Satoru Yoshihara

Biological and mechanical properties of PMMA-based bioactive bone cements

We reported previously that a bioactive PMMA-based cement was obtained by using a dry method of silanation of apatite-wollastonite glass ceramic (AW-GC) particles, and using high molecular weight PMMA particles. But handling and mechanical properties of the cement were poor (Mousa et al., J Biomed Mater Res 1999;47:336-44). In the present study, we investigated the effect of the characteristics of PMMA powder on the cement. Different cements containing different PMMA powders (CMW1, Surgical Simplex, Palacos-R and other two types of PMMA powders with Mw 270,000 and 1,200,000) and AW-GC filler in 70 wt% ratio except Palacos-R (abbreviated as B-CMW1 and B-Surg Simp, B-Palacos 50 [50 wt% AW-GC filler] and B-Palacos 70 [70 wt% AW-GC filler], B-270 and B-1200) were made. Dough and setting times of B-CMW1, B-Surg Simp B-270 and B-1200 were similar to the commercial CMW1 cement which did not contain bioactive powder (C-CMW1), but B-palacos which contained large PMMA beads with high Mw had delayed setting time. B-270 had the highest bending strength among the tested cements. After 4 and 8 weeks of implantation in the medullary canals of rat tibiae, the bone-cement interface was examined using SEM. The affinity index of B-1200 was significantly higher than the other types of cements. B-270 showed good combination of handling properties, high mechanical properties and showed higher bioactivity with minimal soft tissue interposition between bone and cement compared with commercial PMMA bone cement. This may increase the strength of the bone-cement interface and increase the longevity of cemented arthroplasties.

YAG glass-ceramic phosphor for white LED (I): background and development

We have developed a Ce:YAG (Y3Al5O12) glass-ceramic phosphor for the white LED. The glass-ceramic phosphor was obtained by a heat treatment of a Ce-doped SiO2-Al2O3-Y2O3 mother glass between 1200°C and 1500°C for the prescribed time of period. We confirmed that, by XRD measurements, only YAG crystal precipitated in the mother glass after the heat treatment. It was shown from SEM observation that the YAG crystals with a grain size of approximately 20μm were uniformly dispersed in the glass matrix. The yellow emission, around 540nm in wavelength, was observed from the glass-ceramic phosphor, when it was excited by a blue LED (465nm). The white light due to the mix of yellow and blue light was observed from the glass-ceramic plate with a thickness of 0.5mm. The YAG glass-ceramic phosphor showed a high-temperature resistance and a good performance in a damp heat test. Moreover, a higher thermal conductivity of 2.18 Wm-1K-1 and bending strength of 125MPa were observed compared with a conventional soda-lime glass or an epoxy resin. In addition, since the YAG glass-ceramic phosphor can be formed in a plate-like shape, there is no need to be sealed in resins for the fabrication of the LED devices. Therefore, it is expected that this newly developed glass-ceramic phosphor is a promising candidate for the realization of resin-free, high-temperature and high-humidity resistant, long-life white LED devices.

YAG glass-ceramic phosphor for white LED (II): luminescence characteristics

Optical properties of the Ce:YAG glass-ceramic (GC) phosphor for the white LED were investigated. Concentration dependence of fluorescence intensity of Ce3+:5d→4f transition in the GC showed a maximum at 0.5mol%Ce2O3. Quantum efficiency (QE) of Ce3+ fluorescence in the GC materials, the color coordinate and luminous flux of electroluminescence of LED composite were evaluated with an integrating sphere. QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x,y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd2O3 substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelength shifted to longer side up to Gd/(Y+Gd)=0.40 in molar composition. As a result, the color coordinate locus of the LED with various thickness of the GdYAG-GC shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd3+ ions in the precipitated YAG micro-crystals, leading to the increase of lattice constant of unit cell, which was confirmed by X-ray diffraction.

Mechanical and biological properties of two types of bioactive bone cements containing MgO-CaO-SiO2-P2O5-CaF2 glass and glass-ceramic powder.

In this study two types of bioactive bone cement containing either MgO-CaO-SiO2-P2O5-CaF2 glass (type A) or glass-ceramic powder (type B) were made to evaluate the effect of the crystalline phases on their mechanical and biological properties. Type A bone cement was produced from glass powder and bisphenol-a-glycidyl methacrylate (BIS-GMA) resin, and type B from glass-ceramic powder containing apatite and wollastonite crystals and BIS-GMA resin. Glass or glass-ceramic powder (30, 50, 70, and 80 by wt %) was added to the cement. The compressive strength of type A (153-180 MPa) and B (167-194 MPa) cement were more than twice that of conventional polymethylmethacrylate (PMMA) cement (68 MPa). Histological examination of rat tibiae showed that all the bioactive cements formed direct contact with the bone. A reactive layer was seen at the bone-cement interface. In specimens with type A cement the reactive layer consisted of two layers, a radiopaque outer layer (Ca-P-rich layer) and a relatively radiolucent inner layer (low-calcium-level layer). With type B cement, although the Ca-P-rich layer was seen, the radiolucent inner layer was absent. Up to 26 weeks there was progressive bone formation around each cement (70 wt %) and no evidence of biodegradation. The mechanical and biological properties of the cements were compared with those of a previously reported bone cement containing MgO-free CaO-SiO2-P2O5-CaF2 glass powder (designated type C).

Bone bonding ability of bioactive bone cements.

The bone bonding ability of three types of bioactive bone cement A, B, and C consisting of glass or glass ceramic powder and bisphenol-alpha-glycidyl methacrylate resin was evaluated. Type A contained MgO-CaO-SiO2-P2O5-CaF2 glass powder; Type B, MgO-CaO-SiO2-P2O5-CaF2 glass ceramic powder; and Type C, MgO free CaO-SiO2-P2O5-CaF2 glass powder. Rectangular plates (2 x 10 x 15 mm) of Types A, B, C, and polymethylmethacrylate cements were implanted into the tibial metaphyses of male rabbits and the failure load measured by mechanical failure testing (detaching test) 10 and 25 weeks after implantation. The failure loads of Types A, B, C, and polymethylmethacrylate cements were respectively, 29.52, 41.48, 28.22, and 0.29 N at 10 weeks and 33.42, 41.27, 33.64, and 0.20 N at 25 weeks. Examination of the bone cement interface revealed that all the bioactive bone cements achieved direct bone contact with the bone. These results showed that all three types of bioactive bone cement have the ability to bond to bone, and the cement containing glass ceramic powder revealed higher bonding strength than did those containing glass powder.

A novel skeletal drug delivery system using self-setting bioactive glass bone cement. III: the in vitro drug release from bone cement containing indomethacin and its physicochemical properties

Abstract A novel device containing indomethacin as a model drug using a self-setting bioactive cement based on CaOSiO 2 P 2 O 5 glass was investigated. Glass powders containing 2% and 5% indomethacin hardened within 5 min after mixing with a phosphate buffer. After setting, in-vitro drug release from homogeneous or heterogeneous drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37°C continued for more than 2 weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite and shrunk by about 5% in volume during the drug release test in SBF. Therefore, 30% of the loaded drug was extruded from the cement system at the initial stage, thereafter being released more slowly. Since the heterogeneous system consisting of the cement and the drug-loaded pellet avoided this effect, the drug was released more slowly than from the homogeneous drug-loaded cement. The heterogeneous system using the hardened cement after soaking in SBF at 37°C for 10 days released the drug very slowly at the initial stage since it avoided the drug squeezing effect, and the release continued slowly for more than 300 h.

Effects of glass composition on compressive strength of bioactive cement based on CaO-SiO2-P2O5 glass powders

Mixtures of CaO-SiO2-P2O5-CaF2 glass powders with 3.7 m ammonium phosphate solution give bioactive cements which can set in a few minutes and bond to living bone in a few weeks. In the present study, the mechanical strengths of the mixtures, which were held in 100% humidity at 37°C for 1 h and then soaked in a simulated body fluid (SBF) for 23 h, were investigated in terms of the glass composition. Their compressive strengths varied significantly with small changes in the CaO/SiO2/P2O5 ratios under a constant CaF2 content. Addition of CaF2 to a CaO-SiO2-P2O5 composition increased the compressive strength, whereas addition of MgO decreased it. The glass composition of CaO 47.1, SiO2 35.8, P2O5 17.1, CaF2 0.75 wt ratio gave the highest compressive strength among the compositions examined: 56 and 80 MPa, respectively, after soaking in the simulated body fluid for 23 h and 3 days. The variation of the compressive strength with the glass composition was well interpreted in terms of the amount of the hydroxyapatite formed at the intergranular spaces of the glass powders in the simulated body fluid.

The in vitro and in vivo indomethacin release from self-setting bioactive glass bone cement.

The in vivo and in vitro drug release profiles from a self-setting bioactive CaO-SiO2-P2O5 glass bone cement containing indomethacin as a model drug were investigated. The cement containing 2% and 5% indomethacin (IMC) powder hardened within 5 min after mixing with ammonium phosphate buffer. After setting, in vitro drug release from drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for two weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite during the drug release test in SBF. An IMC-loaded cement device (2% and 5% drug) was implanted in the subcutaneous tissue on the back of rats. The in vivo IMC release from the cement increased and attained maximum levels (Cmax of 2% and 5% drug-loaded cements was 0.27 and 3.37 micrograms/ml, respectively) at Tmax, 3 and 0.5 d, respectively, upon subcutaneous (s.c.) administration in rats. This suggested that the s.c. administration of the cement provided IMC release for a much longer period than s.c. administration of the solution, and the plasma IMC concentration was dependent on the drug concentration in the cement. The plasma IMC concentration and the area under the curve from 2% and 5% IMC-loaded cements in rats were dependent on the concentration of IMC in the cements. The in vivo IMC concentration in plasma obtained by the deconvolution method was much lower than that delivered in SBF in vitro. Scanning electron microscopy and photomicrographs of cross sections showed that the bioactive bone cement had excellent biocompatibility with the surrounding soft tissues.

A novel skeletal drug delivery system using self-setting bioactive glass bone cement. IV: Cephalexin release from cement containing polymer-coated bulk powder.

A novel device consisting of Eudragit-coated cephalexin as a model drug and a self-setting bioactive cement based upon CaO-SiO2-P2O5 glass was investigated. The glass cement hardened within 5 min of mixing with a phosphate buffer. After setting, in vitro drug release from homogeneous or heterogeneous drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for over 2 weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite and decreased in volume by about 5% during drug release in SBF. Consequently, 30% of the loaded drug was initially released from the homogeneous cement system, and thereafter it was released more slowly. Since the heterogeneous system consisting of the cement and a 50% polymer coated, drug-loaded pellet avoided this drugs burst, the drug was released over a longer period than that in the homogeneous system. The heterogeneous system released the polymer-coated drug very slowly, because it completely avoided the initial burst, and sustained the release over a long period.

Comparative Study of Two Types of Bioactive Bone Cements Containing MgO-CaO-SiO2-P2O5-CaF2 Glass and Glass-Ceramic Powder

ABSTRACT Two types of bioactive bone cement containing either MgO-CaO-SiO2-P2O5-CaF2 glass or glass-ceramic powder were made to evaluate the influence of crystal phase of the bioactive bone cement on its mechanical and biological properties. The former was produced from glass powder and Bis-GMA resin and the latter from glass-ceramic powder containing apatite and wollastonite crystals and Bis-GMA resin. Histological examination showed direct bonding between the bone and the cement for each bioactive cement. The bioactive bone cements bonded to the bone through reactive layer. In specimens with the bioactive bone cement containing glass powder the reactive layer was composed of two layers: a radiopaque outer layer (Ca-P-rich layer); and a relatively radiolucent inner layer (Si layer). For those with the bioactive bone cement containing glass-ceramic powder the Ca-P-rich layer was formed, however, the Si layer was absent.