Scientific publications

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.

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 (tBuOAlH2)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.

A novel approach to tracking intercalation-induced phase transitions in Li-ion battery materials demonstrated herein consists of simultaneous analysis of intercalation charge and the accompanying mechanical (geometric) changes in a microarray electrode composed of LixFePO4 intercalation particles probed by the electrochemical quartz-crystal admittance (EQCA) method. A recently elaborated approach to population dynamics of active (phase-transforming) nanoparticles has been used here for modeling current transients applying small potential steps to LixFePO4 electrodes. The number fraction of (phase) transformed particles thus calculated was directly compared with the changes in the effective thickness and permeability length of the electrode coating derived by EQCA. Geometric changes of thin active mass originating from different molar volumes of the parent and transformed phase result in nonuniform deformations of intercalation particles. This study confirms the collective behavior of LixFePO4 intercalation particles during electrochemically induced phase transition. The use of EQCA as a highly precise and sensitive probe of mass and geometric changes in the electrode layer of intercalation particles paves the way for dynamic in situ studies of nonuniform intercalation particles deformations which can hardly be assessed by other available techniques.

By decomposing a molecular precursor we fabricated a novel surface based on an aluminium/ aluminiumoxide composite incorporating nanotopography gradient to address high-throughput and fast analysis method for studying stem cell differentiation by nanostructures. Depending on the topography of the nanostructures, mesenchymal stem cells exhibit a diverse proliferation and differentiation behavior.

For a detailed analysis of the biological effects of silver nanoparticles, discrimination between effects related to the nano-scale size of the particles and effects of released silver ions is required. Silver ions are either present in the initial particle dispersion or released by the nanoparticles over time. The aim of this study is to monitor the free silver ion activity {Ag+} in the presence of silver nanoparticles using a silver ion selective electrode. Therefore, silver in the form of silver nanoparticles, 4.2 ± 1.4 nm and 2-30 nm in size, or silver nitrate was added to cell culture media in the absence or presence of A549 cells as a model for human type II alveolar epithelial cells. The free silver ion activity measured after the addition of silver nanoparticles was determined by the initial ionic silver content. The p {Ag+} values indicated that the cell culture media decrease the free silver ion activity due to binding of silver ions by constituents of the media. In the presence of A549 cells, the free silver ion activity was further reduced. The morphology of A549 cells, cultivated in DME medium containing 9.1% (v/v) FBS, was affected by adding AgNO3 at concentrations of ≥30 μM after 24 h. In comparison, silver nanoparticles up to a concentration of 200 μM Ag did not affect cellular morphology. Our experiments indicate that the effect of silver nanoparticles is mainly mediated by silver ions. An effect of silver on cellular morphology was observed at p {Ag+} ≤ 9.2.

Hochauflösungs-TEM/STEM spektroskopiert und bildet Strukturen atomar aufgelöst ab. Mit einer Mikrofluid-Probenkammer eignet sich das Elektronenmikroskop auch für In-situ-Untersuchungen zu lebens- und materialwissenschaftlichen Fragen.