Effect of core and surface area toward hydrogen gas sensing performance using Pd@ZnO core-shell nanoparticles.

A versatile hydrogen gas sensor is fabricated using Pd@ZnO core-shell nanoparticles (CSNPs), which were synthesized through a hydrothermal route. Effect of oxidation behavior of Pd core to hydrogen sensing is also investigated for Pd@ZnO CSNPs. Accordingly, Pd@ZnO-2 sensor (core-shell sample was calcined in argon) demonstrates the best performance with respect to Pd@ZnO-1 (core-shell sample was calcined in air) and pure ZnO. It shows a much higher response (R = Ra/Rg = 22) than those of Pd@ZnO-1 (12) and pure ZnO (7) sensors with faster response and recovery times (1.4 and 7.8 min) to 100 ppm hydrogen at 350 °C. In addition, Pd@ZnO-2 sensor owns high selectivity to hydrogen among interfering target gases. Improvement can be attributed to the high content of metallic Pd0 species in CSNPs as calcined in argon. Thereby, a higher Pd metallic content (77%) still remains in Pd@ZnO-2 compared to Pd@ZnO-1 (56%), which in turn modulates the resistance of sensors as exposed to air and target gas, thus enhancing gas sensing activity. High BET surface area of core-shell materials provides plenty of active sites for accelerating the sensing reactions as well.

In vivo bone formation by human alveolar-bone-derived mesenchymal stem cells obtained during implant osteotomy using biphasic calcium phosphate ceramics or Bio-Oss as carriers.

OBJECTIVES: The aim of this study was to evaluate HA coated with different ratios of TCP as a carrier for hABMSCs obtained during implant osteotomy in comparison to slowly-resorbing biomaterial, Bio-Oss, as a negative control, using in vitro and in vivo experiments. MATERIALS AND METHODS: Human ABMSCs (hABMSCs) harvested during implant osteotomy were transplanted using HA/TCP or Bio-Oss as carriers in a murine ectopic transplantation model (n = 12). Pore size and cell affinity were evaluated in vitro. The area of newly formed bone was analyzed histometrically, the number of osteocytes was counted, and immunohistochemical staining was conducted against several markers of osteogenesis, including alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX-2), osteocalcin (OCN), and osteopontin (OPN). Osteoclast formation was evaluated by tartrate-resistant acid phosphatase staining. RESULTS: The carrier materials had comparable pore sizes. The cell affinity assay resulted in a high proportion of cell adhesion (>90%) in all experimental groups. Substantial new bone and osteocyte formation was observed on both HA/TCP carriers, whereas it was minimal with Bio-Oss. Positive immunostaining for ALP, RUNX-2, OCN, and OPN was observed with HA/TCP, but only limited expression of osteogenic markers with Bio-Oss. Conversely, there was a minimal osteoclast presence with Bio-Oss, but a significant presence of osteoclasts with both HA/TCP carriers. CONCLUSIONS: Both types of scaffolds, BCP and Bio-Oss, showed high stem cell-carrying potential, but the in vivo healing patterns of their complexes with hABMSC could be affected by the microenvironment on the surfaces of the scaffolds.

Two-body wear comparison of zirconia crown, gold crown, and enamel against zirconia.

PROBLEM STATEMENT: Full zirconia crowns have recently been used for dental restorations because of their mechanical properties. However, there is little information about their wear characteristics against enamel, gold, and full zirconia crowns. PURPOSE: The purpose of this study was to compare the wear rate of enamel, gold crowns, and zirconia crowns against zirconia blocks using an in vitro wear test. MATERIALS AND METHODS: Upper specimens were divided into three groups: 10 enamels (group 1), 10 gold crowns (group 2, Type III gold), and 10 zirconia crowns (group 3, Prettau(®)Zirkon 9H, Zirkonzahn, Italy). Each of these specimens was wear tested against a zirconia block (40×30×3mm(3)) as a lower specimen (30 total zirconia blocks). Each specimen of the groups was abraded against the zirconia block for 600 cycles at 1Hz with 15mm front-to-back movement on an abrading machine. Moreover, the load applied during the abrading test was 50N, and the test was performed in a normal saline emulsion for 10min. Three-dimensional images were taken before and after the test, and the statistical analysis was performed using the Krushal-Wallis test and Mann-Whitney test (p=0.05). RESULTS: The mean volume loss of group 1 was 0.47mm(3), while that of group 2 and group 3 was 0.01mm(3). CONCLUSION: The wear volume loss of enamels against zirconia was higher than that of gold and zirconia crowns. Moreover, according to this result, zirconia crowns are not recommended for heavy bruxers.