D. B. Lee

The effects of epidermal keratinocytes and dermal fibroblasts on the formation of cutaneous basement membrane in three-dimensional culture systems

The cutaneous basement membrane (BM) plays an important role in normal and pathological conditions. However, few studies have addressed the formation of the cutaneous BM using three-dimensional culture systems. In this study, to elucidate the effects of human epidermal keratinocytes and dermal fibroblasts on the formation of the cutaneous BM, keratinocytes were cultured on several dermal substrates in the presence or absence of fibroblasts at the air–liquid interface. After 2xa0weeks of culture, immunohistochemical stainings for the components of the BM and electron microscopic studies of the BM zone (BMZ) were performed. In cultures of keratinocytes alone on dead reticular dermis or collagen gel without fibroblasts, β4 integrin chain, laminin, type IV and VII collagens were all expressed. However, ultrastructurally, BMZ was not formed. In cultures of keratinocytes on fibroblast-populated collagen matrix, laminin, and type IV and VII collagens were expressed more strongly than in the absence of fibroblasts. In addition, elements of the BMZ such as hemidesmosomes, lamina lucida, lamina densa and anchoring fibrils were formed, although it was still incomplete. In the culture of keratinocytes alone on de-epidermized dermis (DED) (surface up), β4 integrin chain, laminin, and type IV and VII collagens were strongly expressed. Also, the BMZ appeared similar to that in normal skin. In cocultures of keratinocytes and fibroblasts on DED or cultures of keratinocytes on DED combined with fibroblast-populated collagen matrix, type IV collagen was expressed more strongly than in cultures of keratinocytes alone. Ultrastructurally, similar findings to those of cultures of keratinocytes alone on DED were seen. Interestingly, when keratinocytes and fibroblasts were cocultured on DED, some fibroblasts were seen in the upper dermis as a result of migration into the dermis through partial loss of the lamina densa. These results show that keratinocytes produce most of the components of the BM such as laminin, and type IV and VII collagens. In addition, fibroblasts stimulate the expression of the components of the BM and the formation of a BMZ, suggesting that fibroblasts may produce laminin, and type IV and VII collagens or influence the effects of keratinocytes on the formation of the BM through a keratinocyte–fibroblast interaction.

High temperature oxidation of TiCrN coatings deposited on a steel substrate by ion plating

Abstract The oxidation behavior of TiCrN coatings having compositions of Ti 36 Cr 26 N 38 , Ti 31 Cr 35 N 34 and Ti 14 Cr 52 N 34 was studied between 700 and 1000°C in atmospheric air. The oxidation resistance of TiCrN coatings which were composed of TiN and CrN phases increased in the order of Ti 36 Cr 26 N 38 , Ti 31 Cr 35 N 34 and Ti 14 Cr 52 N 34 , implying that chromium within the coating played a decisive role in providing the oxidation protection. The oxides formed always consisted of TiO 2 and Cr 2 O 3 . During oxidation, all the involved elements diffused either outwardly or inwardly, depending on the concentration gradients. The substrate elements diffused outwardly toward the oxide-gas interface, oxygen from the atmosphere diffused inwardly and the coating elements diffused predominantly outward.

The oxidation of Fe3Al-(0, 2, 4, 6%)cr alloys at 1000 °C

Abstract Thermomechanically treated Fe3Al–(0, 2, 4, 6at.%)Cr alloys were isothermally oxidized at 1000xa0°C in air, and their oxidation characteristics were studied using thermogravimetric analyzer, X-ray diffractometer, scanning electron microscope, electron probe microanalyzer, and TEM/EDS. It was found that Cr decreased the oxidation resistance of Fe3Al alloys to a certain extent. The oxide scales that formed on the unalloyed Fe3Al alloys consisted primarily of α-Al2O3 containing a small percentage of dissolved iron ions. Less than 1% of dissolved chromium ions was additionally present in the oxide scale formed on the Fe3Al–Cr alloys. An Al-free, Fe-enriched zone was formed beneath the oxide scale, owing to Al consumption to form the oxide scale. The oxide scale on all alloys had poor adherence.

High-temperature oxidation behavior of pure Ni3Al

The high-temperature oxidation behaviour of pure Ni3Al alloys in air was studied above 1000°C. In isothermal oxidation tests between 1000 and 1200°C, Ni3Al showed parabolic oxidation behavior and displayed excellent oxidation resistance. In cyclic oxidation tests between 1000 and 1300°C, Ni3Al exhibited excellent oxidation resistance between 1000 and 1200°C, but drastic spalling of oxide scales was observed at 1300°C. When Ni3Al was oxidized at 1000°C, Al2O3 was present as θ-Al2O3 in a whisker form. But, at 1100°C the gradual transformation of initially formed metastable θ-Al2O3 to stable α-Al2O3 was observed after oxidation for about 20 hr. After oxidation at 1200°C for long times, the formation of a thick columnar-grain layer of α-Al2O3 was observed beneath a thin and fine-grain outer layer of α-Al3O3. The oxidation mechanism of pure Ni3Al is described.

Effect of Cr, Co, and Ti additions on the high-temperature oxidation behavior of Ni3Al

The oxidation behavior of Ni3Al+2.90 wt.% Cr, Ni3Al+3.35 wt% Co, and Ni3Al+2.99 wt.% Ti alloys was studied in 1 atm of air at 1000, 1100, and 1200°C. Isothermal tests revealed parabolic kinetics for all three alloys at all temperatures. Cyclic oxidation for 28 two-hour cycles produced little spallation at 1000°C, but caused partial spallation at 1100°C. Especially, at 1200°C severe spallation in all three alloys was observed. Although additions of Cr, Co, or Ti to Ni3Al alloys slightly increased the isothermal-oxidation resistance, the additions tended to decrease the cyclic-oxidation resistance. The major difference in the oxidation of the three alloys compared with the oxidation of pure Ni3Al alloys was the existence of small α-Al2O3 particles in the middle of the α-Al2O3 scale and the formation of irregularly shaped Kirkendall voids at the alloy-scale interface.

The Oxidation of TiB2 Ceramics Containing Cr and Fe

The oxidation behavior of TiB2, TiB2–0.5 wt.% Cr–0.5 wt.% Fe and TiB2–1 wt.% Cr–1 wt.% Fe was studied at 800, 900, and 1000°C in static air. These ceramics oxidized rather rapidly and formed thick oxide scales. The oxidation rates of TiB2-base ceramics were comparable to TiO2 formation on pure titanium. The scale formed on TiB2 consisted of TiO2 and B2O3. For TiB–Cr–Fe ceramics, a small amount of Cr- and Fe-oxides was additionally formed. B2O3 formed during oxidation tended to evaporate because of its high vapor pressure, making oxide scales porous and fragile. The oxidation of the TiB2-base ceramics appeared to be governed by the inward transport of oxygen via the highly porous oxide scale. The oxidation resistance of TiB2–Cr–Fe ceramics was similar to or better than that of TiB2.

Mixed-Type Inhibition of Tyrosinase from Agaricus bisporus by Terephthalic Acid: Computational Simulations and Kinetics

Tyrosinase inhibition studies are needed due to the agricultural and medicinal applications. For probing effective inhibitors of tyrosinase, a combination of computational prediction and enzymatic assay via kinetics were important. We predicted the 3D structure of tyrosinase from Agaricus bisporus, used a docking algorithm to simulate binding between tyrosinase and terephthalic acid (TPA) and studied the reversible inhibition of tyrosinase by TPA. Simulation was successful (binding energies for Autodock4xa0=xa0−1.54 and Fred2.0xa0=xa0−3.19xa0kcal/mol), suggesting that TPA interacts with histidine residues that are known to bind with copper ions at the active site. TPA inhibited tyrosinase in a mixed-type manner with a Kixa0=xa011.01xa0±xa02.12xa0mM. Measurements of intrinsic and ANS-binding fluorescences showed that TPA induced no changes in tertiary structure. The present study suggested that the strategy of predicting tyrosinase inhibition based on hydroxyl groups and orientation may prove useful for screening of potential tyrosinase inhibitors.

Mechanical and oxidation properties of Ti–xFe–ySi alloys

Abstract New Ti-based alloys having reasonable mechanical properties and good oxidation resistance were designed by alloying with low cost elements of iron and silicon. From tensile tests at room temperature and 400 °C, Ti–4 wt.% Fe–(0.5–2)wt.% Si alloys were found to have the optimum combination of strength and ductility, which are comparable to the Ti–6Al–4V alloy. The precipitation of fine Ti-silicides and the reduction in α/β colony sizes are primarily responsible for the obtained mechanical behavior. The air oxidation resistance of Ti–4 wt.% Fe–(0.5–2)wt.% Si alloys between 700 and 1000 °C is far superior to that of the Ti–6Al–4V alloy, and even better than that of TiAl intermetallics. The formation of amorphous silica within the TiO2-rich oxide layers increased the oxidation resistance significantly.

TEM study on oxidized TiCrN coatings ion-plated on a steel substrate

Abstract Coatings of TiCrN having compositions of (TiCr 0.7 )N, (TiCr 1.2 )N and (TiCr 3.6 )N were ion-plated on a steel substrate. The coatings were oxidized at 800 °C for 50 h in air, and the resultant morphology and compositional variance were studied utilizing transmission electron microscopy. The scales consisted of fine TiO 2 and Cr 2 O 3 grains, of which forming-tendency, size and the location in the oxide scale strongly depended on the Ti/Cr ratio of the coatings. During oxidation, not only the coating elements (Ti and Cr) but also the substrate element (iron) predominantly diffused outwards. At the same time, inward diffusion of oxygen from the atmosphere occurred. A detailed oxidation mechanism of TiCrN coatings is presented.

The Oxidation of TiB2 Particle-Reinforced TiAl Intermetallic Composites

The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB2 dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB2 dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB2 dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl–TiB2 composites was triple-layered, consisting mainly of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner (TiO2+Al2O3) mixed layer. No B2O3 was observed within the oxide scale because of its high vapor pressure. A thin Ti3Al sublayer and discrete TiN particles were found at the oxide–substrate interface. During the oxidation of TiAl alloys with and without TiB2 dispersoids, titanium ions diffused outwardly to form the outer TiO2 layer, while oxygen ions transported inwardly to form the inner (TiO2+Al2O3) mixed layer. The increased oxidation resistance by the addition of TiB2 was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.