Biomedical subjects

T Kokubo

Publications and source records attributed to T Kokubo.

At least 37 records · Page 2Linked to original sources

PubMed2002

Formation of apatite layers on modified canasite glass-ceramics in simulated body fluid.

Canasite glass-ceramics were modified by either increasing the concentration of calcium in the glass, or by the addition of P2O5. Samples of these novel materials were placed in simulated body fluid (SBF), along with a control material (commercial canasite), for periods ranging from 12 h to 28 days. After immersion, surface analysis was performed using thin film X-ray diffraction, Fourier transform infrared reflection spectroscopy, and scanning electron microscopy equipped with energy dispersive X-ray detectors. The concentrations of sodium, potassium, calcium, silicon, and phosphorus in the SBF solution were measured using inductively coupled plasma emission spectroscopy. No apatite was detected on the surface of commercial canasite, even after 28 days of immersion in SBF. A crystalline apatite layer was formed on the surface of a P2O5-containing canasite after 5 days, and after 3 days for calcium-enriched canasite. Ion release data suggested that the mechanism for apatite deposition was different for P2O5 and non-P2O5-containing glass-ceramics.

Apatites↗

PubMed2002

Enhancement of bonding strength by graded structure at interface between apatite layer and bioactive tantalum metal.

Tantalum metal is a candidate for use as an implant material in high load-bearing bony defects, due to its attractive features such as high fracture toughness and high workability. This metal, however, does not have bone-bonding ability, i.e. bioactivity, and therefore the development of bioactive tantalum metal is highly desirable. It is known that the essential prerequisite for an artificial material to show bioactivity is to form a bonelike apatite layer on its surface in the body environment. The same type of apatite layer is formed in a simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with 0.5 M-NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously formed the same apatite after a long soaking period. In the present study, the bonding strength of the apatite layer to the substrate was quantitatively evaluated in comparison with that to the untreated tantalum metal. Adhesive strength was measured as an estimation of bonding strength, and the surface microstructure of both the substrates was characterized in order to discuss the difference in the bonding strength in terms of surface structure. The apatite layer formed on the NaOH- and heat-treated tantalum metal shows higher adhesive strength than that formed on the untreated metal. The amorphous sodium tantalate layer formed on the tantalum metal by NaOH and heat treatments, has a smooth graded structure where its concentration gradually changes from the surface into the interior metal. Smooth graded structure with complex of apatite is constructed after soaking in SBF. The higher bonding strength of the apatite layer formed on the treated metal is attributed to its smooth graded structure.

Journal Article↗

PubMed2002

Bioactivity and mechanical properties of polydimethylsiloxane (PDMS)-CaO-SiO2 hybrids with different calcium contents.

Polydimethylsiloxane (PDMS)-CaO-SiO(2) hybrids with starting compositions containing PDMS/(Si(OC(2)H(5))(4)+PDMS) weight ratio=0.30, H(2)O/Si(OC(2)H(5))(4) molar ratio=2, and Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratios=0-0.2, were prepared by the sol-gel method. The apatite-forming ability of the hybrids increased with increasing calcium content in the Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0-0.1. The hybrids with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0.1-0.2 formed apatite on their surfaces in a simulated body fluid (SBF) within 12 h. The hybrid with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio of 0.10 showed an excellent apatite-forming ability in SBF with a low release of silicon into SBF. It also showed mechanical properties analogous to those of human cancellous bones. This hybrid is expected to be useful as a new type of bioactive material.

Journal Article↗

PubMed2001

TEM-EDX study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid.

Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous sodium titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na(+) ions from the surface sodium titanate with H(3)O(+) ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium titanate. After a long soaking time, the amorphous calcium titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite.

Apatites↗

PubMed2001

Bioactive titanium: effect of sodium removal on the bone-bonding ability of bioactive titanium prepared by alkali and heat treatment.

As reported previously, bioactive titanium is prepared by simple alkali and heat treatment, and can bond to living bone directly. The purpose of this study was to accelerate the bioactivity of bioactive titanium in vivo. In in vitro study, sodium removal by hot water immersion enhanced the apatite-forming ability of bioactive titanium in simulated body fluid dramatically. The specific anatase structure of titania gel was effective for apatite formation in vitro. In the current study, we investigated the in vivo effect of sodium removal on the bone-bonding strength of bioactive titanium. Sodium-free bioactive titanium plates were prepared by immersion in an aqueous solution of 5 M NaOH at 60 degrees C for 24 h, followed by immersion in distilled water at 40 degrees C for 48 h before heating them at 600 degrees C for 1 h. Three kinds of titanium plates were inserted into rabbit tibiae, including untreated cp-Ti, conventional alkali- and heat-treated Ti, and sodium-free alkali- and heat-treated Ti. In vivo bioactive performance was examined mechanically and histologically after 4, 8, 16, and 24 weeks. Sodium removal enhanced the bone-bonding strength of bioactive titanium at 4 and 8 weeks postoperatively; however, its bone-bonding strength was inferior to that of conventional alkali- and heat-treated titanium at 16 and 24 weeks. Histological examinations after the detaching test revealed breakage of the treated layer in the sodium-free alkali- and heat-treated titanium group. In conclusion, sodium removal accelerated the in vivo bioactivity of bioactive titanium and achieved faster bone-bonding because of its anatase surface structure, but the loss of the surface's graded structure due to the complete removal of sodium decreased the adhesive strength of the treated layer to the titanium substrate. Further investigations are required to determine the optimum conditions for preparation of bioactive titanium.

Alkalies↗

PubMed2001

Bioactive bone cement: effects of phosphoric ester monomer on mechanical properties and osteoconductivity.

A new bioactive bone cement, designated GBC, has been developed. It consists of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler. The bioactive beads, consisting of MgO--CaO--SiO(2)--P(2)O(5)--CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to evaluate the effects on mechanical properties and osteoconductivity of adding a phosphoric ester (PE) monomer to the cement as an adhesion-promoting agent. Four kinds of cements were prepared: GBC, GBC with PE (designated GBC/PE), a cement consisting of the same PMMA used in GBC with apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC), and AWC with PE (designated AWC/PE). Each filler was added to the cement at 70 wt %. Adding PE to either GBC or AWC resulted in increases in the bending strength and decreases in the Young's modulus compared with the unmodified cements. Cements were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after operation. The affinity index (length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface) was calculated for each cement. Adding PE to either GBC or AWC resulted in significant increases in the affinity index compared with the unmodified cements. The affinity index for GBC was significantly higher than that of AWC, and that for GBC/PE was also significantly higher than that of AWC/PE. The affinity indices for each cement increased significantly with time up to 8 weeks. Our study revealed that the higher osteoconductivity of GBC/PE was due to the large alkyl group in the PE monomer, to the hydrophilicity of the phosphoric acid in the PE monomer, and to the higher bioactivity of the bioactive glass beads at the cement surface. GBC/PE shows promise as an alternative bone cement with improved properties compared with conventional PMMA bone cement.

Animals↗

PubMed2001

Bioactive bone cement: effect of filler size on mechanical properties and osteoconductivity.

A bioactive bone cement (designated GBC), consisting of bioactive glass beads as an inorganic filler and poly(methyl methacrylate) (PMMA) as an organic matrix, has been developed. The purpose of the present study was to examine the effect of the size of the glass beads added as a filler to GBC on its mechanical properties and osteoconductivity. Serial changes in GBC with time were also examined. Four different sizes of beads (mean diameters 4, 5, 9, and 13 microm) consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass were added to four GBC mixes in a proportion of 70 wt %. The bending strength of GBC increased as the mean size of the glass beads decreased. The four GBC mixes were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after surgery. The affinity index, which equaled the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface, was calculated for each cement at each interval. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks. At each time interval, there was a trend for the affinity index of GBC to increase as the mean glass bead size decreased. The affinity indices for all types of GBC increased significantly with time up to 8 weeks. The handling properties of GBC were comparable to those of conventional PMMA bone cement. We concluded that, considering both mechanical properties and osteoconductivity, GBC made with smaller sized glass beads as filler was the most suitable cement. GBC shows promise as an alternative bone cement with improved properties compared to conventional PMMA bone cement.

Animals↗

PubMed2001

Bioactive bone cement: Effect of silane treatment on mechanical properties and osteoconductivity.

A novel bioactive bone cement (GBC) was developed with newly designed bioactive MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass beads as the inorganic filler and high molecular weight poly(methyl methacrylate) as the organic matrix. The purpose of this study was to examine the relationship between the amount of the silane coupling agent (gamma-methacryloxy propyl trimethoxy silane) used to treat the glass beads and the mechanical and biological properties of the resultant bone cement. Serial changes in the cement over time were also investigated. Five different kinds of cement, in which the glass beads were treated with different amounts of the coupling agent, were prepared. The quantities of the coupling agent were 0 (control), 0.1, 0.2, 0.5, and 1.0% (w/w) of the glass beads, and the cements were designated GBCs0, GBCs0.1, GBCs0.2, GBCs0.5, and GBCs1.0, respectively. After soaking in water at 75 degrees C for 5 days, GBCs0.1 and GBCs0.2 had significantly higher bending strengths than the other cements. Each GBC was packed into intramedullar canals of rat tibiae to evaluate osteoconductivity, as determined by affinity indices. Rats were killed 4 and 8 weeks after the operation. The affinity index was calculated for each GBC and equaled the length of bone in direct contact with the cement and was expressed as a percentage of the total length of the cement surface. Histologically, new bone had formed along all of the GBC surfaces within 4 weeks. At each time interval, a decreasing trend in the affinity index of GBC was found as the amount of the coupling agent increased. At 8 weeks, no significant change in the affinity index occurred when the amount of the coupling agent increased from 0 to 0.2%, whereas a significant decrease in the affinity index was observed when the amount of the coupling agent increased from 0 to 0.5 or 1.0%. The affinity indices for all the GBCs increased significantly up to 8 weeks. When both the mechanical properties and osteoconductivity were taken into consideration, GBCs0.1 and GBCs0.2 were the best cements, and they showed excellent osteoconductivity and strong enough mechanical properties for clinical use.

Animals↗

PubMed2001

Requirement for yeast TAF145 function in transcriptional activation of the RPS5 promoter that depends on both core promoter structure and upstream activating sequences.

The general transcription factor TFIID has been shown to be involved in both core promoter recognition and the transcriptional activation of eukaryotic genes. We recently isolated TAF145 (one of TFIID subunits) temperature-sensitive mutants in yeast, in which transcription of the TUB2 gene is impaired at restrictive temperatures due to a defect in core promoter recognition. Here, we show in these mutants that the transcription of the RPS5 gene is impaired, mostly due to a defect in transcriptional activation rather than to a defect in core promoter recognition, although the latter is slightly affected as well. Surprisingly, the RPS5 core promoter can be activated by various activation domains fused to a GAL4 DNA binding domain, but not by the original upstream activating sequence (UAS) of the RPS5 gene. In addition, a heterologous CYC1 core promoter can be activated by RPS5-UAS at normal levels even in these mutants. These observations indicate that a distinct combination of core promoters and activators may exploit alternative activation pathways that vary in their requirement for TAF145 function. In addition, a particular function of TAF145 that is deleted in our mutants appears to be involved in both core promoter recognition and transcriptional activation.

Gene Expression Regulation, Fungal↗

PubMed2001

A new bioactive bone cement: effect of glass bead filler content on mechanical and biological properties.

A new bioactive bone cement (designated GBC), consisting of bioactive glass beads as an inorganic filler and polymethylmethacrylate (PMMA) as an organic matrix, has been developed. The purpose of the present study was to examine the effect of the amount of glass bead filler added to GBC on its mechanical and biological properties, and to decide the most suitable content of filler. Serial changes in GBC with time were also examined. The newly designed bioactive beads, consisting of MgO-CaO-SiO2-P2O5-CaF2 glass, were added to the cement in the proportions 30, 40, 50, 60, and 70 wt %. These cements were designated GBC30, GBC40, GBC50, GBC60, and GBC70, respectively. The compressive strength and the elastic modulus of bending of GBC increased as the glass bead content increased. The various types of GBC were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface. Rats were killed at 4 and 8 weeks after the operation and the affinity index was calculated for each type of GBC. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks, even in GBC30 containing only 30 wt % of glass beads. At each time interval studied, there was a trend for the affinity index of GBC to increase as the glass bead filler content increased. There was no significant increase of affinity index between GBC60 and GBC70. The affinity indices for all types of GBC increased significantly with time up to 8 weeks. The handling properties of GBC were comparable to those of conventional PMMA bone cement. We conclude that when mechanical properties and osteoconductivity are both taken into consideration, GBC60 is the most suitable formulation; it shows excellent osteoconductivity and sufficient mechanical strength for clinical use.

Animals↗

PubMed2001

Evaluation of glass microspheres for intra-arterial radiotherapy in animal kidneys.

PURPOSE: To evaluate the histologic distribution of nonradioactive microspheres when intra-arterially infused into normal kidneys, and to evaluate the histologic changes after the infusion. MATERIALS AND METHODS: The glass microspheres were SiO2 microspheres with a smooth spherical shape measuring 20-30 micrometers in diameter with a specific gravity of 2.2 g/cm3. After the microspheres were mixed with contrast medium, they were infused into the renal artery. Twelve rabbits were sacrificed at 1 day, 3 days, 1 week, and 8 weeks after the treatment, respectively. The specimen was fixed with 10% buffered formalin, specially embedded in methyl methacrylate (MMA) resin and was stained by hematoxylin-eosin. The distribution of the microspheres in the kidney was analyzed microscopically, and histologic changes were also evaluated. RESULTS: The microspheres were found in arterioles whose diameters were about 20-30 micrometers, within normal kidneys. All vessels containing microspheres were confined to arterioles or arteries. No migration of microspheres was detected in the normal lung or the contralateral kidney. Severe ischemic changes were observed in kidneys, developing within 8 weeks of the infusion. CONCLUSION: Glass microspheres seemed to be a useful embolic material for intra-arterial radiation therapy.

Animals↗

PubMed2001

Molecular characterization of L-amino acid oxidase from Agkistrodon halys blomhoffii with special reference to platelet aggregation.

L-Amino acid oxidase (LAO, EC 1.4.3.2) is widely distributed in snake venom, and induces apoptosis in vascular endothelial cells, causing prolonged bleeding from vessel walls at bite sites. The effect of snake venom LAOs on platelet function is controversial. Further, we have little information on their structural characterization. We purified M (mamushi)-LAO, a single-chain glycoprotein with a molecular mass of 60 kDa and a pI of 4.9, from Agkistrodon halys blomhoffii (Japanese mamushi) venom, and determined the N-terminal and several internal amino acid sequences of this enzyme. Molecular cloning based on these data was conducted to elucidate its full-length cDNA structure (2192 nucleotides), which includes a putative 18 amino acid residue signal peptide and a 504 residue mature subunit. The predicted M-LAO translation product shares 87.3% identity with that of Crotalus adamanteus (Southeastern diamondback rattlesnake) LAO. M-LAO, up to a final concentration of 2.6 microM, inhibited both agonist- and shear stress-induced platelet aggregation (SIPA) dose-dependently. In agonist-induced platelet aggregation, M-LAO predominantly inhibited the second aggregation, but with a marginal inhibition of the first. In SIPA, the inhibition was more dramatic under low-shear stress than high-shear stress, and was enhanced by the presence of L-leucine, a substrate of this enzyme. Catalase, a H2O2 scavenger, totally quenched such enhancement. These results suggest that M-LAO inhibits the interaction between activated platelet integrin alphaIIb/beta3 and fibrinogen through the continuous generation of H2O2, and may contribute to prolonged bleeding from the vessels at snake bite sites.

Agkistrodon↗

PubMed2001

Mutations in the TATA-binding protein, affecting transcriptional activation, show synthetic lethality with the TAF145 gene lacking the TAF N-terminal domain in Saccharomyces cerevisiae.

The general transcription factor TFIID, which is composed of the TATA box-binding protein (TBP) and a set of TBP-associated factors (TAFs), is crucial for both basal and regulated transcription by RNA polymerase II. The N-terminal small segment of yeast TAF145 (yTAF145) binds to TBP and thereby inhibits TBP function. To understand the physiological role of this inhibitory domain, which is designated as TAND (TAF N-terminal domain), we screened mutations, synthetically lethal with the TAF145 gene lacking TAND (taf145 Delta TAND), in Saccharomyces cerevisiae by exploiting a red/white colony-sectoring assay. Our screen yielded several recessive nsl (Delta TAND synthetic lethal) mutations, two of which, nsl1-1 and nsl1-2, define the same complementation group. The NSL1 gene was found to be identical to the SPT15 gene encoding TBP. Interestingly, both temperature-sensitive nsl1/spt15 alleles, which harbor the single amino acid substitutions, S118L and P65S, respectively, were defective in transcriptional activation in vivo. Several other previously characterized activation-deficient spt15 alleles also displayed synthetic lethal interactions with taf145 Delta TAND, indicating that TAND and TBP carry an overlapping but as yet unidentified function that is specifically required for transcriptional regulation.

Amino Acid Substitution↗

PubMed2001

Analysis of the microheterogeneity of the IgA1 hinge glycopeptide having multiple O-linked oligosaccharides by capillary electrophoresis.

It was found that the self-aggregation of IgA1 was closely connected with the glycoform of a mucin-type sugar chain on its hinge portion. In this report, normal human serum IgA1 was separated into two subfractions by a jacalin column. The elution condition, 25 mM galactose, used here was similar to that reported for the glycoprotein with a single mucin-type sugar chain per molecule. The IgA1 eluted under this condition was substantially the monomeric form. In contrast, the remaining IgA1 eluted from the column with 0. 8 M galactose was substantially the aggregated form. An analytical method for the microheterogeneity of the IgA1 hinge glycopeptide (HGP33) was developed to determine the difference between these IgA1 fractions by capillary electrophoresis (CE). Native HGP33 from both IgA1 fractions was separated into peaks 1-11, depending on their glycoforms. Because the sialic acid-rich component migrated slowly on CE, the 25 mM fraction was abundant in the sialic acid-rich components (peaks 7-11), but the 0.8 M fraction was abundant in the sialic acid-poor components (peaks 1-4). Comparison of the number of sugar chains per hinge peptide indicated that the 25 mM fraction was relatively well glycosylated. Thus, application of CE analysis to the HGP33 indicated that the monomeric IgA1 was composed of a relatively complete molecule with respect to the glycoform rather than the aggregated IgA1.

Chromatography, Affinity↗

PubMed2001

Alkali- and heat-treated porous titanium for orthopedic implants.

This study was carried out to investigate the effects of the alkali and heat treatments on the bone-bonding behavior of porous titanium implants. Porous titanium implants had a 4.6 mm solid core and a 0.7 mm thick porous outer layer using pure titanium plasma-spray technique. Three types of porous implants were prepared from these pieces: 1.control implant (CL implant) as manufactured 2.AW-glass ceramic bottom-coated implant (AW implant) in which AW-glass ceramic was coated on only the bottom of the pore of the implant 3.alkali- and heat-treated implant (AH implant), where implants were immersed in 5 mol/L NaOH solution at 60 degrees C for 24 h and subsequently heated at 600 degrees C for 1 h. The implants were inserted into bilateral femora of six dogs hemi-transcortically in a randomized manner. At 4 weeks, push-out tests revealed that the mean shear strengths of the CL, AW, and AH implants were about 10.8, 12.7, and 15.0 MPa, respectively. At 12 weeks there was no significant difference between the bonding strengths of the three types of the porous implants (16.0-16.7 MPa). Histologically and histomorphologically, direct bone contact with the implant surface was significantly higher in the AH implants than the CL and AW implants both at 4 and 12 weeks. Thus, the higher bonding strength between bone and alkali- and heat-treated titanium implants was attributed to the direct bonding between bone and titanium surface. In conclusion, alkali and heat treatments can provide porous titanium implants with earlier stable fixation.

Animals↗

PubMed2001

Effects of apatite and wollastonite containing glass-ceramic powder and two types of alumina powder in composites on osteoblastic differentiation of bone marrow cells.

Previously we developed a composite consisting of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyldimethacrylate (Bis-GMA)-based resin (designated AWC), and demonstrated that AWC showed direct contact with living bone. Another new composite consisting of mainly the delta-crystal phase of alumina bead powder and Bis-GMA-based resin (designated ABC) was developed. Although alumina ceramics are bioinert and a composite filled with the pure alpha-crystal phase of alumina powder (designated alphaALC) did not allow direct bone formation in vivo, ABC was shown to have excellent osteoconductivity. One purpose of this study was to investigate whether AW-GC powder in a composite promotes osteoblastic differentiation of rat bone marrow cells as AW-GC bulk did. Another purpose was to evaluate the effects of the delta-crystal phase of alumina powder in a composite on osteoblastic differentiation. In a cell culture with dexamethasone, alkaline phosphatase (AP) activity at both days 7 and 14, and the levels of osteocalcin mRNA and alpha1(I) collagen mRNA at day 14 and osteopontin mRNA at day 7, were highest on AWC, followed by ABC, and finally alphaALC. Scanning electron microscopy showed more abundant mineralized globules and a fibrous collagen matrix on AWC at day 14, followed by ABC. In a cell culture without dexamethasone, AP activity at both days 7 and 14, and the level of osteopontin mRNA at day 7, were higher on ABC than on any other composite, whereas osteocalcin mRNA could not be detected. These results indicate that AW-GC powder in a composite promotes osteoblastic differentiation of bone marrow cells intensively when supplemented with dexamethasone. The delta-crystal phase of alumina powder in a composite promotes greater osteoblastic differentiation than the alpha-crystal phase of alumina powder.

Alkaline Phosphatase↗

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↗

PubMed2001

Ultrastructure of the interface between bioactive composite and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We have developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl dimethacrylate (Bis-GMA)-based resin. In this study, we made three types of composite (designated AWC, HAC, and TCPC) consisting of AW-GC, hydroxyapatite (HA,) or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA-based resin as the organic matrix. The proportion by weight of the filler mixed into the cement was 70%. Rectangular plates (10 x 15 x 2 mm) of each composite were made and abraded with 2000 alumina powder. These composites were implanted into tibial metaphyses of rabbits. Specimens were prepared 10 and 25 weeks after implantation and examined using transmission electron microscopy (TEM). AWC was in direct contact with bone 10 weeks after implantation, and AW-GC particles were partially absorbed at the surface. HAC was in contact with partially mineralized extracellular matrix 10 weeks after implantation. In TCPC-implanted specimens, randomly oriented mineral was observed 10 weeks after implantation; however, collagenous extracellular matrix rarely was observed. In 25-week specimens, AW-GC particles were completely absorbed and replaced by new bone, and there was no intervening soft tissue. Both HAC and TCPC were in contact with bone at 25 weeks. These results indicate that AWC has higher bioactivity than either HAC or TCPC.

Animals↗