Ilenia Viola

Superhydrophobicity Due to the Hierarchical Scale Roughness of PDMS Surfaces

Wettability control has been widely investigated in the last decades for technological applications such as microfluidic devices and self-cleaning surfaces by modifying both the chemical composition and the geometric structure of the surfaces. Inspired by the typical morphology of superhydrophobic leaves (such as lotus leaves), we have developed a dual-scale roughness, micro- and nanosized, on polydimethylsiloxane (PDMS) surfaces. By combining different geometric parameters and plasma treatment conditions, the structures were controlled hierarchically, at different independent length scales. Both the microsized replicated pillars and the nanosized etched posts tuned the wettability of the PDMS surfaces in a very simple way, up to contact angles of 170 degrees . Furthermore, changes in the influence of micro- and nanoscale geometrical structures were investigated. Hysteresis and contact angles of water droplets are evaluated as a combined effect of micropillars and a superimposed roughness, resulting in high advancing contact angles and low sliding angles.

Influence of Chemistry and Topology Effects on Superhydrophobic CF4-Plasma-Treated Poly(dimethylsiloxane) (PDMS)

Superhydrophobic surfaces are gaining considerable interest in a lot of different applications, and nonetheless, precise control over the wettability properties of such surfaces is still a challenge due to difficulties when controlling the effects independently induced on superhydrophobicity by the chemical and topological surface characteristics. We have fabricated engineered superhydrophobic surfaces onto poly(dimethylsiloxane) (PDMS) substrates by means of suitable CF4-plasma treatments. These treatments allowed the modification of both the morphological properties of the PDMS surface, due to a preferential etching of certain components of its macromolecules, and the chemical ones, by the deposition of a fluorinated layer. Chemical effects were separated from topological ones by performing a double replica molding process of the CF4-plasma-treated surfaces. This allowed us to obtain positive copies of the structured surfaces without the overlaying fluorinated coating affecting the surface chemistry. Such replicated surfaces showed a decrease of the contact angle if compared to the treated ones and therefore evidenced chemistrys weight in superhydrophobicity effects. In particular, we found that, for highly dense columnar-like PDMS microstructures, the effect of the plasma-deposited fluorinated layer covering surfaces produces an enhancement of the contact angle of about 20 degrees .

Live-Cell-Permeant Thiophene Fluorophores and Cell-Mediated Formation of Fluorescent Fibrils

In our search for thiophene fluorophores that can overcome the limits of currently available organic dyes in live-cell staining, we synthesized biocompatible dithienothiophene-S,S-dioxide derivatives (DTTOs) that were spontaneously taken up by live mouse embryonic fibroblasts and HeLa cells. Upon treatment with DTTOs, the cells secreted nanostructured fluorescent fibrils, while cell viability remained unaltered. Comparison with the behavior of other cell-permeant, newly synthesized thiophene fluorophores showed that the formation of fluorescent fibrils was peculiar to DTTO dyes. Laser scanning confocal microscopy of the fluorescent fibrils showed that most of them were characterized by helical supramolecular organization. Electrophoretic analysis and theoretical calculations suggested that the DTTOs were selectively recognized by the HyPro component of procollagen polypeptide chains and incorporated through the formation of multiple H-bondings.

Experimental evidence of replica symmetry breaking in random lasers

Spin-glass theory is one of the leading paradigms of complex physics and describes condensed matter, neural networks and biological systems, ultracold atoms, random photonics and many other research fields. According to this theory, identical systems under identical conditions may reach different states. This effect is known as replica symmetry breaking and is revealed by the shape of the probability distribution function of an order parameter named the Parisi overlap. However, a direct experimental evidence in any field of research is still missing. Here we investigate pulse-to-pulse fluctuations in random lasers, we introduce and measure the analogue of the Parisi overlap in independent experimental realizations of the same disordered sample, and we find that the distribution function yields evidence of a transition to a glassy light phase compatible with a replica symmetry breaking.

Catalytic Self‐Propulsion of Supramolecular Capsules Powered by Polyoxometalate Cargos

Multicompartment, spherical microcontainers were engineered through a layer-by-layer polyelectrolyte deposition around a fluorescent core while integrating a ruthenium polyoxometalate (Ru4POM), as molecular motor, vis-à-vis its oxygenic, propeller effect, fuelled upon H2O2 decomposition. The resulting chemomechanical system, with average speeds of up to 25 μm s(-1), is amenable for integration into a microfluidic set-up for mixing and displacement of liquids, whereby the propulsion force and the resulting velocity regime can be modulated upon H2O2-controlled addition.

Engineering transfer of micro- and nanometer-scale features by surface energy modification.

Micropatterning of surfaces is gaining importance in various applications ranging from biosensors to microfluidic and lab-on-a-chip devices, where the control of the surface chemistry is of great importance for the application. In this paper, we introduce a patterning technique of topographical features, which is applicable on different substrates by modifying their surface energy. The textured surface is obtained via polydimethylsiloxane (PDMS) transfer, and the topographical parameters can be systematically tailored by selective treatment with oxygen plasma of either the PDMS stamp, the substrate, or both. Our approach is an alternative technique to create micro- and nanopatterns of various height and shape over a large area on different substrates. The possibility to control cell behavior on different surfaces tailored with this microtransfer patterning approach was also evaluated. The cell culture on patterned surfaces showed the possibility of modulating cell adhesion. Our method is based on simple transfer of silicone elastomeric patterns to the surface, and therefore, it is very simple and fast compared to other complex techniques. These observations could have implications for tissue-scaffold engineering science in areas such as microfluidic devices and control of cell adhesion.

Random laser emission from a paper-based device

Random laser emission is obtained from a fluidic paper-based device realized by conventional soft-lithography techniques on common, flexible, renewable and biocompatible commercial paper. The device is realized exclusively on paper by creating microfluidic porous channels on the cellulose fibres, in which a laser dye (Rhodamine B) can flow by capillarity. The modulation of the random lasing characteristics, in terms of threshold and spectral position, can be tailored by acting on the confinement induced by the lithographic process as well as on the shape and functionalization at the interface of the emitting regions.

Transition from nonresonant to resonant random lasers by the geometrical confinement of disorder

We report on a transition in random lasers that is induced by the geometrical confinement of the emitting material. Different dye doped paper devices with controlled geometry are fabricated by soft lithography and show two distinguished behaviors in the stimulated emission: in the absence of boundary constraints, the energy threshold decreases for larger laser volumes showing the typical trend of diffusive nonresonant random lasers, while when the same material is lithographed into channels, the walls act as cavity and the resonant behavior typical of standard lasers is observed. The experimental results are consistent with the general theories of random and standard lasers and a clear phase diagram of the transition is reported.

Physiological formation of fluorescent and conductive protein microfibers in live fibroblasts upon spontaneous uptake of biocompatible fluorophores.

We have recently reported initial results concerning an original approach to introduce additional properties into fibrillar proteins produced by live fibroblasts and extruded into the ECM. The key to such an approach was biocompatible, fluorescent and semiconducting synthetic molecules which penetrated spontaneously the cells and were progressively encompassed via non-bonding interactions during the self-assembly process of the proteins, without altering cell viability and reproducibility. In this paper we demonstrate that the intracellular secretion of fluorescent microfibers can be generalized to living primary and immortalized human/mouse fibroblasts. By means of real-time single-cell confocal microscopy we show that the fluorescent microfibers, most of which display helical morphology, are generated by intracellular coding of the synthetic molecules. We also describe co-localization experiments on the fluorescent microfibers isolated from the cell milieu demonstrating that they are mainly made of type-I collagen. Finally, we report experimental data indicating that the embedded synthetic molecules cause the proteins not only to be fluorescent but also capable of electrical conductivity.

Corrigendum: Experimental evidence of replica symmetry breaking in random lasers

Nature Communications 6: Article number: 6058 (2015); Published 14 January 2015; Updated 12 February 2015. The data in Fig. 4b of this Article was inadvertently duplicated from panel d. The correct version of the figure appears below. Figure 4