.

X-ray and time of flight neutron diffraction data, FTIR and MAS-NMR spectra, and ICP-AES and carbonate analyses have been collected from a sodium-containing carbonate apatite (CO(3) content 12.5(7)wt%). A structural model based on Holly Springs hydroxyapatite without CO(3)(2-) ions showed an apparent reduction in the PO(4) tetrahedral volume which is ascribed to CO(3)(2-) replacing PO(4)(3-) ions in the lattice. Four structural models from the literature with the CO(3)(2-) ion explicitly modelled were fitted to the neutron diffraction data by the Rietveld method. The best fit was obtained with the CO(3)(2-) ion in disorder between the mirror symmetry related faces of a vacant PO(4)(3-) site and with the normal to the plane of the CO(3)(2-) ion at approximately 30 degrees to the c-axis. This angle is consistent with results from previous polarised IR measurements on single crystals of francolite (a fluorocarbonate apatite) and human dental enamel. Further refinement of the model revealed a hitherto unknown atom site close to the unit cell origin, (possibly a water molecule). The refined hexagonal unit cell parameters from the neutron diffraction data were a=9.3446(3)A and c=6.9199(4)A.

Apatites↗

PubMed2004

Apatite formation on non-woven fabric of carboxymethylated chitin in SBF.

Chitin fibres constituting a non-woven fabric were carboxymethylated in monochloro acetic acid and treated with saturated Ca(OH)(2) aqueous solution. Within 3 days in a simulated body fluid with pH value and ion concentrations nearly equal to those of human blood plasma, a bonelike apatite layer formed on the surface of fibres of the treated fabric. The apatite-chitin fibre composite thus prepared is expected to be useful as a flexible bioactive bone-repairing material.

Adsorption↗

PubMed2005

Rietveld refinements and spectroscopic studies of the structure of Ca-deficient apatite.

Nine samples of Ca-deficient apatite (Ca-def Ap) were prepared from suspensions of CaHPO4 (monetite) at 90 degrees C by raising the pH from approximately 4 through release of NH3 produced by the hydrolysis of urea. Products were dried at 100 degrees C for 24h and studied by chemical analyses, X-ray powder diffraction (XRPD) (and Rietveld analysis of this data), Ca/P ratio determination (quantitative phase analysis of samples after heating to 900 degrees C from Rietveld analysis of XRPD data), scanning electron microscopy, He pycknometry, 1H and 31P MAS NMR spectrometry and Fourier transform infrared and Raman spectroscopy. All samples contained apatite, but three also contained monetite. Infrared and Raman spectroscopy confirmed the presence of HPO4(2-) and absence of carbonate ions in the six monetite-free samples. Mean results for the six samples were: a = 9.4320(40), c = 6.8751(31) A; unit cell formula from chemical analysis neglecting protonation of phosphate ion, Ca(9.303(50))(PO4)6(OH)(0.606(99)).1.97(12)H2O; theoretical density 3.10 g cm(-3); experimental density (mean for three samples) 3.15 g cm(-3); and Ca/P mole ratio from chemical analysis and phase analysis after heating to 900 degrees C, 1.550(8) and 1.550(2), respectively. An earlier assignment of a line at 6 ppm in the 1H NMR spectrum of similar samples to HPO4(2-) ions could not be confirmed; hence no information about the HPO4(2-) ion content could be derived, in disagreement with the previous NMR study. A shoulder at approximately 0.9 ppm relative to 85 wt% H3PO4 in the 31P NMR spectrum was assigned to HPO4(2-) ions. Occupancies from the Rietveld structure refinements indicated preferential loss of Ca from Ca2 sites compared with Ca1, but the loss was substantially smaller than expected from chemical analyses. It is suggested that imperfect modelling of the structure in the refinement, particularly disorder associated with the Ca2 site, resulted in errors in Ca2 occupancies. The P-O bonds were slightly shorter than those in stoichiometric hydroxyapatite, rather than longer as might be expected from protonation of phosphate tetrahedra. However, consideration of known acid phosphate structures indicated that it was unlikely that the increase in P-O lengths would be sufficient to be detected. The observed decrease was tentatively assigned to the presence of Ca2+ ion vacancies.

Algorithms↗

PubMed2005

Modulation of porosity in apatitic cements by the use of alpha-tricalcium phosphate-calcium sulphate dihydrate mixtures.

Calcium phosphate bone cements are injectable biomaterials that are being used in dental and orthopaedic applications through minimally invasive surgery techniques. Nowadays, apatitic bone cements based on alpha-tricalcium phosphate (alpha-TCP) are of special interest due to their self-setting behaviour when mixed with an aqueous liquid phase. In this study, a new method to improve osteointegration of alpha-TCP-based cements is presented. This method consists in the modification of the cement's powder phase with different amounts of calcium sulphate dihydrate (CSD). The resulting hardening properties of the new biphasic cements are a combination between the progressive hardening due to the main alpha-TCP reactant and the progressive dissolution of the CSD phase, which render a porous material. It was observed that the maximum compressive strength of Biocement-H (45 MPa) decreased as the amount of CSD increased in the cement powder mixture ( approximately 30 MPa for 25 wt% of CSD). It was also observed that after complete dissolution of the CSD phase a porous apatitic structure appears with a mechanical compressive strength suitable for cancellous bone applications (10 MPa).

Apatites↗

PubMed2005

Local structure of channel ions in carbonate apatite.

Refinement of the single-crystal X-ray diffraction structure of a type A carbonate apatite [CAp; Ca10(PO4)6-y(CO3)x+(3/2)y(OH)2-2x, x=0.75, y=0.0; space group P3 ] has been continued with independent positional and isotropic displacement parameters for the carbonate oxygen atoms, reducing the residual indices significantly (R=0.024, Rw=0.020) and confirming the earlier structure assignment. The carbonate ion is located in the apatite channel at z approximately 0.5, and oriented with two oxygen atoms close to the c-axis. Rigid body refinement, giving a preferred structure, used a novel procedure for defining the ideal equilateral triangular geometry of the channel carbonate ion. Resolution of the channel carbonate ions in type A-B CAp (x=0.69, y=0.57; P63/m) is also improved. Channel carbonate ions in CAp are canted, rotated and displaced to optimize Ca2-O bond distances. The rotation of the A1 carbonate in type A-B CAp is opposite to that of the channel carbonate in type A CAp, due mainly to the accommodation of a second channel carbonate ion (A2). These structures simulate the local structure of type A carbonate in hydroxyapatite of bone and dental enamel.

Apatites↗

PubMed2006

The formation of an antibacterial agent-apatite composite coating on a polymer surface using a metastable calcium phosphate solution.

A percutaneous device with antibacterial activity and good biocompatibility is desired for clinical applications. Three types of antibacterial agent: lactoferrin (LF), tetracycline (TC), and gatifloxacin (GFLX) were immobilized on the surface of an ethylene-vinyl alcohol copolymer (EVOH) using a liquid phase coating process. In this process, an EVOH plate was alternately dipped in calcium and phosphate ion solutions, and then immersed in a metastable calcium phosphate solution supplemented with 4, 40, or 400 microg/mL of the antibacterial agent. As a result, the antibacterial agent was immobilized on the EVOH surface in the form of an antibacterial agent-apatite composite layer. The amount of immobilized antibacterial agent increased with increasing absorption affinity for apatite in the order: GFLX<TC<LF. On the other hand, the release rate of the antibacterial agent from the composite was ordered in the opposite sense; i.e., LF<TC<GFLX. The composites investigated in this study showed antibacterial activity against Escherichia coli and Staphylococcus aureus, and would be useful as materials in percutaneous devices having antibacterial activity and good biocompatibility.

Anti-Bacterial Agents↗

PubMed2006

Rietveld refinements and spectroscopic structural studies of a Na-free carbonate apatite made by hydrolysis of monetite.

Seven nominally identical samples of Na-free carbonate apatite (CO(3)Ap) were prepared by reaction of CaHPO(4) with ammonium carbonate solution at 70 degrees C over 3 days. They were studied by chemical analysis, Rietveld analysis of powder X-ray diffraction (XRD) data, Ca/P ratio determinations (quantitative phase analysis of CaO, Ca(OH)(2) and hydroxyapatite formed after heating to 900 degrees C from Rietveld analysis of XRD data), He pycknometry, (1)H, (13)C and (31)P MAS NMR spectrometry and Fourier transform infrared and Raman spectroscopy. Spectroscopy showed the apatite products were B-type CO(3)Aps (CO(3)(2-) replacing PO(4)(3-)) and XRD that one sample contained 1.6 wt% calcite with a trace in another. Mean results of the six essentially calcite-free samples were: a=9.405(5)A, c=6.896(2)A; 11.2 wt% CO(3); unit cell contents, Ca(8.241)(PO(4))(4.344)(CO(3))(1.656)(OH)(0.139) x 2.29H(2)O; mole Ca/P ratio from chemical analyses, 1.897(22) and from powder XRD phase analysis of samples decarbonated at 900 degrees C, 1.892(25). Density determinations indicated that the 2.29mol of H(2)O were in the unit cell. Rietveld refinements were undertaken without and with explicit modelling of the CO(3)(2-) ion. The latter used constraints to maintain the CO(3)(2-) ion in its known geometry and the total of PO(4)(3-) and CO(3)(2-) ions per unit cell at six. Without the CO(3)(2-) ion in the model, PO(4) volume, P-O bond lengths and P occupancy were apparently reduced, consistent with CO(3)(2-) replacing PO(4)(3-) ions. With the CO(3)(2-) ion modelled, the reductions were less and the CO(3)(2-) ion occupied the "sloping" face of the replaced PO(4)(3-) ion in two-fold disorder about the mirror plane. The angle between the normal to the plane of the ion and the c-axis was 34 degrees , close to 35.3 degrees , the equivalent angle for the PO(4)(3-) ion. When modelled, the CO(3)(2-) ion occupancy was 1.81 ions per unit cell, in reasonable agreement with unit cell contents determined chemically (1.66). The OH(-) ion occupancy was elevated (2.33 ions per unit cell versus 0.14 inferred from the charge balance), which we ascribe to H(2)O molecules occupying sites in c-axis channels. The Ca/P ratio from occupancies (2.31) was also elevated over that determined chemically (1.90). We attribute this to loss of Ca from Ca sites increasing the apparent anisotropic displacement parameters of remaining Ca atoms, leading to an apparently increased occupancy.

Apatites↗

PubMed2005

Composition of bone and apatitic biomaterials as revealed by intravital Raman microspectroscopy.

Microcharacterization of biominerals allows a better understanding of the pathophysiological events that occur in calcified tissues and synthetic biomaterials. Different methods have been extensively used to conduct such investigations. A new model for the intravital study of the composition and structure of membranous bone by Raman microspectroscopy is described. Titanium bone chambers equipped with a fused-silica optical window were implanted transcutaneously in the calvaria of New Zealand rabbits. The implanted optical windows were well tolerated, and spectral acquisitions were performed without any additional invasive procedure. Bone and implanted apatitic biomaterials were analyzed at different times after surgery. All Raman bands were unambiguously identified in the bone and biomaterial spectra. The main PO4 and CO3 Raman bands in bone spectra were consistent with those found in the carbonated apatite spectrum. The major collagen bands were always observed around 1200-1300 (amide III) and 1600-1700 (amide I) delta cm(-1) and, 1400-1470 and 2800-3100 delta cm(-1) (bending and stretching modes of CH groups, respectively). The phenylalanine (Phe) band was identified in all spectra at 1003 delta cm(-1) and overlapped that of the weak HPO4(2-) ion. The CH bands frequently overlapped the lipid bands. However a distinct protein and lipid bands were detected at 2950 and 2852 delta cm(-1), respectively. In bone areas close to blood vessels, the Raman signature of hemoglobin was detected with a characteristic band at 754 delta cm(-1). The changes observed in bone varied as a function of time and location. The composition and structure of all of the biomaterials studied--including those that were resorbable--seemed to remain stable over time and location. We report for the first time the complete intravital study of Raman spectra of bone and calcium phosphate biomaterials over a period of 8 months. This new approach does not require specimen preparation and allows simultaneous observation of mineral and organic bone constituents over time, which therefore should provide insightful information about their relationship.

Animals↗

PubMed2006

pH-sensing nano-crystals of carbonate apatite: effects on intracellular delivery and release of DNA for efficient expression into mammalian cells.

Two unique and fascinating properties of carbonate apatite which are well-known in hard tissue engineering, have been unveiled, for the first time, for the development of the simplest, but most efficient non-viral gene delivery device - ability of preventing the growth of crystals needed for high frequency DNA transfer across a plasma membrane and a fast dissolution rate for effective release of DNA during endosomal acidification, leading to a remarkably high transgene expression (5 to 100-fold) in mammalian cells compared to the widely used transfecting agents. Moreover, by modulating the crystal dissolution rate of carbonate apatite through incorporation of fluoride or strontium into it, transfection activity could be dramatically controlled, thus shedding light on a new barrier in the non-viral route, which was overlooked so far. Thus we have developed an innovative technology with significant insights, that would come as a promising tool for both basic research laboratories and clinical settings.

Animals↗