Composition and Surface Optical Properties of GaSe:Eu Crystals before and after Heat Treatment.

This work studies the technological preparation conditions, morphology, structural characteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped ß-Ga2O3 nanoformations on ε-GaSe:Eu single crystal substrate, obtained by heat treatment at 750-900 °C, with a duration from 30 min to 12 h, in water vapor-enriched atmosphere, of GaSe plates doped with 0.02-3.00 at. % Eu. The defects on the (0001) surface of GaSe:Eu plates serve as nucleation centers of ß-Ga2O3:Eu crystallites. For 0.02 at. % Eu doping, the fundamental absorption edge of GaSe:Eu crystals at room temperature is formed by n = 1 direct excitons, while at 3.00 at. % doping, Eu completely shields the electron-hole bonds. The band gap of nanostructured ß-Ga2O3:Eu layer, determined from diffuse reflectance spectra, depends on the dopant concentration and ranges from 4.64 eV to 4.87 eV, for 3.00 and 0.05 at. % doping, respectively. At 0.02 at. % doping level, the PL spectrum of ε-GaSe:Eu single crystals consists of the n = 1 exciton band, together with the impurity band with a maximum intensity at 800 nm. Fabry-Perrot cavities with a width of 9.3 µm are formed in these single crystals, which determine the interference structure of the impurity PL band. At 1.00-3.00 at. % Eu concentrations, the PL spectra of GaSe:Eu single crystals and ß-Ga2O3:Eu nanowire/nanolamellae layers are determined by electronic transitions of Eu2+ and Eu3+ ions.

Plasma-Engineering of Oxygen Vacancies on NiCo2O4 Nanowires with Enhanced Bifunctional Electrocatalytic Performance for Rechargeable Zinc-air Battery.

Designing an efficient, durable, and inexpensive bifunctional electrocatalyst toward oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) remains a significant challenge for the development of rechargeable zinc-air batteries (ZABs). The generation of oxygen vacancies plays a vital role in modifying the surface properties of transition-metal-oxides (TMOs) and thus optimizing their electrocatalytic performances. Herein, a H2/Ar plasma is employed to generate abundant oxygen vacancies at the surfaces of NiCo2O4 nanowires. Compared with the Ar plasma, the H2/Ar plasma generated more oxygen vacancies at the catalyst surface owing to the synergic effect of the Ar-related ions and H-radicals in the plasma. As a result, the NiCo2O4 catalyst treated for 7.5 min in H2/Ar plasma exhibited the best bifunctional electrocatalytic activities and its gap potential between Ej = 10 for OER and E1/2 for ORR is even smaller than that of the noble-metal-based catalyst. In situ electrochemical experiments are also conducted to reveal the proposed mechanisms for the enhanced electrocatalytic performance. The rechargeable ZABs, when equipped with cathodes utilizing the aforementioned catalyst, achieved an outstanding charge-discharge gap, as well as superior cycling stability, outperforming batteries employing noble-metal catalyst counterparts.

Surface modification by plasma etching impairs early vascularization and tissue incorporation of porous polyethylene (Medpor® ) implants.

Porous polyethylene (Medpor®) is commonly used in craniofacial reconstructive surgery. Rapid vascularization and tissue incorporation are crucial for the prevention of migration, extrusion, and infection of the biomaterial. Therefore, we analyzed whether surface modification by plasma etching may improve the early tissue response to Medpor®. Medpor® samples were treated in a plasma chamber at low (20 W; LE-PE) and high energy levels (40 W; HE-PE). The samples and non-treated controls were implanted into mouse dorsal skinfold chambers to analyze angiogenesis, inflammation, and granulation tissue formation over 14 days using intravital fluorescence microscopy, histology, and immunohistochemistry. Scanning electron microscopy (SEM) analyses revealed that elevating energy levels of plasma etching progressively increase the oxygen surface content and surface roughness of Medpor®. This did not affect the leukocytic response to the implants. However, LE-PE and HE-PE samples exhibited an impaired vascularization. This was associated with a reduced formation of a collagen-rich granulation tissue at the implantation site. Additional in vitro experiments showed a reduced cell attachment on plasma-etched Medpor®. Thus, plasma etching may not be recommended to improve the clinical outcome of reconstructive interventions using Medpor®. However, it may be beneficial for temporarily implanted polyethylene-based biomedical devices for which tissue incorporation is undesirable. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1738-1748, 2016.

Recombinant Phage Coated 1D Al2O3 Nanostructures for Controlling the Adhesion and Proliferation of Endothelial Cells.

A novel synthesis of a nanostructured cell adhesive surface is investigated for future stent developments. One-dimensional (1D) Al2O3 nanostructures were prepared by chemical vapor deposition of a single source precursor. Afterwards, recombinant filamentous bacteriophages which display a short binding motif with a cell adhesive peptide (RGD) on p3 and p8 proteins were immobilized on these 1D Al2O3 nanostructures by a simple dip-coating process to study the cellular response of human endothelial EA hy.926. While the cell density decreased on as-deposited 1D Al2O3 nanostructures, we observed enhanced cell proliferation and cell-cell interaction on recombinant phage overcoated 1D Al2O3 nanostructures. The recombinant phage overcoating also supports an isotropic cell spreading rather than elongated cell morphology as we observed on as-deposited Al2O3 1D nanostructures.

Differential Behavior of Fibroblasts and Epithelial Cells on Structured Implant Abutment Materials: A Comparison of Materials and Surface Topographies.

PURPOSE: The aim of this study was to compare the proliferation and attachment behavior of fibroblasts and epithelial cells on differently structured abutment materials. MATERIALS AND METHODS: Three different surface topographies were prepared on zirconia and titanium alloy specimens and defined as follows: machined (as delivered without further surface modification), smooth (polished), and rough (sandblasted). Energy-dispersive X-ray spectroscopy, topographical analysis, and water contact angle measurements were used to analyze the surface properties. Fibroblasts (HGF1) and epithelial cells (HNEpC) grown on the specimens were investigated 24 hours and 72 hours after seeding and counted using fluorescence imaging. To investigate adhesion, the abundance and arrangement of the focal adhesion protein vinculin were evaluated by immunocytochemistry. RESULTS: Similar surface topographies were created on both materials. Fibroblasts exhibited significant higher proliferation rates on comparable surface topographies of zirconia compared with the titanium alloy. The proliferation of fibroblasts and epithelial cells was optimal on different substrate/topography combinations. Cell spreading was generally higher on polished and machined surfaces than on sandblasted surfaces. Rough surfaces provided favorable properties in terms of cellular adhesion of fibroblasts but not of epithelial cells. CONCLUSIONS: Our data support complex soft tissue cell-substrate interactions: the fibroblast and epithelial cell response is influenced by both the material and surface topography.

Induction of osteogenic differentiation by nanostructured alumina surfaces.

Permanent orthopedic implants are becoming increasingly important due to the demographic development. Their optimal osseointegration is key in obtaining good secondary stability. For anchorage dependent cells, topographic features of a surface play an essential role for cell adhesion, proliferation, differentiation and biomineralization. We studied the topographical effect of nanostructured alumina surfaces prepared by chemical vapor deposition on osteogenic differentiation and growth of human osteoblasts. Chemical vapor deposition of the single source precursor (tBuOAIH2)2 led to synthesis of one dimensional alumina nanostructures of high purity with a controlled stoichiometry. We fabricated different topographic features by altering the distribution density of deposited one dimensional nanostructures. Although the topography differed, all surfaces exhibited identical surface chemistry, which is the key requirement for systematically studying the effect of the topography on cells. Forty-eight hours after seeding, cell density and cell area were not affected by the nanotopography, whereas metabolic activity was reduced and formation of actin-fibres and focal adhesions was impaired compared to the uncoated control. Induction of osteogenic differentiation was demonstrated via up-regulation of alkaline phosphatase, bone sialoprotein, osteopontin and Runx2 at the mRNA level, demonstrating the potential of nanostructured surfaces to improve the osseointegration of permanent implants.

Development of multi scale structured Al/AI2O3 nanowires for controlled cell guidance.

Cell responses to surface and contact cell guidance are of great interest in bio-applications especially on nano- and micro scale features. Recently we showed selective cell responses on Al/Al2O3, bi-phasic nanowires (NWs). In this context, Al/Al2O3 NWs were synthesized by the chemical vapor deposition of (tBuOAIH2)2. Afterwards, linear periodic nano- and micro structured NWs were formed using laser interference lithography (LIL) technique to study the contact guidance of neurons from rat dorsal root ganglion (DRG), human umbilical vein smooth muscle cells (HUVSMC), human umbilical vein endothelial cells (HUVEC) and human osteoblast (HOB). LIL treatment did not alter surface chemistry of NWs. From our preliminary research LIL patterned NWs lead to alignment of axons contrary to non-patterned NWs. Morphology of HUVSMC changed from poly- to linear shapes and strong alignment was observed while HUVEC and HOB were not affected.

Femtosecond laser treatment of 316L improves its surface nanoroughness and carbon content and promotes osseointegration: An in vitro evaluation.

Cell-material surface interaction plays a critical role in osseointegration of prosthetic implants used in orthopedic surgeries and dentistry. Different technical approaches exist to improve surface properties of such implants either by coating or by modification of their topography. Femtosecond laser treatment was used in this study to generate microspotted lines separated by 75, 125, or 175µm wide nanostructured interlines on stainless steel (316L) plates. The hydrophobicity and carbon content of the metallic surface were improved simultaneously through this method. In vitro testing of the laser treated plates revealed a significant improvement in adhesion of human endothelial cells and human bone marrow mesenchymal stem cells (hBM MSCs), the cells involved in microvessel and bone formation, respectively, and a significant decrease in fibroblast adhesion, which is implicated in osteolysis and aseptic loosening of prostheses. The hBM MSCs showed an increased bone formation rate on the laser treated plates under osteogenic conditions; the highest mineral deposition was obtained on the surface with 125µm interline distance (292±18mg/cm(2) vs. 228±43mg/cm(2) on untreated surface). Further in vivo testing of these laser treated surfaces in the native prosthetic implant niche would give a real insight into their effectiveness in improving osseointegration and their potential use in clinical applications.

Ultra-rapid growth of biphasic nanowires in micro- and hypergravity.

Aluminium/aluminium oxide wires form under microgravity, earth conditions, and hypergravity in different forms. While under 0.04 G the biphasic wires are predominantly linear, they form bundles of wires of high curvature at 1 G and 1.8 G. The absence (0.04 G) and presence (1 G, 1.8 G) of gradients are reflected by the agglomeration and growth direction of the nanowires.

Reduced myofibroblast differentiation on femtosecond laser treated 316LS stainless steel.

In-stent restenosis is a common complication after stent surgery which leads to a dangerous wall narrowing of a blood vessel. Laser assisted patterning is one of the effective methods to modify the stent surface to control cell-surface interactions which play a major role in the restenosis. In this current study, 316 LS stainless steel substrates are structured by focusing a femtosecond laser beam down to a spot size of 50 µm. By altering the laser induced spot density three distinct surfaces (low density (LD), medium density (MD) and high density (HD)) were prepared. While such surfaces are composed of primary microstructures, due to fast melting and re-solidification by ultra-short laser pulses, nanofeatures are also observed as secondary structures. Following a detailed surface characterization (chemical and physical properties of the surface), we used a well-established co-culture assay of human microvascular endothelial cells and human fibroblasts to check the cell compatibility of the prepared surfaces. The surfaces were analyzed in terms of cell adherence, proliferation, cell morphology and the differentiation of the fibroblast into the myofibroblast, which is a process indicating a general fibrotic shift within a certain tissue. It is observed that myofibroblast proliferation decreases significantly on laser treated samples in comparison to non-treated ones. On the other hand endothelial cell proliferation is not affected by the surface topography which is composed of micro- and nanostructures. Such surfaces may be used to modify stent surfaces for prevention or at least reduction of restenosis.