Tetsuya Kameyama

Bond strength improvement of hydroxyapatite/titanium composite coating by partial nitriding during RF-thermal plasma spraying

Abstract The bond strength of plasma-sprayed HA/Ti composite coatings on Ti substrate was significantly improved by the partial nitriding of Ti deposits in the coatings during plasma spraying. HA/Ti composite coatings were deposited on titanium substrates by a radio-frequency thermal plasma spraying method with RF input powers of 12–27 kW. The ratio of HA and Ti powders supplied into the plasma was precisely controlled by two microfeeders so as to change the composition from Ti-rich to HA-rich towards the upper layer of the coating. When sprayed in plasma gas with 0.8% N2 added, the bond (tensile) strength of the obtained HA/Ti composite coatings sprayed at 12 kW was 41.4 MPa. On the contrary, the bond strength of coatings sprayed with pure Ar at 12 kW was 33.6 MPa regardless of the processing parameters which were almost the same except for plasma gas composition. When sprayed with 1.8% N2 added at 27 kW, the bond strength reached 65.3 MPa. XRD patterns of Ti coatings without HA showed that titanium nitrides formed in the titanium deposits sprayed with plasma gas containing N2. Scanning electron microscopic observation showed that these Ti deposits had an acicular texture.

Molecular-scale growth of silicon oxide on polymer substrate through vacuum ultraviolet light-assisted photooxidation of organosilane precursor

Molecular-scale growth of silicon oxide was successfully demonstrated onto a polystyrene (PS) substrate at a relatively low temperature less than the glass transition temperature of PS. Our method consists of three processes. A hydrophobic PS substrate was first photochemically modified using vacuum ultraviolet light (VUV) of 172 nm wavelength from an excimer lamp. Organosilane was then chemisorbed from a precursor vapor of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) onto the VUV-modified PS substrate. Finally, each of our samples was again photoirradiated with the same excimer lamp. Using X-ray photoelectron spectroscopy, we confirmed that the chemisorbed TMCTS was photooxidized and converted to silicon oxide after only 3 min of VUV irradiation. Under atomic force microscopy the resulting oxide surface appeared smooth with its thickness estimated to be less than 1 nm by transmission electron microscopy. Due to the growth of this oxide layer of molecular-scale thickness, the charge density and surface acidity on the PS substrate drastically changed, becoming almost identical to those of native oxide on a Si substrate.

Construction of an Interconnected Pore Network Using Hydroxyapatite Beads

A new method for fabrication of macro porous grafts for bone regeneration w as presented in this study. Spherical hydroxyapatite ceramics 1 mm in diameter with a cylindrical through-hole 300 μm in diameter (HA beads) were fabricated as components of a bone g raft. By integrating the HA beads, the through-holes and inter-bead spaces were connected to each other , forming a single interconnected network. The integrated HA beads showed macro porosity of 47.7 1.9%. The interconnected macro spaces network performed remarkably concerning bone rege ration. The through-holes conducted bone formation during the 7-day-long animal test using rabbits.

Influence of Powder Particle Size of Slurries on Mechanical Properties of Porous Hydroxyapatite Ceramics

The effect of different particle sizes on the flexural strength and microstructure of three different types of hydroxyapatite (HAp) powders was studied. The powder characteristics of laboratory synthesized HAp powder (Lab1 and Lab2) were obtained through a wet milling method, and the median particle size and the specific surface area of powders are different with the dryness period. The median particle sizes of Lab1 and Lab2 are 0.34 µm and 0.74 µm, and the specific surface areas of Lab1 and Lab2 are 38.01 m2/g and 19.77 m2/g. The commercial HAp had median particle size of 1.13 µm and specific surface area of 11.62m2/g. The different powder characteristics affected the slip characteristics, and the flexural strength and microstructure of the sintered porous HAp bodies are also different. The optimum value for the minimum viscosity in these present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were investigated. The flexural strengths of the porous HAp ceramics prepared by heating at 1200°C for 3 hrs in air were 17.59 MPa for Lab1 with a porosity of 60.48％, 10.51 MPa for Lab2 with a porosity of 57.75％, and 3.92 MPa for commercial HAp with a porosity of 79.37％.

Preparation of Biphasic Calcium Phosphate Porous Ceramics Prepared from Fine Powders with Different Particle Size and its Dissolution Behavior in Simulated Body Fluid

Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and betatricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios was prepared. One kinds of HAp and one kind of β-TCP powders were used to produce porous BCP bioceramics with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20. A slip was obtained by adding a mixed powders of HAp and β-TCP to a solution 1.5% of deflocculant and 0.5 wt% of foaming agent. The optimum value for the minimum viscosity in these present slips with respect to its solid loading and the optimum amount of the deflocculant were investigated. The specimen obtained by casting a polyurethane foam with 1.5 wt% of deflocculant into a slip, and drying it under vacuum, was heated at 1150°C for 3 hours. The resultant porous BCP sintered body had large spherical pores of 300 /m with interconnecting rectangular voids. Many small pores in the size range of 2-3 /m or below were observed in the specimen obtained by heating at 1150°C for 3 hours. The dissolution test was done as follows. The obtained porous ceramics samples about 0.5g individually soaked into 30 mL of simulated body fluid (SBF) solution at 36.5°C. The calcium and phosphorous content of the SBF solution was analyzed by ICP. The porous body was dried, and characterized using SEM, XRD, and FT-IR.

Synthesis of Apatite Ceramics with Bimodal Pore Structure Using Mechanochemically Prepared Fine Apatite Powder

Preparation of apatite ceramics with bimodal pore structure was studied. First fine hydroxyapatite powder was obtained through mechanochemical method. The particle size of the product was around 0.64 µm. The slurry with the fine apatite powder content of 55-62.5wt% was prepared using defloculant, and foaming reagent. The organic form was immersed into the slurry, dried under vacuum, and heated at 1100°C, 1200°C, 1300°C. Pore size distribution of the product measured by porosimeter showed that small pores of around 1 µm and large pores of 100 µm exist, and SEM observation confirmed. SEM observation showed that the large pores seemed to be interconnected through the openings of several dozens µm in size. The porosity of the products were found to be 48 – 58.5%, and the bending strength of the products obtained by heat-treatment at 1100°C for 3 hours was 5.6 MPa, and that at 1200°C was 10.5 MPa.

Bimodal Porous Bi-Phasic Calcium Phosphate Ceramics and Its Dissolution in SBF Solution

Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios were prepared from fine powders. Porous BCP ceramic materials with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20 were prepared. In this study, the bioactivity is reduced at a larger HAp content rate, which is likely related to the high driving pore for the formation of a new phase, and the reaction rate was proportional to the β-TCP. The porous BCP ceramics having a bigger porosity rate can easily under up dissolution. The powder having a larger β-TCP content rate can easily generate a new phase. The dissolution results confirmed that the biodegradation of calcium phosphate ceramics could be controlled by simply adjusting the amount of HAp or β-TCP in the ceramics and porosity rate.

Photoinduced decomposition of alkyl monolayers using 172 nm vacuum ultraviolet light

The photoinduced stability of two alkyl monolayers on Si has been investigated using a Xe2 excimer lamp radiating 172 nm vacuum ultraviolet (VUV) light. The photoinduced stability of 1-octadecene monolayer (ODM) was compared with that of alkylsilane monolayer. 1-octadecene was employed as a starting precursor of alkyl monolayer on Si. The alkylsilane monolayer was formed from otadecyltrimethoxysilane monoalyer (OTSM) onto the SiO2/Si substrate. The decomposition of ODM was investigated under VUV irradiation conducted at 10 and 105u200aPa. The VUV light decomposed ODM at both 10 and 105u200aPa. The photodecomposition rate at 105u200aPa was smaller than that at 10 Pa. The decomposed methyl and ethyl groups from the alkyl chain formed carboxyl groups. The carboxyl coverage on the surface of Si increased with increasing VUV irradiation time ranging from 0 to 60 s at 10 Pa, and decreased after 60 s. In contrast, the Si–O component in x-ray photoelectron Siu200a2p spectrum drastically increased after the VUV irradiation time o...

Micro-wear resistance of ultrathin silicon oxide film-covered polymer substrate

Abstract An ultrathin silicon oxide film only several nanometers in thickness was prepared on a poly(methyl methacrylate) (PMMA) substrate at the relatively low temperature of 80 °C, which is below the glass transition temperature of PMMA. Our method consisted of three processes. A hydrophobic PMMA substrate was first photochemically hydrophilized using vacuum ultraviolet light of 172 nm wavelength radiated from an excimer lamp. The photochemically treated sample was then exposed to vapor-phase tetoraethoxysilane (TEOS) as a silica precursor. Because of the chemisorbed TEOS layer thus formed, the sample surface again became relatively hydrophobic with a water-contact angle of about 70°. Finally, in order to eliminate the organic phase from the chemisorbed layer, the sample was again irradiated with the same excimer lamp. As confirmed by X-ray photoelectron spectroscopy, the binding energy (BE) of the Sixa02p spectra for the chemisorbed TEOS layer shifted from 102.8 to 103.5 eV after photooxidation. This final BE value is consisted with that of amorphous silicon dioxide. The actual thickness of the oxide was estimated to be 3 nm or less by a cross-sectional image acquired by transmission electron microscopy. Furthermore, we investigated the micro-wear resistance of the oxide-covered PMMA substrates based on a micro-scratching test using a nanoindenter. Wear depths on the scratched oxide-covered substrates were markedly reduced by about 60–84% compared with those on bare PMMA substrates.

Preparation of Bimodal Porous Apatite Ceramics through Slip Casting Using Fine Hydroxyapatite Powders

A bimodal porous hydroxyapatite (HAp) body with high flexural strength was prepared through slip casting. HAp fine powder used in this study was synthesized by wet milling, drying and heating of a mixture of calcium hydrogen phosphate di-hydrate and calcium carbonate. The synthesized HAp powder was 0.320.05 μm in size and 38.10.8m2/g in specific surface area. The slip was prepared by adding deflocculant and foaming reagent. The optimum value for the minimum viscosity in the present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were studied. The total porosity of the specimens obtained from a slip of 48 wt% HAp solid loading is in the range of 49 – 61vol %, and the resultant porous HAp sintered body had large spherical pores of 300 -m with interconnecting rectangular voids. Many small pores in the size range of 2-3 -m or below were observed in the specimen obtained by heating at 1100, and 1200 . The flexural strength of the bimodal porous HAp ceramics sintered at 1200 C showed a large value of 17.6 MPa, with a porosity of 60.5vol.