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PubMed2003

Apatite deposition on thermally and anodically oxidized titanium surfaces in a simulated body fluid.

By application of a special specimen set-up, thermally oxidized titanium specimen pairs were found able to deposit apatite on the contact surfaces after soaking for 7 days in the simulated body fluid (SBF) of Kokubo's recipe. The specimens oxidized at 400 degrees C and 500 degrees C showed the highest ability of apatite deposition. Both increase and decrease in oxidation temperature from this range caused the apatite deposition ability to decrease. The specimen without treatment failed to deposit any apatite. Specimens anodically oxidized in electrolytes of H(3)PO(4), H(2)SO(4) and acetic acid exhibited very low ability of apatite deposition. Furthermore, the specimen thermally oxidized at 400 degrees C was even able to help the surfaces of PTFE and silicone deposit apatite in the PTFE-Ti and silicone-Ti pairs. This in vitro experimental results indicated that the difference in apatite deposition among various titanium oxides does exist and can be distinguished by applying the present specimen set-up. The mechanism of the apatite deposition on the contact surfaces was discussed in relation to the passive dissolution of titanium in SBF. The release of titanium hydroxide and OH(-) ions from the titanium surfaces and their accumulation inside the confined space between the two contact surfaces were suggested to be responsible for the apatite deposition.

Adsorption↗

PubMed1996

Properties of heterogeneous apatites containing magnesium, fluoride, and carbonate.

Biological apatites present in the mineral phases of normal and pathological calcifications contain magnesium, Mg, and carbonate, CO3. As a consequence of fluctuations in the composition of the micro-environment, these apatites may sometimes form by heterogeneous precipitation. The purpose of this study was to investigate the properties of (Mg, CO3)-apatites formed heterogeneously in the presence of fluoride, F. Two types of fluoridated (Mg, CO3)-apatites formed from solutions with low and high levels of Mg were prepared at 80 degrees C, pH 7.4. We prepared FMgCO3-MgCO3AP (Type 1) by adding the F-containing solution to those containing calcium, Mg, and phosphate ions during the first half of the precipitation period. We prepared MgCO3-FMgCO3Ap (Type 2) by adding the F-containing solution during the final half of the period. The apatites were analyzed by x-ray diffraction (XRD), infrared absorption spectroscopy, and scanning electron microscopy (SEM). SEM and XRD analyses showed evidence of mixed crystals in the heterogeneous apatites. The presence of Mg inhibits, while F promotes, apatite crystal growth. In addition, Mg incorporation increased with increasing fluoride concentration. The extent of dissolution in acid buffer of both types of heterogeneous apatites increased with Mg: Type 1 > Type 2. These results suggest that the crystal and dissolution properties of heterogeneous fluoridated (Mg, CO3)-apatites are greatly affected by the mode of F incorporation and Mg concentrations in the environment.

Apatites↗

PubMed2005

Resorption of apatite-wollastonite containing glass-ceramic and beta-tricalcium phosphate in vivo.

Apatite-wollastonite containing glass ceramic is considered to be difficult to resorb, but we experienced the disappearance of the porous type of Apatite-wollastonite glass ceramic particles . In this study, the resorption of porous apatite-wollastonite glass-ceramic implanted in the femurs of rabbits was investigated, and the process was compared with beta-tricalcium phosphate, a resorbable ceramics. Porous apatite-wollastonite glass-ceramic (70, 80, and 90% porosity) and beta-tricalcium phosphate (75% porosity) were implanted in the femurs of Japanese white rabbits. Samples were harvested and examined 0, 4, 8, 12, 24 and 36 weeks after implantation. Quantitative analysis of the radiographic and histologic findings was performed with NIH Image software. Radiographic examination demonstrated that the radiopacity and size of the porous apatite-wollastonite glassceramic cylinders decreased gradually after implantation. Histologic examination revealed that the surface area of the apatite-wollastonite glass-ceramic cylinders decreased continuously, and approached 20% of the original area 36 weeks after implantation. However, the resorption rate of porous apatite-wollastonite glass-ceramic was slower than that of beta-tricalcium phosphate. Toluidine blue staining showed abundant new bone formation on the surface of the apatite-wollastonite glassceramic matrix. Considering its mechanical strength, gradual resorption characteristics, and good osteochonductive activity, porous apatite-wollastonite glass-ceramic appears to be a suitable artificial bone substitutes.

Absorption↗

PubMed2003

Structural derivation and crystal chemistry of apatites.

The crystal structures of the [A(1)(2)][A(2)(3)](BO(4))(3)X apatites and the related compounds [A(1)(2)][A(2)(3)](BO(5))(3)X and [A(1)(2)][A(2)(3)](BO(3))(3)X are collated and reviewed. The structural aristotype for this family is Mn(5)Si(3) (D8(8) type, P6(3)/mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P6(3)/m, Cmcm and P6(3)cm. Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1)-A(1)-O(2) twist angle phi projected on (001) of the A(1)O(6) metaprism. For apatites that contain the same A cation, it is shown that phi decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P6(3)/m symmetry or cation ordering. The inclusion of A(1)O(6) metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr(5)(BO(3))(3)Br. The most common symmetry for the 74 chemically distinct [A(1)(2)][A(2)(3)](BO(4))(3)X apatites that were surveyed was P6(3)/m (57%), with progressively more complex chemistries adopting P6(3) (21%), P3; (9%), P6 (4.3%), P2(1)/m (4.3%) and P2(1) (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and divalent X anions or X-site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce BO(5) square pyramidal units (as in ReO(5)) or BO(3) triangular coordination (as in AsO(3)). Polysomatism arises through the ordered filling of [001] BO(4) tetrahedral strings to generate the apatite-nasonite family of structures.

Journal Article↗

PubMed2004

The effects of initial hemostatic period on the mechanical strength and transformation of apatite cement.

It is well known that apatite cement causes inflammatory response if it is exposed to blood before setting. In this respect, the hemostatic procedure is very important. However, it has not been clarified how initial hemostasis affects the other basic properties of apatite cement. In the present study, the effect of initial hemostasis on the setting reaction was simulated by allowing the apatite cement paste to be hardened in an incubator for 1 to 30 minutes and then immersed in saline up to 7 days. We found faster transformation of apatite cement to apatitic mineral and higher mechanical strength of the set mass when the cement paste underwent a longer pre-hardening period. We also found that earlier exposure of apatite cement to saline resulted in a set mass with larger porosity. It is thought that the larger porosity of the cement is caused by the penetration of liquid into the cement paste, thus leading to lower mechanical strength and slower transformation of the apatite cement to apatitic mineral. We concluded, therefore, that hemostatic procedure is important not only to prevent inflammatory response but also to obtain a set mass with higher mechanical strength and faster transformation to apatitic mineral.

Analysis of Variance↗

PubMed1998

Sintered carbonate apatites as bioresorbable bone substitutes.

The dissolution behavior of sintered carbonate apatite was investigated in a 10 mM/L acetic acid solution adjusted to pH 5.0 at 37 degrees C, and compared to that of sintered hydroxyapatite and bone apatite for the purpose of establishing some similarities between the physicochemical dissolution of apatite biomaterials in vitro and their ability to be resorbed by osteoclasts in vivo. Both the sintered carbonate apatite and the bone apatite dissolved to an appreciable extent. Their solution compositions changed in an almost identical manner until toward the end of the reaction. The solution compositions for sintered carbonate apatite at 30 s was comparable with that for sintered hydroxyapatite at 3.8 days with respect to the degree of supersaturation, indicating that the former specimen is much more soluble than the latter specimen. Osteoclasts which were obtained from the long bones of 1-day-old neonatal rabbits resorbed bone and sintered carbonate apatite, but not sintered hydroxyapatite. These findings suggest that sintered carbonate apatites, which have characteristics that can be favorably compared with those of bone, especially with respect to its reactivity to acid media, would be useful as bioresorbable bone substitutes.

Animals↗

PubMed1998

Osteoclastic resorption of bone-like apatite formed on a plastic disk as an in vitro assay system.

We have investigated the applicability of a simple and inexpensive osteoclastic assay system using bone-like apatite-coated polyethyleneterephthalate (PET) disks. A 1 microm thick apatite layer, uniform and homogeneous bone-mineral-like with no organic components, was made on PET disks using a biomimetic process. As substrates for an osteoclastic assay, these coated disks were compared with dentine as well as with bone-like or heat-treated apatite of various thicknesses on apatite- and wollastonite-containing glass ceramic (A-W GC) disks. The unfractionated bone cells, including osteoclasts, of a neonatal rabbit were seeded onto these substrates. By scanning electron microscopic examination, the resorption lacunae of the thick bone-like apatite clearly showed track-like shapes at various depths, similar to those of dentine although the border between the A-W GC and the apatite was unclear. In contrast, those of heat-treated apatite showed small and shallow shapes with irregular margins, quite different from those of dentine. By reducing the thickness of bone-like apatite to 1 microm as well as using PET as its substrate, the margins of the resorption lacunae became quite clear, and with the use of phase-contrast microscopy during culture, osteoclasts and resorption pits could be precisely observed. The resorbed area, easily measured with the aid of bright-field microscopy and an image analyzer, was found to have increased in a time-dependent manner and at the end of 4 days of culture was not statistically different from that of dentine.

Animals↗

PubMed2001

A comparative study of in vitro apatite deposition on heat-, H(2)O(2)-, and NaOH-treated titanium surfaces.

Commercially pure titanium specimens are subjected to three different treatments, and their bioactivity are evaluated by immersing the specimens in a simulated body fluid (SBF, Kokubo's recipe) for various periods up to 7 days, with particular attention being paid to the differences in apatite deposition between surfaces open to SBF and surfaces in contact with the container's bottom. The treatment with a H(2)O(2)/HCl solution at 80 degrees C for 30 min followed by heating at 400 degrees C for 1 h produces an anatase titania gel layer on the specimen surface. This gel layer deposits apatite both on the contact and on open surfaces, and apatite deposition ability does not change with pre-staking in distilled water. The treatment with a NaOH solution at 60 degrees C for 3 days produces a sodium titanate gel layer. This gel layer can deposit apatite only on the contact surface, and the apatite deposition ability is completely lost after 1 day of pre-staking in distilled water. It is concluded, therefore, that the bioactivity of the titania gel originates from the favorable structure of the gel itself while the bioactivity of the sodium titanate gel depends heavily on ion release from the gel. The third treatment, a simple heat treatment at 400 degrees C for 1 h, produces a dense (not porous) oxide layer on the specimen surface. The specimens can deposit apatite on the contact surface after only 3 days of staking in SBF, but they cannot deposit apatite on the open surface for up to 2 months of staking. The implications of such apatite deposition behavior have been discussed in relation to the environments of titanium implants in bone as well as to the methodology of the SBF staking experiment.

Apatites↗

PubMed2001

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process.

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.

Apatites↗

PubMed2005

Laminin-apatite composite coating to enhance cell adhesion to ethylene-vinyl alcohol copolymer.

A laminin-apatite composite layer with enhanced cell adhesive properties was successfully formed on the surface of an ethylene-vinyl alcohol copolymer (EVOH) by a liquid phase coating process. The coating process was carried out with the following procedure. First, an EVOH plate was alternately dipped in 200 mM calcium and 200 mM phosphate solutions to introduce nuclei or precursors of apatite to its surface. Second, the surface-modified EVOH was immersed in a calcium phosphate solution, which was supersaturated with respect to apatite and containing laminin. As a result of this procedure, a laminin-apatite composite layer with a thickness of 2.5-3.0 microm was formed on the EVOH surface. Epithelial-like cells (BSCC93) adhered to the laminin-apatite composite layer showed enhanced cell spreading, which was due to the biological effect of laminin. The number of cells adhered to the laminin-apatite composite layer on EVOH was approximately 10 times as large as that adhered to the surface of the untreated, laminin-adsorbed, or apatite-coated EVOH. Therefore, this type of composite material consisting of a synthetic polymer, apatite, and laminin has great potential as a skin terminal, with improved adhesiveness to skin tissue, as well as good biocompatibility.

Apatites↗

PubMed2004

The effect of pH on the structural evolution of accelerated biomimetic apatite.

The classic biomimetic apatite coating process can be accelerated by first immersing substrates into concentrated simulated body fluid, 5x SBF (SBF1), at 37 degrees C, to form an initial coating of precursor apatite spheres, and subsequently transferring to a second 5x SBF (SBF2) solution which is devoid of crystal growth inhibitors to promote phase transformation of SBF1-derived precursor apatite spheres into final crystalline apatite plates. Since SBF1 governs the formation kinetics and composition of the initial precursor spheres, we hypothesized that the pH of the SBF1 solution will also influence the final structure of the SBF2-derived crystalline apatite. To test this hypothesis, polystyrene substrates were immersed into SBF1 with different pH (5.8 or 6.5), and then immersed into the identical SBF2 (pH=6.0). The resultant apatites exhibited similar 2 theta XRD peaks; FTIR spectra in terms of hydroxyl, phosphate and carbonate groups; and Ca/P atomic ratio (1.42 for SBF1(5.8) apatite; 1.48 for SBF1(6.5) apatite). SEM, TEM and electron diffraction show that while SBF1(6.5) (pH 6.5) precursor spheres transform into larger, single crystals plates, SBF1(5.8) (pH 5.8) precursor spheres developed minute, polycrystalline plate-like structures over predominantly spherical precursor substrate.

Apatites↗

PubMed2005

Biomimetic deposition of apatite coating on surface-modified NiTi alloy.

TiO(2) coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 degrees C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO(2) coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 degrees C produced a layer of anatase and rutile TiO(2) on the surface of NiTi. No TiO(2) was detected on the surface of NiTi after heat treatment at 300 and 400 degrees C by X-ray diffraction, while rutile was formed on the surface of the 800 degrees C heat-treated sample. It was found that the 600 degrees C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 degrees C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 degrees C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 degrees C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.

Apatites↗

PubMed2006

The effect of oxygen plasma pretreatment and incubation in modified simulated body fluids on the formation of bone-like apatite on poly(lactide-co-glycolide) (70/30).

In this study, biodegradable poly(lactide-co-glycolide) (PLGA) (70/30) films and scaffolds were first treated with oxygen plasma and then incubated in a modified simulated body fluid 1.5SBF0 to prepare a bone-like apatite layer. The formation of the apatite and its influence on osteoblast-like cells growth were investigated. It was found that the bone-like apatite formability of PLGA(70/30) was enhanced by plasma pretreatment. The changes of surface chemistry and surface topography induced by oxygen plasma treatment were both effective for apatite formation. The apatite formability increased with increasing plasma-treating time. Under a treating condition of 20 W for 30 min, oxygen plasma treatment could penetrate into the inner scaffold. After 6 days incubation, the apatite formed in plasma-treated scaffold was better distributed than in untreated scaffold, and the weight and mechanical strength of the plasma-treated scaffold were both enhanced. Compared with PLGA(70/30), the apatite layer formed on oxygen plasma-treated PLGA(70/30) surface enhanced adhesion and proliferation of OCT-1 osteoblast-like cell, but had no significant effect on cell's ALP activity at day 7. A prolonged investigation is being in process to further verify the bone-like apatite effects on osteogenic differentiation.

Apatites↗

PubMed2006

Theoretical stability assessment of uranyl phosphates and apatites: selection of amendments for in situ remediation of uranium.

Addition of an amendment or reagent to soil/sediment is a technique that can decrease mobility and reduce bioavailability of uranium (U) and other heavy metals in the contaminated site. According to data from literature and results obtained in field studies, the general mineral class of apatites was selected as a most promising amendment for in situ immobilization/remediation of U. In this work we presented theoretical assessment of stability of U(VI) in four apatite systems (hydroxyapatite (HAP), North Carolina Apatite (NCA), Lisina Apatite (LA), and Apatite II) in order to determine an optimal apatite soil amendment which could be used for in situ remediation of uranium. In this analysis we used a theoretical criterion which is based on calculation of the ion-ion interaction potential, representing the main term of the cohesive energy of the matrix/pollutant system. The presented results of this analysis indicate (i) that the mechanism of immobilization of U by natural apatites depends on their chemical composition and (ii) that all analyzed apatites represent, from the point of view of stability, promising materials which could be used in field remediation of U-contaminated sites.

Adsorption↗

PubMed1995

Synergistic effects of magnesium and carbonate on properties of biological and synthetic apatites.

Magnesium (Mg) and carbonate (CO3) are minor elements associated with enamel, dentin and bone apatite. The purpose of this study was to determine the effect of Mg and CO3 on some properties of synthetic apatites to gain insights on their effects on biological apatites. Biological apatites from human enamel and dentin and from bovine bone and synthetic apatites with/without Mg or CO3 were characterized using x-ray diffraction, infrared absorption, thermogravimetry and chemical analyses. Dissolution in acidic buffer was also determined. Results from this study demonstrated: (1) the synergistic effects of Mg and CO3 on reducing the crystallinity and increasing the extent of dissolution of synthetic apatites; (2) dentin and bone, compared to enamel apatite contained higher levels of Mg and CO3; had lower crystallinity and higher extent of dissolution. The lower crystallinity and higher extent of dissolution of dentin and bone compared to enamel apatite may be partly attributed to their higher Mg and CO3 concentrations.

Animals↗

PubMed2003

[A study of bone-like apatite formation on calcium phosphate ceramics in different kinds of animals in vivo].

Bone-like apatite formation on the surface of calcium phosphate ceramics has been believed to be necessary for new bone to grow on the ceramics and to be related to the osteoinductivity of the material. The research of bone-like apatite formation is a great help to understanding the mechanism of osteoinduction. Synthetic porous calcium phosphate ceramics (HA/TCP = 70/30) were implanted intramuscularly in pigs, dogs, rabbits and rats to make a comparative study of the bone-like apatite formation onto the porous HA/TCP ceramics in different animals. Specimens were harvested at 14 days after implantation. Samples were detected for the surface morphology with SEM. The chemical composition of the sample surface after implantation was analyzed with reflection infrared (R-IR). Obvious bone-like apatite formation could be detected in the sections of porous specimens harvested from all animals after 14 days intramuscular implantation. Crystal deposition could be only observed on the surface of the concave regions of the samples collected from dogs, rabbits and rat. On the contrary, evenly distributed flake-shaped crystal could be found on the pore surface and also on the outer surface of the materials implanted in pigs. The morphology of bone-like apatite in pigs was different from that in the others animals. Bone-like apatite was not observed in dense specimen implanted intramuscularly. Bone-like apatite formed faster on specimens implanted in rabbit than that in other animals. This formation sequence is different from the sequence of osteoinductivity of biphasic calcium phosphate ceramics implanted in these animals. The results demonstrated that the formation of bone-like apatite on materials is a prerequisite condition to their osteoinduction but other factors also play important roles in osteoinduction.

Animals↗

PubMed1997

Structure, crystal chemistry and density of enamel apatites.

The apatitic calcium phosphate crystals in dental enamel are too small for single crystal diffraction studies so the only possible direct structure determination must use whole-pattern-fitting Rietveld analysis of X-ray and neutron powder diffraction patterns. As a result, aspects of the structure are not known in detail. Further structural information can be obtained by consideration of published chemical analyses and infrared studies, taking into account studies of the crystal chemistry of synthetic apatitic analogues of enamel apatite. The apatitic constitutional water and total water content of enamel are particularly important, but there are difficulties in their determination. Making reasonable assumptions, a number of models of the unit cell can be derived. The weight per cent (including constitutional water) and density of the enamel apatite crystals for the most probable model are about 98 wt.% and 3.0 g cm-3, respectively. The apatite volume per cent calculated from these values is about 96%. The weight per cent and volume per cent of enamel apatite are higher than normally accepted values because of inclusion of constitutional water and use of a density for enamel apatite that takes into account its known lattice expansion over hydroxyapatite and probable lattice vacancies.

Animals↗

PubMed1996

Integrity and thermal decomposition of apatite in coatings influenced by underlying titanium during plasma spraying and post-heat-treatment.

The integrity and thermal decomposition of calcium apatite are influenced by the underlying titanium during plasma-spraying deposition, especially at the apatite/titanium interface. The destruction of apatite at the interface is governed by substrate temperature, titanium catalysis, and its reaction with titanium dioxide produced from oxidation of titanium in the plasma gas. The apatite in the outer layer of coatings is affected mainly by the substrate temperature and can keep its integrity with a suitable plasma-spraying procedure to minimize the increase of substrate temperature. The heat treatment of the coatings in vacuum results in the decomposition of apatite to alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate monoxide (TCPM) with the increase of intensity approaching the interface, which roughens the surface of the coatings. In the air-heat treatment, oxidation of titanium produces a thickened, dense rutile layer at the interface which prevents titanium atoms from diffusing into the coatings and inhibits the titanium-catalyzed decomposition of apatite. The apatite adjacent to the rutile layer reacts moderately with rutile to produce calcium titanate (CaTiO3), alpha- and beta-TCP, while the apatite in the outer layer, separated from the rutile layer, maintains its integrity without decomposition even in a prolonged air-heat treatment. The retention of apatite integrity leads to a decreased surface roughness of the coating.

Biocompatible Materials↗