Peptidic biofunctionalization of laser patterned dental zirconia: A biochemical-topographical approach.

A dual approach employing peptidic biofunctionalization and laser micro-patterns on dental zirconia was explored, with the aim of providing a flexible tool to improve tissue integration of restorations. Direct laser interference patterning with a femtosecond Ti:Sapphire laser was employed, and two periodic grooved patterns were produced with a periodicity of 3 and 10 µm. A platform containing the cell-adhesive RGD and the osteogenic DWIVA peptides was used to functionalize the grooved surfaces. Topography and surface damage were characterized by confocal laser scanning (CLSM), scanning electron and scanning transmission electron microscopy techniques. The surface patterns exhibited a high homogeneity and subsurface damage was found in the form of nano-cracks and nano-pores, at the bottom of the valleys. Accelerated tests in water steam were carried out to assess hydrothermal degradation resistance, which slightly decreased after the laser treatment. Interestingly, the detrimental effects of the laser modification were reverted by a post-laser thermal treatment. The attachment of the molecule was verified trough fluorescence CLSM and X-ray photoelectron spectroscopy. Finally, the biological properties of the surfaces were studied in human mesenchymal stem cells. Cell adhesion, morphology, migration and differentiation were investigated. Cells on grooved surfaces displayed an elongated morphology and aligned along the patterns. On these surfaces, migration was greatly enhanced along the grooves, but also highly restricted in the perpendicular direction as compared to flat specimens. After biofunctionalization, cell number and cell area increased and well-developed cell cytoskeletons were observed. However, no effects on cell migration were found for the peptidic platform. Although some osteogenic potential was found in specimens grooved with a periodicity of 10 µm, the largest effects were observed from the biomolecule, which favored upregulation of several genes related to osteoblastic differentiation in all the surfaces.

Eutectic modification by ternary compound cluster formation in Al-Si alloys.

Al-alloys with Si as the main alloying element constitute the vast majority of Al castings used commercially today. The eutectic Si microstructure in these alloys can be modified from plate-like to coral-like by the addition of a small amount of a third element to improve ductility and toughness. In this investigation the effects of Eu and Yb are studied and their influence on the microstructure is compared to further understand this modification. The two elements impact the alloy differently, where Eu modifies Si into a coral-like structure while Yb does not. Atom probe tomography shows that Eu is present within the Si phase in the form of ternary compound Al2Si2Eu clusters, while Yb is absent in the Si phase. This indicates that the presence of ternary compound clusters within Si is a necessary condition for the formation of a coral-like structure. A crystallographic orientation relationship between Si and the Al2Si2Eu phase was found, where the following plane normals are parallel: 011Si//0001Al2Si2Eu, 111Si//6[Formula: see text]10Al2Si2Eu and 011Si//6[Formula: see text]10Al2Si2Eu. No crystallographic relationship was found between Si and Al2Si2Yb. The heterogeneous formation of coherent Al2Si2Eu clusters inside the Si-phase is suggested to trigger the modification of the microstructure.

Mechanical reliability of dental grade zirconia after laser patterning.

The aim of this work is to test the mechanical properties of dental zirconia surfaces patterned with Nd:YAG laser interference (λ = 532 nm and 10 ns pulse). The laser treatment produces an alteration of the topography, engraving a periodic striped pattern. Laser-material interaction results mainly in thermal effects producing microcracking, phase transformation and texturization. The role of such microstructural modifications and collateral damage on the integrity and mechanical performances has been assessed. Laser patterned discs of zirconia doped with 3% mol yttria (3Y-TZP) have been tested before and after a thermal treatment to anneal residual stresses and revert phase transformation. Both groups of samples behave in a similar manner, excluding residual stresses and phase transformation from the origin of properties modification. Result show that laser patterning induces a minor decrease in mechanical properties and surface integrity of 3Y-TZP surfaces. The biaxial strength decreases as a consequence of the damage induced by laser patterning. Fractographic observations identify preexisting defects enlarged by local laser interaction as the fracture origins. The Hardness and Young modulus of treated surfaces tested with nanoindentation also decrease slightly after laser treatment and this may be attributed to laser-induced microcracking.

Pure and Oxidized Copper Materials as Potential Antimicrobial Surfaces for Spaceflight Activities.

Microbial biofilms can lead to persistent infections and degrade a variety of materials, and they are notorious for their persistence and resistance to eradication. During long-duration space missions, microbial biofilms present a danger to crew health and spacecraft integrity. The use of antimicrobial surfaces provides an alternative strategy for inhibiting microbial growth and biofilm formation to conventional cleaning procedures and the use of disinfectants. Antimicrobial surfaces contain organic or inorganic compounds, such as antimicrobial peptides or copper and silver, that inhibit microbial growth. The efficacy of wetted oxidized copper layers and pure copper surfaces as antimicrobial agents was tested by applying cultures of Escherichia coli and Staphylococcus cohnii to these metallic surfaces. Stainless steel surfaces were used as non-inhibitory control surfaces. The production of reactive oxygen species and membrane damage increased rapidly within 1 h of exposure on pure copper surfaces, but the effect on cell survival was negligible even after 2 h of exposure. However, longer exposure times of up to 4 h led to a rapid decrease in cell survival, whereby the survival of cells was additionally dependent on the exposed cell density. Finally, the release of metal ions was determined to identify a possible correlation between copper ions in suspension and cell survival. These measurements indicated a steady increase of free copper ions, which were released indirectly by cells presumably through excreted complexing agents. These data indicate that the application of antimicrobial surfaces in spaceflight facilities could improve crew health and mitigate material damage caused by microbial contamination and biofilm formation. Furthermore, the results of this study indicate that cuprous oxide layers were superior to pure copper surfaces related to the antimicrobial effect and that cell density is a significant factor that influences the time dependence of antimicrobial activity. Key Words: Contact killing-E. coli-S. cohnii-Antimicrobial copper surfaces-Copper oxide layers-Human health-Planetary protection. Astrobiology 17, 1183-1191.

Room temperature self-assembled growth of vertically aligned columnar copper oxide nanocomposite thin films on unmatched substrates.

In this work, we report the self-assembled growth of vertically aligned columnar Cu2O + Cu4O3 nanocomposite thin films on glass and silicon substrates by reactive sputtering at room temperature. Microstructure analyses show that each phase in nanocomposite films has the columnar growth along the whole thickness, while each column exhibits the single phase characteristics. The local epitaxial growth behavior of Cu2O is thought to be responsible for such an unusual microstructure. The intermediate oxygen flow rate between those required to synthesize single phase Cu2O and Cu4O3 films produces some Cu2O nuclei, and then the local epitaxial growth provides a strong driving force to promote Cu2O nuclei to grow sequentially, giving rise to Cu2O columns along the whole thickness. Lower resistivity has been observed in such kind of nanocomposite thin films than that in single phase thin films, which may be due to the interface coupling between Cu2O and Cu4O3 columns.

Long-lasting solid lubrication by CNT-coated patterned surfaces.

The use of lubricants (solid or liquid) is a well-known and suitable approach to reduce friction and wear of moving machine components. Another possibility to influence the tribological behaviour is the formation of well-defined surface topographies such as dimples, bumps or lattice-like pattern geometries by laser surface texturing. However, both methods are limited in their effect: surface textures may be gradually destroyed by plastic deformation and lubricants may be removed from the contact area, therefore no longer properly protecting the contacting surfaces. The present study focuses on the combination of both methods as an integral solution, overcoming individual limitations of each method. Multiwall carbon nanotubes (MWCNT), a known solid lubricant, are deposited onto laser surface textured samples by electrophoretic deposition. The frictional behaviour is recorded by a tribometer and resulting wear tracks are analysed by scanning electron microscopy and Raman spectroscopy in order to reveal the acting tribological mechanisms. The combined approach shows an extended, minimum fivefold longevity of the lubrication and a significantly reduced degradation of the laser textures. Raman spectroscopy proves decelerated MWCNT degradation and oxide formation in the contact. Finally, a lubricant entrapping model based on surface texturing is proposed and demonstrated.

Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials.

Established and already commercialized energetic materials, such as those based on Ni/Al for joining, lack the adequate combination of high energy density and ductile reaction products. To join components, this combination is required for mechanically reliable bonds. In addition to the improvement of existing technologies, expansion into new fields of application can also be anticipated which triggers the search for improved materials. Here, we present a comprehensive characterization of the key parameters that enables us to classify the Ru/Al system as new reactive material among other energetic systems. We finally found that Ru/Al exhibits the unusual integration of high energy density and ductility. For example, we measured reaction front velocities up to 10.9 (± 0.33) ms(-1) and peak reaction temperatures of about 2000 °C indicating the elevated energy density. To our knowledge, such high temperatures have never been reported in experiments for metallic multilayers. In situ experiments show the synthesis of a single-phase B2-RuAl microstructure ensuring improved ductility. Molecular dynamics simulations corroborate the transformation behavior to RuAl. This study fundamentally characterizes a Ru/Al system and demonstrates its enhanced properties fulfilling the identification requirements of a novel nanoscaled energetic material.

Structural evolution and strain induced mixing in Cu-Co composites studied by transmission electron microscopy and atom probe tomography.

A Cu-Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu-26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain.

3D and 2D structural characterization of 1D Al/Al2 O3 biphasic nanostructures.

1D Al/Al2 O3 nanostructures have been synthesized by chemical vapour deposition (CVD) of the molecular precursor [(t) BuOAlH2 ]2 . The deposited nanostructures grow chaotically on the substrate forming a layer with a high porosity (80%). Depending on the deposition time, diverse nanostructured surfaces with different distribution densities were achieved. A three-dimensional (3D) reconstruction has been evaluated for every nanostructure density using the Focus Ion Beam (FIB) tomography technique and reconstruction software tools. Several structural parameters such as porosity, Euler number, geometrical tortuosity and aspect ratio have been quantified through the analysis with specified software of the reconstructions. Additionally roughness of the prepared surfaces has been characterized at micro- and nanoscale using profilometry and AFM techniques, respectively. While high aspects ratio around 20-30 indicates a strong anisotropy in the structure, high porosity values (around 80%) is observed as a consequence of highly tangled geometry of such 1D nanostructures.

A direct and quantitative image of the internal nanostructure of nonordered porous monolithic carbon using FIB nanotomography.

A direct study of the shape, size and connectivity of nonordered pores in carbon materials is particularly challenging. A new method that allows direct three-dimensional (3D) investigations of mesopores in monolithic carbon materials and quantitative characterization of their physical properties (surface area and pore size distribution) is reported. Focused ion beam (FIB) nanotomography technique is performed by combination of focused ion beam and scanning electron microscope. Porous monolithic carbon is produced by carbonization of a resorcinol-formaldehyde gel in the presence of a cationic polyelectrolyte as a pore stabilizer.

TEM foil preparation of sub-micrometre sized individual grains by focused ion beam technique.

Analysis of presolar silicate grains provides new knowledge on interstellar and circumstellar environments and can be used to test models of the Galactic chemical evolution. However, structural information of these grains is rare because sample preparation for transmission electron microscopy is very difficult due to the small dimensions of these grains (<0.5 mum). With the use of the focused ion beam technique thin foils from these grains for transmission electron microscopy analysis can be prepared. Nevertheless, reaching the required precision of some tens of nanometres for the preparation of the transmission electron microscopy foil in the place of interest is not trivial. Furthermore, in the current samples, the grain of interest can only be identified by its different isotopic composition; i.e. there is no contrast difference in scanning electron microscopy or transmission electron microscopy images which allow the identification of the grain. Therefore, the grain has to be marked in some way before preparing the transmission electron microscopy foil. In the present paper, a method for transmission electron microscopy foil preparation of grains about 200 to 400 nm in diameter is presented. The method utilizes marking of the grain by Pt deposition and milling of holes to aid in the exact orientation of the transmission electron microscopy foil with respect to the grain. The proposed method will be explained in detail by using an example grain.

Site-specific structural investigations of oxidized nickel samples modified by plasma erosion processes.

A focused ion beam was employed for local target preparation for EBSD analysis. The volume of the ion-solid interaction is well below 50 nm at glancing incidence for metallic and transition metal oxide samples. Therefore, focused ion beam can successfully be used for electron backscatter diffraction (EBSD) sample preparation. The sample investigated consists of Ni covered with a NiO layer of approximately 5 microm thickness. Focused ion beam cross-sectioning of these layers and subsequent electron imaging in addition to EBSD maps shows a bimodal structure of the oxide layer. In order to test the potential of such oxidized samples as electrode materials, single spark erosion experiments were performed. The erosion craters have diameters up to 40 microm and have a depth corresponding to the thickness of the oxide layer. In addition, a deformation zone produced by thermoshock accompanies the formation of the crater. This deformation zone was further investigated by EBSD analysis using a new way of sample preparation employing the focused ion beam technology. This target preparation routine is called Volume of Interest Transfer and has the potential of providing a full three-dimensional characterization.