Quasi-3D morphology and modulation of focal adhesions of human adult stem cells through combinatorial concave elastomeric surfaces with varied stiffness.

In vivo cell niches are complex architectures that provide a wide range of biochemical and mechanical stimuli to control cell behavior and fate. With the aim to provide in vitro microenvironments mimicking physiological niches, microstructured substrates have been exploited to support cell adhesion and to control cell shape as well as three dimensional morphology. At variance with previous methods, we propose a simple and rapid protein subtractive soft lithographic method to obtain microstructured polydimethylsiloxane substrates for studying stem cell adhesion and growth. The shape of adult renal stem cells and nuclei is found to depend predominantly on micropatterning of elastomeric surfaces and only weakly on the substrate mechanical properties. Differently, focal adhesions in their shape and density but not in their alignment mainly depend on the elastomer stiffness almost regardless of microscale topography. Local surface topography with concave microgeometry enhancing adhesion drives stem cells in a quasi-three dimensional configuration where stiffness might significantly steer mechanosensing as highlighted by focal adhesion properties.

Highly sticky surfaces made by electrospun polymer nanofibers.

We report on a comprehensive study of the unique adhesive properties of mats of polymethylmethacrylate (PMMA) nanofibers produced by electrospinning. Fibers are deposited on glass, with varying of the diameter and the relative orientation of the polymer filaments (random vs. aligned configuration). While no significant variation is observed in the static contact angle (∼130°) of deposited water drops upon changing the average fiber diameter up to the micrometer scale, fibers are found to exhibit unequalled water adhesion. Placed vertically, they can hold up water drops as large as 60 µL, more than twice the values typically obtained with hairy surfaces prepared by different methods. For aligned fibers with anisotropic wetting behavior, the maximum volume measured in the direction perpendicular to the fibers goes up to 90 µL. This work suggests new routes to tailor the wetting behavior on extended areas by nanofiber coatings, with possible applications in adsorbing and catalytic surfaces, microfluidic devices, and filtration technologies.

Hybrid planar microresonators with organic and InGaAs active media.

The authors report on the fabrication of hybrid planar micro-resonators based on InGaAs microdisks with an evaporated organic material. Samples of InGaAs grown on InP(100) substrates are obtained by Chemical Beam Epitaxy, and microdisks of InGaAs with different diameters are fabricated by focused ion beam. The hybrid disks are obtained by the subsequent evaporation of 8-hydroxyquinoline aluminium doped with 4-Dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran on the InGaAs microdisks. The devices, characterized by micro- and confocal photoluminescence imaging and spectroscopy, exhibit emission around 650 nm, from the organic material for disks with different radius. Finally, simultaneous emission in the visible and at whispering gallery resonant modes in the 1350-1450 nm range are observed due to excitation transfer to InGaAs. These devices open the possibility to combine the flexibility of organics with the high gain of III-V compounds for wavelength down conversion and telecom applications.

Luciferase a light source for the silica-based optical waveguides (spicules) in the demosponge Suberites domuncula.

Two classes of sponges (animal phylum Porifera) possess a siliceous skeleton which is composed of spicules. Studying the optical fiber-mechanical properties of large spicules from hexactinellid sponges (> 5 cm) it was demonstrated that they are effective light-collecting optical fibers. Here, we report that the demosponge Suberites domuncula is provided with a biosensor system composed of the (organic) light producing luciferase and the (inorganic) light transducing silica spicules. The light transmission feature of these smaller spicules (200 microm) has been demonstrated and the ability of sponge tissue to generate light has been proven. Screening for a luciferase gene in S. domuncula was successful; the recombinant luciferase was prepared and shown to be bioactive. The luciferase protein is abundantly present in the close neighborhood of the spicules. The expression of the luciferase gene is under the control of light.

Biocompatible surfactants for water-in-fluorocarbon emulsions.

Drops of water-in-fluorocarbon emulsions have great potential for compartmentalizing both in vitro and in vivo biological systems; however, surfactants to stabilize such emulsions are scarce. Here we present a novel class of fluorosurfactants that we synthesize by coupling oligomeric perfluorinated polyethers (PFPE) with polyethyleneglycol (PEG). We demonstrate that these block copolymer surfactants stabilize water-in-fluorocarbon oil emulsions during all necessary steps of a drop-based experiment including drop formation, incubation, and reinjection into a second microfluidic device. Furthermore, we show that aqueous drops stabilized with these surfactants can be used for in vitro translation (IVT), as well as encapsulation and incubation of single cells. The compatability of this emulsion system with both biological systems and polydimethylsiloxane (PDMS) microfluidic devices makes these surfactants ideal for a broad range of high-throughput, drop-based applications.

Capillary filling in patterned channels.

We show how the capillary filling of microchannels is affected by posts or ridges on the sides of the channels. Ridges perpendicular to the flow direction introduce contact line pinning, which slows, or sometimes prevents, filling, whereas ridges parallel to the flow provide extra surface that may enhance filling. Patterning the microchannel surface with square posts has little effect on the ability of a channel to fill for equilibrium contact angle theta_{e} less than approximately 30 degrees . For theta_{e} greater than approximately 60 degrees , however, even a small number of posts can pin the advancing liquid front.

Dielectric tensor of tetracene single crystals: the effect of anisotropy on polarized absorption and emission spectra.

The full UV-visible dielectric tensor and the corresponding directions of the principal axes of triclinic tetracene crystals are reported as deduced either by polarized absorption and ellipsometry measurements or by calculations based on the molecular and crystallographic data. The results allow the attribution of the polarized bands observed in both absorption and photoluminescence emission spectra. In particular, the spectral line shape and polarization of the emission are found to depend on the sample thickness, and the effect is attributed to the modification of the state of polarization of the emitted light during its propagation inside the crystal. Indeed, the directions of polarization of the lowest optical transitions and the directions of the principal axes of the dielectric tensor are demonstrated not to coincide, in contrast to the assumptions typically made in the literature, thus causing the mixed transverse/longitudinal character of light propagation.

[Nanotechnology and nephrology]. / Nanotecnologie e nefrologia.

Nowadays, nanotechnology and microfluidic technologies are emerging as enabling factors for the operation of lab-on-chip devices and micro total analysis systems in the biotechnological and biomedical fields. These devices allow to reduce the waste of reagents and products, and to increase analytical precision and operational throughput. The field of nanotechnology is introduced in this paper and some manufacturing methods at the nanometer and micrometer scale are presented, together with their potential application in producing biomedical devices for filtration and solute elimination. Examples will include electron-beam lithography, soft lithography, and electrospinning of nanofiber scaffolds for tissue engineering.

Exciton self-trapping in tetrafluoro-dimethyl-aminoacridine single crystals.

The UV-visible optical spectra of 1,2,3,4-tetrafluoro-7-(N,N)dimethyl-amino-acridine single crystals are reported. The results are discussed on the basis of the molecular transitions and crystal packing in the framework of the theory of molecular excitons under a fluctuating potential field due to dynamic disorder. A strong local geometry distortion is demonstrated by applying the Urbach rule to the absorption tails, which is the amplitude of the local potential fluctuation being larger than the intermolecular transfer energy. The lineshape and linewidth of the emission band and its temperature dependence give further evidence of exciton self-trapping.

Low-loss and highly polarized emission from planar polymer waveguides.

The waveguiding properties and amplified spontaneous emission (ASE) of a blend of light-emitting gain-conjugated polymers were investigated. ASE-induced line narrowing occurs for excitation fluences larger than 100 microJ cm(-2), with a maximum optical-gain coefficient of 8 cm(-1). Energy transfer between the host and guest polymers, significantly reducing the self-absorption, leads to a loss coefficient of the waveguide as low as 0.3 cm(-1), which is believed to be the lowest value reported for active organic gain slabs and a highly polarized emission, with a polarization contrast up to 0.65. These results indicate that gain-conjugated polymer blends are state-of-the-art organic materials for lasing devices.

Making silicon hydrophobic: wettability control by two-lengthscale simultaneous patterning with femtosecond laser irradiation.

We report on the wettability properties of silicon surfaces, simultaneously structured on the micrometre-scale and the nanometre-scale by femtosecond (fs) laser irradiation to render silicon hydrophobic. By varying the laser fluence, it was possible to control the wetting properties of a silicon surface through a systematic and reproducible variation of the surface roughness. In particular, the silicon-water contact angle could be increased from 66° to more than 130°. Such behaviour is described by incomplete liquid penetration within the silicon features, still leaving partially trapped air inside. We also show how controllable design and tailoring of the surface microstructures by wettability gradients can drive the motion of the drop's centre of mass towards a desired direction (even upwards).

Study of the surface morphology of a cholesteryl tethering system for lipidic bilayers.

The immobilization of functional molecules embedded in lipidic membranes onto inorganic substrates is of great interest for numerous applications in the fields of biosensors and biomaterials. We report on the preparation and the morphological characterization of a tethering system for lipidic bilayers, which is based on cholesteryl derivatives deposited on hydrophilic surfaces by self-assembling and microcontact printing techniques. The investigation of the structural properties of the realized films by atomic, lateral, and surface potential microscopy allowed us to assess the high quality of the realized cholesteryl layers.

Self-assembling of proteins and enzymes at nanoscale for biodevice applications.

Different nanotechnological strategies have been selected to implement biomolecular devices following a bottom-up or top-down approach depending on the biomolecule and on its functionality. Biomolecules have particular functionality and self-assembling capabilities that can be exploited for the implementation of both bioelectronic devices and multipurpose engineered biosurfaces. Surface preparation with supramolecular methods and microcontact printing have been developed and optimised to realise suitable functionalised surfaces. These surfaces can be used to link metalloproteins and enzymes for the implementation of nanobioelectronic devices and planar biosensors or to bind cells in order to promote their growth along predefined tracks and grooves. Some possible applications of these biosurfaces are shown and discussed. Results are presented for the realisation of a biomolecular nanodevice working in air based on the metalloprotein azurin immobilised in the solid state, the formation and characterisation of functional glutamate Dehydrogenase monolayers for nanobiosensing applications, the results of soft lithography processes on azurin for biosensor implementation, and the development of physiological self-assembled patterns of laminin-1 for cell culture applications and hybrid devices.