59 research outputs found
Structure and Corrosion Resistance of Cerium-Oxide Films on AZ31 as Deposited by High-Power Ultrasound Supported Conversion Chemistry
In the present study a conversion layer mainly composed by ceria oxide was prepared by means of a novel ultrasound assisted coating process. The formation of a conversion layer on top of the Mg alloy provides physical barrier properties improving the corrosion protection. In addition the incorporation of cerium oxide within the coating enables the formation of a protective layer on the pores and defect inhibiting localized corrosion.The chemical composition of the conversion layer was evaluated by means of Raman spectros-copy, FT-IR spectroscopy and XPS. The prepared porous films were rich in Ce4+ and featured a very low content of oxygen deficient cerium oxide. FE-SEM measurements were performed in order to assess the morphology of the prepared coating revealing homogeneous and uniform surfaces. Self-repair ability was verified by monitoring capacitance of the system after polarization by means of electrochemical impedance spectroscopy. Additional, Raman spectroscopic measurements showed presence of cerium ions in defect sites which may suggest self-repair mechanism
Superstructure-Dependent Loading of DNA Origami Nanostructures with a Groove-Binding Drug
Peer reviewe
Arranging Small Molecules with Subnanometer Precision on DNA Origami Substrates for the SingleâMolecule Investigation of ProteinâLigand Interactions
DNA origami nanostructures are versatile substrates for the singleâmolecule investigation of biomolecular interactions as they enable the display of molecular species in complex arrangements. Herein, the fundamental limitations of this approach are explored by displaying pairs of smallâmolecule ligands of the protein trypsin on DNA origami substrates and adjusting their ligandâligand spacing with subnanometer precision. Bidentate binding of trypsin to the ligand pairs is investigated by atomic force microscopy (AFM), microscale thermophoresis (MST), and molecular dynamics simulations. Bidentate trypsin binding is strongly affected by the distance of the ligand pairs and the accessibility of the protein's binding pockets. MST cannot resolve the differences in bidentate trypsin binding because of the nonspecific binding of trypsin to the DNA origami substrates, rendering the AFMâbased singleâmolecule detection of binding events superior to ensemble measurements. Finally, even monodentate binding to a single ligand may be affected by subnanometer variations in its position, highlighting the importance of local microenvironments that vary even over molecular distances. While this singleâmolecule approach can provide viable information on the effects of ligand arrangements on bidentate protein binding, inâdepth investigations into the nature of local microenvironments will be required to exploit its full potential
FeMn with Phases of a Degradable Ag Alloy for Residue-Free and Adapted Bioresorbability
The development of bioresorbable materials for temporary implantation enables progress in medical technology. Iron (Fe)-based degradable materials are biocompatible and exhibit good mechanical properties, but their degradation rate is low. Aside from alloying with Manganese (Mn), the creation of phases with high electrochemical potential such as silver (Ag) phases to cause the anodic dissolution of FeMn is promising. However, to enable residue-free dissolution, the Ag needs to be modified. This concern is addressed, as FeMn modified with a degradable Ag-Calcium-Lanthanum (AgCaLa) alloy is investigated. The electrochemical properties and the degradation behavior are determined via a static immersion test. The local differences in electrochemical potential increase the degradation rate (low pH values), and the formation of gaps around the Ag phases (neutral pH values) demonstrates the benefit of the strategy. Nevertheless, the formation of corrosion-inhibiting layers avoids an increased degradation rate under a neutral pH value. The complete bioresorption of the material is possible since the phases of the degradable AgCaLa alloy dissolve after the FeMn matrix. Cell viability tests reveal biocompatibility, and the antibacterial activity of the degradation supernatant is observed. Thus, FeMn modified with degradable AgCaLa phases is promising as a bioresorbable material if corrosion-inhibiting layers can be diminished
Corrosion fatigue behavior of electron beam melted iron in simulated body fluid
Pure iron is very attractive as a biodegradable implant material due to its high biocompatibility. In combination with additive manufacturing, which facilitates great flexibility of the implant design, it is possible to selectively adjust the microstructure of the material in the process, thereby control the corrosion and fatigue behavior. In the present study, conventional hot-rolled (HR) pure iron is compared to pure iron manufactured by electron beam melting (EBM). The microstructure, the corrosion behavior and the fatigue properties were studied comprehensively. The investigated sample conditions showed significant differences in the microstructures that led to changes in corrosion and fatigue properties. The EBM iron showed significantly lower fatigue strength compared to the HR iron. These different fatigue responses were observed under purely mechanical loading as well as with superimposed corrosion influence and are summarized in a model that describes the underlying failure mechanisms
Large-area deposition of protective (Ti,Al)N coatings onto polycarbonate
Polycarbonate (PC) and protective (Ti,Al)N coatings exhibit extremely
different material properties, specifically crystal structure, thermal
stability, elastic and plastic behavior as well as thermal expansion
coefficients. These differences present formidable challenges for the
deposition process development as low-temperature synthesis routes have to be
explored to avoid a thermal overload of the polymer substrate. Here, a
large-area sputtering process is developed to address the challenges by
systematically adjusting target peak power density and duty cycle. Adhering
(Ti,Al)N coatings with a critical residual tensile stress of 2.2 +/- 0.2 GPa
are obtained in the pulsed direct current magnetron sputtering range, whereas
depositions at higher target peak power densities, realized by high power
pulsed magnetron sputtering, lead to stress-induced adhesive and/or cohesive
failure. The stress-optimized (Ti,Al)N coatings deposited onto PC with a target
peak power density of 0.036 kW cm-2 and a duty cycle of 5.3% were investigated
by cross-cut test confirming adhesion. By investigating the bond formation at
the PC | (Ti,Al)N interface, mostly interfacial CNx bonds and a small fraction
of (C-O)-(Ti,Al) bonds are identified by X-ray photoelectron spectroscopy,
indicating reactions at the hydrocarbon and the carbonate groups during
deposition. Nanoindentation reveals an elastic modulus of 296 +/- 18 GPa for
the (Ti,Al)N coating, while a Ti-Al-O layer is formed during electrochemical
impedance spectroscopy in a borate buffer solution, indicating protective
passivation. This work demonstrates that the challenge posed by the extremely
different material properties at the interface of soft polymer substrates and
hard coatings can be addressed by systematical variation of the pulsing
parameters to reduce the residual film stress
Chemical composition and barrier properties of Ag nanoparticle-containing solâgel films in oxidizing and reducing low-temperature plasmas
Effect of concentration on the adsorption of organophosphonic acids on nanocrystalline ZnO surfaces
The effect of the presence of Zn2+ ions on the adsorption of octadecylphosphonic acid (ODPA) on nanocrystalline
ZnO films has been studied by means of Quartz Crystal Microbalance (QCM) technique and complementary exsitu analysis of film properties. Phosphonic acid moiety has sufficient acidity, even in organic solvents, to cause
dissolution of ZnO. Dissolved Zn2+ ions form complexes with the ODPA molecules in the solution, leading to
the deposition of thick and undefined precipitation layers. Our results indicate that the formation of such precipitation layers could be prevented by the addition of appropriate amounts of Zn2+ ions into the deposition solution. Bi-functional monomolecular linkers with phosphonic acid head-groups are excellent candidates for
application-specific functionalization of nanostructured ZnO films as well as ZnO nanoparticles. The results presented here demonstrate a straight forward method to increase the film qualit
Time-Dependent DNA Origami Denaturation by Guanidinium Chloride, Guanidinium Sulfate, and Guanidinium Thiocyanate
Guanidinium (Gdm) undergoes interactions with both hydrophilic and hydrophobic groups and, thus, is a highly potent denaturant of biomolecular structure. However, our molecular understanding of the interaction of Gdm with proteins and DNA is still rather limited. Here, we investigated the denaturation of DNA origami nanostructures by three Gdm salts, i.e., guanidinium chloride (GdmCl), guanidinium sulfate (Gdm2SO4), and guanidinium thiocyanate (GdmSCN), at different temperatures and in dependence of incubation time. Using DNA origami nanostructures as sensors that translate small molecular transitions into nanostructural changes, the denaturing effects of the Gdm salts were directly visualized by atomic force microscopy. GdmSCN was the most potent DNA denaturant, which caused complete DNA origami denaturation at 50 °C already at a concentration of 2 M. Under such harsh conditions, denaturation occurred within the first 15 min of Gdm exposure, whereas much slower kinetics were observed for the more weakly denaturing salt Gdm2SO4 at 25 °C. Lastly, we observed a novel non-monotonous temperature dependence of DNA origami denaturation in Gdm2SO4 with the fraction of intact nanostructures having an intermediate minimum at about 40 °C. Our results, thus, provide further insights into the highly complex GdmâDNA interaction and underscore the importance of the counteranion species
Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD)
Densely
sintered aluminum oxide (α-Al<sub>2</sub>O<sub>3</sub>) is chemically
and biologically inert. To improve the interaction
with biomolecules and cells, its surface has to be modified prior
to use in biomedical applications. In this study, we compared two
deposition techniques for adhesion promoting SiO<sub><i>x</i></sub> films to facilitate the coupling of stable organosilane monolayers
on monolithic α-alumina; physical vapor deposition (PVD) by
thermal evaporation and plasma enhanced chemical vapor deposition
(PE-CVD). We also investigated the influence of etching on the formation
of silanol surface groups using hydrogen peroxide and sulfuric acid
solutions. The film characteristics, that is, surface morphology and
surface chemistry, as well as the film stability and its adhesion
properties under accelerated aging conditions were characterized by
means of X-ray photoelectron spectroscopy (XPS), energy dispersive
X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively
coupled plasmaâoptical emission spectroscopy (ICP-OES), and
tensile strength tests. Differences in surface functionalization were
investigated via two model organosilanes as well as the cell-cytotoxicity
and viability on murine fibroblasts and human mesenchymal stromal
cells (hMSC). We found that both SiO<sub><i>x</i></sub> interfaces
did not affect the cell viability of both cell types. No significant
differences between both films with regard to their interfacial tensile
strength were detected, although failure mode analyses revealed a
higher interfacial stability of the PE-CVD films compared to the PVD
films. Twenty-eight day exposure to simulated body fluid (SBF) at
37 °C revealed a partial delamination of the thermally deposited
PVD films whereas the PE-CVD films stayed largely intact. SiO<sub><i>x</i></sub> layers deposited by both PVD and PE-CVD
may thus serve as viable adhesion-promoters for subsequent organosilane
coupling agent binding to α-alumina. However, PE-CVD appears
to be favorable for long-term direct film exposure to aqueous solutions
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