Publikationen

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, 316LS 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.

Modification of topography is an effective tool to control the cellular response such as cell function, adhesion and proliferation on surfaces. In this work, we present a novel method for fabrication of periodic surface structures by laser interference patterning (LIP) of biphasic Al/Al2O3 nanowires (NWs). These structures have a periodicity of 1-8 µm and a depth of 300-600 nm, depending on the incidence angle of the laser beam. Such hierarchical structures are composed of both micro- and nanofeatures. These periodic patterns lead to an alignment of glial cells and an axonal guidance from cultured dorsal root ganglia (DRG), along defined directions. The most pronounced alignment was seen at a periodicity of 2 µm.

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 175 μm 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 125 μm interline distance (292 ± 18 mg/cm2 vs. 228 ± 43 mg/cm2 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.

Al/Al2O3 bi-phasic nanowires (Al-core/Al2O3 shell) are prepared by chemical vapor deposition (CVD) using single source precursor (SSP) approach. Such bi-phasic nanostructures were heat-treated using an argon laser operating at visible wavelengths. Al core seems to act as an active binder, which might decrease the inhomogeneous heating and thermal gradients. Nanoindentation method is used to estimate the hardness of the laser treated surfaces. Hardness values and pop-in behaviour in loading-curve indicate a formation of α-Al2O3 with very low defect density. It is believed that Al/Al2O3 bi-phasic layers exhibit a dynamic change by transforming into alumina after the laser irradiation and this leads to alteration of the optical absorption especially in the visible wavelength region. Following the full transformation to alumina, the surface reflects back the laser light which hinders inhomogeneous and excessive heating. In this context, laser treatment of Al/Al2O3 bi-phasic nanowires provides a controlled sintering process which can open up various applications in different fields.

This paper reports the production of gold nanoparticles (NPs) with controlled morphology in an aqueous solution of sodium dodecyl sulfate (SDS) by Ti:Sapphire laser. When nanostructures were exposed to an additional laser irradiation/exposure at a particular wavelength corresponding to resonant excitation of surface plasmons or to an interband transition, a considerable size reduction of NPs from 78 nm to 15 nm has been achieved. This can simply be defined as size refining of NPs by a two-step laser ablation. The relationship between supercontinuum (SC) emission and absorption spectrum of gold NPs has been explored. Additionally the transformation of gold NPs into fractal-like structures has been examined. At longer exposure periods, it is observed that there is a tendency of assembling of NPs into one-dimensional (1d) nanostructures.

Plasma and laser treatments are used in combination to modify the wetting properties of polyetheretherketone (PEEK), which is one of the preferred polymers in various applications ranging from aerospace to medical devices. Wetting is a critical issue especially for biomedical applications of PEEK. Here we present a novel approach to create hierarchically patterned PEEK surfaces composed of nano- and microstructures. This method is fast, easy and applicable to large areas without using complicated lithography and mask-based techniques. We achieved surfaces exhibiting a wide spectrum of wetting ranging from super-hydrophilic to hydrophobic nature.

In a recent study, Wimalasiri and Zou [1] have reported the use and performance of composite electrodes of carbon nanotubes (CNT) and graphene for application as porous electrodes in capacitive deionization (CDI). While CDI is emerging as an attractive technology for water desalination, and novel electrode materials and composites are important contributions to the advancement of the field, there are several issues in this study that we must comment on.

Inflammatory activation of alveolar macrophages by ambient particles can be facilitated via Toll-like receptors (TLR). The action of TLR agonists and antagonists has been reported to depend on the formation of nanoparticulate structures. Aim of the present study was to identify the signaling pathways induced by nanoparticulate structures in human macrophages, which might be critical for inflammatory cell activation. Methods Studies were performed in primary human alveolar macrophages or in differentiated THP-1 macrophages. Silica nanoparticles were prepared by Stöber synthesis and characterized by dynamic light scattering and scanning electron microscopy. Mycobacterial DNA was isolated from Mycobacterium bovis BCG, and nanoparticle formation was assessed by atomic force microscopy and dynamic light scattering. Actin polymerization was measured by phalloidin-TRITC staining, and cell activation was determined by reverse transcription quantitative PCR analysis, L929 cytotoxicity assay (cytokine induction), and pull-down assays (Rho GTPases). Results In contrast to immune stimulatory sequence ISS 1018, BCG DNA spontaneously formed nanoparticulate structures and induced actin polymerization as did synthetic silica nanoparticles. Co-incubation with silica nanoparticles amplified the responsiveness of macrophages toward the TLR9 ligand ISS 1018. The activation of Rac1 was induced by silica nanoparticles as well as BCG DNA and is suggested as the critical signaling event inducing both cytoskeleton changes as well as inflammatory cell activation. Conclusion Nanoparticles can induce signaling pathways, which amplify an inflammatory response in macrophages.

Different types of tetragonal BaTiO3 particles were synthesized in a wet chemical process including an autoclave treatment. The synthesis and autoclaving medium was varied from isopropyl alcohol to water in different ratios, leading to a size variation of the particles from 38 to 145 nm. By applying combustion analysis of carbon and hydrogen (C/H analysis) released from the samples, it can be demonstrated that the amount of hydroxyl impurities incorporated into the crystal lattices of the particles increases with the water content of the synthesis medium. C/H analysis is a suitable tool for this characterization task as it allows discriminating different sources of these elements, i.e., different impurities. By comparing the self-synthesized particles with commercial ones, it can be concluded that the particle size has the dominant influence on the tetragonality, if the amount of internal hydroxyl groups is relatively low. In contrast, if the amount of water originating from the internal OH groups is elevated (greater than ~0.4 wt%) an impairment of the tetragonality is caused.

Nanocrystalline titanium oxide (TiO2) coatings with different phases and surface topographies were deposited using chemical vapor deposition (CVD) of different homo- and heteroleptic titanium precursors of general formula [XTi(OiPr)3] (X = Cl (1), -NEt2 (2), -N(SiMe3)2 (3), -C5H5 (4), -OiPr (5) and -OtBu (6)) to elucidate the influence of molecular configuration on resulting material properties. The interdependence of precursor chemistry and materials features of the CVD deposits was verified by performing film growth under similar conditions using different precursor molecules (1-6). Studies on composition (XPS), structure (SEM, XRD) and bio-functional properties (cell tests) revealed that the decomposition process is markedly influenced by the auxiliary ligands, which led to incorporation of heteroelements (Si, Cl, N) in the films. Cell tests performed to evaluate the biocompatibility of the coatings towards the growth of bone cells showed a pronounced correlation between cell adhesion and surface morphology as well as the chemical composition. Growth of osteoblast cells was strongly enhanced on films obtained using [Ti(OiPr)4] and [CpTi(OiPr)3], whereas TiO2 coatings produced by [ClTi(OiPr)3] significantly inhibited the cell growth and their proliferation due to Cl contamination. Also, the nanomorphological features of the films were found to stimulate the cell adhesion and growth.