Stefan Romeis

In vitro reactivity of Cu doped 45S5 Bioglass® derived scaffolds for bone tissue engineering

Cu-doped 45S5 bioactive glasses with varying Cu contents were fabricated and used to process 3D porous scaffolds via the foam replica technique. Cu-doping results in the weakening of the glass network and a decrease in its glass transition temperature. Acellular in vitro studies revealed very high bioactivity independent of Cu doping as indicated by the fast formation of a carbonated hydroxyapatite layer (CHA) on scaffold surfaces after immersion in simulated body fluid (SBF). The kinetics of the glass-ceramic scaffolds transition to an amorphous calcium phosphate layer (ACP) and the crystallisation of CHA were explored by FT-IR and SEM analyses. The elemental distribution in the scaffold/fluid interface region was monitored by the advanced micro-PIXE-RBS (particle induced X-ray emission/Rutherford backscattering spectrometry) method. Cu-containing glasses showed slower release of Si, Ca and P from the scaffold periphery, whereas traces of Cu were found incorporated in the CaP layer on the scaffold surface. Cu release kinetics from the scaffolds in SBF were found to depend on culturing conditions while highest Cu concentrations of ∼3.1 ppm and ∼4.6 ppm under static and quasi-dynamic conditions, respectively, were observed. Since Cu exhibits potential angiogenic and osteogenic properties, the Cu-containing scaffolds are suggested as promising materials for bone tissue engineering applications.

Noble-Metal-Free Photocatalytic Hydrogen Evolution Activity: The Impact of Ball Milling Anatase Nanopowders with TiH2.

Ball milling TiO2 anatase together with TiH2 can create an effective photocatalyst. The process changes the lattice and electronic structure of anatase. Lattice deformation created by mechanical impact combined with hydride incorporation yield electronic gap-states close to the conduction band of anatase. These provide longer lifetimes of photogenerated charge carriers and lead to an intrinsic cocatalytic activation of anatase for H2 evolution.

Biocompatibility of submicron Bioglass® powders obtained by a top-down approach.

In this study in vitro bioactivity and biocompatibility of two submicron 45S5 Bioglass® powders obtained by topdown processing have been evaluated and are compared to the as-received powder. Both submicron powders exhibited flake-like morphologies with lateral extensions of only a few microns; the flake thickness accounted for a few tens of nanometers. Enhanced in vitro bioactivity was found for the comminuted powders upon immersion in simulated body fluid. In vitro biocompatibility was evaluated by incubation of MG-63 osteoblast-like cells with various amounts (0–200 μg/mL) of the glass powders. Neither LDH-activity nor mitochondrial activity (WST-8) tests indicated cell toxicity. Increased mitochondrial activity was found for the submicron powders: incubation with high amounts revealed up to a threefold increase of osteoblast activity (ALP-activity). An overgrowth of the formed mineralized phase with phenotypical MG-63 cells was found by staining only for the submicron glasses. A distance ring is formed for the as-received powder. Superior bioactivity markers are found for shorter process times, that is, lower mass specific surface areas. This is attributed to the formation of carbonates during the comminution process.

From evaporation-induced self-assembly to shear-induced alignment.

The functionality of compact nanostructured thin films depends critically on the degree of order and hence on the underlying ordering mechanisms during film formation. For dip coating of rigid nanorods the counteracting mechanisms, evaporation-induced self-assembly (EISA) and shear-induced alignment (SIA) have recently been identified as competing ordering mechanisms. Here, we show how to achieve highly ordered and homogeneous thin films by controlling EISA and SIA in dip coating. Therefore we identify the influences of the process parameters including temperature, initial volume fraction and nanorod aspect ratio on evaporation-induced convective flow and externally applied shear forces and evaluate the resulting films. The impact of evaporation and shear can be distinguished by analysing film thickness, surface order and bulk order by careful in situ SAXS, Raman and SEM-based image analysis. For the first time we derive processing guidelines for the controlled application of EISA and SIA towards highly ordered thin nematic films.

Production of PBT/PC particle systems by wet grinding

Comminution of plastic or visco-elastic materials is known to be energy-intensive and costly. Typically impact mills, cutting mills and jet mills are applied for comminution and the feed material frequently is pre-cooled using liquid nitrogen or solid carbon dioxide. Therefore, especially the production of fine polymer particles by the aforementioned dry grinding methods is challenging. We demonstrate that wet grinding of polymers is a feasible approach for production of fine polymer particles that e.g. may be used as a starting material in a process chain for production of spherical polymer particles that can be used in in additive manufacturing. Wet comminution of polymers will be discussed for polybutylene terephthalate (PBT) and polycarbonate (PC). The products are thoroughly characterized by means of vibrational spectroscopy, X-ray diffraction and dynamic scanning calorimetry. The dependency of the grinding result on fundamental process parameters like stirrer tip speed, grinding media size, process time, process temperature and system composition will be discussed. In any case high load conditions, i.e. high stress energies are needed to initiate breakage of polymer materials. Optimization of the process with respect to process time and energy consumption by appropriate selection of process temperature and solvent will be addressed. The selection of appropriate solvents allows for remarkable reduction of mass-specific comminution energy needed.Comminution of plastic or visco-elastic materials is known to be energy-intensive and costly. Typically impact mills, cutting mills and jet mills are applied for comminution and the feed material frequently is pre-cooled using liquid nitrogen or solid carbon dioxide. Therefore, especially the production of fine polymer particles by the aforementioned dry grinding methods is challenging. We demonstrate that wet grinding of polymers is a feasible approach for production of fine polymer particles that e.g. may be used as a starting material in a process chain for production of spherical polymer particles that can be used in in additive manufacturing. Wet comminution of polymers will be discussed for polybutylene terephthalate (PBT) and polycarbonate (PC). The products are thoroughly characterized by means of vibrational spectroscopy, X-ray diffraction and dynamic scanning calorimetry. The dependency of the grinding result on fundamental process parameters like stirrer tip speed, grinding media size, process ...

A Novel Approach for Preparation and In Situ Tensile Testing of Silica Glass Membranes in the Transmission Electron Microscope

The mechanical behavior of glasses in the micro- and/or nanometer regime increasingly gains importance in nowadays modern technology. However, suitable small scale preparation and mechanical testing approaches for a reliable assessment of the mechanical properties of glasses still remain a big challenge. In the present work, a novel approach for site-specific preparation and quantitative in situ tensile testing of thin silica glass membranes in the transmission electron microscope is presented. Thereby, advanced focused ion beam techniques are used for the preparation of nanoscale dog bone shaped silica glass specimens suitable for in situ tensile testing. Small amounts of gallium are detected on the surface of the membranes resulting from redeposition effects during the focused ion beam preparation procedure. Possible structural changes of silica glass upon irradiation with electrons and gallium ions are investigated by controlled irradiation experiments, followed by a structural analysis using Raman spectroscopy. While moderate electron beam irradiation does not alter the structure of silica glass, ion beam irradiation results in minor densification of the silica glass membranes. In situ tensile testing of membranes under electron beam irradiation results in distinctive elongations without fracture confirming the phenomenon of superplasticity. In contrast, in situ tensile testing in the absence of the electron beam reveals an elastic/plastic deformation behavior, and finally leads to fracture of the membranes. The Young’s moduli of the glass membranes pulled at beam off conditions in the TEM are comparable with values known for bulk fused silica, while the tensile strength is in the range of values reported for silica glass fibers with comparable dimensions. The impact of electron beam irradiation on the mechanical properties of silica glass membranes is further discussed. The results of the present work open new avenues for dedicated preparation and nanomechanical characterization of silica glasses, and further contribute to a fundamental understanding of the mechanical behavior of such glasses when being scaled down to the nanometer regime.