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Dental implant materials must exhibit excellent mechanical and biochemical properties, such as high strength, corrosion resistance, nontoxicity, biocompatibility, and phase stability. Zirconia implants manufactured by CAD/CAM machining and the sintering process have low bone-bonding ability owing to bioinertness and low surface roughness, resulting in prolonged implantation period or implant debinding. In this study, bioactive wollastonite was coated on bioinert zirconia substrates by room temperature spray processing, and the microstructural and characteristics of the coated layers were investigated. Wollastonite powder for the coatings was prepared through calcination and pulverization processes. Homogeneous wollastonite coatings on dense zirconia substrates were obtained via the aforementioned room temperature spray processing. Notably, the phase composition and microstructural characteristics of wollastonite-coating layers were dependent on the number of coating cycles. The wollastonite-coating layers showed a uniform thickness and tough surface microstructure, depending on the number of deposition cycles and coating thickness. In vitro tests of the coated specimens in an SBF solution at pH 7.4 for 14 days revealed that the biological activity of the zirconia substrate changed depending on the thickness and surface morphology of the coatings. As a result, the wollastonite coating surfaces exhibit superior bioactivity compared with that of the original zirconia substrate. This is owing to the bioactive wollastonite phase and high surface roughness of the coated layer.

Bacterial biofilms formed through secretion of extracellular polymeric substances (EPS) have been implicated in many serious infections and can increase antibiotic resistance by a factor of more than 1000. Here, we examined the abilities of the antimicrobial peptide HPA3NT3-A2 to inhibit and reduce biofilm formation, eliminate EPS, and suppress inflammation in mice infected with clinical isolates of drug-resistant Pseudomonas aeruginosastrains. HPA3NT3-A2 was developed from a desirable analogue peptide, HPA3NT3, derived from residues 2–20 of the Helicobacter pyloriribosomal protein L1. HPA3NT3-A2 showed stronger activity against planktonic cells (MIC: 8 μM) compared to ciprofloxacin or tobramycin (>512 μM), and a favorable minimum biofilm inhibition and elimination concentration. This peptide also neutralized LPS; decreased levels of EPS; inhibited the production of pro-inflammatory cytokines in the lung, kidney, and spleen; decreased white blood cell counts; and increased survival among infected mice.

Although engineered cardiac tissues (ECTs) derived from induced pluripotent stem cells (iPSCs) are promising for myocardial regenerative therapy, the appropriate ratio of cardiomyocytes to non-cardiomyocytes is not fully understood. Here, we determined whether ECT-cell content is a key determinant of its structure/function, thereby affecting ECT therapeutic potential for advanced heart failure. Scaffold-free ECTs containing different ratios (25%, 50%, 70%, or 90%) of iPSC-derived cardiomyocytes were generated by magnetic-activated cell sorting by using cardiac-specific markers. Notably, ECTs showed synchronized spontaneous beating when cardiomyocytes constituted ≥50% of total cells, with the electrical-conduction velocity increasing depending on cardiomyocyte ratio; however, ECTs containing 90% cardiomyocytes failed to form stable structures. ECTs containing 25% or 50% cardiomyocytes predominantly expressed collagen and fibronectin, whereas ECTs containing 70% cardiomyocytes predominantly expressed laminin and exhibited the highest contractile/relaxation properties. Furthermore, transplantation of ECTs containing 50% or 70% cardiomyocytes into a rat chronic myocardial infarction model led to a more profound functional recovery as compared with controls. Notably, transplanted ECTs showed electrical synchronization with the native heart under Langendorff perfusion. Collectively, these results indicate that the quantity of non-cardiomyocytes is critical in generating functional iPSC-derived ECTs as grafts for cardiac-regeneration therapy, with ECTs containing 50–70% cardiomyocytes exhibiting stable structures and increased cardiotherapeutic potential.

ABSTRACTCA-MA is a hybrid antimicrobial peptide (AMP) derived from two naturally occurring AMPs, cecropin A and magainin 2. CA-MA shows strong antimicrobial activity against Gram-negative and Gram-positive bacteria but also exhibits cytotoxicity toward mammalian cells. Our objective was to identify CA-MA analogues with reduced cytotoxicity by systematic replacement of amino acids with positively charged R groups (His and Lys), aliphatic R groups (Leu), or polar R groups (Glu). Among the CA-MA analogues studied (CMA1 to -6), CMA3 showed the strongest antimicrobial activity, including against drug-resistant Escherichia coliand Pseudomonas aeruginosastrains isolated from hospital patients. CMA3 appeared to act by inducing pore formation (toroidal model) in the bacterial membrane. In cytotoxicity assays, CMA3 showed little cytotoxicity toward human red blood cells (hRBCs) or HaCaT cells. Additionally, no fluorescence was released from small or giant unilamellar vesicles exposed to 60 μM CMA3 for 80 s, whereas fluorescence was released within 35 s upon exposure to CA-MA. CMA3 also exerted strong lipopolysaccharide (LPS)-neutralizing activity in RAW 264.7 cells, and BALB/c mice exposed to LPS after infection by Escherichia colishowed improved survival after administration of one 0.5-mg/kg of body weight or 1-mg/kg dose of CMA3. Finally, in a mouse model of septic shock, CMA3 reduced the levels of proinflammatory factors, including both nitric oxide and white blood cells, and correspondingly reduced lung tissue damage. This study suggests that CMA3 is an antimicrobial/antiendotoxin peptide that could serve as the basis for the development of anti-inflammatory and/or antimicrobial agents with low cytotoxicity.

In this study, we investigated the crack nucleation and growth and propagation on the surface of Y-TZP during isothermal phase transformation by low temperature ageing. Crack initiation and growth on the surface of Y-TZP specimen was dependent on the sintered microstructure, i.e, sintered density, grain size, pore structure, residual stress etc.. In the case of Y-TZP with 2mol % yttria content, phase transformation of tetragonal to monoclinic began on the surface and induced a crack nucleation of specimen at the initial stage of low temperature ageing. Most of cracks in 2Y-TZP by low temperature ageing were firstly formed on the surface of specimens (free surface, weak bonding grains, etc.) where the change of strain free energy for a tetragonal to monoclinic transformation was small, and surface cracks grew into the bulk interior through the grain boundaries.

Refractory castables containing calcium aluminate cement (CAC) are widely used in a range of furnace lining applications in the iron and steel, cement, glass, ceramic, and petrochemical industries. However, magnesia-phosphate cement (MPC) based material could be a new types of cement material, with many advantages such as rapid hydration, high early strength and circumstance suitability, which has very important value and wide application. In this study, MPC was used at Chromia/Alumina castable as binder addition instead of conventional calcium aluminate cement. Meanwhile, it also explains the relationship between the micro-mechanism and performance by micro methods such as SEM. The results shows that MPC based castables have good corrosion resistance, interface adhesiveness and abrasion resistance.

The response of human bone marrow cell to bone ash derived hydroxyapatite (HA) and tuna bone derived HA powders was compared. HA ceramics were prepared from the commercial bone ash and waste of tuna bone. HA powders were prepared by soaking the bone ash and tuna bone in 0.1M of NaOH solution at 80℃ for 4h. Both powders were calcined at 800℃ for 1h to completely remove organic, and were attritor-milled for 24 h. The bone ash derived HA (AHA) and tuna bone derived HA (THA) ceramics were prepared by cold isostatically pressed and sintered 1200℃ with a dwell time of 1h. A human bone cell line MG-63 cells were used to test biocompatibility of AHA and THA ceramics. Cell suspensions in DMEM containing 10% FBS and 1% penicillin-streptomycin were seeded onto 24-well plate containing THA and AHA ceramics. Cell proliferation was evaluated by MTS assay and cell morphology was observed by SEM

Biphasic calcium phosphate bioceramics were fabricated from the recycling of bone ash which is mostly used as raw materials of bone china. Precursor calcium phosphate powders were prepared by soaking the commercial bone ash in 0.1 M of NaOH solution at 80˚C for 4 h. Calcium phosphate powders was obtained by calcination at 800˚C for 1 h to completely remove residual organics. Biphasic calcium phosphate bioceramics which is composed of hydroxyapatite and tricalcium phosphate was fabricated by the sintering of pressed compacts at 1200˚C for 1 h under moisture protection. The bone ash derived-biphasic calcium phosphate ceramics consists of mostly HA and small amounts of α-tricalcium phosphate, magnesium oxide and calcium oxide. After polishing the HA ceramics, they were immersed in buffered water at 37˚C for 3 and 7 days. The bone ash derived- biphasic calcium phosphate ceramics show high biostability in liquid environment with immersion time compared with commercial calcium phosphate ceramics.

This work describes dissolution and related mechanical weakening of phase-pure and dense hydroxyapatite (HA) in distilled water of pH 7.4. Phase-pure HA powder has been synthesized by a wet precipitation method. After uniaxial and cold isostatic pressing, and sintering at 1200℃, dense HA with 98% above of the theoretical density has been obtained. The results show that HA powder has stoichiometric composition with a Ca/P ratio 1.67 ± 0.02. Even after extended exposure for 10 h, no second phases, such as tricalcium phosphate (TCP) and calcium oxide can be observed. Although the HA is supposed to be stable in liquid environment, surface dissolution appears specifically at material’s grain boundaries after immersion for 7 days. Following further immersion to 14 days, grain boundary dissolution progresses interior to the bulk following these paths. This dissolving behavior generates HA particles, disintegrates dense microstructure and at least forms micron-scale cavity. Mechanical property of the HA has been also affected. Fracture toughness (KIc) of the HA sintered body is approximately 1.0 MPa•m1/2. It drastically decreases to almost half of the initial value due to the severe surface dissolution

Hydroxyapatite (HA) ceramics were prepared from the bone ash which is mostly used as animal feeds or raw materials. Dissolving behaviors of the HA in buffered water were investigated and compared with commercial HA for further use as biomaterials. HA ceramics were prepared by soaking the bone ash in 0.1 M of NaOH solution at 80˚C for 4 h. The ash was calcined at 800˚C for 1 h to completely remove organics, and then sintered at 1200˚C for 1 h under moisture protection. The bone ash derived-HA consists of mostly HA and small amounts of α-tricalcium phosphate, calcium oxide phosphate, magnesium oxide and calcium oxide. After polishing the HA ceramics, they were immersed in buffered water at 37˚C for 3 and 7 days. We previously found that grain boundaries of synthetic HA were intensively dissolved in buffered water. On the other hand, the bone ash derived-HA shows high stability in liquid environment with immersion time compared with commercial HA.

Mechanical degradation of hydroxyapatite ceramics due to the slow crack growth was observed in water. Microstructural crack on the surface of hydroxyapatite initiated by grain boundary dissolution in liquid environment resulting in particle loosening and microstructural-level degradation, followed by a drastic decrease of mechanical properties. In this study, slow crack growth by the dissolution behavior of hydroxyapatite ceramics was investigated based on microstructural observation by field emission microscopy. The crack growth and morphological change of hydroxyapatite surface, especially at the initial stage of dissolution and related surface roughness were observed with immersion time. The surface dissolution occurred from the initial stage of immersion showing increase in surface roughness. Following certain period of immersion time, the surface dissolution initiated at grain boundaries and generated many separated grains.

Increasing resistance of pathogenic bacteria to antibiotics is a serious problem in health care system and has intensified the search for potent novel drugs. Cationic antibacterial peptides are the most abundant antibiotics in nature and have been frequently proposed as new anti-infective agents. In this study, a set of diastereomeric peptides is researched about their antibiotic activity against multiple drug resistant clinical isolates and their modes of action against gram-positive cocci. MIC was suggested by the NCCLS against ten clinically isolated antibiotic-resistant strains. Mode of action studies included killing kinetics and a series of experiments designed to characterize the impact of the diastereomeric peptides on bacterial membranes. The tested diastereomers displayed high antimicrobial and broad spectrum activity with D-P5-18mer. The antimicrobial activity of diastereomeric-P5-18mer was two times stronger against gram-negative bacteria than either CA-MA-20mer or P5-18mer. When tested against ten clinically isolated antibiotic-resistant strains in the presence of 0, 150, or 300 mM NaCl, diastereomeric-P5-18mer retained strong activity against all bacteria, yet showed little or no cytotoxicity against the HaCaT human keratinocyte cell line. Finally, D-P5-18mer showed resistance against trypsin digestion unlike other analogues. © 2010 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 96: 130–136, 2011.

Dissolving behavior of hydroxyapatite ceramics prepared from bovine teeth (BTHA) was investigated. The bovine teeth were soaked in 0.1 M of NaOH at 80˚C for 1 h. After soaking, the teeth were calcined at 800˚C for 1 h, and then they were attritor-milled for 24 h. BTHA powder consisted of mainly HA and small amount of MgO. The powders obtained were cold isostatically pressed and sintered at 1200˚C with a dwell time of 1 h. Sintered density of BTHA was about 70%. After polishing the surface of sintered specimen, BTHA was immersed in buffered water at 37˚C for 3 and 7 days. After immersion period, there is no evidence of dissolution for BTHA at the end of the immersion time. In addition, there is no change of peak intensity in XRD after immersion time. It was found that hydroxyapatite from bovine teeth was more stable than commercial HA in liquid environment.

Hydroxyapatite (HA) ceramics derived from tuna bone (THA) was prepared and their mechanical property was investigated with immersion in buffered water. Tuna bones were soaked in 0.1 M of NaOH solution at 80˚C for 1 h. After soaking, the bones were calcined at 800˚C for 1 h to completely remove organic, and then attritor-milled for 24 h. The powders obtained were cold isostatically pressed and sintered at 1300˚C with a dwell time of 1 h. Sintered densities of the THA was about 93%. After polishing, the THA were immersed in buffered water at 37 ˚C for 3 and 7 days. The THA ceramics consisted of HA and small amount of magnesium oxide. Immersion test revealed that there was no clear evidence of dissolution for the THA which sintered at high temperatures. Vickers hardness test showed that the hardness value of THA ceramics was not changed with immersion time indicating that dense hydroxyapatite from tuna bone was stable in liquid environment.

The inorganic binders, fly ash and meta kaolin were used to prepare geopolymer. Water glass was added to the recycled inorganic binders to improve compressive strength of geopolymers. The ratio of the solid materials (inorganic binder and alkali activators) and liquid materials (distilled water, water glass) for the polymerization was optimized as 3:1. Compressive strength of the geopolymers increased because water glass improved the extent of polymerization of the inorganic binder and resulted in dense microstructure. It was found that geopolymers using fly ash showed the higher value of compressive strength, compared with meta kaolin- based geopolymers.

Geopolymers were prepared by using the dried fly ash from industrial by-product, NaOH as alkaline activator and Na2SiO3 as liquid glass. Calcium carbonate from a clam shell was added to provide attachment and growth of environmental organisms on the geopolymers. We investigated the effects of a shell powder contents on the microstructure and bonding properties of the geopolymers to normal cement. The major chemical compositions of fly ash were Si and Al at the ratio of 2 to 1 in wt%. The shell powder with layer sheet consisted of aragonite phase. As increasing the amount of the shell powder, fly ash was not polymerized and remained spherical. The bonding between geopolymers and normal cement was obtained when 0-15 wt% of the shell powder was added. On the other hand, bonding was not achieved with higher shell contents of 20-25 wt%.

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A small amount of misch metal was added to CuZnAl alloy in order to study the effect of grain refinement and mechanical properties, phase transformation behavior and stabilization of martensite. It was found that the addition of misch metal was very effective for reducing the grain size. The coarse grains over 1000 μm have been refined to the size of 30 μm by the addition of 0.43wt% misch metal. The grain size of thermo-mechanically treated alloys was barely affected by cold working. The fracture strength and ductility have been significantly increased with the increase of misch metal content when tensile test is carried out below Mf temperature. Also, the fracture strength has been more increased in the case of post-quench ageing treatment than the direct quench ageing treatment. The fracture mode has been changed from transgranular brittle fracture to ductile fracture with void formation and coalescence by the addition of misch metal.

Titanium-based nitride coatings on cutting tools, press molds and dies can prolong their life cycle because of superior corrosion and oxidation resistance of coatings. In this study, TiAlN/ZrN and TiCrN/ZrN multilayer coatings were prepared by R.F magnetron sputtering, and microstructural evolution and corrosion resistance of the coatings were investigated during heat treatment. The TiAlN/ZrN and TiCrN/ZrN multilayer coatings were degraded by heating up to 600 oC with formation of oxides particles on the surface. During the heat treatment, the TiCrN/ZrN and TiAlN/ZrN multilayer coatings showed the lowest corrosion current density and the highest polarization resistance at temperature range of 400 oC and 500 oC. Consequently, the TiAlN/ZrN and TiCrN/ZrN multilayer coatings showed good corrosion resistance at temperature range of 400°C and 500°C during heating.

Dissolution of calcium phosphate powders with different compositions in simulated body fluid was investigated. Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and by controlling pH of the solution. Biphasic calcium phosphate (BCP) powders were prepared by mixing the HA and β-TCP powders with ratio of 80:20 and 60:40 in weight % in a planetary mill for 4 h. For dissolution test, 0.5g of each β-TCP, HA and BCP powders were immersed in 50 ml of SBF at 37°C for 3-28 days. HA powders with stoichiometric composition showed no significant morphological change regardless of the immersion time. β-TCP powders were not dissolved in SBF in spite of its high solubility. The surface of BCP powders became rough due to dissolution with increasing immersion time. This surface dissolution gradually extended into the core region of the particles resulting in disintegration of the dense particle into fine crystallites. It may be caused that the milling process during preparation of BCP powders may induce stress concentration or formation of dislocation on the surface of particles.

Hydroxyapatite derived from human teeth was sintered at 1200°C for 2 h. Dissolving behavior of the biologically derived HA (BHA) in distilled water was investigated and compared with an artificial hydroxyapatite (HA) made of synthetic HA powder. All disks were immersed in 40 ml of pH 7.4 distilled water (buffered using 0.05 M Tris.) for 7 and 14 days at 37°C. All detectable peaks in the HA are identical only to HA lattice planes, whereas BHA consisted of a mixture of HA and β-tricalcium phosphate (TCP). In the case of the HA specimen, the surface dissolution was initiated at grain boundaries followed by generated many separated grains and large defect like cavities. On the other hand, biologically derived HA showed that definite grains considered as β-TCP was predominantly dissolved and the grains were separated from the matrix leaving pores. In the mean time, the rest region, mainly consisting of HA, did not show any evidence of dissolution. It seems that BHA is more stable than the artificial HA in liquid environment.

Calcium phosphate ceramics (CPC) have been attractively used in different areas of biomedical applications, such as substances of artificial hard tissue replacement implants, drug delivery system due to their biocompatibility and bioactivity. In this work, three calcium phosphate powders between Ca/P molar ratio 1.50-1.67 were synthesized by aqueous precipitation method, using the mixture of Ca(NO3)2·4H2O and H3PO4 solutions to ammonia solution. During the precipitation reaction, Ca/P molar ratio was adjusted by controlling pH of the solution between 8.0 and 10.5 by the addition of ammonium hydroxide solution. All powders were treated at 800 oC for 2 hrs. The calcined powders were immersed in pH 7.4 distilled water at 37°C for 3 and 7 days. Decomposition and related dissolution with the various Ca/P ratios were investigated by XRD, FTIR, and TEM observation.

Particle separations occurred frequently in sintered hydroxyapatite when immersed in distilled water or simulated body fluid. This dissolution initiated at grain boundary creating nano-size defects such as small pores and grew up to micro scale by increasing immersion time. The dissolution, probably due to the appearance of secondary phases in grain boundary, resulted in grain separation at the surfaces and finally in degradation and fracture. And the dissolution concentrated on those grains adjacent to pores rather than those in the dense region. Hydroxyapatite ceramics incorporated with calcium silicate glass were prepared by slip casting to enhance the sinterability as well as to reduce dissolution. Glass phase was incorporated into hydroxyapatite to act as sintering aids followed by crystallization in order to improve the mechanical properties without reducing biocompatibility. From dissolution test, significant damage was reduced even more than 7 days and the dissolution pattern somewhat changed than pure hydroxyapatite. X-ray diffraction and SEM showed no decomposition of secondary phases in grain boundary and fracture toughness somewhat increased.

Series of TiCrN wear resistant coatings have been known to be superior to other coatings in protecting tools which may be damaged corrosion, oxidization, abrasion and hardness of mold materials. The corrosion and oxidation resistance of TiN/CrN(TiCrN) multilayer coatings is better than that of single TiN and CrN coatings. TiCrN coated layer was formed by coating a layer of TixCr1-xN by non-stoichiometry. In this study, TiCrN coated layer by R.F magnetron sputtering was executed heat treatment each other temperature by tube furnace. And then surfaces of coated layer and cross sections were observed by FE-SEM and XRD. Corrosion resistance tester measured characterizations of coated layers. When the temperature increased, TiN was partially transformed to Ti2N and TiNX, and CrN was also transformed to Cr2N. The formation of non-stoichiometric phases decreased corrosion resistance.

This research has been performed to investigate the effect of ageing onto the grain refinement of 82wt%Cu-13.5wt%Al-4.5wt%Ni-0.1wt% misch metal alloy with ageing temperature and time. The variation of transformation temperature with ageing has been found to be heavily dependent on ageing time and temperature. In the second reversed transformation cycle, the temperature of Ms point decreases with ageing time at 300[removed info], but no variation at 100[removed info]. The temperature of As point increases with ageing time at both temperatures. After the second reversed transformation cycle, the transformation temperature does not show any significant changes in martensitic phase with ageing, the temperature of Ms point being the same afterwards. Parent phase after ageing appears to show M18R and N2H martensitic phases depending on the ageing time and temperature. It is also found that α and γ2 phases are formed only at the condition of 300[removed info] and 24h.

Fabrication of paste at low temperature has been developed in order to apply for various electronic devices, such as bus electrode and address electrode in PDP, especially for enlargement of a screen size. In this study, nano-sized silver particles with 10 - 30 nm were synthesized from silver nitrate (AgNO3) by a chemical reduction method. To prepare Pb-free silver paste, the silver nanoparticles were mixed with conventional silver powder with an average particle size of 1.6 [removed info] and conventional Pb-free frit. Thick films were fabricated from silver paste by a screen printing on alumina substrate and the films were fried at temperatures ranging from 550 °C to 600 °C. Microstructures of the fried thick films were analyzed by FE-SEM. Sheet resistivity of fried thick films was measured and also the relationship between sinterability and conductivity of these films were investigated.

Nano-sized silver particles are considered to apply a silver paste for electrode because of its high conductivity on sintering at low temperature. In this study, silver nanoparticles as seeds were prepared by chemical reduction method with capping agent. Silver particles were prepared using SDS (Sodium dodecyl sulfate) as a surfactant and silver nanoparticles as seeds and reacted with ascorbic acid as a reduction agent. The silver seeds with 10-20 nm in size with uniform distribution were formed and the size and shape of silver particles were strongly dependent on the concentration of surfactant.

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Effective micro-organisms (EM) increase the natural resistance of soil and plants, and it considerably improves the quality and fertility of soil as well as the growth and quality of crops. In this study, we prepared two types of porous ceramics with high and low porosity, and observed the attaching behavior of micro-organisms to the surface of ceramics. In the case of highly porous ceramics with large pore (80% in porosity), many of micro-organisms were observed in the pores of interior as well as on the ceramic surfaces. However, most of micro-organisms attached on the surface of the low porous ceramics with small pore (45% porosity), and only a few micro-organisms observed in pore inside.

The effect of Ca/P ratio on surface dissolution of hydroxyapatite [Ca10(PO4)6(OH)2, HA] in distilled water was investigated. The stoichiometric HA powder and desired Ca/P ratio achieved by adding either Ca3(PO4)2 for a Ca/P ratio of 1.62 or CaO for a Ca/P ratio of 1.72 were used as starting materials. Dense HA ceramics were obtained by sintering at 1200 oC for 2 h in air with under moisture protection. The sintered specimens were then placed into 40 ml of pH 7.4 distilled water. After immersing for certain period of time at 37 oC, crystal structure, weight loss and microstructure of the specimens were investigated. As increasing the immersion time, circular cavities similar to that normally attributed to osteoclast resorption lacunae were observed. As a result, it was found that the dissolution of HA along the grain boundary and subsequently microstructural disintegration was more distinct in 1.62 and 1.72 samples compared to pure HA.

In this work, tricalcium phosphate [TCP, β-Ca3(PO4)2]/titania composite were prepared with different ratio of 75/25, 50/50 and 25/75 (HA/TiO2, wt %). The TiO2 and hydroxyapatite (HA) powders, as starting materials, were synthesized by precipitation and hydrothermal methods, respectively. The sintered bodies of β-TCP/TiO2 composite were prepared by hot pressing at pressure of 30 MPa and temperature of 800-1000 oC for 30 min under the pressure of 30 MPa in N2 atmosphere. During the sintering process, hydroxyapatite was decomposed to β-TCP and CaTiO3 at elevated temperature because TiO2 could accelerate the decomposition of hydroxyapatite. The hot-pressed composite with 98% of sintered density, showed high value of 1080 Hv in hardness, compared with the pure hydroxyapatite (600 Hv) before immersion in distilled water. Increasing sintering temperature led densification of the composite with moderately uniform microstructures. As increasing the amount of TiO2, the surface of the composite was less damaged or dissolved.

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CuAlNi shape memory alloy with Cu-13.5Al-4.5Ni(wt%) composition was prepared by cross-rolling method and the aging effect, phase transformation characteristics, microstructural variation were investigated. Transformation temperature was greatly increased in aged specimens at 250˚C. Transformation temperature was not changed after the second reversed transformation, and Ms point was same in most specimens with third reversed transformation cycle. The variation of Ms point was not seen with aging at 100˚C, but it was decreased with aging at 250˚C. Transformation temperatures appear to be constant, to an measurable extent, in specimens prepared by both hotrolling and cross-rolling at 900˚C. Plate shaped-specimen with the thickness of about 1mm was prepared by cross-rolling treatment at 350˚C. The transformation temperatures did not change after the second transformation-reverse transformation cycling, and specially transformation start temperature was the same in most specimens experiencing third thermal cycle and thereafter. Undesirable tweed-like structure was observed in 250˚C-aged specimen after a cross-rolling at 350˚C. On aging the specimen prepared by cross-rolling, G.P zone was formed easier than that of γ2 phase. This phase was transformed to plate-like θ phase during aging.

TiO2 photocatalyst has attracted much attention in recovering valuable metal ions from industrial wastewater because TiO2 shows chemical stability and good wear resistant, and a photocatalytic reaction occurs by illumination of the sun or fluorescent light. In this study, Au removal and recovery in a gilding wastewater using TiO2 photocatalyst was evaluated. Commercially obtained TiO2 powder and TiO2 film prepared by spray and screen print method were used for Au adsorption. The cyanide existed in a plating wastewater was firstly removed with peroxide or persulfate because a driving force for Au ion reduction during photocatalytic process could decrease by the existed cyanide. Compared with persulfate, peroxide shows relatively slow removal rate of cyanide but no precipitation occurs. With respect to photocatalytic reaction of TiO2 powder and film for Au removal and recovery, it was found that the addition of 10 vol% of methanol as a hole scavenger increases the rates of Au ion reduction and Au adsorption on the TiO2 powder and film, subsequently the reaction of Au photoadsorption was completed within 60 min. Au lumps on the TiO2 particles obtained by photocatalytic reduction of TiO2 was confirmed by XRD analysis and TEM observation.

In this study, it was demonstrated how second phases with small amount, which are hardly detected by XRD analysis, affect grain boundary dissolution and related mechanical properties of HA. All HA disks sintered at 1200 oC for 2 h in air with under moisture protection were phase pure and had Ca/P molar ratio of 1.67. Following certain period of exposure to the distilled water, the surface dissolution initiated at grain boundaries and particle loosening, subsequently resulting in decrease in mechanical properties of HA. In order to understand the dissolution mechanism, grain boundary structure of HA was identified by transmission electron microscopy (TEM) and high resolution TEM observation. From the analysis, it was found that the non-stoichiometric phase as α-tricalcium phosphate (TCP) transformed from β-TCP was existed at grain boundaries and caused surface dissolution of HA. From the XRD analysis, it was found that (211) and (112) planes of hydroxyapatite were susceptible to dissolution, whereas (300) plane was relatively stable.

Several sintering additives for hydroxyapatite have been tested in order to enhance its sinterability without decomposing the hydroxyapatite(Ca10(PO4)6(OH)2) and without decreasing the bioactivity and/or biocompatibility. In case of sintered pure hydroxyapatites significant dissolution was occurred after immersion in distilled water or in simulated body fluid. At first the dissolution was iniciated at grain boundary creating the nano-size defects such as small pores and grew up to micro scale by increasing the immersion time. This dissolution resulted in grain separation at the surfaces and finally in fracture. And the dissolution was concentrated on those grains adjacent to pores rather than those in the dense region. So glass-reinforced hydroxyapatite(GR-HA) ceramics were prepared to strengthening the grain boundary to prevent dissolution. Several glasses were added at 0 to 10wt.% and sintered at 1200 ℃ for 2h in air with moisture protection. Glass phase was incorporated into hydroxyapatite to act as the sintering aids followed by crystallization in order to improve the mechanical properties without reducing the biocompatibility. From dissolution test, significant damage was reduced even more than 7days. X-ray diffraction and SEM showed no decomposition of hydroxyapatite to secondary phases and fracture toughness was increased more than pure hydroxyapatite.

The aim of this study was to prepare dense hydroxyapatite (HA) by microwave sintering and to evaluate the dissolution behavior in distilled water. Commercially-obtained HA powders having Ca/P ratio of 1.67 were used as a starting material. The as-received powder of granular type consists of nano-sized particles. Microwave sintering was operated at 1200℃ for 5 min with a heating rate of 50℃/min. Microwave sintering process reduced grain size of HA, compared with the case of conventional sintering. During the immersion in distilled water for 3-14 days, grain boundary dissolution occurred and the dissolution extended into the bulk following this path. As a result, particles were separated from the structure leaving micron-scale defects.

The reaction-sintered alumina ceramics with low firing shrinkage were prepared from Al/Al2O3 powder mixture by attrition milling and the effect of milling characteristics of raw powders on reaction sintering was investigated. Powder mixtures of flaky shape Al with coarse alumina was much more effectively comminuted by the attrition milling than the mixtures of globular shape Al with coarse alumina powders. Furthermore the coarse alumina was much more useful in pulverizing and grinding the ductile Al particles than fine alumina. After attrition milling and isopressing at 400MPa, the Al/Al2O3 specimen was oxidized at 1200℃ for 8 hours followed by sintering at 1550℃ for 3 hours. Because mixed powder of coarse alumina with flaky Al was much more effectively comminuted than the globular Al, sintered body of more than 97% theoretical density was achieved, but low contents of Al leads to relatively higher shrinkage of about 8%. As the coarse alumina particles are much more useful in cutting and reducing the ductile Al particles, the use of the coarse alumina powder was much more effective in reaction-sintering.

Nanocrystalline α-Al2O3 powders have been prepared by the pyrolysis of a resin compound of aluminum with polyester by a two-step calcination process. A polymeric precursor was prepared using a complexing agent to keep the metal ions in homogeneous solution, which gives sufficient flexibility for the system to exist homogeneously throughout the reaction without undergoing precipitation. The metal-ion-polyester resin forms the precursor material on complete polymerization reaction of aluminum nitrate, citric acid and ethylene glycol. A single-phase α-Al2O3 powder resulted after calcinations above 1150ºC, but during heat treatment α-Al2O3 particles grow very fast by coalescence. So 2-step calcination was used, where the first step was done in a reducing atmosphere at above 1150ºC and second calcinations were done in oxidizing atmosphere at the relatively low temperature of 1000ºC. The precursors and the heat-treated final powders have been characterized by X-ray diffractometry, thermogravimetry , transmission electron microscopy(TEM), and BET surface area analysis. The nanocrystalline α-Al2O3 particles obtained by this 2-step calcinations method had an average specific surface area of >170m2/g, with an average particle size between 40 and 60nm.

To prepare the vibrated casting slurries of waste tile particles, ultrafine colloids of the waste tile was added as a binder materials and as a thixotropic agent to avoid segregation between large and fine grains. The plasticity of the slurries was controlled by the rheology of colloids of the waste tile. To give thixotropic behavior, the dispersion and coagulation behavior of the colloidal suspension were investigated by the zeta potentiometer. The point of zero charge of the suspension was shown near pH 5 and maximum zeta potential was -55[mV] near pH 11. Maximum agglomerate particles were appeared near to the point of zero charge. The bending strength and water absorption of sintered bodies were more than 8.35kgf/cm2, and less than 5.0% above 1100 oC respectively. In addition, crystalline phase of sintered bodies were quarts and mullite. The micro-structure of the sintered body has a uniform pore size and distribution.

Tricalcium phosphate [TCP, β-Ca3(PO4)2]/titania composite having high mechanical properties was prepared and characterized. The TiO2 and HAp powders, as starting materials, were synthesized by precipitation and hydrothermal methods, respectively. The sintered β-TCP/TiO2 composite was prepared by hot pressing at 1000°C for 30 min under the pressure of 30 MPa in N2 atmosphere or by pressureless sintering at 1200°C for 2 h in air with moisture protection. The influence of sintering condition on the microstructures and mechanical properties of the composite was investigated. During the sintering process, hydroxyapatite used as a starting material was decomposed to β-TCP and CaTiO3 at elevated temperature because TiO2 could accelerate the decomposition of hydroxyapatite. The hot-pressed composite with 98% of sintered density showed high hardness[removed info]value of 1080 Hv compared with the pure hydroxyapatite (600 Hv).

To improve the mechanical properties of Al2O3/ZrO2 composites, the homogeneous dispersion of ultra low size ZrO2 particles in Al2O3 ceramics have been controlled by partial dispersion of ZrO2 by chemical processes such as coprecipitation or polymeric precursor method(Pechini process). So nanosized Zr/Y hydroxide were coprecipitated or polymerized directly to the surfaces of commercial sub-micron size α-alumina powder(Sumitomo: AES-11[removed info](0.4 μm)) using ZrOCl2 /Y(NO3)3 solution. By the partial coprecipitation method, dispersion of relatively small sized ZrO2 in Al2O3/ZrO2 composites could be achieved at 1500~1600° C of sintering temperature. In case of the polyesterization of Zr/Y(NO3)3-citric acid solution in ethylene glycol directly to the commercial sub-micron size α-alumina powder, more homogeneous dispersion of relatively low sized ZrO2 in Al2O3/ZrO2 composites could be obtained at 1450~1600°C of sintering temperature range and their mechanical strength was more enhanced.

Dissolution of hydroxyapatite (HAp) in distilled water and related mechanical properties were investigated. The commercially obtained stoichiometric HAp powders were used as starting materials. After preparing powder compacts, the disks were sintered at 1200oC for 2 h in air with under moisture protection. The sintered specimens were then placed into 40 ml of 7.4 distilled water. After immersing for certain period of time at 37oC, weight loss, microstructure, and mechanical characteristics of the specimens were investigated. Fracture toughnesses were measured for both sintered and immersed HAp for comparison. Evidence for the surface damage was observed with appearance of micron-level of pitting and grain boundaries dissolved. The value for fracture toughness decreased due to dissolution of the materials.

Polymer/layered silicate nanocomposities were prepared by in situ polymerization with microwave process. The influence of the amount of clay on the structure and thermal properties for the synthesized nanocomposites were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). It was found that the structure of nanocomposites, an intercalated/exfoliated structure, depended on the clay content.

Waste sludges produced from the recycling of concretes contain a large amount of aggregate powders and pre-reacted cements so that they have no more cementing properties. However, since they contain unreacted Ca(OH)2, pozzolanics such as blast slag or meta kaoline can activate the waste concrete, and they can be reused as low-grade cement or pozzolanics. When meta kaoline was added with some other pozzolanic materials such as gypsum or blast slags, the density was increased so that the compressive strength, especially early stage of curing time, was enhanced. When meta kaolin was added, more densified C-S-H gel networks were formed at aggregates, and ettringites were produced between the C-S-H gel networks.

Re-expression of fetal genes has been considered to underlie ionic remodeling in diseased heart. T-type Ca2+channels have been reported to be functionally expressed in embryonic hearts. In this review, we summarize developmental changes of T-type Ca2+channels in mouse ventricles from 9.5 days postcoitum (dpc) to adulthood, using patch clamp and quantitative PCR. In addition, we introduced T-type Ca2+channel expression in hypertrophied ventricles caused by myocardial infarction (MI) and aortic banding (AOB). Substantial T-type Ca2+channel current was recorded at both 9.5 and 18 dpc. The currents were inhibited by Ni2+at low concentrations. The current was not detectable in the adult stage. Cav3.2 (α1H) mRNA is expressed dominantly at both 9.5 and 18 dpc. Cav3.1 (α1G) increases from 9.5 to 18 dpc, but remains at low level compared with Cav3.2. In contrast, Cav3.1 is greater than Cav3.2 at the adult stage. In MI, Cav3.1 mRNA correlates negatively with brain natriuretic peptide (BNP) mRNA, whereas Cav3.2 mRNA correlates positively with BNP mRNA. In AOB, these correlations are weak. We also analyzed the neuron-restrictive silencer factor (NRSF) in these hearts because it is the suppressor of transcription of the fetal cardiac gene program. The negative correlation between NRSF and BNP was stronger in MI than in AOB. Our findings show that Cav3.2 underlies the functional T-type Ca2+channel in embryonic heart and suggest that NRSF may regulate Cav3.2 expression in diseased hearts.

Three types of calcium phosphate ceramics, i.e. tricalcium phosphate, biphasic calcium phosphate and near stoichiometric hydroxyapatite, were prepared by sintering at 1200oC for 2 h in air with moisture protection. Their dissolution processes were investigated by taking microstructural observations after immersion in distilled water for 3 or 7 days. It was found that the surface dissolution of the ceramics was initiated at grain boundaries and generated many separated grains. In case of the materials with high porosity, the residual pores on the surface appeared to be a primary defect site where the dissolution starts although the soluble compound was existed on the matrix.

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The continuous shrinkage of integrated circuit devices provides the advantage of having more electrical functions on the smaller chips. However, it has posed severe challenges to the manufacturing of these products. In patterning steps, the depth of focus becomes small, due to the nature of patterning small features and is aggravated by the presence of step height differences in the exposure field. When the aspect ratio of holes increases, aluminum, which has been the choice of metal to fill holes, no longer effectively fills small holes. On some occasions, discontinuous aluminum exists in the holes, resulting from poor step coverage. Tungsten (W), on the other hand, can satisfactorily fill small holes by chemical vapor deposition and thus fills a need to replace aluminum as an electrical connector plug for layers separated by this plug. Chemical mechanical polish (CMP) has been used recently to planarize substrates and improve the depth of focus, as in the case of hole patterning. It is also used to prepare the metal plug effectively. CMP processing involves various parameters, such as machine configuration, slurry chemistry and formulation, polishing pad configuration, pad hardness, etc. Although the mechanism is not fully understood, these parameters are known to significantly influence the degree of planarization, contamination, defects, etc. In this paper we explore the effects of consumables used in the W-CMP process on the control of several problems, such as recessed plug, dishing and oxide erosion, etc. Based on our findings, we implement a two-step W-CMP process to improve the qualities of the polished wafers. The first step involves a proper combination of slurry and pad to polish most of the bulk tungsten with a high polish rate. The second step uses the same pad, slurry and a proprietary additive to slowly polish the remaining tungsten. In this way, we are able to obtain a workable W-CMP process. © 2001 Kluwer Academic Publishers

Mechanisms and residues responsible for slow activation and Ba2+block of the cardiac muscarinic K+channel, Kir3.1/Kir3.4, were investigated using site-directed mutagenesis. Mutagenesis of negatively charged residues located throughout the pore of the channel (in H5, M2, and proximal C terminus) reduced or abolished slow activation. The strongest effects resulted from mutagenesis of residues in H5 close to the selectivity filter; mutagenesis of residues in M2 and proximal C terminus equivalent to those identified as important determinants of the activation kinetics of Kir2.1 was less effective. In giant patches, slow activation was present in cell-attached patches, lost on excision of the patch, and restored on perfusion with polyamine. Mutagenesis of residues in H5 and M2 close to the selectivity filter also decreased Ba2+block of the channel. A critical residue for Ba2+block was identified in Kir3.4. Mutagenesis of the equivalent residue in Kir3.1 failed to have as pronounced an effect on Ba2+block, suggesting an asymmetry of the channel pore. It is concluded that slow activation is principally the result of unbinding of polyamines from negatively charged residues close to the selectivity filter of the channel and not an intrinsic gating mechanism. Ba2+block involves an interaction with the same residues.