Zirconia Nanoparticles Made in Spray Flames at High Production Rates

Synthesis of zirconia nanoparticles by flame spray pyrolysis (FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80–95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals.     

Artificial Light Regulation of an Allosteric Bienzyme Complex by a Photosensitive Ligand

The artificial regulation of proteins by light is an emerging subdiscipline of synthetic biology. Here, we used this concept to photocontrol both catalysis and allostery within the heterodimeric enzyme complex imidazole glycerol phosphate synthase (ImGP‐S). ImGP‐S consists of the cyclase subunit HisF and the glutaminase subunit HisH, which is allosterically stimulated by substrate binding to HisF. We show that a light‐sensitive diarylethene (1,2‐dithienylethene, DTE)‐based competitive inhibitor in its ring‐open state binds with low micromolar affinity to the cyclase subunit and displaces its substrate from the active site. As a consequence, catalysis by HisF and allosteric stimulation of HisH are impaired. Following UV‐light irradiation, the DTE ligand adopts its ring‐closed state and loses affinity for HisF, restoring activity and allostery. Our approach allows for the switching of ImGP‐S activity and allostery during catalysis and appears to be generally applicable for the light regulation of other multienzyme complexes.     

Binding of external ligands onto an engineered virus capsid

The development of novel delivery systems for therapeutic substancesincludes targeting of the carriers to a specific site or tissuewithin the body of the recipient. This can be accomplished byappropriate receptor-binding domains and requires linking ofthese domains to the carrier. We have used recombinantly expressedpolyomavirus-like particles as a model system and inserted thesequence of a WW domain into different surface loops of theviral capsid protein VP1. In one variant, the WW domain maintainedits highly selective binding properties of proline-rich ligandsand showed an increased affinity but also an accelerated association/dissociationequilibrium compared to the isolated WW domain, thus allowinga short-term coupling of external ligands onto the surface ofthe virus-like particles.     

Polyionic fusion peptides function as specific dimerization motifs

The de novo design of a molecular adapter for directed associationand covalent linkage of two polypeptides is presented. Usingpeptides containing charged amino acid residues and an additionalcysteine residue (AlaCysLys₈ and AlaCysGlu₈) we demonstratethat the electrostatic interaction promotes the associationof two synthetic peptides and, subsequently, disulfide bondformation. The reaction depends on both the redox potentialand on the ionic strength of the buffer. Varying the redox potential,the interaction of the peptides was quantified by a G^0' of 6.6± 0.2 kcal/mol. Heterodimerization of the peptides ishighly specific, a competition of association by other cysteinecontaining compounds could not be observed. Two proteins comprisingcysteine-containing polyionic fusion peptides, a modified Fabfragment and an -glucosidase fusion, could be specifically conjugatedby directed association and subsequent disulfide bond formation.Both proteins retain their functional characteristics withinthe bifunctional conjugate: enzymatic activity of the glucosidaseand antigen-binding capacity of the Fab fragment are equivalentto the non-conjugated components.     

Synthesis of Hard Materials by Field Activation: The Synthesis of Solid Solutions and Composites in the TiB2–WB2–CrB2 System

The synthesis of solid solutions of (Ti,W,Cr)B₂ from elemental reactants using the field-activated, pressure-assisted synthesis method and employing the SPS apparatus was investigated. The nature of the products depended on temperature; they were nearly pure solid solutions at 1900°C with minor amounts of β-WB. The product density and microhardness depended on the temperature of synthesis for the same value of applied pressure (64 MPa). Samples with the highest density (94%) corresponded to a hardness of 22.7 GPa. When annealed at 1500°C, the solid solutions decomposed, precipitating a (W,Ti,Cr)B₂ phase in a spinodal form. In addition, β-WB precipitates in the form of thin (0.4–5.3 nm) layers were observed. They existed in a 60°/120° orientation to the (Ti,W,Cr)B₂ matrix, in agreement with previous observations. Highly faceted, small (nanosized) pores associated with the β-WB precipitates were also observed.     

Evaluation of polycaprolactone − poly‐D,L‐lactide copolymer as biomaterial for breast tissue engineering

The potential of the copolymer polycaprolactone‐co‐ poly‐d ,l ‐lactic acid (PCLLA ) as a biomaterial for scaffold‐based therapy for breast tissue engineering applications was assessed. First, the synthesized PCLLA was evaluated for its processability by means of additive manufacturing (AM ). We found that the synthesized PCLLA could be fabricated into scaffolds with an overall gross morphology and porosity similar to that of polycaprolactone. The PCLLA scaffolds possessed a compressive Young's modulus (ca 46 kPa ) similar to that of native breast (0.5 ? 25 kPa ), but lacked thermal stability and underwent thermal degradation during the fabrication process. The PCLLA scaffolds underwent rapid degradation in vitro which was characterized by loss of the scaffolds' mechanical integrity and a drastic decrease in mass‐average molar mass (M _w) and number‐average molar mass (M _n) after 4 weeks of immersion in phosphate buffer solution maintained at 37 °C. The tin‐catalysed PCLLA scaffold was also found to have cytotoxic effects on cells. Although the initial mechanical properties of the PCLLA scaffolds generally showed potential for applications in breast tissue regeneration, the thermal stability of the copolymer for AM processes, biocompatibility towards cells and degradation rate is not satisfactory at this stage. Therefore, we conclude that research efforts should be geared towards fine‐tuning the copolymer synthesizing methods. © 2016 Society of Chemical Industry     

Schnelle optische Tomographie zum Nachweis von OH*‐Verteilungen in Flammen

A recently developed and patented fast tomographic reconstruction system has been applied to detect two‐dimensional distributions of the OH* chemiluminescence in laminar and turbulent flames. This could be achieved by the arrangement at exposure times down to 100 – 200 μs at a spatial resolution of < 1 – 2 mm, even though the concentration of OH* in flames is in the order of some ppb and, therefore, extremely small. Among other things the results provide important information regarding the determination of the heat release rate in flames to predict unstable operating points of gas turbines.     

Development of Electrical Discharge Machinable ZTA Ceramics with 24 vol% of TiC,TiN, TiCN,TiB2 and WC as Electrically Conductive Phase

In order to develop ED‐machinable ceramics with high strength, toughness and wear resistance, ZTA was chosen as matrix material. A dispersion of 24 vol% electrically conductive phase (TiC, TiN, TiCN, TiB₂ and WC) was added. These composites were hot pressed for 1 h at 60 MPa and temperatures ranging from 1475°C to 1550°C. Mechanical and electrical properties were investigated. The influence of the electrically conductive phase on the surface quality after EDM was analyzed. The mechanical properties and machining quality were found to depend significantly on the type of conductive phase added. Machining of a complex shaped ZTA‐TiC component was demonstrated.     

Semiconductor/Polymer Nanocomposites of Acrylates and Nanocrystalline Silicon by Laser‐Induced Thermal Polymerization

In this work, a novel method for the preparation of polymer/semiconductor nanocomposites is presented. The nanocomposite is directly prepared from a suspension of nanocrystalline silicon (nc‐Si) in bulk vinyl monomers (acrylates) and focused heating of the nc‐Si by irradiation with a pulsed laser at 532 nm wavelength. The silicon nanocrystals are the inorganic component of the composite and simultaneously act as initiation points of the free radical polymerization forming the hybrid composite. By this method, patterned nanocomposite films with thicknesses up to ≈250 µm can be readily prepared. Furthermore, the polymerization kinetics were investigated for different reaction conditions such as irradiation time, laser intensity, nc‐Si content, and addition of radical initiators.

     

Effect of Melt Processing on Crystallization Behavior and Rheology of Poly(3‐hydroxybutyrate) (PHB) and its Blends

Poly(3‐hydroxybutyrate) (PHB) is sensitive to high processing temperatures. This leads to a decrease in molar mass as well as a lower melt viscosity. The crystallization temperature shifts to lower values, and crystallization kinetics is slow. A mixture was developed in order to improve the manufacturing properties and the final product. The blends exhibit a slight reduction in molar mass because they have a lower melting point than pure PHB, and can be extruded at their melt temperature of 170 to 180°C. Then they immediately crystallize at 125 to 100°C. Differential scanning calorimetry (DSC) shows the effect of holding time in the melt on crystallization behavior. It has been shown that the crystallization time has to be longer in the case of PHB and shorter for the blends. Thermal degradation of PHB and its blends has been investigated using thermogravimetry analysis (TG). Derivative thermogravimetry coupled with TG (TG/DTG) curves show three decomposition stages for blends at 290, 340 and 445°C, respectively. Acetic acid, water, carbon dioxide and methane are produced by degradation at a higher temperature.