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Fluid flows hosting electrical phenomena make the subject of a fascinating and highly interdisciplinary scientific field. In recent years, the extraordinary success of electrospinning and solution blowing technologies for the generation of polymer nanofibers has motivated vibrant research aiming at rationalizing the behavior of viscoelastic jets under applied electric fields or other stretching fields including gas streams. Theoretical models unveiled many original aspects in the underpinning physics of polymer solutions in jets, and provided useful information to improve experimental platforms. This article reviews advances in the theoretical description and numerical simulation of polymer solution jets in electrospinning and solution blowing. Instability phenomena of electrical and hydrodynamic origin are highlighted, which play a crucial role in the relevant flow physics. Specifications leading to accurate and computationally viable models are formulated. Electrohydrodynamic modeling, theories for the jet bending instability, recent advances in Lagrangian approaches to describe the jet flow, including strategies for dynamic refinement of simulations, and effects of strong elongational flow on polymer networks are reviewed. Finally, the current challenges and future perspectives of the field are outlined and discussed, including the task of correlating the physics of the jet flows with the properties of realized materials, as well as the development of multiscale techniques for modelling viscoelastic jets., Comment: 135 pages, 42 figures

Nanoscale generation of individual photons in confined geometries is an exciting research field aiming at exploiting localized electromagnetic fields for light manipulation. One of the outstanding challenges of photonic systems combining emitters with nanostructured media is the selective channelling of photons emitted by embedded sources into specific optical modes and their transport at distant locations in integrated systems. Here, we show that soft-matter nanofibers, electrospun with embedded emitters, combine subwavelength field localization and large broadband near-field coupling with low propagation losses. By momentum spectroscopy, we quantify the modal coupling efficiency identifying the regime of single-mode coupling. These nanofibers do not rely on resonant interactions, making them ideal for room-temperature operation, and offer a scalable platform for future quantum information technology.

We implemented and developed a number of different mechanical patterning methods, including soft hot embossing, rapid prototyping, sub-μm fluidics, high-temperature and room-temperature nanoimprinting lithography, to fabricate planar periodic structures based on organic materials. Patterns were faithfully transferred to many different organic compounds, including polymers, low-molar-mass compounds, and blends, up to 100-nm scale resolution. Lithography does not reduce the emission yields of light-emitting organic compounds, thus opening the way to the one-step realization of organic-based confined optoelectronic devices. We carefully investigated the possible changes in the optical properties (absorbance, luminescence, and quantum yield) of light-emitting species, thus ruling out any possible degradation of the active materials after patterning. In particular, the observed increase in the external luminescence yield is ascribed to the reduced self-absorption within the dielectric slab of the organic film, as a consequence of the pattern-induced enhanced forward scattering. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Anthracene derivative compounds are currently investigated because of their unique physical properties (e.g., bright luminescence and emission tunability), which make them ideal candidates for advanced optoelectronic devices. Intermolecular interactions are the basis of the tunability of the optical and electronic properties of these compounds, whose prediction and exploitation benefit from the knowledge of the crystal structure and the packing architecture. Polymorphism can occur due to the weak intermolecular interactions, asking for detailed structural analysis clarifying the origin of observed material property modifications. Here, two silylethyne-substituted anthracene compounds are characterized by single-crystal synchrotron X-ray diffraction, identifying a new polymorph. Additionally, laser confocal microscopy and fluorescence lifetime imaging microscopy confirm the results obtained by the X-ray diffraction characterization, i.e., shifting the substituents towards the external benzene rings of the anthracene unit favours {\pi}-{\pi} interactions, impacting on both the morphology and the microscopic optical properties of the crystals. The compounds with more isolated anthracene units feature shorter lifetime and emission spectra more similar to those ones of isolated molecules. The crystallographic study, supported by the optical investigation, sheds light on the influence of non-covalent interactions on the crystal packing and luminescence properties of anthracene derivatives, providing a further step towards their efficient use as building blocks in active components of light sources and photonic networks., Comment: 39 pages, 16 figures, 3 tables

Azobenzene molecules switch efficiently and repeatedly their isomerization state upon absorption of UV/visible photons. Such dynamic initiates several light-induced phenomena in materials in which they are included. In particular, amorphous azobenzene–containing materials develop superficial reliefs in response to the irradiation with spatially structured UV/visible light as result of a light-driven macroscopic mass transport of the host material to which the azomolecules are bonded. The mass migration happens only in illuminated areas of the material and it is highly directional, with a very peculiar dependence on both the intensity and the polarization distribution of the irradiating light field. This dependence allows the design of topographic superficial textures, whose geometrical complexity can be controlled by accurately tailoring the illuminating vector optical field. In this chapter, the fundamental aspects of the phenomenology related to the light-induced structuration of azopolymer surfaces are described. Additionally, several illumination schemes suitable for the inscription of surface reliefs with increasing complexity and spatial scalability are presented.

Molybdenum disulfide (MoS2) has been attracting extraordinary attention for its intriguing optical, electronic and mechanical properties. Here we demonstrate hybrid, organic-inorganic light-emitting nanofibers based on MoS2 nanoparticle dopants obtained through a simple and inexpensive sonication process in N-methyl-2-pyrrolidone and successfully encapsulated in polymer filaments. Defectiveness is found to be kept low, and stoichiometry preserved, by the implemented, gentle exfoliation method that allows the MoS2 nanoparticles to be produced. So-achieved hybrid fibers are smooth, uniform, flawless, and exhibit bright and continuous light emission. Moreover, they show significant capability of waveguiding self-emitted light along their longitudinal axis. These findings suggest the use of emissive MoS2 fibers enabled by gentle exfoliation methods as novel and highly promising optical material for building sensing surfaces and as components of photonic circuits., 22 pages, 9 figures, Nanoscale, 2018

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, varying 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 (about 130{\deg}) 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 microL, 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 {\mu}L. 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., Comment: 17 pages, 5 figures, 2 tables

While most of the studies on molecular machines have been performed in solution, interfacing these supramolecular systems with solid-state nanostructures and materials is very important in view of their utilization in sensing components working by chemical and photonic actuation. Host polymeric materials, and particularly polymer nanofibers, enable the manipulation of the functional molecules constituting molecular machines, and provide a way to induce and control the supramolecular organization. Here, we present electrospun nanocomposites embedding a self-assembling rotaxane-type system that is responsive to both optical (UV-visible light) and chemical (acid/base) stimuli. The system includes a molecular axle comprised of a dibenzylammonium recognition site and two azobenzene end groups, and a dibenzo[24]crown-8 molecular ring. The dethreading and rethreading of the molecular components in nanofibers induced by exposure to base and acid vapors, as well as the photoisomerization of the azobenzene end groups, occur in a similar manner to what observed in solution. Importantly, however, the nanoscale mechanical function following external chemical stimuli induces a measurable variation of the macroscopic mechanical properties of nanofibers aligned in arrays, whose Young's modulus is significantly enhanced upon dethreading of the axles from the rings. These composite nanosystems show therefore great potential for application in chemical sensors, photonic actuators and environmentally responsive materials., 39 pages, 16 figures

In this work we study the reinforcement of polymers by mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare the mechanical properties of fibers made of polymers and of composites with pristine single-walled carbon nanotubes (SWNTs), mechanically interlocked derivatives of SWNTs (MINTs) and the corresponding supramolecular models. Improvements of both Young's modulus and tensile strength of up to 200 % were observed for the polystyrene-MINTs samples with an optimized loading of just 0.01 wt.%, while the supramolecular models with identical chemical composition and loading showed negligible or even detrimental influence. This behavior is found for three different types of SWNTs and two types of macrocycles. Molecular dynamics simulations show that the polymer adopts an elongated conformation parallel to the SWNT when interacting with MINT fillers, irrespective of the macrocycle chemical nature, whereas a more globular structure is taken upon facing with either pristine SWNTs or supramolecular models. The MINT composite architecture thus leads to a more efficient exploitation of the axial properties of the SWNTs and of the polymer chain at the interface, in agreement with experimental results. Our findings demonstrate that the mechanical bond imparts distinctive advantageous properties to SWNT derivatives as polymer fillers., 39 pages, 19 figures

We study the effects of a controlled gas flow on the dynamics of electrified jets in the electrospinning process. The main idea is to model the air drag effects of the gas flow by using a non-linear Langevin-like approach. The model is employed to investigate the dynamics of electrified polymer jets at different conditions of air drag force, showing that a controlled gas counterflow can lead to a decrease of the average diameter of electrospun fibers, and potentially to an improvement of the quality of electrospun products. We probe the influence of air drag effects on the bending instabilities of the jet and on its angular fluctuations during the process. The insights provided by this study might prove useful for the design of future electrospinning experiments and polymer nanofiber materials., 16 pages, 8 figures in J. Phys. Chem. A, Article ASAP, 2016

Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments., 29 pages, 9 figures, 1 Table

Bioactive, electrospun polymer nanofibers (NFs) are attractive building-block materials for realizing scaffolds for tissue engineering, as these filaments structurally mimic the hierarchical organization of natural extracellular matrix. As presented in this article, demonstrated applications involve the commitment to adipogenic, chondrogenic, osteogenic, neural lineages, and so on, by different types of stem cells obtained from various sources (adult, embryonic, induced pluripotent stem cells, etc.). Since a poor cellular colonization may limit the usefulness of scaffolds for culturing delicate stem cell populations, coupling NFs with cell-adhesive domains is highly desirable. In our work, the surface of either isotropic (randomly orienteor anisotropic (highly aligneelectrospun poly(l-lactic acid) fibrous scaffolds with fibronectin (FN)-mimetic peptides is tailored. The effects of the peptide immobilization on the adhesion and spreading of human, adult renal stem cells are investigated. Functionalized, aligned NFs are suitable scaffolds to promote the confluent growth of stem cells and to enhance their differentiation toward the tubular epithelial lineage. It is anticipated that the functionalization of aligned NFs with FN-mimetic peptides might be a promising method to target a specific response of stem cells in renal tissue engineering. The design and realization of electrospun nanofibers coupled with a fibronectin-mimetic peptide is described. The effect of the scaffolds on the behavior of renal stem cells is analyzed. These bioactive fibers might be useful for the definition of new biomimetic platforms to effectively culture and commit renal stem cells, allowing confluent and functional cell layers to be generated which are analogous to the renal proximal tubule epithelium.

Core–shell fibers are emerging as interesting microstructures for the controlled release of drugs, proteins, and complex biological molecules, enabling the fine control of microreservoirs of encapsulated active agents, of the release kinetics, and of the localized delivery. Here we load luminescent molecules and enhanced green fluorescent proteins into the core of fibers realized by coaxial electrospinning. Photoluminescence spectroscopy evidences unaltered molecular emission following encapsulation and release. Moreover, the release kinetics is microscopically investigated by confocal analysis at individual-fiber scale, unveiling different characteristic time scales for diffusional translocation at the core and at the shell. These results are interpreted by a two stage desorption model for the coaxial microstructure, and they are relevant in the design and development of efficient fibrous systems for the delivery of functional biomolecules.

The optomechanical properties of a silicon-nitride membrane mirror covered by Alq3 and Silver layers are investigated. Excitation at two laser wavelengths, 780 and 405 nm, corresponding to different absorptions of the multilayer, is examined. Such dual driving will lead to a more flexible optomechanical operation. Topographic reconstruction of the whole static membrane deformation and cooling of the membrane oscillations are reported. The cooling, observed for blue laser detuning and produced by bolometric forces, is deduced from the optomechanical damping of the membrane eigenfrequency. We determine the presence of different contributions to the photothermal response of the membrane. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Conjugated polymers are complex multi-chromophore systems, with emission properties strongly dependent on the electronic energy transfer through active sub-units. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical timescale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties., Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical Society, (2016)

We investigate the optical anisotropy of single nanofibers realized by electrospinning a conjugated polymer. Polarized infrared and micro-Raman measurements evidence a higher degree of molecular orientation in fibers processed from tetrahydrofuran solutions, with respect to samples spun from mixture with dimethyl sulfoxide. The fraction of ordered molecules is correlated to the fibers morphology. Polarized photoluminescence highlights a larger red shift (60 meV) for spectra from fibers processed from tetrahydrofuran, confirming the higher achieved molecular order resulting in reduced interchain separation and hence excitonic emission with lower transition energies compared to that from randomly aligned molecules. Conjugated polymer fibers are obtained, emitting light with polarization ratios up to 5, usable as polarized photonic nanosources.

Blue amplified spontaneous emission at room temperature is demonstrated from the exposed face of the strongly emitting organic semiconductor 1,1,4,4-tetraphenyl-1,3-butadiene in single crystal form. The symmetry of the crystal and calculation of lattice sums indicate the J-type organization of the molecular transition moments. The minimum in the lowest exciton dispersion branch, from which emission takes place, is found at the edge of the Brillouin zone leading to a dominant vibronic emission since the zero-phonon line is forbidden. The observed gain narrowed line is attributed to the vibronic replica which becomes amplified with increased pumping. The reported emission is along the normal to the exposed crystal face, important for the development of vertical cavity geometry lasers based on organic single crystals. The threshold excitation fluence of 400 microJ cm(-2) is comparable to other organic crystalline systems, even if the amplification path is much reduced as a consequence of the vertical geometry. Considering these relevant aspects, the optical characterization of this material is provided. The polarized absorption spectra are reported and the properties of the lowest-energy excitonic state investigated. Calculation of the electronic transitions for the isolated molecule, lattice sums for the transition at lowest energy, and the symmetry of the crystal allow attributing the largest face of the samples and the observed optical bands in the spectra. Polarized time-resolved spectra are also reported allowing to identify the intrinsic excitonic emission.

A study was conducted to demonstrate lasing action by composite electrospun polymer nanofibers emitting in the visible and near-infrared (NIR) spectral region. It also demonstrated the significant potential of electrospun and flexible gain nanofibers as active waveguides and lasers. Single-mode optically pumped lasing sources on individual electrospun nanofibers emitting at 585 nm with linewidth 0.3 nm and excitation threshold fluence of 60 μJ cm -2 were demonstrated as a prototype system. The single fiber surface was found to exhibit a root-mean-square roughness of about 6 nm using atomic force microscopy (AFM). The fibers were tested for laser emission and it was revealed that each fiber constituted a Fabry-Pérot cavity for spectral selection and light amplification, due to the high confinement of the emitted light.

The realization of isolated light-emitting dots, with lateral dimension down to a few tens of nanometers, by direct particle replication in nonwetting templates (PRINT) on dissolved conjugated polymers, and on their optical characterization.

A fundamental issue in biomedical and environmental sciences is the development of sensitive and robust sensors able to probe the analyte of interest, under physiological and pathological conditions or in environmental samples, and with very high spatial resolution. In this work, novel hybrid organic fibers that can effectively report the analyte concentration within the local microenvironment are reported. The nanostructured and flexible wires are prepared by embedding fluorescent pH sensors based on seminaphtho-rhodafluor-1-dextran conjugate. By adjusting capsule/polymer ratio and spinning conditions, the diameter of the fibers and the alignment of the reporting capsules are both tuned. The hybrid wires display excellent stability, high sensitivity, as well as reversible response, and their operation relies on effective diffusional kinetic coupling of the sensing regions and the embedding polymer matrix. These devices are believed to be a powerful new sensing platform for clinical diagnostics, bioassays and environmental monitoring., Comment: 32 pages, 14 figures, Small, 2015

In metal-enhanced fluorescence (MEF), the localized surface plasmon resonances of metallic nanostructures amplify the absorption of excitation light and assist in radiating the consequent fluorescence of nearby molecules to the far-field. This effect is at the base of various technologies that have strong impact on fields such as optics, medical diagnostics and biotechnology. Among possible emission bands, those in the near-infrared (NIR) are particularly intriguing and widely used in proteomics and genomics due to its noninvasive character for biomolecules, living cells, and tissues, which greatly motivates the development of effective, and eventually multifunctional NIR-MEF platforms. Here we demonstrate NIR-MEF substrates based on Au nanocages micropatterned with a tight spatial control. The dependence of the fluorescence enhancement on the distance between the nanocage and the radiating dipoles is investigated experimentally and modeled by taking into account the local electric field enhancement and the modified radiation and absorption rates of the emitting molecules. At a distance around 80 nm, a maximum enhancement up to 2-7 times with respect to the emission from pristine dyes (in the region 660 nm-740 nm) is estimated for films and electrospun nanofibers. Due to their chemical stability, finely tunable plasmon resonances, and large light absorption cross sections, Au nanocages are ideal NIR-MEF agents. When these properties are integrated with the hollow interior and controllable surface porosity, it is feasible to develop a nanoscale system for targeted drug delivery with the diagnostic information encoded in the fluorophore., Comment: 41 pages, 18 figures

The use of UV light sources is highly relevant in many fields of science, being directly related to all those detection and diagnosis procedures which are based on fluorescence spectroscopy. Depending on the specific application, UV light-emitting materials are desired to feature a number of opto-mechanical properties, including brightness, optical gain for being used in laser devices, flexibility to conform with different lab-on-chip architectures, and tailorable wettability to control and minimize their interaction with ambient humidity and fluids. In this work, we introduce multifunctional, UV-emitting electrospun fibers with both optical gain and anisotropic hydrophobicity greatly enhanced compared to films. Fibers are described by the onset of a composite wetting state and their arrangement in uniaxial arrays further favours liquid directional control. The low gain threshold and optical losses, the plastic nature and the flexibility and stability of these UV-emitting fibers make them interesting for building light-emitting devices and microlasers. Furthermore, the found anisotropic hydrophobicity is strongly synergic with optical properties, reducing interfacial interactions with liquids and enabling smart functional surfaces for droplet microfluidic and wearable applications., 25 pages, 11 figures

Electrospun polymer jets are imaged for the first time at an ultra-high rate of 10,000 frames per second, investigating the process dynamics, and the instability propagation velocity and displacement in space. The polymer concentration, applied voltage bias and needle-collector distance are systematically varied, and their influence on the instability propagation velocity and on the jet angular fluctuations analyzed. This allows us to unveil the instability formation and cycling behavior, and its exponential growth at the onset, exhibiting radial growth rates of the order of 10^3 s^-1. Allowing the conformation and evolution of polymeric solutions to be studied in depth, high-speed imaging at sub-ms scale shows a significant potential for improving the fundamental knowledge of electrified jets, leading to obtain finely controllable bending and solution stretching in electrospinning, and consequently better designed nanofibers morphologies and structures., 23 pages, 9 figures

When it comes to spinning polymer fibers, spiders are much better than scientists. However, the authors have narrowed the gap: Extensive simulations show that for by judiciously oscillating the spinneret, instabilities can be tamed and extremely thin fibers can be extracted. Remarkably, this effect is independent of the rheology of the polymeric solution used. These ultrathin fibers open up a new length scale for applications ranging from photonics and organic field-effect transistors to artificial ligaments and scaffolds used in tissue culture.

We demonstrate the multilevel patterning of organic light-emitting polymers by room-temperature nanoimprint lithography (RT-NIL), which is impossible to obtain by conventional hot embossing. In particular, we realize one- and two-dimensional photonic crystals with 500 nm periodic features and investigate the changes in the optical properties (luminescence and quantum yield) of the organic active layer. An increase of the quantum yield by 2.4% for the patterned film with respect to the untextured one and the enhancement of the output light emitted at a particular angle (Theta = 69 degrees) are observed for gratings whose Bragg periodicity matched the emission wavelength of the polymer. The employment of RT-NIL to pattern polymer semiconductors without degradation of their optical properties represents a strategic route for the realization of novel nanopatterned optoelectronic devices.

Cholesteryl polysulfides derivatives, containing a number of sulfur atoms comprised from 2 to 6 and suitable for the formation of self-assembled monolayer have been prepared utilizing a known procedure modified by us. The compounds were isolated and characterized by HPLC–MS, 1 H NMR, FT-IR techniques. Self-assembly methodology was adopted in order to obtain uniform layers and the patterning suitability was tested with microcontact printing technique. Contact angle measurements and atomic force microscopy revealed interesting surface modifications.

Glass-forming liquids, polymer solutions, and biofluids have additional inertial and elastic macroscopic degrees of freedom that are related to the elasticity of the molecular coils and affect the determination of the structural dynamical parameters. In this work, we propose a new approach for the direct evaluation of the fundamental material parameters (viscosity, fragility, glass transition temperature) of a viscoelastic liquid in a capillary flow inside a microfluidic device. The proposed technique substantially reduces the complexity of the theoretical analysis and provides an evaluation of the most relevant functional parameters of the fluid dynamics. Moreover, the approach allows the investigation of localization phenomena in geometrical confined systems, such as those required in miniaturized devices.

Oligomer molecules offer a number of advantages for the study of their photo-physical properties and for the application to optoelectronic devices. We investigated the optical properties of a substituted quinquethiophene by first-principles calculations, determining the absorption and the emission energies, and compared these to the experimental data. The optical gain properties of the oligomer were exploited for the realization of a solid-state laser device exhibiting single-mode emission at 637 nm , with a full-width half-maximum of about 0.7 nm and a pump fluence threshold as low as 220 μJ / cm 2 .

In this contribution we report on the preparation and characterisation of both 2,5-di-(9,9-dimethylfluoren-2-yl)-3,4-dihexyl-thiophene-1,1-dioxide and the corresponding polymer with longer alkyl substituents at 9 fluorene position. Optical and structural characterisations performed on both crystalline and amorphous films showed noticeable luminescence properties depending on the molecular aggregation. Both polymer and oligomer based LEDs showed external efficiency of more than 10−1%.

The relaxational dynamics of poly(propyleneglycol) (PPG) and poly(propyleneglycol)-diglycidylether (PPGDE) compounds, the latter with different average number of repeating units, was studied by broadband dielectric spectroscopy (10 mHz to 10 GHz) from above to below the glass transition temperature in the range 115–350 K. The dielectric response of all systems showed a high temperature single relaxation while below a crossover temperature TB it split in a main (α-) and a secondary (β-) relaxation. The effect on the main and secondary relaxation of different groups terminating the polymer chain was analyzed: in particular, a decrease of the secondary relaxation time was observed for PPGDE with respect to PPG with the same molecular weight. Moreover the change of the Vogel temperature T0 paralleled what previously found for similar systems. The relationship between main and secondary relaxation and the microscopic nature of this latter were analyzed in the framework of the coupling model.

Streptomycetes are exploited for the production of a wide range of secondary metabolites, including antibiotics. Therefore, both academic and industrial research efforts are focused on enhancing production of these precious metabolites. So far, this has been mostly achieved by classical or recombinant genetic techniques, in association with process optimization for either submerged or solid state fermentation. New cultivation approaches addressing the natural mycelial growth and life cycle would allow the biosynthetic potential of filamentous strains to be much better exploited. We developed a cultivation system for antibiotic-producing microorganisms which involves electrospun organic nanofibers deposited onto agar plates or immersed in liquid media. Dense filamentous networks of branched hyphae formed by bacterial colonies were found to wrapped around the fibers. We analyzed the effects of fibers on growth and antibiotic production in Streptomyces lividans, and found that the actinorhodin, undecylprodigiosin and calcium dependent antibiotic productions were positively modulated, with a two- to sixfold enhancement compared to standard culture conditions. Highlighting the secondary metabolism-promoting role of nanofibers in bacterial cultures, these results open a route to the design of improved culture systems for microorganisms based on organic nanostructures.

© 2014 Vandrangi et al. In this work, we evaluate the in vitro response of endothelial cells (EC) to variation in precisely-defined, micrometer to submicrometer scale topography on two different substrate materials, titanium (Ti) and silicon (Si). Both substrates possess identically-patterned surfaces composed of microfabricated, groove-based gratings with groove widths ranging from 0.5 to 50 mm, grating pitch twice the groove width, and groove depth of 1.3 μm. These specific materials are chosen due to their relevance for implantable microdevice applications, while grating-based patterns are chosen for the potential they afford for inducing elongated and aligned cellular morphologies reminiscent of the native endothelium. Using EA926 cells, a human EC variant, we show significant improvement in cellular adhesion, proliferation, morphology, and function with decreasing feature size on patterned Ti substrates. Moreover, we show similar trending on patterned Si substrates, albeit to a lesser extent than on comparably patterned Ti substrates. Collectively, these results suggest promise for sub-micrometer topographic patterning in general, and sub-micrometer patterning of Ti specifically, as a means for enhancing endothelialization and neovascularisation for novel implantable microdevice applications. Copyright

Light-emitting nanostructures made by conjugated polymers show interesting emission and electronic properties. In this work we report on novel approaches for the fabrication and control of light-emitting nanofibers by electrospinning. The shape, size and light-emitting properties of the fibers can be specifically tailored by acting on the composition of the solution used for the electrospinning process, an approach allowing for obtaining fibers ranging from micrometer-sized ribbons to almost cylindrical fibers with diameters down to few hundreds of nanometers. Moreover, following proper process optimization these fibers can also be precisely positioned in ordered arrays by near-field electrospinning, a method that exploits the stable region of the polymer jet. The possibility of precisely shaping the conjugated polymer fibers and of assembling the fiber in ordered arrays, combined with enhanced emission properties, opens interesting perspectives for developing novel emitting flexible nanomaterials suitable for light sourcing and optical sensing.

A new procedure for the alignment of carbon nanotubes in a thermosetting matrix is proposed in this study. The two-step approach is based on (i) the alignment of carbon nanotubes (CNTs) in thermoplastic fibres by electrospinning and (ii) the transfer of these nanocompositefibres into a reactive thermosetting resin, in which they are easily soluble. After fibre dissolution, the CNTs remain aligned in the cured thermosetting matrix.The proof of concept is demonstrated by producing electrospunpolymethyl methacrylate (PMMA) fibres filled with single wall carbon nanotubes (SWCNTs) in the form of unidirectional tape, which are then solubilised into a vinylester (VE) matrix. The PMMA is easily dissolved by the styrene present in the VE resin, leaving SWCNTs aligned in the cured VE network, as confirmed by Raman spectroscopy studies. A 50% increase in elastic modulus (SWCNT 1.3. wt.%) has been obtained by dynamic mechanical analysis carried out in tensile mode at 1. Hz. Thanks to its ability to orient carbon nanotubes in a thermosetting matrix, the proposed method can be exploited also to transfer oriented nanofillers into continuous fibre composites, thus obtaining multiscale or hierarchical composites. © 2014 Elsevier Ltd.

Molecular packing in molecular crystalline solids and aggregates influences both the redistribution of oscillator strength between the excitons involved in optical transitions and also their effective masses. 1,1,4,4-Tetraphenyl-1,3- butadiene is taken into consideration because it is often used in light-emitting solid-state devices and it is also a promising material for solid-state laser applications, owing to the observed amplified spontaneous emission at room temperature of its ? polymorph. This paper concerns a combined experimental and computational study of the photoluminescence emission of the ? phase. The emission is demonstrated to originate from the lowest-energy exciton, which takes almost the whole available oscillator strength from the four molecules in the unit cell, and it is also the heaviest one in terms of effective mass. On the basis of the balance between nuclear relaxation energy, free-exciton Davydov splitting, and also exciton effective mass, as discussed in the framework of the recent reclassification reported in J. Chem. Phys. 2007, 127, 184703, the exciton-phonon coupling turns out to be effective in limiting the delocalization of this heavy exciton and in influencing the phonon progression in the emission spectra. © 2014 American Chemical Society.

Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, characterizing the fiber drawing process. Although enhanced physical properties were observed in polymer fibers produced under strong stretching conditions, studies of the process-induced nanoscale organization of the polymer molecules are not available, and most of fiber properties are still obtained on an empirical basis. Here we reveal the orientational properties of semiflexible polymers in electrospun nanofibers, which allow the polarization properties of active fibers to be finely controlled. Modeling and simulations of the conformational evolution of the polymer chains during electrostatic elongation of semidilute solutions demonstrate that the molecules stretch almost fully within less than 1 mm from jet start, increasing polymer axial orientation at the jet center. The nanoscale mapping of the local dichroism of individual fibers by polarized near-field optical microscopy unveils for the first time the presence of an internal spatial variation of the molecular order, namely the presence of a core with axially aligned molecules and a sheath with almost radially oriented molecules. These results allow important and specific fiber properties to be manipulated and tailored, as here demonstrated for the polarization of emitted light., Comment: 45 pages, 10 figures, Macromolecules (2014)

We report on flexible, single electrospun nanofiber field-effect transistors made by a blend of poly(3-decylthiophene) and poly(3-hexylthiophene), assessing for the first time the performances of this class of devices in terms of stability upon repeated tensile bending. Charge-carrier mobilities in the nanofiber-based device are estimated of the order of 10 (3) cm(2)/(V s). Repeated cycles of bending and relaxing are performed, and the evolution of the device current-voltage characteristics is monitored up to 1000 cycles. We find that during bending the mobility is higher than that measured in planar conditions, and that after about 100 bending cycles it rapidly stabilizes. The here observed bending stability suggests a high compatibility of electrospun nanofibers with devices fabricated by roll-to-roll processes, and with bendable or wearable electronics. (C) 2014 Elsevier B.V. All rights reserved.

Imprinted, distributed feedback lasers are demonstrated on individual, active electrospun polymer nanofibers. In addition to advantages related to miniaturization, optical confinement and grating nanopatterning lead to a significant threshold reduction compared to conventional thin-film lasers. The possibility of imprinting arbitrary photonic crystal geometries on electrospun lasing nanofibers opens new opportunities for realizing optical circuits and chips. (Figure Presented).

Ca-carbonate, the inorganic matrix of the spicules from the calcareous sponges, is formed as the result of an enzyme-catalyzed reaction with the carbonic anhydrase [CA] as a decisive component. The growth and the morphology of the spicules are genetically controlled, and are taxon-specific. In the present study it is shown that the silicatein-interacting protein silintaphin-2 is present at the surface of the siliceous spicules of the demosponge Suberites domuncula and prevents the association of calcareous crystals synthesized in vitro to these skeletal elements. Silintaphin-2 comprises a Ca2+-binding domain that is formed by a 22 amino acid-long peptide, N-DDDSQGEIQSDMAEEEDDDNVD-C. This very acidic 22-meric peptide, termed D/E-peptide, is shown to decelerate the in vitro synthesis of calcite through blocking the transformation of amorphous Ca-carbonate to the crystalline morph calcite at the level of vaterite. This effect is seen at a molar ratio of D/E-peptide : Ca2+ of 1 : 5000. During the deposition of Ca-carbonate the peptide becomes incorporated into the crystallites. Determinations of the mechanical characteristics of the formed Ca-carbonate deposits revealed a hardness of 1.98 +/- 0.31 GPa (calcite) and 1.38 +/- 0.39 GPa (vaterite), an elastic modulus of 72.83 +/- 11.68 GPa (calcite) and 39.13 +/- 8.04 GPa (vaterite) and a creep of 5.44 +/- 1.15 (calcite) and 9.95 +/- 1.60 (vaterite) per maximal depth (%). It is concluded that the D/E-peptide interferes with the Ca2+ ions within the growing vaterite crystals and freezes this unstable phase formed during calcite formation. It is postulated that proteins, like silintaphin-2 with its Ca2+-binding domain D/E-peptide, are involved in the taxon-specific control of the synthesis of the inorganic matrix of the sponge spicules.

We present a bio-inspired renal microdevice that resembles the in vivo structure of a kidney proximal tubule. For the first time, a population of tubular adult renal stem/progenitor cells (ARPCs) was embedded into a microsystem to create a bioengineered renal tubule. These cells have both multipotent differentiation abilities and an extraordinary capacity for injured renal cell regeneration. Therefore, ARPCs may be considered a promising tool for promoting regenerative processes in the kidney to treat acute and chronic renal injury. Here ARPCs were grown to confluence and exposed to a laminar fluid shear stress into the chip, in order to induce a functional cell polarization. Exposing ARPCs to fluid shear stress in the chip led the aquaporin-2 transporter to localize at their apical region and the Na+K+ ATPase pump at their basolateral portion, in contrast to statically cultured ARPCs. A recovery of urea and creatinine of (20 +/- 5)% and (13 +/- 5)%, respectively, was obtained by the device. The microengineered biochip here-proposed might be an innovative "lab-on-a-chip" platform to investigate in vitro ARPCs behaviour or to test drugs for therapeutic and toxicological responses.

The properties of polymeric nanofibers can be tailored and enhanced by properly managing the structure of the polymeric molecules at the nanoscale. Although electrospun polymer fibers are increasingly exploited in many technological applications, their internal nanostructure, determining their improved physical properties, is still poorly investigated and understood. Here, we unravel the internal structure of electrospun functional nanofibers made by prototype conjugated polymers. The unique features of near field optical measurements are exploited to investigate the nanoscale spatial variation of the polymer density, evidencing the presence of a dense internal core embedded in a less dense polymeric shell. Interestingly, nanoscale mapping the fiber Young's modulus demonstrates that the dense core is stiffer than the polymeric, less dense shell. These findings are rationalized by developing a theoretical modeling and simulations of the polymer molecular structural evolution during the electrospinning process. This model predicts that the stretching of the polymer network induces a contraction towards the jet center of the network with a local increase of the polymer density, as observed in the solid structure. The found complex internal structure opens interesting perspective for improving and tailoring the molecular morphology and multifunctional electronic and optical properties of polymer fibers., 33 pages, 9 figures

Light emitting electrospun nanofibers of poly-[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N'-diphenyl)-N,N'-di(p-butyl-oxy-phenyl)-1,4-diaminobenzene)] (PFO-PBAB) are produced by electrospinning under different experimental conditions. In particular, uniform fibers with average diameter of 180 nm are obtained by adding an organic salt to the electrospinning solution. The spectroscopic investigation assesses that the presence of the organic salt does not alter the optical properties of the active material, therefore providing an alternative approach for the fabrication of highly emissive conjugated polymer nanofibers. The produced nanofibers display self-waveguiding of light, and polarized photoluminescence, which is especially promising for embedding active electrospun fibers in sensing and nanophotonic devices., 31 pages, 9 figures, 1 table. Macromolecules (2013)

Spatiotemporal image correlation spectroscopy (STICS) is a simple and powerful technique, well established as a tool to probe protein dynamics in cells. Recently, its potential as a tool to map velocity fields in lab-on-a-chip systems was discussed. However, the lack of studies on its performance has prevented its use for microfluidics applications. Here, we systematically and quantitatively explore STICS microvelocimetry in microfluidic devices. We exploit a simple experimental setup, based on a standard bright-field inverted microscope (no fluorescence required) and a high-fps camera, and apply STICS to map liquid flow in polydimethylsiloxane (PDMS) microchannels. Our data demonstrates optimal 2D velocimetry up to 10 mm/s flow and spatial resolution down to 5 ?m. © 2013 American Chemical Society.

In this work, we investigate the effect of illumination parameters which is light polarization, wavelength, and beam focalization, on the large-scale patterning of the surface of azobenzene-containing polymer films by means of spontaneous surface structuring. This is a phenomenon due to the interference at the sample surface between different light modes originated by scattering from the primary illuminating beam. In particular, the surface patterning in regions of a few squared millimeters with a spatial resolution down to 180 nm is achieved by means of a single beam illumination. The realized topographical structures are both preferentially oriented gratings and isotropically distributed topographical protrusions (dots), with sub-wavelength features.

The objective of this study is elucidating the mechanisms by which the wettability of nanofibrous electrospun mats varies in polymer blends, and highlighting how this can play a pivotal role in enhancing the viability of cultured microvascular endothelial cells (EC). A functional microvascular network is essential for supplying bioengineered tissues with oxygen and nutrients while removing metabolic wastes. An in vitro pre-vascularization strategy consists of seeding EC on scaffolds, which in turn promotes cells infiltration, adhesion and functionality. We use electrospun poly-L-lactic acid (PLLA) and gelatin (Gel) as prototype materials for realizing nanofibrous scaffolds as bioartificial architectures to improve the proliferation and the functionality of human microvascular ECs (HMEC-1). HMEC-1 seeded on electrospun scaffolds adhere, remain viable, proliferate and positively express the endothelial cell marker CD31 particularly on blend PLLA/Gel fibers, which exhibit wettability enhanced with respect to both the constituent polymers, and are therefore especially promising constructs for promoting the formation of functional endothelial tissue. The wettability characteristics of the blend polymer fibrous scaffolds are modeled and discussed. These results can be valuable for the future design of pre-vascularized scaffolds with enhanced wettability properties for functional tissue engineered implants, with ECs able to form in perspective an effectively functioning vasculature upon implantation.

The inorganic matrix of the siliceous skeletal elements of sponges, that is, spicules, is formed of amorphous biosilica. Until a decade ago, it remained unclear how the hard biosilica monoliths of the spicules are formed in sponges that live in a silica-poor (

We report on the unique emission features of light-emitting fibers made of a prototype conjugated polymer, namely, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (F8BT), realized by electrospinning with diameters in the range of 500-1000 nm. The fibers display emission polarized along their axis, evidencing a favoured alignment of the polymer molecules. Emission efficiency and time resolved measurements reveal an enhancement of both the quantum efficiency and the radiative rate (up to 22.5%) of the fibers compared to spin-coated films, shedding more light on their potential as miniaturized photon sources in optoelectronic devices requiring high recombination rates.