Response of Human Corneal Fibroblasts on Silk Film Surface Patterns

Transparent, biodegradable, mechanically robust, and surface‐patterned silk films were evaluated for the effect of surface morphology on human corneal fibroblast (hCF) cell proliferation, orientation, and ECM deposition and alignment. A series of dimensionally different surface groove patterns were prepared from optically graded glass substrates followed by casting poly(dimethylsiloxane) (PDMS) replica molds. The features on the patterned silk films showed an array of asymmetric triangles and displayed 37–342 nm depths and 445–3 582 nm widths. hCF DNA content on all patterned films were not significantly different from that on flat silk films after 4 d in culture. However, the depth and width of the grooves influenced cell alignment, while the depth differences affected cell orientation; overall, deeper and narrower grooves induced more hCF orientation. Over 14 d in culture, cell layers and actin filament organization demonstrated that confluent hCFs and their cytoskeletal filaments were oriented along the direction of the silk film patterned groove axis. Collagen type V and proteoglycans (decorin and biglycan), important markers of corneal stromal tissue, were highly expressed with alignment. Understanding corneal stromal fibroblast responses to surface features on a protein‐based biomaterial applicable in vivo for corneal repair potential suggests options to improve corneal tissue mimics. Further, the approaches provide fundamental biomaterial designs useful for bioengineering oriented tissue layers, an endemic feature in most biological tissue structures that lead to critical tissue functions.

     

Evaluation of quantum dots applied as switchable layer in a light-controlled electrochemical sensor

Gold electrodes with switchable conductance are created by coating the gold surface with different colloidal quantum dots. For the quantum dot immobilization, a dithiol compound was used. By polarizing the electrode and applying a light pointer, local photocurrents were generated. The performance of this setup was characterized for a variety of different nanoparticle materials regarding drift and signal-to-noise ratio. We varied the following parameters: quantum dot materials and immobilization protocol. The results indicate that the performance of the sensor strongly depends on how the quantum dots are bound to the gold electrode. The best results were obtained by inclusion of an additional polyelectrolyte film, which had been fabricated using layer-by-layer assembly.      

Manipulation and behavior modeling of one-dimensional nanomaterials on a structured surface

Different diameters of multiwall carbon nanotubes (CNTs) are manipulated by a cantilever tip of an atomic force microscope (AFM) to investigate the motion properties of one-dimensional nanomaterials on a structured surface. To describe the mechanical behaviors of this kind of samples, two mechanical models based on continuum mechanics are proposed. Through foreseeable manipulation procedures, we are able to position the tubes onto pre-etched micro trenches, and then measure their Young's moduli by the three-point bending method. Both string-like and beam-like deformation forms are observed on the tested samples. Additionally, we present a reparable ‘collapse’ phenomenon of the nanotube bridges.     

Determination of the main component in high-purity organic substances: Current status and prospects

The current status of the determination of the purity of high-purity organic substances using direct and indirect chromatographic methods is discussed. It is shown that the results of the chromatographic determination of the main component in high-purity organic materials are generally ambiguous and unreliable. The possibility of determining the purity of organic compounds using an elemental analyzer of C, H, and N without involving standard samples of analytes is examined; the advantages and drawbacks of this approach are discussed. It is demonstrated experimentally by the example of several nitrogenated compounds that the main component can be determined with an error no worse than 0.6 rel. %, whereas the error of element (nitrogen) determination in the molecule does not exceed the permissible error of elemental analysis.     

Qualitative and quantitative comparison of N‐glycans between pig endothelial and islet cells by high‐performance liquid chromatography and mass spectrometry‐based strategy

N‐glycan structures released from miniature pig endothelial and islet cells were determined by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF), negative ion electrospray ionization (ESI) MS/MS and normal‐phase high performance liquid chromatography (NP‐HPLC) combined with exoglycosidase digestion. Totally, the identified structures were 181 N‐glycans including 129 sialylated and 18 α‐galactosylated glycans from pig endothelial cells and 80 N‐glycans including 41 sialylated and one α‐galactosylated glycans from pig islet cells. The quantity of the α‐galactosylated glycans from pig islet cells was certainly neglectable compared to pig endothelial cells. A number of NeuGc‐terminated N‐glycans (80 from pig endothelial cells and 13 from pig islet cells) are newly detected by our mass spectrometric strategies. The detailed structural information will be a matter of great interest in organ or cell xenotransplantation using α 1,3‐galactosyltransferase gene‐knockout (GalT‐KO) pig. Copyright © 2009 John Wiley & Sons, Ltd.     

Symmetry‐Based Design for the Chemoenzymatic Synthesis of Oseltamivir (Tamiflu) from Ethyl Benzoate

A short chemoenzymatic formal synthesis of oseltamivir from ethyl benzoate has been achieved. The key steps involve a toluene dioxygenase‐mediated dihydroxylation, hetero‐Diels–Alder cycloaddition, and generation of C4 acetamido functionality. The formal synthesis of oseltamivir is achieved in ten steps and incorporates a unique translocation of the olefin with concomitant elimination of the C2 hydroxy group (see scheme).

     

Strategic absentmindedness in finitely repeated games

In this paper we consider finitely repeated games in which players can unilaterally commit to behave in an absentminded way in some stages of the repeated game. We prove that the standard conditions for folk theorems can be substantially relaxed when players are able to make this kind of compromises, both in the Nash and in the subgame perfect case. We also analyze the relation of our model with the repeated games with unilateral commitments studied, for instance, in García-Jurado et al. (Int. Game Theory Rev. 2:129–139, 2000). Authors acknowledge the financial support of Ministerio de Educaci ón y Ciencia, FEDER and Fundación Séneca de la Región de Murcia through projects SEJ2005-07637-C02-02, ECO2008-03484-C02-02, MTM2005-09184-C02-02, MTM2008-06778-C02-01 and 08716/PI/08.     

A new subspace method for blind estimation of selective MIMO‐STBC channels

In this paper, a new technique for the blind estimation of frequency and/or time‐selective multiple‐input multiple‐output (MIMO) channels under space‐time block coding (STBC) transmissions is presented. The proposed method relies on a basis expansion model (BEM) of the MIMO channel, which reduces the number of parameters to be estimated, and includes many practical STBC‐based transmission scenarios, such as STBC‐orthogonal frequency division multiplexing (OFDM), space‐frequency block coding (SFBC), time‐reversal STBC, and time‐varying STBC encoded systems. Inspired by the unconstrained blind maximum likelihood (UML) decoder, the proposed criterion is a subspace method that efficiently exploits all the information provided by the STBC structure, as well as by the reduced‐rank representation of the MIMO channel. The method, which is independent of the specific signal constellation, is able to blindly recover the MIMO channel within a small number of available blocks at the receiver side. In fact, for some particular cases of interest such as orthogonal STBC‐OFDM schemes, the proposed technique blindly identifies the channel using just one data block. The complexity of the proposed approach reduces to the solution of a generalized eigenvalue (GEV) problem and its computational cost is linear in the number of sub‐channels. An identifiability analysis and some numerical examples illustrating the performance of the proposed algorithm are also provided. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of paramagnetic microparticles through emulsion-templated free radical polymerization

A novel method is described for the preparation of high-magnetization paramagnetic microparticles functionalized with a controlled density of poly(ethylene glycol) (PEG) and carboxyl groups. These microparticles were synthesized using four steps: (1) creation of an oil-in-water emulsion in which hydrophobic iron oxide nanoparticles and a UV-activated initiator were distributed in hexane; (2) formation of uniform microparticles through emulsion homogenization and evaporation of hexane; (3) functionalization of the microparticle with a PEG-functionalized surfactant and acrylic acid; and (4) polymerization of the microparticles. Characterization of the microparticles with electron microscopy and light scattering revealed that they were composed of densely packed iron oxide nanoparticles and that the size of the microparticles may be controlled through the pore size of the membrane used to homogenize the emulsion. The concentration of surfactant and acrylic acid used in the third processing step was found to determine the surface chemistry, iron content, and magnetization of the microparticles. Increasing the PEG surfactant to acrylic acid ratio resulted in higher PEG surface densities, lower iron content, and lower magnetization. The resulting microparticles were readily functionalized with antibodies and showed a low propensity for nonspecific protein adsorption. We believe that these microparticles will be useful for magnetic tweezers measurements and bioanalytical devices that require microparticles with a high magnetization.     

Nanoliter-scale reactor arrays for biochemical sensing

A general approach is described for array-based biochemical sensing that uses contact-free dispersal of compounds into addressable microfabricated reactors. The arrays are composed of 1 to 100 nL volume open reactors that have been microfabricated on quartz substrates using lithography. The open architecture of these reactors allows them to be addressed in parallel or individually with an ink-jet arrayer that is capable of distributing 0.004 to 1 nL volumes of reagents. A seven-step biochemical assay has been conducted on a small array of reactors to demonstrate how they can be integrated with an ink-jet arrayer and optical detector. This nanoreactor assay format appears to overcome several limitations that chip-based microarray technology currently imposes on protein assays: the arrays can be created in a manner that does not expose the biochemical reagents to osmotic stress, independent reactions can be conducted in individual reactors, and the conditions in all of the reactors (e.g., concentration and pH) can be rapidly scanned. We believe that these nanoreactor arrays will be useful for biochemical sensing that involves delicate proteins and protein assemblies.