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PubMed2002

Mechanism of bonelike apatite formation on bioactive tantalum metal in a simulated body fluid.

Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta-OH groups by exchange of Na+ ion in the amorphous sodium tantalate on its surface with H3O+ ion in SBF. Both the formed Ta-OH groups combined with Ca2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta-OH groups on the treated tantalum metal predominates the following process including adsorption of Ca2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta-OH group, followed by combination of the Ta-OH groups with Ca2+ and phosphate ions.

Apatites↗

PubMed2003

A comparative study between in vivo bone ingrowth and in vitro apatite formation on Na2O-CaO-SiO2 glasses.

This study compared in vivo bioactivity with the in vitro apatite-forming ability of biomaterials. Granules of five kinds of P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, showing different apatite-forming ability in simulated body fluid (SBF), were implanted into a defect on the femoral condyle of rabbits. Bone ingrowth was evaluated using scanning electron microscopy among five kinds of glasses at 1, 2, 3, 6, and 12 weeks. Quantitative analysis was performed measuring the depth of new bone ingrowth from the periphery. In addition, the total areas of newly formed bone among glass particles were examined at 3 and 6 weeks using confocal laser scanning microscopy (CLSM) after weekly administration of fluorescent calcein. The depth of bone ingrowth among glass particles increased in proportion to their apatite-forming ability in vitro. The CLSM study showed a correlation between the quantities of labeled newly formed bone and in vitro apatite-forming ability. In the P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, the periods within 3-6 days for inducing apatite in SBF considered a necessary condition to convey bioactivity in vivo, and in vivo evaluations at 2-3 weeks is important to determine this. The in vivo bioactivity was precisely reproduced by apatite-forming ability in SBF. Therefore, evaluating apatite formation in SBF is a good screening test for the in vivo bioactivity of materials, resulting in reduction of the need for animal sacrifices and savings in experimental time.

Animal Testing Alternatives↗

PubMed2003

Apatite-forming ability of carboxyl group-containing polymer gels in a simulated body fluid.

Carboxymethylated chitin, gellan gum, and curdlan gels were soaked in a simulated body fluid (SBF) having ion concentrations nearly equal to those of human blood plasma. Some of the gels had been soaked in a saturated Ca(OH)(2) solution, while others had not. The carboxymethylated chitin and gellan gum gels have carboxyl groups, while the curdlan gel has hydroxyl groups. None of the gels formed apatite on their surfaces in the SBF when they had not been subjected to the Ca(OH)(2) treatment, whereas the carboxymethylated chitin and gellan gum gels formed apatite on their surfaces when they had been subjected to the Ca(OH)(2) treatment. The curdlan gel did not form an apatite deposit even after the Ca(OH)(2) treatment. Apatite formation on the carboxymethylated chitin and gellan gum gels was attributed to the catalytic effect of their carboxyl groups for apatite nucleation, and acceleration of apatite nucleation from released Ca(2+) ions. This result provides a guiding principle for obtaining apatite-organic polymer fiber composites. This composite is expected to have an analogous structure to that of natural bone.

Apatites↗

PubMed1999

Bonelike apatite coating on organic polymers: novel nucleation process using sodium silicate solution.

A bonelike apatite layer was formed on organic polymers when sodium silicate was used as a catalyst for the apatite nucleation, and modified simulated body fluid was used as a medium for the apatite growth. The apatite-forming ability was the highest when the SiO2 concentration and SiO2/Na2O mole ratio of the sodium silicate solution were above 2.0 M and 1.0-1.5, respectively. It is assumed that particular silicate oligomers with structures such as dimer, linear trimer and cyclic tetramer contribute to the apatite nucleation the most. The apatite layer was formed not only on limited surfaces but also on the whole surfaces of fine PET fibers constituting a fabric. This method is expected to enable the bonelike apatite coating on various kinds of materials with complex shapes.

Apatites↗

PubMed1993

Maclura pomifera agglutinin-binding glycoconjugates on converted apatite from synthetic octacalcium phosphate implanted into subperiosteal region of mouse calvaria.

We have previously shown that the mineral in granules of synthetic octacalcium phosphate (OCP) implanted subperiosteally in mouse calvariae was converted to apatitic crystals and that the OCP implantation stimulated bone formation. The matrix components accumulated on the converted apatite were very similar to those of bone nodules (starting locus of calcification) in intramembranous osteogenesis. In the present study, the nature of the matrices accumulated on OCP implants in calvariae was compared with that of the matrices accumulated in abdominal subcutaneous implants. The comparison was facilitated by the use of Maclura pomifera agglutinin (MPA) lectin which is known to have a high affinity for the primary intramembranous bone matrix. Micro-beam x-ray diffraction indicated conversion of the implanted OCP to apatitic crystals in situ, both in subperiosteal and subcutaneous sites, after 10 days. Additional bone formation was detected on the converted apatite after 13 days in subperiosteal implantation, whereas bone was not formed in the subcutaneous implantation. MPA reaction was strongly manifested after 10 days in matrices accumulated on the converted apatite in both subperiosteal and subcutaneous implantations. Biochemical data showed that intensely and weakly MPA-blotted molecules (53.0 and 152.6 kDa, respectively) were in all the mouse sera, in the guanidine HCl-EDTA extracts of mouse calvarial bone and in the extracts of the implanted OCP in both subperiosteal and subcutaneous sites. These findings indicated that the glycoconjugates accumulated on the converted apatite from OCP were similar to the glycoconjugates in the serum in terms of reactivity with MPA and molecular weights. Furthermore, the results suggest that MPA-binding glycoconjugates which had accumulated on the converted apatite may be a requisite for the differentiation of mesenchymal cells into osteoblasts in periosteum but not in subcutaneous sites.

Animals↗

PubMed2004

Sorption and desorption of Cd2+ and Zn2+ ions in apatite-aqueous systems.

As a low-soluble phosphate mineral capable of binding various metal ions, apatite can be used to immobilize toxic metals in soils and waters. In the present research the factors affecting sorption and desorption of Cd2+ and Zn2+ ions on/from apatites are investigated. Batch experiments were carried out using synthetic hydroxy-, fluoride-, and carbonate-substituted apatites having various specific surface area (SSA). Apatite sorption capacity was found to depend mainly on its SSA, ranging from 16 to 78 and from 11 to 79 mmol per 100 g of apatite for Cd2+ and Zn2+, respectively. The solution composition (pH, and presence of Cl- and NO3- ions) had no essential impact on sorption. Desorption of bound cations depended both on the sorption level and solution composition. The amount of desorbed Cd2+ and Zn2+ increased proportionally to the amount of sorbed cations. However, apatites having higher sorption capacity release relatively less sorbed cations. Desorption increases with increasing Ca2+ concentration in the solution, reaching 8-20% of sorbed Cd2+ in 0.002 M, 10-35% in 0.01 M, and 33-45% in 0.05 M Ca(NO3)2 solution. Compared to nitrate solutions, the presence of Cl- ions in the solution promotes the release of bound cations. Desorption of Zn2+ is slightly higher than that of Cd2+. The desorption mechanism was assumed to include both ion-exchange and adsorption of Ca2+ ions on apatite surface.

Adsorption↗

PubMed1977

Effect of naturally occurring apatites on growth and morphology of algae.

Crystals (30--100 micrometer) of selected naturally occurring apatite (Ca10 (PO4)6(OH, F)2) samples were added to P-free (less than 0.001 microgram/ml total P) Bristol's medium (1-1000 microgram/ml of apatite) as the sole source of ortho-PO43-. The media were inoculated with washed, non-axenic cells of three chlorophycean algal species cultivated under PO43--deficient conditions. Phase-contrast and scanning electron microscopy revealed that at low slurry densities (1-10 microgram/ml of apatite), Ankistrodesmus braunii (ATCC 2744) cells were morphologically distorted. At concentrations of 100 and 1000 microgram/ml of apatite, more than 85% of the cells had undergone autospore formation within 7--10 days of incubation at 20 degrees C. Most autospores formed failed to germinate under high nutrient conditions. Scenedesmus longus (No. 1236) formed colonies when cultivated in Bristol's medium but daughter cells displayed a Chodatella-like unicellular morphology when grown in apatite media. Test algal species (Chlamydomonas dysosmos, S. longus, A. braunii) showed a marked preference for growth on apatite crystals over non-nutritive surfaces. Unialgal and mixed-algal cultures produced an extensive matrix of extracellular fibrous material in response to growth on crystals at concentrations greater than 10 microgram/ml of apatite.

Apatites↗

PubMed2001

Modification of electrochemically deposited apatite using supercritical water.

Supercritical water was used as a modification method of electrochemically deposited apatite on pure titanium. The apatites were coated on a commercially pure titanium plate using a hydrothermal-electrochemical method. A constant direct current at 12.5 mA/cm2 was loaded for 1 hr at 25, 60, 100, 150 and 200 degrees C in an electrolyte containing calcium and phosphate ions. The deposited apatite on the titanium substrate was stored in supercritical water at 450 degrees C under 45 MPa for 8 hr. With this treatment, the crystallinity of the apatites increased, sharp edges of the deposited apatites were rounded off, and the bonding strength of the titanium substrate to the deposited apatites significantly increased. On the other hand, weight loss in 0.01 N HCl decreased and the weight gain rate in a simulated body fluid also decreased with this treatment. It is suggested that the modification using supercritical water improved the mechanical strength of the deposited apatite, but worsened its bioactivity.

Apatites↗

PubMed2005

Biocompatibility of apatite-coated titanium mesh prepared by hydrothermal-electrochemical method.

The hydrothermal-electrochemical method is best suited for producing homogeneous apatite coatings on electro-conductive materials with complicated shape, such as the mesh. This study was undertaken to examine the effect of the apatite coating prepared by this coating method on cell adhesion, proliferation, and differentiation of MC3T3-E1 cells in culture. The cells attached and spread well on the electrochemically deposited apatite on titanium mesh. The number of cells that adhered on the deposited apatite on titanium mesh was much greater than that on the surface without coating, and that it also depended on the morphology of apatites. When alkaline phosphatase activity as well as collagen and osteocalcin of the extracellular matrix were measured, the electrochemically apatite-coated titanium mesh showed higher measurement values than the titanium mesh without coating. These results suggested that the apatite-coated titanium mesh prepared by hydrothermal-electrochemical method has excellent biocompatibility.

3T3 Cells↗

PubMed2002

Apatite formation on bioactive zirconium metal prepared by chemical treatment.

Bioactive metallic materials, which can directly bond to living bone, are badly needed in dental and orthopedic implants for better long-term results. Forming a layer of bone-like apatite on the surface of the metal is one of the most promising methods to increase its bioactivity. This study creates a new chemical treatment for zirconium metal to induce apatite formation in a simulated body fluid (SBF), and analyzes the apatite layer by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). Zirconium samples were soaked in 10% CuCl2 aqueous solution at 80 degrees C for 72 hours, heat-treated at 500 degrees C for one hour and soaked in SBF for various periods. An apatite-like layer appeared on the zirconium surface as early as three days in SBF, and increased with immersion time. EDS and FTIR confirmed that the deposited layer was apatite. This implies that bioinert zirconium metal can become bioactive by forming an apatite layer in a simulated body fluid after a suitable chemical treatment. The ZrOOH+ hydrogel layer produced on the zirconium surface by CuCl2 and heat-treatments is thought to induce the apatite formation.

Apatites↗

PubMed2003

[Hydrolysis of poly(L-lactic acid) fibers and formation of low crystalline apatite on their surface by a biomimetic process].

Low crystalline apatite coating was formed on the surface of biodegradable poly(L-lactic acid) (PLLA) fibers by a biomimetic process, i.e., 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 apatite was characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Results showed that the fiber hydrolysis could accelerate the apatite formation but had little effect on the chemical and crystalline structure of the apatite. The structure of the apatite coating formed by the biomimetic method was similar to that of apatite in the natural bone. The bone-like low crystalline apatite coating might exhibit enhanced osteo-conductivity when the PLLA fibers are applied in bone reconstruction biomaterials.

Apatites↗

PubMed2004

Mechanism of apatite formation on pure titanium treated with alkaline solution.

The mechanism of bone-like apatite formation on the surface of pure titanium pretreated with NaOH solution is still being investigated. The apatite formation may depend on the solution that is used. In the present study, several types of solutions such as simulated body fluid (SBF), calcium aqueous solution (CAS), and phosphate aqueous solution (PAS) were used to investigate bone-like apatite formation on alkali-treated titanium. In order to observe the effect of hydrolysis on the apatite formation, experiments of pretreated titanium immersed in distilled water before the immersion in SBF were also conducted. The results showed that the mechanism of apatite formation was the hydrolysis reaction of sodium titanate which induced the apatite formation. The pre-precipitation of either calcium or phosphate could prevent the apatite formation on the surface of alkaline treated titanium.

Adsorption↗

PubMed2004

Selective protein adsorption and blood compatibility of hydroxy-carbonate apatites.

We examined the blood compatibility and protein adsorption on hydroxyapatite and hydroxy-carbonate apatite. Those apatites were synthesized under a 0, 5, or 15% CO(2)-containing N(2) atmosphere by a wet-chemical method with a strong ammonia alkali solution of calcium nitrate and diammonium hydrogen phosphate (5:3 in molar ratio) and subsequent calcination in the range of 105-700 degrees C. From infrared (IR) analysis, the carbonate ions substituted both phosphate ions and hydroxyl ions in the hydroxyapatite lattice; the intensities of IR bands assignable to phosphate ions and hydroxyl ions were reduced on calcinations. The specific surface areas of synthesized apatites decreased with increasing calcination temperature. Blood-clotting properties were evaluated in terms of active partial thromboplastin time, prothrombin time, and the amount of fibrinogen for the plasma in contact with the apatites, indicating that all the apatites barely influenced the blood clotting system. The apatites were in contact with a solution containing both bovine serum albumin (BSA) and beta(2)-microglobulin (beta(2)-MG), and the amounts of those proteins adsorbed on them were examined: the amount of absorbed BSA and beta(2)-MG gradually increased with the calcination temperature below 500 degrees C, while it showed a sudden increase when more than 600 degrees C. Hydroxy-carbonate apatite synthesized under a 15% CO(2)-containing N(2) atmosphere and calcined below 400 degrees C had the greatest selectivity in adsorbing beta(2)-MG. Thus, a higher selectivity for beta(2)-MG adsorption was empirically correlated to carbonate ions incorporated in the hydroxyapatite lattice.

Adsorption↗

PubMed1989

Osteonectin inhibiting de novo formation of apatite in the presence of collagen.

The effect of bone matrix protein of osteonectin on de novo formation of apatite was studied in a wide range of calcium phosphate solutions in the presence of collagen. In every solution, from which amorphous calcium phosphate, octacalcium phosphate, or apatite precipitated as a possible initial phase, osteonectin at concentrations less than 1 microM retarded the precipitation, subsequent transformation to apatite, and ripening crystal growth of apatite. Collagen present as either reconstituted or denatured form had no effect on the osteonectin-associated reactions as well as osteonectin-free reactions, and no structural correlation was observed between collagen fibrils and any of the calcium phosphates that appeared in our system. Direct measurement of free calcium levels in the solutions suggested that the reduction in calcium activity due to complexing with osteonectin hardly explained the inhibitory activity of osteonectin in retarding the formation of apatite. Instead, our transmission electron microscopic (TEM) observation strongly suggested that the primary mechanism for osteonectin to inhibit the formation of apatite is to block growth sites of calcium phosphates nucleated. The apatite thus formed in the presence of osteonectin showed less resolved X-ray diffraction patterns, partly because of smaller crystallites as suggested by TEM.

Animals↗

PubMed1989

[Influence of acid buffer on the crystallinity of enamel apatite].

The affects of acetic buffers on the crystallinity of an enamel apatite were examined in the present study. Dual aspects, crystallite size and lattice imperfection related to the crystallinity were analyzed by the process of Variance and Fourier analysis based on the X-ray diffraction line profiles. For this purpose both enamel apatite and synthetic hydroxyapatite were analyzed through acetic acid buffer decalcification, and comparison was made. In addition to the analysis, morphological change of the apatite after acid decalcification was observed by a transmission electron microscope (TEM). The results obtained in the present study were as follows: 1) Wedge-shaped defects formed on a prism plane were observed. In the further stage, wedge-shaped defects were also formed on a basal plane, and it proceeded into the center of the crystallite and consequentry slit similar to defected image was observed. 2) Lattice imperfection of the enamel and synthetic apatite were noticed both on the c-axis and a-axis. Among the factors which contributed to the variance, the "mistake" of lattice was much more likely than the crystallite size, and more mistakes in the direction of the a-axis rather than the c-axis was noticed. 3) A diminished crystallites size was found after acid treatment and diminishing on the c-axis was more apparent than the a-axis. 4) The crystallinity of the apatite was improved through acid treatment, and this improvement was attributed to a diminishing of mistakes. 5) Diminishing of mistakes through acid treatment was detected apparently along the c-axis. According to the results obtained in the present study, crystallite of enamel apatite showed decrease in size, although crystallinity through acid treatment was improved due to the diminishing of mistakes along the c-axis. This may be explained as following in that when apatite crystals were acid treated, the loci of lattice dislocation was selectively dissolved and consequently the more stable crystallite was left.

Analysis of Variance↗

PubMed1997

Surface functional group dependence on apatite formation on self-assembled monolayers in a simulated body fluid.

Self-assembled monolayers (SAMs) of alkanethiols having CH3, PO4H2, COOH, CONH2, OH, and NH2 terminal groups formed on a gold surface via sulfur attachment were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 37 degrees C for up to 40 days. The effect of their terminal functional groups on apatite formation was assessed using X-ray photo-electron spectroscopic (XPS) measurement and a quartz crystal microbalance (QCM) technique. The Ca and P atoms were detected, of which element intensities increased with time, on SAMs except for the alkanethiol having the methyl terminal group. The Ca/P atomic ratios of the apatites formed on the SAMs ranged from around 1.0 to around 1.3. The most potent inducer for apatite formation, judged from the growth rate (micrometers per day) calculated from the weight change during QCM measurement, was the SAM of the alkanethiol with the PO4H2 group, followed by that of the alkanethiol with the COOH group. The SAMs of the alkanethiols with the CONH2, OH, and NH2 groups possessed much weaker inducing powers than the former two SAMs. Little weight change was observed for the methyl-group-terminated alkanethiol SAM. The growth rates increased with time, irrespective of the terminal group species among apatite formation-inducing groups. During the experimental observation period, the following relationship held. The growth rate decreased in the order PO4H2 > COOH >> CONH2 approximately equal to OH > NH2 >> CH3 approximately equal to 0. Some negatively charged groups strongly induced apatite formation but the positively charged group did not, it can be said that the apatite formation initiated via calcium ion-absorption upon complexation with a negative surface-charged group may be dominant in biomaterial calcification where ionic species directly contact the biomaterial surface in body fluids.

Alkanes↗

PubMed2001

An X-ray photoelectron spectroscopy study of the process of apatite formation on bioactive titanium metal.

Bioactive titanium metal, prepared by treatment with NaOH followed by an annealing stage to form a sodium titanate layer with a graded structure on its surface, forms a biologically active bone-like apatite layer on its surface in the body, and bonds to bone through this apatite layer. In this study, process of apatite formation on the bioactive titanium metal in a simulated body fluid was investigated using X-ray photoelectron spectroscopy. The bioactive titanium metal formed Ti-OH groups soon after soaking in the simulated body fluid, via the exchange of the Na(+) ions in the sodium titanate on its surface with H(3)O(+) ions in the fluid. The Ti-OH groups on the metal combined with the calcium ions in the fluid immediately to form a calcium titanate. After a long period, the calcium titanate on the metal took the phosphate ions as well as the calcium ions in the fluid to form the apatite nuclei. The apatite nuclei then proceeded to grow by consuming the calcium and phosphate ions in the fluid. These results indicate that the Ti-OH groups formed on the metal induce the apatite nucleation indirectly, by forming a calcium titanate. The initial formation mechanism of the calcium titanate may be attributable to the electrostatic interaction of the negatively charged Ti-OH groups with the positively charged calcium ions.

Apatites↗

PubMed1994

Apatite coated on organic polymers by biomimetic process: improvement in its adhesion to substrate by NaOH treatment.

A dense, uniform and highly biologically active bone-like apatite layer can be formed in arbitrary thickness on any kind and shape of solid substrate surface by the following biomimetic method at ordinary temperature and pressure. First, a substrate is set in contact with particles of bioactive CaO SiO2 based glass soaked in a simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. Second, the substrate is soaked in another solution with ion concentrations 1.5 times those of SBF (1.5 SBF). In the present study, organic polymer substrates treated with 5 M NaOH solution were subjected to the above mentioned biomimetic process. The induction periods for the apatite nucleation on polyethyleneterephthalate (PET), polymethylmethacrylate (PMMA), polyamide 6 (PA6), and polyethersulfone (PESF) substrates were reduced from 24 to 12 h with the NaOH treatment. The adhesive strength of the formed apatite layer were increased from 3.5 to 8.6 MPa, from 1.1 to 3.4 MPa, and from 0.6 to 5.3 MPa with the NaOH treatment, for PET, PMMA, and PA 6, respectively. It was assumed that highly polar groups, such as carboxyl and sulfinyl ones formed by the hydrolysis of an ester group on PET and PMMA and of an amide group on PA 6, or of a sulfonyl group on PESF with the NaOH treatment, attached a large number of hydrated silica dissolved from the glass particles, to accelerate the apatite nucleation, and also to form a strong bond with the apatite. The apatite-organic polymer composites thus obtained are expected to be useful as bone-repairing as well as soft tissue-repairing materials.

Adhesiveness↗