Scientific publications

Light is fundamental to life on earth. Therefore, nature has evolved a multitude of photoreceptors that sense light across all kingdoms. This natural resource provides synthetic biology with a vast pool of light-sensing components with distinct spectral properties that can be harnessed to engineer novel optogenetic tools. These devices enable control over gene expression, cell morphology and signaling pathways with superior spatiotemporal resolution and are maturing towards elaborate applications in basic research, in the production of biopharmaceuticals and in biomedicine. This article provides a summary of the recent advances in optogenetics that use light for the precise control of biological functions in mammalian cells. © 2013 The Royal Society of Chemistry.

Time-resolved quantitative analysis of auxin-mediated processes in plant cells is as of yet limited. By applying a synergistic mammalian and plant synthetic biology approach, we have developed a novel ratiometric luminescent biosensor with wide applicability in the study of auxin metabolism, transport, and signalling. The sensitivity and kinetic properties of our genetically encoded biosensor open new perspectives for the analysis of highly complex auxin dynamics in plant growth and development.

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.

Alanes of the formula HxAlX3–x (x = 0, 1, 2, 3; X = Cl, Br, I) and the mixed halogen species HAlClBr were synthesized as N-methyl-piperidin (nmp) adducts HxAlX3–x·znmp (z = 1, 2) and HAlClBr·2nmp by different routes. The crystal and molecular structures of (H3Al·nmp)2, H2AlBr·2nmp, H2AlI·2nmp, the isotypic and isomorphous HAlBr2·2nmp, HAlI2·2nmp, as well as ACl3·nmp, ABr3·nmp, AI3·nmp, and HAlClBr·2nmp are described. The aluminum atoms in these molecular structures either form a pentagonal bipyramid as coordination sphere with the amine bases in apical positions or are in the center of a distorted tetrahedron (AlCl3·nmp, ABr3·nmp, AI3·nmp). In the nmp adduct of alane, a central Al2H2 ring is formed by dimerisation of AlH3, each aluminum atom displaying a further nmp ligand together with two terminal hydrogen atoms. The influence of the halogen atoms on the hydrogen bonds in the iso-structural compounds were studied by IR spectroscopy, showing in both series H2AlX·2nmp and HAlX2·2nmp (X = Cl, Br, I) a dependence of ν(Al–H) on the substitution pattern: 1770.2–1775.2–(not measured) cm–1 (H2AlX) and 1785.0–1788.0–1791.0 cm–1 (HAlX2). The δ values of the 27Al-NMR spectra in solution show dependences on the halide numbers bonded to aluminum and display a regular growth with heavier element in the H2AlX·2nmp series δ (27Al): 121.2 (Cl), 126.0 (Br), 131.5 (I)], whereas they have an unsteady evolution in the HAlX2·2nmp series [δ (27Al): 118.0 (Cl), 122.0 (Br), 108.0 (I)] and the AlX3·nmp series [δ (27Al): 102.1 (Cl), 104.8 (Br), 61.9 (I)].

The production of nano-calcium phosphate powders, such as HA (hydroxyapatite), from synthetic chemicals can be expensive and time consuming. The skeleton or shells of sea creatures (e.g. sea urchins, shells, corals) could be an alternative source of materials to produce very fine and even nano-structured calcium phosphate biomaterial powders. Ηydrothermal conversion under very high pressures or methods such as hot-plating (chemical) or ultrasonication (mechano-chemical), have been proposed to transform naturally derived CaCO3, e.g. aragonite, into apatite based materials. The aim of the present work was to prepare inexpensive nano-sized HA and TCP bioceramics powders from a local sea snail shells as a possible raw material for HA/TCP bioceramics. Empty shells of a local sea snail (Nassarius hinia reticulatus) from Marmara Sea, Turkey were collected from a beach near Istanbul. The collected shells were ground to a particle size 75μm. Thermal analyses (DTA/TGA) were performed to determine the exact CaCO3 content and thermal behavior. The raw powder was suspended in an aqueous media which was placed in an ultrasonic bath. The temperature was set at 80°C for 15min. Then, an equivalent (to CaO content) amount of H3PO4 was added drop by drop very gently into the solution. The reaction continued for 8h, following which the liquid component was evaporated off in an incubator at 100°C for 24h. The dried sediment was collected and heat treated at two different temperatures, 400 and 800°C. The morphology of the powders produced was examined using SEM. The crystalline phases were indentified using X-ray analysis.

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.