To clarify the effect of micro/nanosizing of materials onto biological organism, the particle size dependence of reaction of cells and tissue as investigated by both biochemical cell functional test and animal implantation test. Especially for nanoparticles the behavior of invasion and internal diffusion inside body was visualized using an XSAM (X-ray Scanning Analytical Microscope). The increase of specific surface area is usually counted as nanosizing effect which causes the enhancement of chemical reactivity and therefore toxicity of materials such as carcinogenicity found in 500 nm Ni particles for the long term implantation in the soft tissue of rat. Even biocompatible materials such as Ti and TiO₂ shows stimulus with the decrease of particle size. They cause phagocytosis to cells and inflammation to tissue when the size of particles is below 3 μm. For the size below 50 nm, they may invade into the internal body through the respiratory or digestive system and diffuse inside body. After compulsory exposure test of 30 nm TiO₂ particles through the respiratory system, the Ti mapping by XSAM showed the internal diffusion inside the whole body. Nanoparticles injected from caudal vein diffused with time course to lung, liver and spleen. The uptake of 30 nm TiO₂ particles through the digestive system and diffusion into these organs was also confirmed. These phenomena observed in biocompatible or bioinert materials are the nonspecific, physical particle and shape effects which occur independent of materials. Nanoparticles might be the objects whose existence has not been assumed by the living body defense system.

View full abstract

Hydroxyapatite (HA) porous ceramics are useful for bone regeneration because HA shows a bone-bonding capability. The preparation of HA porous ceramics with controlled pore structures was attempted using a hydrothermal treatment of porous ceramics consisting of alpha tricalcium phosphate (α-TCP). The α-TCP porous ceramics were hydrothermally treated with various aqueous solutions containing NaCl, CaCl₂, Na₃PO₄, Na₂HPO₄, NaH₂PO₄, or H₃PO₄ at 150°C for a period of 10 h. The α-TCP phase of the porous ceramics was transformed into HA by the hydrothermal treatment in ultrapure water, NaCl, CaCl₂, Na₃PO₄ or Na₂HPO₄ solutions, to form porous ceramics consisting of rod-shaped HA particles. The size of the rod-shaped HA particles prepared in Na₃PO₄ or Na₂HPO₄ solutions was smaller than that prepared in ultrapure water, NaCl, or CaCl₂ solutions. The α-TCP phase of the porous ceramics was transformed into a biphase consisting of HA and monetite (DCPA) after treatment in NaH₂PO₄ solution, and into DCPA in the H₃PO₄ solution, resulting in porous ceramics consisting of plate-shaped particles. These results indicate that we could control the size and shape of the HA particles using the hydrothermal conditions, and this also provides a way of controlling the porous structure of the HA porous ceramics.

View full abstract

Collagen/calcium phosphate composite materials were prepared using an alkaline phosphatase-catalyzed hydrolysis of water-soluble phosphate esters in the presence of calcium ions. We prepared a collagen/calcium phosphate composite film by adding sequentially calcium chloride, disodium glycerophosphate and alkaline phosphatase to collagen solution and subsequent drying of the resultant composite suspension in a template. The calcium phosphate contained in the film was determined to be mainly hydroxyapatite from FT-IR and X-ray diffraction analysis. The film little swelled in water to keep its original morphology, while a collagen film became solubilized. This suggests the binding between collagen and calcium phosphate in complex materials. When the preosteoblast cell line, MC3T3-E1 cells were cultured on the film, the film was found to support the osteoblastic differentiation from the measurement of alkaline phosphatase activity, which is an early differentiation marker.

View full abstract

A preparation method of bone-like hydroxyapatite (b-HA) coating with silicon-ion releasability on ceramic substrates was investigated for developing scaffolds with high mechanical strength and cellular compatibility for bioreactors. A trace amount of silicon ion has been reported to stimulate the activities of osteoblastic cells. A mullite ceramic substrate was covered with a silica layer derived from water glass through two steps, i.e., heat-treatment at 500°C for 2 h and subsequent acid-treatment using 0.1 mol•dm^-3 HCl solution at 50°C for 2 h, and then coated with nano-sized vaterite particles in monolayer. The monolayer was produced by the balance of the surface potentials between the negatively charged silica layer and the positively charged vaterite. The resulting substrate was homogeneously coated with b-HA layer of about 2 μm in thickness after 3 d of immersing in an aqueous solution with inorganic ion concentrations of 1.5 times those of simulated body fluid. The b-HA-coated sample was immersed for 7 d in culture medium and 260 μmol•dm^-3 of silicon ion was released simultaneously. On the other hand, 130 μmol•dm^-3 of the ion was released from the b-HA-coated sample after heating at 800°C for 3 h. The silicon-ion releasability of the b-HA-coated sample was controllable by the heat-treatment, which was expected to be ascribed to increase in the crystallinity of the b-HA coating and in the durability of the silica layer in culture medium by the heat-treatment. The b-HA-coated samples showed good compatibility with mesenchymal stem cells. The proliferation and osteogenic differentiation of the cells changed on the b-HA-coated samples between before and after the heat-treatment. The b-HA coating with silicon-ion releasability on ceramic substrates is expected as bioreactor scaffolds with the high activity of the cellular proliferation.

View full abstract

The aim of this study was to develop a novel hydroxyapatite (HA) coating method on zirconia using glass coating technique. A borosilicate glass, the mixture of the glass and HA (30, 50, 70, and 90 mass%), and the 100% HA were coated on two kinds of zirconia discs and fired at 900-950°C. After the final coating, the surface of the sample was etched for 3 min in an acid-mixture of 3% HF and 5%HNO₃ to remove the surface layer covered with glass and to obtain the biocompatible surface layer with HA. The shear bonding strength of the glass to zirconia fired at 950 and 1050°C were determined. There were no significant difference in the bonding strengths between the kind of zirconia (p>0.05). Whereas, the bonding strengths fired at 1050°C were significantly higher than those at 950°C (p<0.05). These results suggest that the HA containing glass-coated zirconia, namely functionally gradient structure, could be systematically produced using the glass coating technique and the acid etching.

View full abstract

Porous hydroxyapatite (HA) disks and blocks with interconnecting pores (pore size≅150 μm, interconnecting window size≅30 μm, and porosity≅75%) were polarized and bone-like apatite formations on the pore surfaces were investigated by immersion test using simulated body fluid (SBF) to estimate the electrovector effect in porous bodies. Thermally stimulated depolarization current (TSDC) measurements were used to estimate the stored charges of polarized porous HA disks and blocks as 11 and 7 μC cm^-2, respectively, demonstrating that both the porous disks and blocks were successfully polarized. After immersion in SBF for 14 d, bone-like apatite formations within the pores were observed in the polarized and non-polarized HA disks and blocks. Based on scanning electron microscopic (SEM) images of the pores located around the center of the disks and the blocks (inside-pores), formation of bone-like apatite was accelerated in the polarized HA compared with that in the non-polarized HA. Although the weight of the polarized and non-polarized porous HA increased linearly with immersion time regardless of shape, the rate of weight change of the polarized HA was greater than that of the non-polarized HA. It was demonstrated that the electric charges on the inside-pore surface of porous HA have a positive effect on the formation of bone-like apatite crystals.

View full abstract

In this study, two types of tetragonal zirconia polycrystals (TZP) were used: a conventional yttria stabilized TZP (3Y-TZP) and a ceria stabilized TZP/alumina nanocomposite (CZA). All specimens were sandblasted with 70 μm-alumina and 125 μm-SiC. Heat treatment was performed at 1100°C for 10 min. XRD patterns of the specimens with grinding, sandblasting and heat treatment were determined, and the content of monoclinic zirconia was calculated using the XRD peak intensity ratios. The biaxial flexure strength of both zirconia increased with the sandblasting and decreased with the heat treatment. The biaxial flexure strength of CZA was higher than that of 3Y-TZP in each treatment. After sandblasting, the content of the monoclinic zirconia of CZA was much higher than that of 3Y-TZP. Although the monoclinic content with SiC-sandblasting was larger than alumina-sandblasting, the biaxial flexure strength with SiC-sandblasting was smaller than that with alumina-sandblasting. These results indicated that the volume expansion due to the phase transformation from tetragonal to monoclinic zirconia induced the compressive stress in the surface area. Furthermore, it suggests that CZA is more susceptible to stress-induced phase transformation by sandblasting than 3Y-TZP.

View full abstract

In this study, hydroxyapatite-coated biopolymer nanofibrous membrane was synthesized by mineralizing the electrospun polycaprolactone nanofiber. The effect of the hydroxyapatite-coated nanofibrous membrane was mainly investigated on the proliferation and differentiation of human periodontal ligament fibroblast, which is necessary for periodontal tissue regeneration. Scanning electron microscopy revealed favorable cell attachment and spreading appearance on 1 d and MTS assay showed increased cell proliferation on the hydroxyapatite-coated nanofiber membrane during 14 d. From 7 to 14 d, alkaline phosphatase activity of the hydroxyapatite-coated nanofiber was significantly increased when compared to that of control group. Hydroxyapatite-coated nanofibrous membrane showed prominent mineral formation on day 14. As a result, it was clarified that the developed hydroxyapatite-coated nanofibrous membrane had favorable effects on the proliferation and differentiation of human periodontal ligament fibroblast and might be a good candidate material for periodontal tissue regeneration.

View full abstract

Recently, calcium phosphate cements have been considered in medicine and dentistry because of their excellent biocompatibility and advantages in situ handling and shaping abilities. Nevertheless, low mechanical strength of these cements limits wider the clinical applications. The aim of this work was the synthesis of chitosan/brushite powders for preparing the calcium phosphate cements. The synthesis of brushite was carried out in the chitosan matrix from calcium chloride and sodium phosphate at moderate pH of 4 and then dried from 60 to 100°C. The obtained powders were characterized by XRD and FT-IR technique. With increasing the drying temperature, phase of dicalcium phosphate anhydrous increased. Moreover, FTIR indicate the bands attributable to chitosan and brushite. The brushite synthesized using this route was used to be a starting powder for calcium phosphate cement (CPC). To prepare CPC, the mixture of chitisan/brushite and α-tricalcium phosphate powders was mixed with various liquid phases and then cured at 100% humidity for 7 d The compressive strength of the cements was determined to evaluate the potential use for the bone cement. Cements formed with chitosan/brushite dried at 100°C had the greatest compressive strength of all cement tests. The improvement of compressive strength seemed to depend on the affinity of chitosan incorporated in the cements.

View full abstract

Hydrothermal treatment and subsequent post sintering were used to fabricate porous and strong hydroxyapatite. Here, steam curing method was used as a hydrothermal treatment and subsequent post sintering treatment was done in air. As a result, samples prepared by steam curing and subsequent post sintering had higher porosity and compressive strength than those prepared by normal sintering process because of the structural changes introduced during steam curing and subsequent post sintering. Moreover, the effect of synthetic condition of these processes on the microstructure for porous hydroxyapatite was investigated.

View full abstract

So-called bioactive ceramics have attractive features such as direct bone-bonding in living body via formation of bone-like apatite layer on their surfaces. However, there is limitation on clinical applications due to their inappropriate mechanical properties such as higher Young's modulus and lower fracture toughness than natural bone. Bioactive ceramics bond to bone through bone-like apatite layer formed on their surfaces by chemical reaction with body fluid. To overcome the problem of bioactive ceramics, hybrid materials have been developed by organic modification of silanol (Si-OH) group and calcium ions, that are basic component of bioactive ceramics. In this study, we prepared organic-inorganic hybrids from glucomannan, a kind of complex polysaccharide, by modification with alkoxysilane and calcium salts. The apatite formation on the hybrids with different alkoxysilane content was examined in simulated body fluid (SBF). All the samples formed the apatite in SBF irrespective of alkoxysilane content, when they were previously treated with CaCl₂ solution. The hybrids had tendency to be fractured into small pieces in SBF and release large amount of Ca²⁺ at low alkoxysilane content. This means that addition of alkoxysilane is effective for not only providing the hybrids with the apatite-forming ability but also improving stability in aqueous environment.

View full abstract

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HAp) is one of inorganic components of bone and teeth, and has an osteoconductivity and execellent biocompatibility. Thus, the HAp has been used as biomaterials for bone graftings. Clinically-used HAp cements are set on the basis of the acid-base reaction of Ca₄O(PO₄)₂ and CaHPO₄. This mechanism accompany the changes of pH during hardening, leading to inflammation around tissues, together with slow setting time. We have succeeded to develop novel HAp cement, which is created by mixing the HAp powder modified with inositol phosphate (IP6) and water. The present IP6-HAp cement is set based on the chelate-bonding of IP6 without the acid-base reaction. The IP6 is not only biocompatible but also has able to chelate to some metal ions as strongly as EDTA. In the present study, we fabricated four kinds of IP6-HAp cements using commercially-available HAp powders with diferent morphology and specific surface area (SSA): HAp-100 (fine particle), HAp-200 (hexagonal shape), HAp-400 (plate shape), and s-HAp (spherical shape). Among the cement specimens examined, the IP6/HAp-100 cement derived from HAp-100 powder had maximum compressive strength of 10 MPa under following condition: Powder/Liquid (P/L) ratio=1/0.45[w/w]. The HAp-100 powder was composed of microcrystals with the highest SSA of 62.4 m²•g^-1 among the HAp powder used in the present work. On the other hand, the compressive strength of the IP6/HAp-200 cements showed the lowest value of 2 MPa under following condition: P/L ratio=1/0.35[w/w]. The HAp-200 powder of a starting material was composed of hexagonal-shaped crystals, and had the lowest SSA of 7.0 m²•g^-1. These results indicate that the compressive strength of novel IP6/HAp cements was affected by powder properties, especially, the morphology and SSA of starting HAp powders.

View full abstract

Sol-gel processing from tetraethoxysilane (TEOS) under coexistence of polyethylene glycol (PEG) allows controlled morphology of the formed silica because of the phase separation during the polycondensation of the hydrated sol. The presence of PEG controlled the morphology effective in preparation of the ceramics, even in the CaO-SiO₂ binary system, starting from TEOS and Ca(NO₃)₂. In the present study, some ceramics were prepared using the MO_n/2-SiO₂ binary systems, where M is given as Na⁺ (n=1), Mg²⁺ (n=2) and Al³⁺ (n=3), through sol-gel processing in the presence of PEG, to compare the compositional changes in the morphology of the ceramics. In the case of NaO_1/2-SiO₂, the framework size increased remarkably with increasing amounts of Na⁺ in the starting compositions up to 30 mol%, while continuous pores of approximately 10 μm were observed at 5 mol% of Na⁺. In the case of MgO-SiO₂, the framework size increased with increasing amounts of Mg²⁺ up to 20 mol% in the starting composition. Aggregation of particles with approximately 3 μm in size was observed at 25 mol% and more. The trend in morphological change with addition of Mg²⁺ was quite similar to that with Ca²⁺. With AlO_3/2-SiO₂, particles were obtained when the starting composition was more than 10 mol% Al³⁺. The size of the particles appeared to decrease with increasing amounts of Al³⁺. The morphology and phase separation behavior are strongly affected by the charge value of the metal ions, because the number of non-bridging oxygens coordinated to the metal ion increased with increasing charge value in the sol-gel processing. A specimen prepared with starting composition 20NaO_1/2•80SiO₂ and heated at 600°C formed hydroxyapatite on the particle surfaces within 7 d after soaking in a simulated body fluid (SBF), suggesting a potential for bioactivity on application of bone repair.

View full abstract

We have previously prepared spherical-shaped tetracalcium phosphate (s-TTCP) with plasma melting method. We found that apatite cement (AC) containing s-TTCP showed excellent injectability from syringe and handling property when compared with AC that contained irregular-shaped TTCP (i-TTCP). However, transformation of AC containing s-TTCP (s-AC) to apatitic mineral was suppressed and thus mechanical strength of set s-AC was low. In the present study, thermal treatment was attempted on s-TTCP to convert heat decomposition products formed in s-TTCP during plasma melting process to TTCP. X-ray diffraction (XRD) analysis revealed that some heat decomposition products in s-TTCP converted to TTCP when s-TTCP was heated at 1,500°C for four hours and quenched at room temperature (q-TTCP). AC containing q-TTCP transformed to apatitic monolith and showed equivalent mechanical strength similar to AC that contained i-TTCP —without sacrificing excellent injectability from syringe and handling property. Based on these findings, we concluded that AC containing q-TTCP would benefit patients since it delivered excellent injectability without sacrificing basic setting properties of AC.

View full abstract

Titanium (Ti) metal substrates were etched in sulfuric acid (H₂SO₄) with concentrations of 25, 50, 75 and 97% at 60°C for 30 min. Hydroxyapatite (HA) films were deposited onto unetched and etched substrates by an electrodeposition method under a pulse current. The electrolyte was metastable calcium phosphate solution that had 1.5 times the ion concentrations of human body fluid, but did not contain magnesium ion at 36.5°C. Deposition times were 90 min. We used the average current density of 0.01 A/cm² and ON time equal to OFF time of 15 s. In the electrodeposition, hydrogen was incorporated into the surface of the Ti substrates to form titanium hydride (TiH₂) on the substrate surfaces. After the electrodeposition, all specimens were heated at 600°C for 60 min. The adhesion between apatite and substrates were greatly improved by the heat treatment for the substrates etched in 50 and 75% H₂SO₄. It is considered that in these specimens the anchoring effect due to the microstructural roughness formed by etching was enhanced by the shrinking of HA crystals during the heat treatment.

View full abstract

Apatite-polymer hybrids are expected as novel bone substitutes exhibiting bone-bonding ability, i.e. bioactivity, and mechanical performances analogous to those of natural bone. To fabricate such hybrids, biomimetic process has been paid much attention where bone-like apatite is deposited on organic polymers that have specific functional groups in simulated body fluid (SBF) or more concentrated solutions. Previous studies showed that carboxyl groups (-COOH) have a catalytic effect for heterogeneous apatite nucleation in SBF. In this study, we chose pectin as an organic polymer. Pectin is a natural polysaccharide containing carboxyl groups. Hydrogels were prepared from various pectins including pectic acid, apple-derived pectin and citrus-derived pectin by treatment with CaCl₂ solution. Ability of apatite formation in SBF and mechanical properties of the gels were examined. The apatite-forming ability increased in the order (pectic acid)<(apple-derived pectin)<(citrus-derived pectin). It was suggested that the apatite-forming ability of the pectin gels is governed by not only the amount of carboxyl groups but also changes in Ca²⁺ concentration and pH in surrounding solutions. Young's modulus of the pectin gels was similar to natural bone, although tensile strength is a little lower.

View full abstract

Hydroxyapatite (HAp) is a type of calcium phosphate widely applied in the biomedical field. HAp is a main inorganic component of hard tissues of vertebrates and is a bioactive ceramic which shows a high biological affinity. The crystal of HAp exhibits an anisotropic nature depending on its crystal planes which is stemmed from its anisotropic crystal structure belonging to the hexagonal system. For instance, anions and acidic proteins are mainly adsorbed onto the a-plane of HAp crystals while cations and basic proteins are adsorbed onto the c-plane. Anisotropic nature like so can be utilized by controlling the alignment of crystals consisting the material. Alignment control of HAp crystals in a particular direction is an effective way to improve the properties like absorbability, bioactivity and biological affinity on the surface of biomedical materials. On the other hand, the recent development of superconducting technology has enabled us to control the crystal alignment of not only magnetic substances but also nonmagnetic substances with magnetic anisotropy like HAp by imposing a high magnetic field. In this study, we formed crystallographically aligned HAp bulks by using a high magnetic field and evaluated the degree of the crystal alignment. In addition, we evaluated the biological affinity on the surface of the samples.

View full abstract

Addition of tricalcium silicate (Ca₃SiO₅; alite) to apatite cement (AC) may be effective to increase the osteoconductivity of AC. However, only limited studies have been made so far for the effect of alite addition on the basic setting properties of α-tricalcium phosphate [α-Ca₃(PO₄)₂; α-TCP] based cement. In the present study, effects of added alite on the basic properties of α-TCP based AC was studied. α-TCP powder containing 0.0, 2.5, 5.0, 10.0, and 20.0 mass% alite were mixed with 0.25 mol/L sodium dihydrogen phosphate solution (NaH₂PO₄) and the obtained cement pastes were stored in 100% relative humidity at 37°C. Initial setting time was delayed with increase in alite content. The 2.5-5.0 mass% of alite added cements were completely transformed into apatite within 24 h and the final mechanical strength of the set cement increased reaching approximately 15 MPa in terms of diametral tensile strength when compared with alite-free cement which showed approximately 9 MPa. However, 10.0-20.0 mass% of alite addition suppressed the apatite formation and decreased the mechanical strength of the set cement. We concluded therefore, that addition of appropriate amount of alite to α-TCP is desirable with respect to the setting properties of AC.

View full abstract

Silicon-substituted hydroxyapatite (Si-HAP) foam may be an ideal bone substitute since Si-HAP has stimulating effect for bone formation and the foam morphology provides interconnected macro porous structure which is ideal for bone formation. However, lower temperature was reported to be required for the fabrication of pure Si-HAP whereas higher temperature was required for the fabrication of HAP foam. In the present investigation, three calcium silicate compounds (CaSiO₃, wollastonite; Ca₂SiO₄, belite; Ca₃SiO₅, alite) were evaluated for their feasibility as a silicon source for the fabrication of Si-HAP foam. Sintering temperature at 1300°C resulted in a very weak HAP foam, whereas sintering at 1400°C resulted in HAP foam with improved compressive strength up to approximately 9 kPa. XRD analysis showed the appearance of a secondary phase, α-tricalcium phosphate, when wollastonite was used as the silicon source. In contrast, pure Si-HAP phase was obtained when belite or alite was used as the silicon source. The porosities of the Si-HAP foams were approximately 95% regardless of composition of the foam. We therefore concluded that Si-HAP foam with fully interconnecting pores could be fabricated when belite or alite was used as the silicon source. Further evaluation is expected based on this initial finding.

View full abstract

Aiming at creating an apical barrier material that promotes recovery of defects in the root canal, a composite of apatite and collagen was developed. To achieve this, reconstitution and cross-link of atelocollagen, and calcification of reconstituted collagen fibers, were conducted under controlled stirring at 37°C. Deposits were identified as CO₃-containing apatite and its crystallinity was comparable to that of bone apatite. After 20 hours of calcification, the composite contained apatite of about 60 wt%. The composite and saline mixture had a pH of about 9. The mixture was easily set into a narrow space, such as the root canal, and was liquid permeable after being set into a root canal. The biological property of the composite was examined in vivo using the molar teeth of dogs. After 8 weeks, a thin layer of new bone-like tissue was formed along the inner wall of root canal. Without the composite paste, such a new bone-like tissue was not observed. Thus, the apatite/collagen composite showed potential as an apical barrier material with osteoconductivity.

View full abstract

Tricalcium phosphate (TCP) is used as biodegradable bone substitutes. When TCP is implanted in a bony defect, it is gradually decomposed in living body, and finally substituted by living bone tissue. Solubility of α-phase of TCP (α-TCP) is higher than that of β-phase (β-TCP), and hence the degradation of α-TCP is faster than that of β-TCP. Recently, we fabricated α-TCP porous ceramic with continuous pores in the range of 10-50 μm as highly bioabsorbable bone fillers. The rate of bioabsorption was controlled by combination of β-TCP with α-TCP. Although the TCP ceramic is suggested to form hydroxyapatite in a simulated body fluid (SBF), the ability of the apatite formation is affected not only by the phase contents, but also by the porosity of the ceramics. In this study, we fundamentally investigated behavior of the hydroxyapatite formation on α-TCP ceramics with different surface and biphasic TCP ceramic in SBF proposed by Kokubo et al. Hydroxyapatite formation was observed on the surface of the biphasic TCP consisting of α-TCP and β-TCP, after soaking in SBF. The surface of the polished α-TCP ceramic showed the hydroxyapatite formation, but the surface of the as-sintered α-TCP ceramic did not. The polished surface of the α-TCP ceramic acted as a significant parameter on the hydroxyapatite formation in body environment. Thus, the polishing of the surface allows the osteoconductivity due to the potential of the hydroxyapatite formation on their surfaces in body environment.

View full abstract

The crystallographic orientation relationship between hydroxyapatite (HAp) nanocrystals and poly (acrylic acid) (PAA) graftpolymer-modified poly (ethylene terephthalate) (PET) substrate was studied using transmission electron microscopy (TEM). We observed the microstructure of fabricated rod-like HAp nanocrystals and the interface of HAp/PET composite where, the HAp nanocrystals are bonded onto PAA graftpolymer-modified PET substrate. The selected-area electron diffraction (SAED) pattern of interface of the HAp/PET composite indicated that some low index planes in HAp prism plane tended to be contact plane with the PET substrate surface. In particular, the {1120} plane was distinctly found as the contact plane with PET substrate. In this material, it has been reported that the carboxyl groups of PAA graft-polymer are ionically-bonded with Ca ions on surface of the HAp nanocrystal. It was suggested that the periodic ionic arrangements of the {1120} plane play an important role on the bonding between the HAp nanocrystals and the carboxyl groups of graft-polymer on the PET substrate.

View full abstract

Injectable Calcium Phosphate Cements (CPC) are the emerging class of bone substitute materials as they can be moulded and shaped to fill intricate bone cavities and narrow dental sites. Various amounts of hydroxyapatite (HA) were mixed with tri-calcium phosphate (TCP) using sodium hydrogen phosphate as the liquid medium. The formulations have a setting time of 15-30 min. These cements with setting time around 20 min, which is also clinically preferred, were found to have better wash out resistance. The X-ray diffraction method (XRD) and Fourier transform infrared spectroscopy (FT-IR) analysis confirmed HA as the setting phase. Gelatin has been incorporated to the selected formulations to induce porosity in the above selected cements. Scanning electron microscopy (SEM) reveals a macroporous structure as also confirmed by BET measurements. Injectability of the cement is being evaluated using chitosan.

View full abstract

Mn-doped β-tricalcium phosphate (β-TCP) is synthesized by the solid-state reaction method. The local environment of doped Mn ions in β-TCP is investigated by the near-edge X-ray absorption fine structure (NEXAFS) measurements. The first principles calculations are also carried out to obtain the theoretical NEXAFS spectra within the density functional theory (DFT). Observed NEXAFS spectra from the Mn ions in β-TCP are quantitatively well reproduced by the present theoretical calculations, which show Mn ions are substituted for Ca²⁺ site in β-TCP.

View full abstract

Tubular agglomerates of calcium carbonate crystals (the CC-tubes) were formed from 1 M calcium chloride and 1 M sodium carbonate, and the formation mechanism was investigated. A cylindrical jacketed glass vessel was used as a crystallizer. The newly designed crystallizer was composed of two compartments that were divided by a cation-exchange membrane. The crystallizer was vertically placed and the two solutions were separately placed in each compartment. The CC-tubes were formed in vertical against the surface of the cation-exchange membrane in the upper sodium carbonate solution side. The growth of the CC-tubes was observed through a plane window of the top of the crystallizer by a digital microscope in order to study the growth mechanism of the tubes. In the early stage of crystallization, small cubic crystals appeared on the membrane. Although most parts of the membrane surface were covered with crystals, some small spots on the membrane surface were not covered with crystals. The CC-tubes grew from the uncovered parts. We concluded that the uncovered spots are important for the generation of the CC-tubes. A possible mechanism of the growth of the CC-tubes was proposed.

View full abstract

Apatite forming and hydroxyapatite ceramics bonding ability of titanium (Ti)-based bulk metallic glasses (Ti₄₀Zr₁₀Cu₃₆Pd₁₄ and (Ti_0.40Zr_0.10Cu_0.36Pd_0.14)₉₉Ca₁: BMGs) were investigated as a new type of biomaterials. Powder mixture of CaHPO₄•2H₂O and Ca(OH)₂ and the BMGs disks were treated with autoclave for hydrothermal hot-pressing (HHP) simultaneously (150°C, 40 MPa, 2hours). Direct bonding hydroxyapatite ceramics and both type of BMGs could not be achieved. And then, the BMGs disks with the HHP treatment were soaked in simulated body fluid for 7-10 days. It was observed that apatite are deposited and covered on the surface of the BMGs with the HHP treatment. It was firstly demonstrated that surfaces of Ti based bulk metallic glasses can be made bioactive and that HHP techniques were useful methods in purpose of making Ti-based bulk metallic glass surface bioactive.

View full abstract

Delafossite-type oxide AgYbO₂ (3R-polytype) was synthesized by a cation-exchange reaction of NaYbO₂ and AgNO₃ in a KNO₃ flux. An almost single phase was obtained at 190°C for 192 h. The structure of AgYbO₂ was refined by Rietveld analysis, giving a trigonal unit cell (R3m, a=337.17 pm, c=1821.4 pm) with a reasonably small S value of 1.48.

View full abstract

Precursors for silicon carbide nano particles were prepared from carbon black and polymethylsilsesquioxane (PMSQ). Ceramization process of PMSQ was characterized as preliminary information. The ²⁹Si NMR study indicated the existence of SiC₃O (or SiC₄) environment even at 1073 K. The chemical composition of pyrolyzed PMSQ was SiO_1.5C_0.68. Carbon black (CB) was dispersed in a PMSQ benzene solution and the mixture was freeze-dried to obtain precursor powders. The powders were hot pressed at 573 K for making contacts between CB and PMSQ. The cured precursor sheets were crushed and heat-treated at 1838 K in an inert atmosphere to synthesize SiC particles with a carbothermal reduction process. The conversion process of the CB-PMSQ hybrids to SiC was monitored by thermogravimetric analysis. The influence of the size and content of carbon blacks on conversion rates and the resulting SiC particle morphology was investigated.

View full abstract

It had been well known that the fracture of SiC manufactured by conventional reaction sintering method was caused by one of the pores in that. However, according to the recent studies, pore free SiC so called APF-SiC was developed by improvement of reaction sintering method. As the result, the strength and the damage tolerance ability rise and then the cause of fracture of APF-SiC changed from pores to something else. Therefore we have investigated fracture surface of APF-SiC by using FE-SEM and EDS in order to demonstrate the cause of fracture. As the result, we found the inclusion that consisted of allotropes of Carbon covered with very thin SiO₂ and SiN layer. And the size of the inclusion is ten times larger than that of SiC grain. Considering from present results, the inclusion is the one of the cause of fracture of APF-SiC.

View full abstract

The sintering behavior and the mechanical and oxidation properties of Sialon were investigated by varying the composition, amount, and cationic radii of sintering additives composed of AlN-Er₂O₃-M₂O₃ (M=Y or Sc). The optimum additive composition for the pressureless sintering of Sialon was determined to be (0.6 AlN:0.4 [0.3 Er₂O₃:0.7 M₂O₃]) and the optimum content was 10-15 mass%. The maximum relative densities of Sialon using AlN-Er₂O₃-Y₂O₃ and AlN-Er₂O₃-Sc₂O₃ additives (termed SAEY and SAES) were 94.4 and 97.9% at 0.1 MPa N₂, respectively. The pressureless sintered SAES sample showed fairly high strength (506 MPa) using the optimized additive composition. In both systems, the oxidation resistance was improved by decreasing the total amount of sintering additives.

View full abstract

Porous alumina with glassy boundary phase consisting of with silica and calcia components was fabricated by unidirectional solidification under pressurized hydrogen atmosphere using alumina feed rod with silica and calcia additives. The pores were elongated along the solidification direction. The glassy boundary phase was directly introduced in the solidified sample during the solidification. The porosity and pores size decrease with increasing total pressure. When a high purity alumina feed rod was used for the solidification, no glassy boundary phase was formed on the grain boundary and the grain boundary cracks in the porous alumina were observed. For comparison, non-porous alumina samples were fabricated by unidirectional solidification in Ar atmosphere using alumina feed rods with and without the additives. The former sample with the additives possesses a boundary phase, while the grain boundary cracks were formed in latter sample. The compressive strengths of non-porous solidified alumina samples with and without boundary glassy phase were 1679 and 267 MPa, respectively; that with boundary phase slightly increased by a heat treatment at 1600°C. The compressive strength of porous alumina with 25.9% porosity was 512 MPa which is larger than that of non-porous alumina without glassy boundary phase. The compressive strength of unidirectionally solidified alumina samples were improved by formation of glassy boundary phase at their grain boundary.

View full abstract

Nano-sized lanthanum manganites (LaMnO₃) were prepared by spray pyrolysis process from the spray solution with citric acid as organic additive. The LaMnO₃ precursor powders obtained from the spray solution with citric acid had thin wall and hollow structures. The thickness of the wall of the precursor powders was below 50 nm. The post-treated LaMnO₃ powders had slightly aggregated morphology of the primary powders with nanometer size. The post-treated LaMnO₃ turned to nano-sized powders after simple milling by hand using agate mortar. The mean sizes of the LaMnO₃ powders obtained from the spray solutions with concentrations of citric acid as 0.4 and 0.8 M at a post-treatment temperature of 800°C were 80 and 200 nm, respectively. The mean size of the LaMnO₃ powders changed from several tens nanometer to submicron size according to the post-treatment temperatures. The mean crystallite sizes of the LaMnO₃ powders obtained from the spray solution with citric acid at post-treatment temperatures between 700 and 1000°C changed from 26 to 36 nm.

View full abstract

The manufacturing of ceramic tiles is a very complex process, where a wide range of variables has an important influence in the final product. With regard to external appearance, the most of the production defects take place in the decoration station. Nevertheless, these defects are usually detected before baking, when the product is already finished, causing an important loss of effectives. Under this perspective, a mechanism able to detect the printing defects in the green parts would achieve 2 goals: on one hand, the reduction of the nonquality costs since green parts can be more easily recycled; and on the other hand, it would point out the real root cause of the failure by indicating, for instance, which ink is causing the problem. Color Prediction Models (CPM) are mathematical approaches which relate the microscopic distribution of the printed dots of a halftone image with the resulting macroscopic color. Its usage is extended in the field of the Graphic Arts, especially for calibration and fine image reproduction. However, they are barely known in the ceramic tile industry, a sector that keeps many similarities with the Graphic Arts one in terms of decorating. In this paper, we analyzed the prediction quality of 4 successful CPM (Murray-Davies, Yule-Nielsen, Neugebauer and Neugebauer Modified Yule-Nielsen) on 1 and 2 inks halftones printed on ceramic substrates, setting a comparison between them by means of linear and non-linear optimization techniques. Moreover, we proposed a value for the enigmatic “n” parameter on ceramic surfaces, which is said to model the optical dot gain phenomenon.

View full abstract

TiO₂ water/ethanol sol capable of interparticle connection was prepared through a sol-gel process and used to the fabrication of organic binder-free TiO₂ paste for photo-electrode layer formation of all plastic dye-sensitized solar cells. The average particle size in TiO₂ water/ethanol sol was in the range of 27 nm-80 nm and the crystal phase confirmed by XRD was anatase, brookite and rutile. The viscosity of the binder sol showed the strong dependence on the water/alcohol ratio in solution. The organic binder-free TiO₂ paste including P-25 powder as the main photoelectrode was prepared by using the TiO₂ water/ethanol sol as an inorganic binder and coated on an ITO-PEN (ITO coated on Polyethylene Naphthalate) conductive electrode by a squeeze method. And the processing parameters of TiO₂ paste fabrication on the energy conversion efficiency, η, were investigated. The maximum energy conversion efficiency of an assembled plastic dye-sensitized solar cell in this work was found to be 2.58%.

View full abstract

A commercially available soft lead titanate zirconate (PZT) wafer that is poled in thickness direction is subjected to various magnitudes of constant longitudinal tensile stress. The evolutions of electric displacement in thickness direction and longitudinal strain over time are measured. The measured total responses are divided into linear responses, immediate switching-induced responses, and creep responses. It is found that immediate switching-induced responses can be described by stress power functions and creep responses by stress and time power laws, within the current range of tensile stress.

View full abstract

Wood from balsa and Japanese cypress was transformed into carbonaceous preforms by pyrolysis and subsequently converted into cellular SiC ceramics by heating with Na and Si at 973 K for 86.4 ks. X-ray diffraction showed the structure of the formed SiC to be cubic β-type. Cellular structures similar to those of the preforms were observed for the resulting porous SiC ceramics by scanning electron microscopy.

View full abstract

On page 854, the line 16th line contains an error. “2.6μm and 6.5μm” should be changed to “0.26μm and 0.65μm.”
The authors apologize for any inconvenience caused. Wrong:2.6μm and 6.5μm
Right:0.26μm and 0.65μm

View full abstract