Cooperative mixing induced surface roughening in bilayer metals: a possible novel surface damage mechanism

Molecular dynamics simulations have been used to study a collective atomic transport phenomenon by repeated Ar$^+$ irradiations in the Ti/Pt interfacial system. The ion-induced injection of surface atoms to the bulk, the ejection of bulk atoms to the top layers together with surface erosion is strongly enhanced by interfacial mixing. This process leads to a dense interfacial material, and broadening of the interface region. The process scales with the relative difference of the atomic masses. We find that surface roughening and interfacial mixing is strongly coupled via an enhanced counterflow material transport normal to the surface which might be a novel surface damage mechanism. This cooperative phenomenon is active when the bilayer system is subjected to a high dose ion irradiation (multiple ion irradiations) and leads to surface cavity growth.Comment: 6 pages, 6 figures. accepted in Nucl. Instrum. Meth.

Silica thin-films from perhydropolysilazane for the protection of ancient glass

Silica coatings from polysilazane precursors were prepared to protect ancient glass from weathering. Polysilazane can be converted to silica by simple exposition to air or basic vapours and the properties of the synthesized film make this precursor a valuable choice to obtain solid, crack-free, highly adhesive and protective coatings. The coating is prepared starting from a Perhydropolysilazane precursor (20% PHPS in n-butyl ether) that allows to achieve high-quality thin-films of silica at room temperature. The obtained films are uncoloured, even in absence of strong heat-treatment. Perhydropolysilazane (PHPS) is a polymer of [-SiH2-NH-SiH2-]n units. When deposited on a soda-lime microscope slide, it reacts with atmospheric moisture (Si-H and Si-NH bonds are hydrolysed to Si-O) and a silica film is produced. The conversion to silica is completed in about 2.5 hours, using vapours of a 10 mol L-1 ammonia solution. The reaction is promoted with the application of a weak heat-treatment (45-50 \ub0C), achievable using as heater a common tungsten filament lamp. The reaction of PHPS with atmospheric moisture produces a migration phenomenon of the mobile ions from the soda-lime glass to the film (in particular sodium, calcium and magnesium). The characteristics of the migration process vary according to the concentration of the precursor solution and the thickness of the film. Laboratory samples have been investigated by optical microscopy and surface techniques: XPS and SIMS. Preliminary evidences, obtained through the laser scanning confocal microscope (LEXT), on the application of such coatings at the surface of ancient stained glass are also discussed

Silicon based oxidation-resistant coatings on Ti6242 alloy by dynamic ion mixing

The influence of SixCy and SixNy amorphous coatings on the oxidation resistance of a Ti6242 (Ti–6Al–2Sn–4Zr–2Mo) alloy was investigated. They were produced at room temperature by the dynamic ion mixing technique combining physical vapour deposition with simultaneous bombardment with 120 keV Ar+ ions. Isothermal oxidation tests were carried out at 600 °C in 1 atm flowing synthetic air (80% N2, 20% O2) demonstrating a considerable reduction (not, vert, similartwo orders of magnitude) of the oxidation rate for at least 100 h. The structural modifications after oxidation were investigated by XPS, XRD, SEM, SIMS. The formation of SiO2 is detected as the main oxidation product in the coating and the formation of Ti–Si compounds is also observed in the coating/substrate interface region. The crystallisation of SixNy is not detected and for SixCy only some traces of β-SiC could exist. The improvement of oxidation resistance of Ti6242 is discussed in relation with the intrinsic properties of the coatings and with the interface mixing and ion beam densification

Characterization of Cell Glycocalyx with Mass Spectrometry Methods.

The cell membrane plays an important role in protecting the cell from its extracellular environment. As such, extensive work has been devoted to studying its structure and function. Crucial intercellular processes, such as signal transduction and immune protection, are mediated by cell surface glycosylation, which is comprised of large biomolecules, including glycoproteins and glycosphingolipids. Because perturbations in glycosylation could result in dysfunction of cells and are related to diseases, the analysis of surface glycosylation is critical for understanding pathogenic mechanisms and can further lead to biomarker discovery. Different mass spectrometry-based techniques have been developed for glycan analysis, ranging from highly specific, targeted approaches to more comprehensive profiling studies. In this review, we summarized the work conducted for extensive analysis of cell membrane glycosylation, particularly those employing liquid chromatography with mass spectrometry (LC-MS) in combination with various sample preparation techniques

Micro- and nanoengineering approaches to control stem cell-biomaterial interactions.

As our population ages, there is a greater need for a suitable supply of engineered tissues to address a range of debilitating ailments. Stem cell based therapies are envisioned to meet this emerging need. Despite significant progress in controlling stem cell differentiation, it is still difficult to engineer human tissue constructs for transplantation. Recent advances in micro- and nanofabrication techniques have enabled the design of more biomimetic biomaterials that may be used to direct the fate of stem cells. These biomaterials could have a significant impact on the next generation of stem cell based therapies. Here, we highlight the recent progress made by micro- and nanoengineering techniques in the biomaterials field in the context of directing stem cell differentiation. Particular attention is given to the effect of surface topography, chemistry, mechanics and micro- and nanopatterns on the differentiation of embryonic, mesenchymal and neural stem cells