X-Ray Nano-Diffraction on Epitaxial Crystals

The concept of growing epitaxial Ge and SiGe crystals onto tall Si pillars may provide a means for solving the problems associated with lattice parameter and thermal expansion coefficient mismatch, i.e., dislocations, wafer bowing and cracks. For carefully tuned epitaxial growth conditions the lateral expansion of crystals stops once nearest neighbors get sufficiently close. We have carried out scanning nano-diffraction experiments at the ID01 beam-line of the European Synchrotron Radiation Facility (ESRF) in Grenoble on the resulting space-filling arrays of micron-sized crystals to assess their structural properties and crystal quality. Elastic relaxation of the thermal strain causes lattice bending close to the Si interface, while the dislocation network is responsible for minute tilts of the crystals as a whole. To exclude any interference from nearest neighbors, individual Ge crystals were isolated first by chemical etching followed by micro-manipulation inside a scanning electron microscope. This permitted us to scan an X-ray beam, focused to a spot a few hundreds of nm in size, along the height of a single crystal and to record three-dimensional reciprocal space maps at chosen heights. The resolution limited width of the scattered X-ray beams reveals that the epitaxial structures evolve into perfect single crystals sufficiently far away from the heavily dislocated interface

A thermally self-sustained micro-power plant with integrated micro-solid oxide fuel cells, micro-reformer and functional micro-fluidic carrier

Low temperature micro-solid oxide fuel cell (micro-SOFC) systems are an attractive alternative power source for small-size portable electronic devices due to their high energy efficiency and density. Here, we report a thermally self-sustainable reformer – micro-SOFC assembly. The device consists of a micro-reformer bonded to a silicon chip containing 30 micro-SOFC membranes and a functional glass carrier with gas channels and screen-printed heaters for start-up. Thermal independence of the device from the externally powered heater is achieved by this exothermic reforming reaction above 470 °C. The reforming reaction and the fuel gas flow rate of the n-butane/air gas mixture controls the operation temperature and gas composition on the micro-SOFC membrane. In the temperature range between 505 °C and 570 °C, the gas composition after the micro-reformer consists of 12 vol% to 28 vol% H2. An open-circuit voltage of 1.0 V and maximum power density of 47 mW/cm2 at 565 °C is achieved with the on-chip produced hydrogen at the micro-SOFC membranes

Micro-solid oxide fuel cells running on reformed hydrocarbon fuels

Micro‐solid oxide fuel cell (micro‐SOFC) systems are predicted to have a high energy density and specific energy and are potential power sources for portable electronic devices. A micro‐SOFC system is under development in the frame of the ONEBAT project [1‐3]. In this presentation, we report on the fabrication and characterization of a sub‐system assembly consisting of a startup heater and a micro‐reformer bonded to a Si chip with electrochemically‐active micro‐SOFC membranes. A functional carrier including fluidic channels for gas feed and integrated heaters was bonded to a microreformer with an overall size of 12.7 mm x 12.7 mm x 1.9 mm [4‐7]. As a catalyst, a foam‐like material made of ceria‐zirconia nanoparticles doped with rhodium was used to fill the 58.5 mm3 reformer cavity. This micro‐reformer allows for high methane and butane conversion of > 90 % with a hydrogen selectivity of > 80 % at 550 °C in the reformer [7, 8]. A silicon chip with 30 free‐standing micro‐SOFC membranes (390 μm x 390 μm) with a thickness of less than 500 nm was bonded to the carrier‐reformer assembly described above. The micro‐SOFC membrane consisted of an yttria‐ stabilized zirconia thin film electrolyte. Both Pt‐based and ceramic‐based electrode materials were tested regarding the thermal stability and carbon poisoning at temperatures below 600 °C. The functional‐carrier mirco‐reformer micro‐SOFC assembly was electrochemically tested with hydrocarbon fuel between 300 °C and 600 °C. The fuel cell performance and the microstructural evolution of the anode are discussed as well

MACI - a new era?

Full thickness articular cartilage defects have limited regenerative potential and are a significant source of pain and loss of knee function. Numerous treatment options exist, each with their own advantages and drawbacks. The goal of this review is to provide an overview of the problem of cartilage injury, a brief description of current treatment options and outcomes, and a discussion of the current principles and technique of Matrix-induced Autologous Chondrocyte Implantation (MACI). While early results of MACI have been promising, there is currently insufficient comparative and long-term outcome data to demonstrate superiority of this technique over other methods for cartilage repair

Micro-solid oxide fuel cells as power supply for small portable electronic equipment

Micro-solid oxide fuel cell (SOFC) systems are anticipated for powering small, portable electronic devices, such as laptop, personal digital assistant (PDA), medical and industrial accessories. It is predicted that micro-SOFC systems have a 2-4 higher energy density than Li-ion batteries [1]. However, literature mainly focuses on the fabrication and characterization of thin films and membranes for micro-SOFC systems [2-12]; the entire system approach is not yet studied in detail. We will therefore discuss in this paper the entire approach from the fabrication of thin films and membranes up to the complete system, including fuel processing, thermal management and integration

Enhanced articular cartilage by human mesenchymal stem cells in enzymatically mediated transiently RGDS-functionalized collagen-mimetic hydrogels

Recapitulation of the articular cartilage microenvironment for regenerative medicine applications faces significant challenges due to the complex and dynamic biochemical and biomechanical nature of native tissue. Towards the goal of biomaterial designs that enable the temporal presentation of bioactive sequences, recombinant bacterial collagens such as Streptococcal collagen-like 2 (Scl2) proteins can be employed to incorporate multiple specific bioactive and biodegradable peptide motifs into a single construct. Here, we first modified the backbone of Scl2 with glycosaminoglycan-binding peptides and cross-linked the modified Scl2 into hydrogels via matrix metalloproteinase 7 (MMP7)-cleavable or non-cleavable scrambled peptides. The cross-linkers were further functionalized with a tethered RGDS peptide creating a system whereby the release from an MMP7-cleavable hydrogel could be compared to a system where release is not possible. The release of the RGDS peptide from the degradable hydrogels led to significantly enhanced expression of collagen type II (3.9-fold increase), aggrecan (7.6-fold increase), and SOX9 (5.2-fold increase) by human mesenchymal stem cells (hMSCs) undergoing chondrogenesis, as well as greater extracellular matrix accumulation compared to non-degradable hydrogels (collagen type II; 3.2-fold increase, aggrecan; 4-fold increase, SOX9; 2.8-fold increase). Hydrogels containing a low concentration of the RGDS peptide displayed significantly decreased collagen type I and X gene expression profiles, suggesting a major advantage over either hydrogels functionalized with a higher RGDS peptide concentration, or non-degradable hydrogels, in promoting an articular cartilage phenotype. These highly versatile Scl2 hydrogels can be further manipulated to improve specific elements of the chondrogenic response by hMSCs, through the introduction of additional bioactive and/or biodegradable motifs. As such, these hydrogels have the possibility to be used for other applications in tissue engineering. Statement of Significance Recapitulating aspects of the native tissue biochemical microenvironment faces significant challenges in regenerative medicine and tissue engineering due to the complex and dynamic nature of the tissue. The ability to take advantage of, mimic, and modulate cell-mediated processes within novel naturally-derived hydrogels is of great interest in the field of biomaterials to generate constructs that more closely resemble the biochemical microenvironment and functions of native biological tissues such as articular cartilage. Towards this goal, the temporal presentation of bioactive sequences such as RGDS on the chondrogenic differentiation of human mesenchymal stem cells is considered important as it has been shown to influence the chondrogenic phenotype. Here, a novel and versatile platform to recreate a high degree of biological complexity is proposed, which could also be applicable to other tissue engineering and regenerative medicine applications

Diamond electrodes and microelectrodes

Synthetic boron doped diamond electrodes and microelectrodes were manufd. with techniques usually utilized in microelectronics: HFCVD coating, optical photolithog. and plasma etching. These electrodes were characterized in terms of their electrochem. properties: the overpotentials for O2 and H2 evolution, the reversibility for simple electron transfer reactions (ferri-ferrocyanide), complex electron transfer reactions (oxidn. of org. compds.), chlorine detection and O3 prodn. A comparison with other types of electrodes (IrO2, SnO2) is given concerning hydroxyl radical formation. Ozone prodn. has been measured; showing an electrochem. efficiency of 12-15 % at -2 DegC. Oxidn. of phenol to CO2 can also be achieved without the formation of intermediate. [on SciFinder (R)

Fabrication of nanopore arrays and ultrathin silicon nitride membranes by block-copolymer-assisted lithography

Here we show a method for patterning a thin metal film using self-assembled block-copolymer micelles monolayers as a template. The obtained metallic mask is transferred by reactive ion etching in silicon oxide, silicon and silicon nitride substrates, thus fabricating arrays of hexagonally packed nanopores with tunable diameters, interspacing and aspect ratios. This technology is compatible with integration into a standard microtechnology sequence for wafer-scale fabrication of ultrathin silicon nitride nanoporous membranes with 80 nm mean pore diameter