Ricardo J.B. Pinto

Antibacterial activity of nanocomposites of silver and bacterial or vegetable cellulosic fibers.

Cellulose/Ag nanocomposites were prepared using two distinct methodologies and two cellulose substrates: vegetable and bacterial cellulose. These nanocomposites were characterized in terms of their morphology and chemical composition. Detailed studies on the antibacterial activity of these materials were carried out for Bacillus subtilis, Staphylococcus aureus and Klebsiella pneumoniae. Silver nanoparticles present in the cellulosic fibers in concentrations as low as 5.0x10(-4)wt.% make these nanocomposites effective antibacterial materials. We anticipate that the versatile use of these cellulose-based nanocomposites can bring a promising strategy to produce a wide range of interesting materials where antibacterial properties are crucial.

Antibacterial activity of optically transparent nanocomposite films based on chitosan or its derivatives and silver nanoparticles

Colloidal silver nanoparticles (NPs) were prepared using the citrate and borohydride reduction methods and were then investigated as fillers in three matrices: unmodified chitosan, water-soluble chitosan and a N-alkyl chitosan derivative. The nanocomposites were used to prepare cast thin films (9-19 μm thickness) and characterized for their optical and antimicrobial properties. The optical properties of the materials were adjusted either by varying the Ag NPs content in the films (0.5-3.9% w/w) or by using samples of Ag NPs with distinct particle size distributions. The antibacterial activity towards both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Klebsiella pneumoniae and Escherichia coli) was investigated for the various composites. For the unmodified chitosan nanocomposites, the bactericidal effect depended on their Ag content while such an effect was always observed for water-soluble chitosan and N-alkyl chitosan based materials. This research provides a basis for the evaluation of chitosan/silver composites in applications requiring flexible films with tuned optical properties and antimicrobial activity.

Electrostatic assembly of Ag nanoparticles onto nanofibrillated cellulose for antibacterial paper products

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.

Transparent bionanocomposites with improved properties prepared from acetylated bacterial cellulose and poly(lactic acid) through a simple approach

The preparation and characterization of biocomposite materials with improved properties based on poly(lactic acid) (PLA) and bacterial cellulose, and, for comparative purposes, vegetal cellulose fibers, both in their pristine form or after acetylation, is reported. The composite materials were obtained through the simple and green mechanical compounding of a PLA matrix and bacterial cellulose nanofibrils (or vegetable fibers), and were characterized by TGA, DSC, tensile assays, DMA, SEM and water uptake. The bionanocomposites obtained from PLA and acetylated bacterial cellulose were particularly interesting, given the considerable improvement in thermal and mechanical properties, as evidenced by the significant increase in both elastic and Young moduli, and in the tensile strength (increments of about 100, 40 and 25%, respectively) at very low nanofiller loadings (up to 6%). These nanocomposites also showed low hygroscopicity and considerable transparency, features reported here for the first time.

Antifungal activity of transparent nanocomposite thin films of pullulan and silver against Aspergillus niger

Silver has been mainly investigated as an antibacterial agent and less as a fungicide in which concerns antimicrobial properties. In this research, the antifungal activity of composite films of pullulan and Ag nanoparticles (NP) against Aspergillus niger was evaluated using standard protocols. These new materials were prepared as transparent cast films (66-74 μm thickness) from Ag hydrosols containing the polysaccharide. Fungal growth inhibition was observed in the presence of such silver nanocomposite films. Moreover, disruption of the spores cells of A. niger was probed for the first time by means of scanning electron microscopy (SEM). This effect occurred in the presence of the nanocomposites due to Ag NP dispersed as fillers in pullulan. This polysaccharide was used here as a biocompatible matrix, hence making these nanocomposites beneficial for the development of antifungal packaging materials.

Antibacterial Activity of Nanocomposites of Copper and Cellulose

The design of cheap and safe antibacterial materials for widespread use has been a challenge in materials science. The use of copper nanostructures combined with abundant biopolymers such as cellulose offers a potential approach to achieve such materials though this has been less investigated as compared to other composites. Here, nanocomposites comprising copper nanofillers in cellulose matrices have been prepared by in situ and ex situ methods. Two cellulose matrices (vegetable and bacterial) were investigated together with morphological distinct copper particulates (nanoparticles and nanowires). A study on the antibacterial activity of these nanocomposites was carried out for Staphylococcus aureus and Klebsiella pneumoniae, as pathogen microorganisms. The results showed that the chemical nature and morphology of the nanofillers have great effect on the antibacterial activity, with an increase in the antibacterial activity with increasing copper content in the composites. The cellulosic matrices also show an effect on the antibacterial efficiency of the nanocomposites, with vegetal cellulose fibers acting as the most effective substrate. Regarding the results obtained, we anticipate the development of new approaches to prepare cellulose/copper based nanocomposites thereby producing a wide range of interesting antibacterial materials with potential use in diverse applications such as packaging or paper coatings.

Fluorescent Bioactive Corrole Grafted-Chitosan Films.

Transparent corrole grafted-chitosan films were prepared by chemical modification of chitosan with a corrole macrocycle, namely, 5,10,15-tris(pentafluorophenyl)corrole (TPFC), followed by solvent casting. The obtained films were characterized in terms of absorption spectra (UV-vis), FLIM (fluorescence lifetime imaging microscopy), structure (FTIR, XPS), thermal stability (TGA), thermomechanical properties (DMA), and antibacterial activity. The results showed that the chemical grafting of chitosan with corrole units did not affect its film-forming ability and that the grafting yield increased with the reaction time. The obtained transparent films presented fluorescence which increases with the amount of grafted corrole units. Additionally, all films showed bacteriostatic effect against S. aureus, as well as good thermomechanical properties and thermal stability. Considering these features, promising applications may be envisaged for these corrole-chitosan films, such as biosensors, bioimaging agents, and bioactive optical devices.

Composites of Cellulose and Metal Nanoparticles

Research on inorganic/organic nanocomposite materials is a fast growing interdisciplinary area in materials science and engineering. In particular, extensive work has been undertaken in the development of sustainable and environmentally friendly resources and methods. A key idea has been the production of nanocomposites comprising biopolymers that in specif‐ ic contexts can replace conventional materials such as synthetic polymers. It is well known that the properties of nanocomposite materials depend not only on the properties of their individual components but also on morphological and interfacial characteristics arising from the combination of distinct materials [1]. Therefore the use of polymers such as cellu‐ lose, starch, alginate, dextran, carrageenan, and chitosan among others, gain great relevance not only due to their renewable nature and biodegradability, but also because a variety of formulations can be exploited depending on the envisaged functionality [2, 3].

Unveiling the Chemistry behind the Green Synthesis of Metal Nanoparticles

Nanobiotechnology has emerged as a fundamental domain in modern science, and metallic nanoparticles (NPs) are one of the largest classes of NPs studied because of their wide spectrum of possible applications in several fields. The use of plant extracts as reducing and stabilizing agents in their synthesis is an interesting and reliable alternative to conventional methodologies. However, the role of the different components of such extracts in the reduction/stabilization of metal ions has not yet been understood clearly. Here we studied the behavior of the main components of a Eucalyptus globulus Labill. bark aqueous extract during metal-ion reduction followed by advanced chromatographic techniques, which allowed us to establish their specific role in the process. The obtained results showed that phenolic compounds, particularly galloyl derivatives, are mainly responsible for the metal-ion reduction, whereas sugars are essentially involved in the stabilization of the NPs.

Implementation of social features over regular IPTV stb

Social TV research area has benefited in the late years from the dissemination of IPTV services and related technological possibilities. Features of presence, communication and recommendation have been proposed and are now more common in the prototypes being developed. However a high number of these experiments and proposals are not yet implemented over regular commercial IPTV platforms and can take some time to be available with a compelling graphical and interaction design. The Social TV application WeOnTV, covered in this paper, was developed in the staging platform of PT Inovação IPTV infrastructure. The work and evaluation so far showed promising results including a successful test over the MEO - IPTV commercial solution. The paper focuses on feasible approaches taken towards the interface design and implementation of WeOnTVs social features, which can be useful as directions to other iTV developments over regular browser based set-top boxes.