Artificial Microbial Arenas: Materials for Observing and Manipulating Microbial Consortia

From the smallest ecological niche to global scale, communities of microbial life present a major factor in system regulation and stability. As long as laboratory studies remain restricted to single or few species assemblies, however, very little is known about the interaction patterns and exogenous factors controlling the dynamics of natural microbial communities. In combination with microfluidic technologies, progress in the manufacture of functional and stimuli‐responsive materials makes artificial microbial arenas accessible. As habitats for natural or multispecies synthetic consortia, they are expected to not only enable detailed investigations, but also the training and the directed evolution of microbial communities in states of balance and disturbance, or under the effects of modulated stimuli and spontaneous response triggers. Here, a perspective on how materials research will play an essential role in generating answers to the most pertinent questions of microbial engineering is presented, and the concept of adaptive microbial arenas and possibilities for their construction from particulate microniches to 3D habitats is introduced. Materials as active and tunable components at the interface of living and nonliving matter offer exciting opportunities in this field. Beyond forming the physical horizon for microbial cultivates, they will enable dedicated intervention, training, and observation of microbial consortia.     

Physically Based Failure Criterion for Dimensioning of Thick-Walled Laminates

The extreme lightweight potential of modern composites for the application in highly strained and thick walled components can only be sucessfully utilized with the help of adapted design procedures. Therefore, the stress and strain analysis of fibre reinforced components has experienced a tremendous improvement in recent years. The derived mechanical methods and the existing computing facilities are now capable of calculating complex and three-dimensional states of stress for single layers within laminated structures. The adequate development of appropriate failure criteria for the evaluation of such stress states has unfortunately not been promoted in the desired manner. In 1980, Hashin proposed a new generation of physically based failure analysis which could only be realized by a considerably increased numerical effort. Recently, Puck made a new attempt based on Hashin's concept using fundamental elements of the failure criterion by Mohr and Coulomb. Applying this model, the three-dimensional state of stress is evaluated in a realistic manner. It is assumed that besides the occurence of fibre failure only tensile stresses and shear stresses in loading planes tangential to the fibre direction induce the inter-fibre failure of the unidirectionally reinforced composite, whereas compressive stresses in these planes obstruct failure.     

Metal nitride cluster fullerenes: their current state and future prospects

The world of endohedral fullerenes was significantly enlarged over the past seven years by the cluster fullerenes, which contain structures such as the M(2)C(2) carbides and the M(3)N nitrides. While the carbide clusters are generated under the standard arc-burning conditions according to stabilization conditions, the nitride cluster fullerenes (NCFs) are formed by varying the composition of the cooling gas atmosphere in the arc-burning process. The special conditions for NCF synthesis is described in detail and the optimum conditions for the production of NCFs as the main product in fullerene syntheses are given. A general review of all NCFs reported to date consists of the structures, properties, and stability of the NCFs as well as the abundance of the NCFs in the fullerene soot. It is shown that all cages with even carbon atoms from C(68) to C(98) are available as endohedral nitride cluster structures (with the exception of C(72), C(74), and C(76)). Specifically, the NCFs form the largest number of structures that violate the isolated pentagon rule (IPR). Finally some practical applications of these cluster fullerenes are illustrated and an outlook is given, taking the superior stability of these endohedral fullerenes into account.     

Microfabricated system for parallel single-cell capillary electrophoresis

Performing single-cell electrophoresis separations using multiple parallel microchannels offers the possibility of both increasing throughput and eliminating cross-contamination between different separations. The instrumentation for such a system requires spatial and temporal control of both single-cell selection and lysis. To address these problems, a compact platform is presented for single-cell capillary electrophoresis in parallel microchannels that combines optical tweezers for cell selection and electromechanical lysis. Calcein-labeled acute myloid leukemia (AML) cells were selected from an on-chip reservoir and transported by optical tweezers to one of four parallel microfluidic channels. Each channel entrance was manufactured by F2-laser ablation to form a 20- to 10-microm tapered lysis reservoir, creating an injector geometry effective in confining the cellular contents during mechanical shearing of the cell at the 10-microm capillary entrance. The contents of individual cells were simultaneously injected into parallel channels resulting in electrophoretic separation as recorded by laser-induced fluorescence of the labeled cellular contents.     

Minimal dissipation theory and shear bands in biaxial tests

True biaxial tests of granular materials are investigated by applying the principle of minimal dissipation and comparing to two dimensional contact dynamics simulations. It is shown that the macroscopic steady state manifested by constant stress ratio and constant volume is the result of the ever changing microscopic structure which minimizes the dissipation rate. The shear band angle in the varying shear band structures is found to be constant. We also show that introducing friction on the walls reduces the degeneracy of the optimal shear band structures to one for a wide range of parameters which gives a non-constant stress ratio curve with varying aspect ratio that can be calculated.     

Novel catalysts, room temperature, and the importance of oxygen for the synthesis of single-walled carbon nanotubes

In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.     

Influence of Grain Refinement on Slurry Formation and Surface Segregation in Semi-solid Al-7Si-0.3Mg Castings

This study aims to evaluate the effect of grain refinement on slurry formation and surface segregation in semi-solid castings produced by the Rheometal™ process. The effect of two grain refiners, Al-8B and Al-5Ti-1B, on the slurry α-Al grain size, shape factor and solid fraction was evaluated. The results suggest that the addition of a grain refiner can affect the solid fraction obtained in the Rheometal^TM process and, consequently, reduce the solute content near the casting surface. Grain refiner addition resulted in a larger fraction of α-Al grains ≤ 60 µm for the refined alloys compared with the unrefined alloy. Additionally, the growth of α-Al slurry globules was greater for the unrefined alloy compared with the refined alloy during solidification in the die-cavity. A more homogeneous and finer microstructure was observed near the surface in the grain-refined castings compared with the unrefined castings. Evidence of significant liquid penetration was identified in some α-Al globules, indicating that disintegration of α-Al globules may occur during the Rheometal™ casting process.

     

Schichten über Schichten

Films over films: innovative coatings for complex applications Thin films and coatings have developed as a prerequisite for many technical applications. In this paper, some applications for electrical, electronic, biomedical and optical applications are presented. In this contribution, examples for coatings for conductive and transparent films in photovoltaics, films for biomedical electrodes, for semiconductor contacts and for high‐temperature contacts are presented and discussed. The films are prepared by magnetron‐sputtering and pulsed laser deposition. The influence of the processing parameters on the functional properties of the films is presented.     

Biocide polymers, 19. Modification of carboxyl groups containing resins with 3(5)-methylpyrazole

Polymeric inhibitors of nitrification have been prepared by reversible attachment of 3(5)-methylpyrazole to poly(acrylic acid-co-divinylbenzene) and poly(4-vinylbenzoic acid-co-divinylbenzene) containing 86 mol-% and 88 mol-% carboxyl groups, respectively. Pyrazolide bonds between the bioactive agent and crosslinked copolymers were formed by means of aminolysis of reactive derivatives of the resins containing mixed anhydride groups or acid chloride groups. The modified resins had pendantly bound 3(5)-methylpyrazole residues in the range of 7 to 36.4 wt.-% and were subjected to hydrolysis in order to study the influence of crosslinking on the release rate of the active ingredient. The results obtained were discussed.