Elisa Mele

Patterning of light-emitting conjugated polymer nanofibres

Organic materials have revolutionized optoelectronics by their processability, flexibility and low cost, with application to light-emitting devices for full-colour screens, solar cells and lasers. Some low-dimensional organic semiconductor structures exhibit properties resembling those of inorganics, such as polarized emission and enhanced electroluminescence. One-dimensional metallic, III-V and II-VI nanostructures have also been the subject of intense investigation as building blocks for nanoelectronics and photonics. Given that one-dimensional polymer nanostructures, such as polymer nanofibres, are compatible with sub-micrometre patterning capability and electromagnetic confinement within subwavelength volumes, they can offer the benefits of organic light sources to nanoscale optics. Here we report on the optical properties of fully conjugated, electrospun polymer nanofibres. We assess their waveguiding performance and emission tuneability in the whole visible range. We demonstrate the enhancement of the fibre forward emission through imprinting periodic nanostructures using room-temperature nanoimprint lithography, and investigate the angular dispersion of differently polarized emitted light.

Biophysical properties of normal and diseased renal glomeruli

The mechanical properties of tissues and cells including renal glomeruli are important determinants of their differentiated state, function, and responses to injury but are not well characterized or understood. Understanding glomerular mechanics is important for understanding renal diseases attributable to abnormal expression or assembly of structural proteins and abnormal hemodynamics. We use atomic force microscopy (AFM) and a new technique, capillary micromechanics, to measure the elastic properties of rat glomeruli. The Youngs modulus of glomeruli was 2,500 Pa, and it was reduced to 1,100 Pa by cytochalasin and latunculin, and to 1,400 Pa by blebbistatin. Cytochalasin or latrunculin reduced the F/G actin ratios of glomeruli but did not disrupt their architecture. To assess glomerular biomechanics in disease, we measured the Youngs moduli of glomeruli from two mouse models of primary glomerular disease, Col4a3(-/-) mice (Alport model) and Tg26(HIV/nl) mice (HIV-associated nephropathy model), at stages where glomerular injury was minimal by histopathology. Col4a3(-/-) mice express abnormal glomerular basement membrane proteins, and Tg26(HIV/nl) mouse podocytes have multiple abnormalities in morphology, adhesion, and cytoskeletal structure. In both models, the Youngs modulus of the glomeruli was reduced by 30%. We find that glomeruli have specific and quantifiable biomechanical properties that are dependent on the state of the actin cytoskeleton and nonmuscle myosins. These properties may be altered early in disease and represent an important early component of disease. This increased deformability of glomeruli could directly contribute to disease by permitting increased distension with hemodynamic force or represent a mechanically inhospitable environment for glomerular cells.

Strelitzia reginae leaf as a natural template for anisotropic wetting and superhydrophobicity.

Artificial surfaces that exhibit unidirectional water spreading and superhydrophobicity are obtained by Strelitzia reginae leaves. Both green and dried leaves are used, thus exploiting the plant senescence. We demonstrate that the natural drying process of the leaves strongly affects the surface morphology and wettability. Polymeric stamps from the green leaf show an arrangement of periodic microridges/microgrooves that favor anisotropic wetting, with a water contact angle (WCA) variation of about 21% along the two principal directions. Instead, the shrinkage of the leaf tissue, as a consequence of the natural dehydration process, induces an enhancement of the superficial corrugation. This results in the establishment of a superhydrophobic state, which shows a WCA of up to 160°, and water rolling off. S. reginae leaves are therefore easily accessible stamps suitable for controlling wettability and realizing surfaces that exhibit various wetting behaviors.

Near-infrared imprinted distributed feedback lasers

The authors report on the fabrication and characterization of an organic distributed feedback laser operating in the near infrared. The device, fabricated by room-temperature nanoimprint lithography, is based on an organic dye hosted by a poly(methylmethacrylate) matrix. The laser emission from an imprinted 620nm period grating is peaked at 918nm with a linewidth of 8A and a pumping threshold of 37μJ∕cm2, and it is strongly polarized with a polarization contrast as high as 0.99. The lasing wavelength is tunable in the range of 890–930nm by adjusting the grating period, and the operational lifetime is up to 6×103 excitation pulses in vacuum environment. These results demonstrate the possibility of realizing imprinted organic-based near-infrared lasers, thus approaching spectral regions relevant for optical communication applications.

Fibrous wound dressings encapsulating essential oils as natural antimicrobial agents

Preventing infections is one of the main focuses of wound care. The colonisation of wounds by microorganisms can in fact have negative consequences on the healing process, delaying it. Here, we propose the use of essential oils as natural antimicrobial agents for cellulose-based fibrous dressings. We demonstrate the production of composite electrospun fibres that effectively encapsulate three different types of essential oils (cinnamon, lemongrass and peppermint). The fibrous scaffolds are able to inhibit the growth of Escherichia coli, even when small amounts of essential oils were used. At the same time, they are not cytotoxic, as proved by biocompatibility assays on skin cell models. The created dressings are promising as advanced biomedical devices for topical treatments.

Polymeric distributed feedback lasers by room-temperature nanoimprint lithography

Room temperature nanoimprinting lithography is used to realize a distributed feedback laser by direct dry pressing of the conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]). The laser device exhibits emission at 630nm with a pump threshold of 25μJ∕cm2 and a polarization contrast of the emitted light as large as 0.91. Therefore, room temperature nanoimprint lithography turns out to be very effective for producing stable patterns on light-emitting polymers for the one-step fabrication of nanopatterned optoelectronic devices.

Monolithic polymer microcavity lasers with on-top evaporated dielectric mirrors

We report on a monolithic polymeric microcavity laser with all dielectric mirrors realized by low-temperature electron-beam evaporation. The vertical heterostructure was realized by 9.5 TiOx∕SiOx pairs evaporated onto an active conjugated polymer, that was previously spincast onto the bottom distributed Bragg reflector (DBR). The cavity supports single-mode lasing at 509nm, with a linewidth of 1.8nm, and a lasing threshold of 84μJ∕cm2. We also report on the emission properties of the polymer we used, investigated by a pump-probe technique. These results show that low-temperature electron-beam evaporation is a powerful and straightforward fabrication technique for molecular-based fully integrable microcavity resonators.

Electrospinning of natural polymers for advanced wound care: towards responsive and adaptive dressings

In the last few years, the health-care services have registered worldwide an increased number of patients suffering from chronic wounds and ulcers, which are mainly associated with diabetes, obesity and cancer. The need for regenerating rapidly and effectively the injured skin has stimulated the research of advanced therapies for wound care. This review will discuss how biomimetic architectures produced by electrospinning natural biopolymers fulfil most of the requirements of ideal wound dressings. It will also examine the recent progress in the area of portable electrospinning systems and of multiscale instructive materials that integrate stimuli responsive and sensing elements.

Enhancement of light polarization from electrospun polymer fibers by room temperature nanoimprint lithography

We demonstrate the enhancement of the polarization ratio of light emitted from electrospun conjugated polymer nanofibers, by means of nanoimprint lithography carried out at room temperature. We provide evidence of tailoring the polarization properties by patterning light-emitting fibers at the nanoscale. The polarization ratios are increased up to a factor of 2.4 by gratings with periodicity (560 nm) matching the emission wavelength of the employed conjugated polymer. The use of room temperature nanoimprint lithography to pattern light-emitting polymer nanofibers represents a strategic route for realizing photonic crystals and distributed feedback polarized emitters on one-dimensional organic nanostructures.

Microvascular endothelial cell spreading and proliferation on nanofibrous scaffolds by polymer blends with enhanced wettability

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.