Preparation and properties of carbon dental implant with fine rahmen surface layer

Blade- and tooth-root-form carbon dental implants were prepared by fixing fine Rahmen surface (FRS) layers of carbon fabric on a carbon fiber-reinforced carbon (CFRC) core. The fixing was successfully performed through the low-temperature deposition of pyrolytic carbon using cis-1,2-dichloroethylene as the raw material. The resultant implants showed flexural and compressive strength more than 150 and 100 MPa, respectively. The outer part of this FRS layer contained many pores ranging from 30 to 300 μm in diameter and 40–75% in volume fraction.New bone was generated in the open pores after being embedded in the femur of a monkey for 6 months. The shear strength of the embedded implant vs bone interface was 15 MPa. On the other hand, the blade-form FRS implant in the mandible of a monkey gave a locking system consisting of “bone-collagen fiber-calcified layer” after two years under a masticating pressure. The latter is very similar to the natural tooth system.     

Molecular dynamics of DNA and nucleosomes in solution studied by fast-scanning atomic force microscopy

Nucleosome is a fundamental structural unit of chromatin, and the exposure from or occlusion into chromatin of genomic DNA is closely related to the regulation of gene expression. In this study, we analyzed the molecular dynamics of poly-nucleosomal arrays in solution by fast-scanning atomic force microscopy (AFM) to obtain a visual glimpse of nucleosome dynamics on chromatin fiber at single molecule level. The influence of the high-speed scanning probe on nucleosome dynamics can be neglected since bending elastic energy of DNA molecule showed similar probability distributions at different scan rates. In the sequential images of poly-nucleosomal arrays, the sliding of the nucleosome core particle and the dissociation of histone particle were visualized. The sliding showed limited fluctuation within ∼50 nm along the DNA strand. The histone dissociation occurs by at least two distinct ways: a dissociation of histone octamer or sequential dissociations of tetramers. These observations help us to develop the molecular mechanisms of nucleosome dynamics and also demonstrate the ability of fast-scanning AFM for the analysis of dynamic protein–DNA interaction in sub-seconds time scale.     

Novel g-C3N4 nanosheets/CDs/BiOCl photocatalysts with exceptional activity under visible light

We fabricated novel ternary nanocomposites through integration of C-dots (carbon dots), BiOCl, and nanosheets of graphitic carbon nitride (g-C₃N₄ nanosheets) by a cost-effective route. The fabricated photocatalysts were subsequently characterized by XRD, EDX, TEM, HRTEM, XPS, FT-IR, UV-vis DRS, TGA, BET, and PL methods to gain their structure, purity, morphology, optical, textural, and thermal properties. In addition, the degradation intermediates were identified by gas chromatography-mass spectroscopy (GC-MS). Photocatalytic performance of the synthesized samples was studied by photodegradations of three cationic (RhB, MB, and fuchsine), one anionic (MO) dyes, one colorless (phenol) pollutant and removal of an inorganic pollutant (Cr(VI)) under visible light. It was revealed that the ternary nanocomposite with loading 20% of BiOCl illustrated superlative performances in the selected photocatalytic reactions compared with the corresponding bare and binary photocatalysts. Visible-light photocatalytic activity of the g-C₃N₄ nanosheets/CDs/BiOCl (20%) nanocomposite was 42.6, 27.8, 24.8, 20.2, and 15.9 times higher than the pure g-C₃N₄ for removal of RhB, MB, MO, fuchsine, and phenol, respectively. Likewise, the ternary photocatalyst showed enhanced activity of 15.3 times relative to the g-C₃N₄ in photoreduction of Cr(VI). Moreover, the ternary nanocomposite exhibited excellent chemical stability and recyclability after five cycles. Finally, the mechanism for improved photocatalytic performance was discussed based on the band potential positions.     

“Fabrication of arbitrarily shaped carbonate apatite foam based on the interlocking process of dicalcium hydrogen phosphate dihydrate”

Carbonate apatite (CO₃Ap) foam with an interconnected porous structure is highly attractive as a scaffold for bone replacement. In this study, arbitrarily shaped CO₃Ap foam was formed from α-tricalcium phosphate (α-TCP) foam granules via a two-step process involving treatment with acidic calcium phosphate solution followed by hydrothermal treatment with NaHCO₃. The treatment with acidic calcium phosphate solution, which is key to fabricating arbitrarily shaped CO₃Ap foam, enables dicalcium hydrogen phosphate dihydrate (DCPD) crystals to form on the α-TCP foam granules. The generated DCPD crystals cause the α-TCP granules to interlock with each other, inducing an α-TCP/DCPD foam. The interlocking structure containing DCPD crystals can survive hydrothermal treatment with NaHCO₃. The arbitrarily shaped CO₃Ap foam was fabricated from the α-TCP/DCPD foam via hydrothermal treatment at 200?°C for 24?h in the presence of a large amount of NaHCO₃.     

Properties of poly(vinyl chloride) fibers crosslinked by 2-dibutylamino-4,6-dimercapto-1,3,5-triazine

PVC fibers, fastened to a needle frame, were crosslinked by 2-dibutylamino-4, 6-dimercapto-1,3,5-trizine in the presence of tetra-n-butylammonium bromide and alkali in water at 96°C. Solvent resistance, characterized by the gel fraction of THF, improves markedly. Mechanical properties of the fibers investigated by tensile tests at 20°C show that both the modulus and tensile strength at break increase, while elongation at break decreases over 40% gel content. Creep tests indicate that the resistance to heat deformation improves by crosslinking. The heat distortion temperature increases by 12°C at 75% gel content. Results of dynamic tests show that the T_g of PVC fibers determined by a peak in the loss modulus (E'') increases from 40% gel content. Dynamic modulus (E') increases by 74% at 23°C and the T_g by 37°C in the case of crosslinked PVC fibers having a 92% gel content. The shrinkage of PVC fibers in hot water at 94°C for 30 min decreases more than 50% over 75–80% gel content indicating the improved resistance to heat deformation.     

Change of viscoelastic properties of epoxy resin in the curing process

This paper is concerned with the relation between the time and temperature dependences of the flexural properties and the curing conditions for the bisphenol A-type epoxy resin with acid anhydride hardener. Relaxation moduli of epoxy resin, prepared at several curing temperatures and times, were measured in the temperature range from T_g ?70°C to T_g. The master curves of relaxation modulus for the epoxy resin could be constructed, using their thermorheological simple properties. The time–temperature shift factors of the epoxy resin could be approximately expressed by the Arrhenius equation with the activation energy 59.4 kcal/mole. independent of its curing conditions. The curing time and temperature were equivalent, that is, the short curing time at high temperature corresponded to the long curing time at low temperature. The curing time–temperature shift factor could be approximately expressed by the Arrhenius equation with the activation energy 21.3 kcal/mole, which was higher than the activation energy 14.2 kcal/mole obtained in the measurements of gel times. The increase in the values shows that the temperature dependences of reaction rates increase with progressing gelation.     

Modification of poly(vinyl chloride). XIX. Electroplating of poly(vinyl chloride)

As a preliminary treatment in the PVC-electroplating procedure, treatment with dimethylformamide followed by sensitization leads to a finely roughened and a highly hydrophilic surface with reducing power. This is caused by the formation of an ionic complex compound between dimethylformamide and tin(II) chloride absorbed in the PVC surface. A much more finely and deeply etched surface which exhibits higher adhesion through the mechanical interlocking effect is obtained with the PVC blends containing the plasticizer with a low value of interaction parameter and with a solubility parameter approximate to that of PVC. Adhesion of the metal layer to the PVC surface thus obtained is improved about 1.5 times by thermal aging at 120°C for 20 min.     

Simultaneous determination of dissolved organic carbon and phosphorus in waters using flame ionization and photometric detectors

An apparatus with flame ionization and photometric detectors was assembled for the simultaneous determination of dissolved organic carbon (DOC) and phosphorus (DP) in waters. The optimum operating conditions were described. The long-term precision (relative standard deviation) is 5.8% for DOC and 5.2% for DP. The detection limits are 0.09 μg ml⁻¹ for DOC and 0.03 μg ml⁻¹ for DP. The responses for various DOC and DP compounds agreed almost with those obtained by combustion-infrared and persulfate digestion-colorimetric methods, respectively. DOC and DP in several water samples were determined by this method and other methods, and the results obtained by those methods were discussed.     

Effect of molding pressure on fabrication of low-crystalline calcite block

We have reported that low-crystalline porous calcite block, which is useful as a bone substitute or a source material to prepare apatite-type bone fillers could be fabricated by exposing calcium hydroxide compact to carbon dioxide gas saturated with water vapor. In the present study, we investigated the effect of molding pressure on the transformation of calcium hydroxide into calcite and the mechanical strength of the carbonated compact. Transformation into calcite was almost completed within 72 h, however, a small amount of Ca(OH)₂ still remained unreacted at higher molding pressure because of incomplete penetration of CO₂ gas into the interparticle space due to dense packing of Ca(OH)₂ particles. On the other hand, high molding pressure resulted in an increase in diametral tensile strength (DTS) of the calcite compact formed. Critical porosity of the calcite block was calculated as approximately 68%.