Luis Gustavo Pagotto Simões

The effects of implant surface nanoscale features on osteoblast- specific gene expression

This study investigated the influence of nanoscale implant surface features on osteoblast differentiation. Titanium disks (20.0 x 1.0 mm) with different nanoscale materials were prepared using sol-gel-derived coatings and characterized by scanning electron microscopy, atomic force microscopy and analyzed by X-ray Photoelectron Spectrometer. Human Mesenchymal Stem Cells (hMSCs) were cultured on the disks for 3-28 days. The levels of ALP, BSP, Runx2, OCN, OPG, and OSX mRNA and a panel of 76 genes related to osteogenesis were evaluated. Topographical and chemical evaluation confirmed nanoscale features present on the coated surfaces only. Bone-specific mRNAs were increased on surfaces with superimposed nanoscale features compared to Machined (M) and Acid etched (Ac). At day 14, OSX mRNA levels were increased by 2-, 3.5-, 4- and 3-fold for Anatase (An), Rutile (Ru), Alumina (Al), and Zirconia (Zr), respectively. OSX expression levels for M and Ac approximated baseline levels. At days 14 and 28 the BSP relative mRNA expression was significantly up-regulated for all surfaces with nanoscale coated features (up to 45-fold increase for Al). The PCR array showed an up-regulation on Al coated implants when compared to M. An improved response of cells adhered to nanostructured-coated implant surfaces was represented by increased OSX and BSP expressions. Furthermore, nanostructured surfaces produced using aluminum oxide significantly enhanced the hMSC gene expression representative of osteoblast differentiation. Nanoscale features on Ti implant substrates may improve the osseointegration response by altering adherent cell response.

The Influence of Excess Precipitate on the Non-Ohmic Properties of SnO2-Based Varistors

Based on our background in the field of nonlinear electrical properties of SnO2-based varistors, we have been observing the influence of microstructural heterogeneities, e.g., the precipitate phase at triple points of the grain boundary region. In this study, we have prepared a SnO2-based varistor system with excess precipitates at triple points in the grain boundary region in order to discuss their influence on the systems non-ohmic properties, including thermal treatment at oxidizing atmospheres. Our results indicate that an excessive amount of such precipitates may be deleterious to the non-ohmic properties because they may create adjacent regions at grain boundaries with lower concentrations of segregated metal atoms, thus increasing the presence of a non-active potential barrier and increasing leakage current paths. Under these circumstances, the effect of thermal treatment in oxidizing atmospheres is to decrease the leakage current density instead of increasing the nonlinear coefficient.

Nonohmic behavior of SnO2-MnO polycrystalline ceramics. I. Correlations between microstructural morphology and nonohmic features

This report discusses important microstructural features of SnO2.MnO-based polycrystalline ceramics. The influence of the sintering time and the concentration of donor Nb2O5 on the microstructure of these ceramics are investigated, and the correlation between the microstructural features and nonohmic behavior are also discussed. High resolution analytical electron microscopy was used for a detailed characterization of the microstructure and grain boundary chemistry of the compositions, revealing that SnO2-MnO dense ceramics consist of two phases, SnO2 grains and Mn2SnO4, precipitated mainly at triple grain points. In addition, two types of SnO2-SnO2 grain boundary were identified: type I, Mn-rich and thin, and type II, Mn-poor and thick. Changes in Mn concentrations at the grain boundaries are ascribed to both grain misorientation and Mn diffusivity along the grain boundary. The identification of two kinds of junctions in SnO2-MnO has significant implications in the material’s nonohmic behavior, as will b...