Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors.

The capacitance of electrode materials used in electrochemical double-layer capacitors (EDLCs) is currently limited by several factors, including inaccessible isolated micropores in high-surface area carbons, the finite density of states resulting in a quantum capacitance in series to Helmholtz double-layer capacitance, and the presence of surface impurities, such as functional groups and adsorbed species. To unlock the full potential of EDLC active materials and corresponding electrodes, several post-production treatments are commonly proposed to improve their capacitance and, thus, the energy density of the corresponding devices. In this work, we report a systematic study of the effect of a prototypical treatment, namely H2-assisted thermal treatment, on the chemical, structural, and thermal properties of activated carbon and corresponding electrodes. By combining multiple characterization techniques, we clarify the actual origins of the improvement of the performance (e.g., > +35% energy density for the investigated power densities in the 0.5-45 kW kg-1 range) of the EDLCs based on treated electrodes compared to the case based on the pristine electrodes. Contrary to previous works supporting a questionable graphitization of the activated carbon at temperatures <1000 °C, we found that a "surface graphitization" of the activated carbon, detected by spectroscopic analysis, is mainly associated with the desorption of surface contaminants. The elimination of surface impurities, including adsorbed species, improves the surface capacitance of the activated carbon (CsurfAC) by +37.1 and +36.3% at specific currents of 1 and 10 A g-1, respectively. Despite the presence of slight densification of the activated carbon upon the thermal treatment, the latter still improves the cell gravimetric capacitance normalized on the mass of the activated carbon only (CgAC), e.g., + 28% at 1 A g-1. Besides, our holistic approach identifies the change in the active material and binder contents as a concomitant cause of the increase of cell gravimetric capacitance (Cg), accounting for the mass of all of the electrode materials measured for treated electrodes compared to pristine ones. Overall, this study provides new insights into the relationship between the modifications of the electrode materials induced by H2-assisted thermal treatments and the performance of the resulting EDLCs.

Modified Carbon Nanotubes Favor Fibroblast Growth by Tuning the Cell Membrane Potential.

As is known, carbon nanotubes favor cell growth in vitro, although the underlying mechanisms are not yet fully elucidated. In this study, we explore the hypothesis that electrostatic fields generated at the interface between nonexcitable cells and appropriate scaffold might favor cell growth by tuning their membrane potential. We focused on primary human fibroblasts grown on electrospun polymer fibers (poly(lactic acid)─PLA) with embedded multiwall carbon nanotubes (MWCNTs). The MWCNTs were functionalized with either the p-methoxyphenyl (PhOME) or the p-acetylphenyl (PhCOMe) moiety, both of which allowed uniform dispersion in a solvent, good mixing with PLA and the consequent smooth and homogeneous electrospinning process. The inclusion of the electrically conductive MWCNTs in the insulating PLA matrix resulted in differences in the surface potential of the fibers. Both PLA and PLA/MWCNT fiber samples were found to be biocompatible. The main features of fibroblasts cultured on different substrates were characterized by scanning electron microscopy, immunocytochemistry, Rt-qPCR, and electrophysiology revealing that fibroblasts grown on PLA/MWCNT reached a healthier state as compared to pure PLA. In particular, we observed physiological spreading, attachment, and Vmem of fibroblasts on PLA/MWCNT. Interestingly, the electrical functionalization of the scaffold resulted in a more suitable extracellular environment for the correct biofunctionality of these nonexcitable cells. Finally, numerical simulations were also performed in order to understand the mechanism behind the different cell behavior when grown either on PLA or PLA/MWCNT samples. The results show a clear effect on the cell membrane potential, depending on the underlying substrate.

Electrostatic polarization fields trigger glioblastoma stem cell differentiation.

Over the last few years it has been understood that the interface between living cells and the underlying materials can be a powerful tool to manipulate cell functions. In this study, we explore the hypothesis that the electrical cell/material interface can regulate the differentiation of cancer stem-like cells (CSCs). Electrospun polymer fibres, either polyamide 66 or poly(lactic acid), with embedded graphene nanoplatelets (GnPs), have been fabricated as CSC scaffolds, providing both the 3D microenvironment and a suitable electrical environment favorable for CSCs adhesion, growth and differentiation. We have investigated the impact of these scaffolds on the morphological, immunostaining and electrophysiological properties of CSCs extracted from human glioblastoma multiform (GBM) tumor cell line. Our data provide evidence in favor of the ability of GnP-incorporating scaffolds to promote CSC differentiation to the glial phenotype. Numerical simulations support the hypothesis that the electrical interface promotes the hyperpolarization of the cell membrane potential, thus triggering the CSC differentiation. We propose that the electrical cell/material interface can regulate endogenous bioelectrical cues, through the membrane potential manipulation, resulting in the differentiation of CSCs. Material-induced differentiation of stem cells and particularly of CSCs, can open new horizons in tissue engineering and new approaches to cancer treatment, especially GBM.

Graphene Nanoplatelets Render Poly(3-Hydroxybutyrate) a Suitable Scaffold to Promote Neuronal Network Development.

The use of composite biomaterials as innovative bio-friendly neuronal interfaces has been poorly developed so far. Smart strategies to target neuro-pathologies are currently exploiting the mixed and complementary characteristics of composite materials to better design future neural interfaces. Here we present a polymer-based scaffold that has been rendered suitable for primary neurons by embedding graphene nanoplatelets (GnP). In particular, the growth, network formation, and functionality of primary neurons on poly(3-hydroxybutyrate) [P(3HB)] polymer supports functionalized with various concentrations of GnP were explored. After growing primary cortical neurons onto the supports for 14 days, all specimens were found to be biocompatible, revealing physiological growth and maturation of the neuronal network. When network functionality was investigated by whole patch-clamp measurements, pure P(3HB) led to changes in the action potential waveform and reduction in firing frequency, resulting in decreased neuronal excitability. However, the addition of GnP to the polymer matrix restored the electrophysiological parameters to physiological values. Interestingly, a low concentration of graphene was able to promote firing activity at a low level of injected current. The results indicate that the P(3HB)/GnP composites show great potential for electrical interfacing with primary neurons to eventually target central nervous system disorders.

Green Composites of Poly(3-hydroxybutyrate) Containing Graphene Nanoplatelets with Desirable Electrical Conductivity and Oxygen Barrier Properties.

Poly(3-hydroxybutyrate), a green polymer originating from prokaryotic microbes, has been used to prepare composites with graphene nanoplatelets (GnP) at different concentrations. The films were fabricated by drop-casting and were hot-pressed at a temperature lower than their melting point to provide the molecular chains enough energy to reorientate while avoiding melting and degradation. It was found that hot-pressing increases crystallinity and improves mechanical properties. The Young's modulus increased from 1.2 to 1.6 GPa for the poly(3-hydroxybutyrate) (P(3HB)) films and from 0.5 to 2.2 GPa for the 15 wt % P(3HB)/GnP composites. Electrical resistivity decreases enormously with GnP concentration and hot-pressing, reaching 6 Ω sq-1 for the hot-pressed 30 wt % P(3HB)/GnP composite. Finally, the hot-pressed P(3HB) samples exhibit remarkable oxygen barrier properties, with oxygen permeability reaching 2800 mL µm m-2 day-1, which becomes 895 mL µm m-2 day-1 when 15% GnP is added to the biopolymer matrix, one of the lowest values known for biopolymers and biocomposites. We propose that these biocomposites are used for elastic packaging and electronics.

Sustainable Active Food Packaging from Poly(lactic acid) and Cocoa Bean Shells.

Sustainable biocomposites have been developed by solvent mixing of poly(lactic acid) (PLA) with a fine powder of cocoa bean shells (CBS) and subsequent solution casting, using different concentrations of CBS. The inclusion of CBS recovers the crystallinity of the initially amorphous PLA films and improves the physical properties of the composites. Young's modulus increases by 80% with 75 wt % CBS inclusion; however, the composites maintain plasticity. The barrier properties of the hydrophobic composites were characterized, and the water vapor permeability is found to be ca. 3.5 × 10-5 g·m-1·day-1·Pa-1 and independent of the CBS content. On the other hand, oxygen permeability is found to depend on the CBS content, with values as low as 10 000 mL·µm·m-2·day-1·atm-1 for 50 wt % CBS. Furthermore, CBS confer antioxidant activity to the composites and improve swelling properties rendering the composites biodegradable in aquatic environments, reaching 70% of the maximum biodegradability in just 30 days. The above, in conjunction with the low level of migration measured in food simulant, make the PLA/CBS composites a highly promising material for active food packaging.

Fabrication of Visible Light-Induced Antibacterial and Self-Cleaning Cotton Fabrics Using Manganese Doped TiO2 Nanoparticles.

Ordinary textiles are very often malodorous and the origin of cross-infection. Their microclimate, consisting of moisture, contaminants, and sweat, provides favorable conditions for microbial growth. Therefore, simple approaches of surface modification using functional materials are widely adopted to introduce antibacterial properties. This study reports a simple and low cost technique that renders cotton fabrics antibacterial. Manganese (Mn)-doped photocatalytic titanium dioxide (TiO2) nanoparticles of ∼150 nm average diameter have been prepared by sol gel and applied on textile fabrics using a silicone binder. The treated fabrics displayed 100% reduction of Staphylococcus aureus (Gram-positive) and Klebsiella pneumoniae (Gram-negative) populations within 120 min under sunlight, demonstrating first order of reduction kinetics. Moreover, the functionalized fabrics demonstrated complete degradation of a methylene blue (MB) dye adsorbed on their surface, under both UV and visible light irradiation, turning them white. A similar effect was observed when the treated fabrics were immersed in a MB dye solution and subsequently irradiated. Here, the cotton fabrics functionalized with Mn-doped TiO2 nanoparticles were able to discolour the dissolved MB dye, demonstrating a water purification effect. In addition, the modified fabrics were resistant to several laundry cycles. Physical properties like mechanical strength, color, breathability, and aesthetic of the treated cotton fabrics remained unchanged. The modified cotton fabrics can be envisioned as antibacterial, antiodorous, and self-cleaning textiles for sports, medical uses, uniforms, fashion, home furnishing, and leisure activities. Finally, the treated textiles were found to be biocompatible.

Investigation of the electro-spinnability of alginate solutions containing gold precursor HAuCl4.

Alginate nanofibers with an average diameter of 75nm have been prepared by the electrospinning process. In addition, the spinnability of the solutions in the presence of the gold precursor HAuCl4 was investigated. At low concentrations of HAuCl4 well-formed nanofibers were produced, whereas as its concentration increases the nanofibrous mats present an increased number of bead-like defects. Herein, the in situ preparation of gold nanoparticles (Au NPs) is discussed since sodium alginate (SA) acts as the reducing agent and a mechanism is proposed in order to explain the bead-effect as well as the surface morphology of the alginate fibers decorated with Au NPs.

Zwitterionic Nanofibers of Super-Glue for Transparent and Biocompatible Multi-Purpose Coatings.

Here we show that macrozwitterions of poly(ethyl 2-cyanoacrylate), commonly called Super Glue, can easily assemble into long and well defined fibers by electrospinning. The resulting fibrous networks are thermally treated on glass in order to create transparent coatings whose superficial morphology recalls the organization of the initial electrospun mats. These textured coatings are characterized by low liquid adhesion and anti-staining performance. Furthermore, the low friction coefficient and excellent scratch resistance make them attractive as solid lubricants. The inherent texture of the coatings positively affects their biocompatibility. In fact, they are able to promote the proliferation and differentiation of myoblast stem cells. Optically-transparent and biocompatible coatings that simultaneously possess characteristics of low water contact angle hysteresis, low friction and mechanical robustness can find application in a wide range of technological sectors, from the construction and automotive industries to electronic and biomedical devices.

Self-cleaning organic/inorganic photo-sensors.

We present the fabrication of a multifunctional, hybrid organic-inorganic micropatterned device, which is capable to act as a stable photosensor and, at the same time, displaying inherent superhydrophobic self-cleaning wetting characteristics. In this framework several arrays of epoxy photoresist square micropillars have been fabricated on n-doped crystalline silicon substrates and subsequently coated with a poly(3-hexylthiophene-2,5-diyl) (P3HT) layer, giving rise to an array of organic/inorganic p-n junctions. Their photoconductivity has been measured under a solar light simulator at different illumination intensities. The current-voltage (I-V) curves show high rectifying characteristics, which are found to be directly correlated with the illumination intensity. The photoresponse occurs in extremely short times (within few tens of milliseconds range). The influence of the interpillar distance on the I-V characteristics of the sensors is also discussed. Moreover, the static and dynamic wetting properties of these organic/inorganic photosensors can be easily tuned by changing the pattern geometry. Measured static water contact angles range from 125° to 164°, as the distance between the pillars is increased from 14 to 120 µm while the contact angle hysteresis decreases from 36° down to 2°.

Silicon scaffolds promoting three-dimensional neuronal web of cytoplasmic processes.

Primary neurons were grown on structured silicon (Si) substrates, in the absence of chemotropic factors or synthetic extracellular matrix. The Si substrates used for the study comprise hierarchical structures in the micro- and nanolength scales. The substrates were structured via femtosecond laser irradiation of the Si wafer, in a reactive SF(6) environment. Electron microscopy revealed that the neurons formed an elaborate web of cytoplasmic processes in the absence of glial elements. The neuronal cytoplasm autografted the depth of the spikes, and the neurite sprouting took place over the spikes surface. Here we demonstrate how microfabrication of a Si surface provides an excellent platform for multifaceted studies of neuronal specimens.