Biomedical subjects

F Miyaji

Publications and source records attributed to F Miyaji.

33 records · Page 2Linked to original sources

PubMed1997

Bonding of chemically treated titanium implants to bone.

A study was undertaken in rabbit tibiae to determine the effects of chemical treatments and/or surface-induced bonelike apatite on the bone-bonding ability of titanium (Ti) implants. Smooth-surfaced plates (10 x 10 x 2 mm) of pure Ti, alkalil- and heat-treated Ti, and bonelike apatite-formed Ti after the treatments were implanted into the tibial metaphyses of mature rabbits. The tibiae containing the implants were harvested at 4, 8, and 16 weeks after implantation and subjected to a tensile testing and histologic evaluation. Biomechanical results showed that both treated implants exhibited significantly higher failure loads compared with untreated Ti implants at all time periods. Histologic examination by Giemsa surface staining, contact microradiography (CMR), and scanning electron microscopy (SEM) in backscatter mode revealed that both treated Ti implants directly bonded to bone tissue during the early postimplantation period, whereas untreated Ti implants formed direct contact with the bone only at 16 weeks. SEM-electron-probe microanalysis (EPMA) examination showed a Ca-P-rich layer at the interface between the treated implants and bone, although the Ca-P-rich layer was not detected on the surface of untreated implants during observation periods. The results of this study suggest that chemical treatments may accelerate the bone-bonding behavior of titanium implants and enhance the strength of bone-implant bonding by inducing a bioactive surface layer on Ti implants.

Animals↗

PubMed1997

Bonding strength of bonelike apatite layer to Ti metal substrate.

Our previous study showed that titanium metal forms a bonelike apatite layer on its surface in simulated body fluid when it was subjected to NaOH and heat treatments to form a sodium titanate hydrogel or amorphous sodium titanate surface layer. In the present study, bonding strength of the apatite layer formed on the titanium metals to the substrates were examined under tensile stress, in comparison with those of the apatite layers formed on Bioglass 45S5-type glass, dense sintered hydroxyapatite, and glass-ceramic A-W, which are already clinically used. The NaOH-treated titanium metals showed higher bonding strength of the apatite layer to the substrates, which was maximized by heat treatments at 500 and 600 degrees C, than all the examined bioactive ceramics. It is believed that bioactive metals thus obtained are useful as bone substitutes, even under load-bearing conditions.

Apatites↗

PubMed1997

Preparation of radiotherapy glass by phosphorus ion implantation at 100 keV.

A chemically durable glass containing a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to be a beta emitter (half-life of 14.3 days) by neutron bombardment. Microspheres of the activated glass injected into the tumors can irradiate the tumors directly with beta rays without irradiating neighboring normal tissues. In the present study a P+ ion was implanted into a pure silica glass in a plate form at 100 keV in order to find the fundamental conditions for obtaining such a glass. Little phosphorus was present in the surface region, at least to a depth of 2.4 nm for doses of 5 x 10(16) and 1 x 10(17) cm-2, whereas an appreciable amount of it was distributed on the glass surface and a part of it was oxidized for doses above 5 x 10(17) cm-2. The glasses implanted with doses of 5 x 10(16) and 1 x 10(17) cm-2 hardly released the P and Si into water at 95 degrees C, even after 7 days, whereas the glasses implanted with doses above 5 x 10(17) cm-2 released appreciable amounts of these elements. Implantation energies of 20 and 50 keV (even at doses of 5 x 10(16) and 1 x 10(17) cm-2, respectively), formed oxidized phosphorus on the glass surfaces and gave appreciable release of the P and Si into the hot water. This indicates that a chemically durable glass containing a larger amount of phosphorus could be obtained if a P+ ion is implanted at higher energies to localize in a deeper region of the glass surface.

Biocompatible Materials↗

PubMed1997

Bioactivity of ferrimagnetic glass-ceramics in the system FeO-Fe2O3-CaO-SiO2.

Bioactive and ferrimagnetic glass-ceramics are useful as thermoseeds for hyperthermia treatment of cancer. A heat treatment of a 40(FeO, Fe2O3)-60CaO x SiO2 wt% glass gives a ferrimagnetic glass-ceramic containing 36 wt% magnetite in a CaO x SiO2 matrix. However, it does not show bioactivity since a small amount of iron ion remains in the matrix. In the present study, bioactivities of ferrimagnetic glass-ceramics which were prepared by heat treatment of glasses of the composition 40(FeO, Fe2O3)-60CaO x SiO2 (wt%) with various components added at 100:3 weight ratio were evaluated in vitro by examining bone-like apatite formation on their surfaces in a simulated body fluid. It was found that glass-ceramics with Na2O or B2O3 added in combination with P2O5 show bioactivity.

Apatites↗

PubMed1997

Induction of bioactivity of a non-bioactive glass-ceramic by a chemical treatment.

Glass-ceramic A-W(Al), which was prepared by heat treatment of a MgO-CaO-SiO2-P2O5-Al2O3 glass to precipitate crystalline apatite and wollastonite, shows a higher mechanical strength than glass-ceramic A-W, which was prepared by heat treatment of a MgO-CaO-SiO2-P2O5 glass to precipitate the same types of crystalline phases. The former, however, does not show bone-bonding ability, i.e. bioactivity, whereas the latter shows it. In the present study, in order to induce bioactivity of glass-ceramic A-W(Al), it was treated with HCl or NaOH solutions with different concentrations, and its bioactivity was evaluated by examining the apatite formation on its surface in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. When the glass-ceramic A-W(Al) was pretreated with HCl aqueous solutions with concentrations over 0.1 M, it formed the bone-like apatite on its surface in SBF. This was attributed to the formation of a hydrated silica on its surface by the HCl treatment.

Apatites↗

PubMed1997

Effect of heat treatment on apatite-forming ability of Ti metal induced by alkali treatment.

The present authors previously showed that titanium metal forms a bone-like apatite layer on its surface in a simulated body fluid (SBF), when it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mechanically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel layer into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400-500 degrees C, fairly densified at 600 degrees C and converted into crystalline sodium titanate and rutile above 700 degrees C. The induction period for the apatite formation on the NaOH-treated Ti metal in SBF increased with the transformation of the surface gel layer by the heat treatment. Ti metal heat treated at 600 degrees C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.

Journal Article↗

PubMed1996

Apatite-forming ability of silicate ion dissolved from silica gels.

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels.

Apatites↗

PubMed1996

Preparation of bioactive Ti and its alloys via simple chemical surface treatment.

A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti-6A1-4V, Ti-6A1-2Nb-Ta, and Ti-15Mo-5Zr-3A1 substrates were treated with 10M NaOH aqueous solution and subsequently heat-treated at 600 degrees C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali- and heat-treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load-bearing conditions.

Alkalies↗

PubMed1995

Bone-bonding behavior of three heat-treated silica gels implanted in mature rabbit bone.

Silica gel has been reported to induce apatite nucleation on its surface in vitro and it can act as a stimulant that induces formation of chemical apatite (Ca-P) layers on the surfaces of bioactive glass-ceramics. In this study, apatite formation in response to and the bone-bonding behavior of silica gels implanted in the tibiae of mature rabbits were studied. Implants were made from three silica gels treated at 400, 800, and 1000 degrees C, and the effects of such heat treatment on the above parameters were investigated. The silica gel was made by hydrolysis and polycondensation of tetraethoxysilane in aqueous solution containing polyethylene glycol. Rectangular implants (15 mm x 10 mm x 2 mm) of each heat-treated silica gel were implanted into both tibial bones of mature male rabbits, which were killed 4 or 8 weeks after implantation, and the tibiae containing the implants were dissected out. The bone-implant interfaces were investigated using Giemsa surface staining, contact microradiography, scanning electron microscopy-electron probe microanalysis, and X-ray diffraction. Histologically, no bonding of bone to any of the silica gels was observed at any time postimplantation. Soft tissue was observed at the bone-silica gel interface, but there were no giant foreign body or inflammatory cells. A Ca-P-rich layer was observed only on small areas of the surfaces of the silica gels treated at 400 and 800 degrees C 4 and 8 weeks after implantation. X-ray diffraction analysis confirmed the presence of hydroxyapatite in these Ca-P-rich layers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1983