In Situ Growth of Silver Nanoparticles on Chitosan Matrix for the Synthesis of Hybrid Electrospun Fibers: Analysis of Microstructural and Mechanical Properties.

A viable alternative for the next generation of wound dressings is the preparation of electrospun fibers from biodegradable polymers in combination with inorganic nanoparticles. A poly(vinyl alcohol)-chitosan-silver nanoparticles (PVA-CTS-Ag NPs) system has been developed for antimicrobial and wound healing applications. Here, the preparation of PVA-CTS-Ag electrospun fibers using a two-step process is reported in order to analyze changes in the microstructural, mechanical, and antibacterial properties and confirm their potential application in the biomedical field. The Ag nanoparticles were well-dispersed into the chitosan matrix and their cubic structure after the electrospinning process was also retained. The Ag NPs displayed an average diameter of ~33 nm into the CTS matrix, while the size increased up to 213 nm in the PVA-CTS-Ag(NPs) fibers. It was observed that strong chemical interactions exist between organic (CTS) and inorganic phases through nitrogenous groups and the oxygen of the glycosidic bonds. A defect-free morphology was obtained in the PVA-CTS-Ag NPs final fibers with an important enhancement of the mechanical properties as well as of the antibacterial activity compared with pure PVA-CTS electrospun fibers. The results of antibacterial activity against E. coli and S. aureus confirmed that PVA-CTS-Ag(NPs) fibers can be potentially used as a material for biomedical applications.

CVD Conditions for MWCNTs Production and Their Effects on the Optical and Electrical Properties of PPy/MWCNTs, PANI/MWCNTs Nanocomposites by In Situ Electropolymerization.

In this work, the optimal conditions of synthesizing and purifying carbon nanotubes (CNTs) from ferrocene were selected at the first stage, where decomposition time, argon fluxes, precursor amounts, decomposition temperature (at 1023 K and 1123 K), and purification process (HNO3 + H2SO4 or HCl + H2O2), were modulated through chemical vapor deposition (CVD) and compared to commercial CNTs. The processing temperature at 1123 K and the treatment with HCl + H2O2 were key parameters influencing the purity, crystallinity, stability, and optical/electrical properties of bamboo-like morphology CNTs. Selected multiwalled CNTs (MWCNTs), from 1 to 20 wt%, were electropolymerized through in-situ polarization with conductive polymers (CPs), poly(aniline) (PANI) and poly(pyrrole) (PPy), for obtaining composites. In terms of structural stability and electrical properties, MWCNTs obtained by CVD were found to be better than commercial ones for producing CPs composites. The CNTs addition in both polymeric matrixes was of 6.5 wt%. In both systems, crystallinity degree, related to the alignment of PC chains on MWCNTs surface, was improved. Electrical conductivity, in terms of the carrier density and mobility, was adequately enhanced with CVD CNTs, which were even better than the evaluated commercial CNTs. The findings of this study demonstrate that synergistic effects among the hydrogen bonds, stability, and conductivity are better in PANI/MWCNTs than in PPy/MWCNTs composites, which open a promissory route to prepare materials for different technological applications.

Continuous Microalgal Cultivation for Antioxidants Production.

Microalgae, including cyanobacteria, represent a valuable source of natural compounds that have remarkable bioactive properties. Each microalga species produces a mixture of antioxidants with different amounts of each compound. Three aspects are important in the production of bioactive compounds: the microalga species, the medium composition including light supplied and the photobioreactor design, and operation characteristics. In this study, the antioxidant content and productivity performance of four microalgae were assessed in batch and continuous cultures. Biomass productivity by the four microalgae was substantially enhanced under continuous cultivation by 5.9 to 6.3 times in comparison with batch cultures. The energetic yield, under the experimental conditions studied, ranged from 0.03 to 0.041 g biomass kJ-1. Phenols, terpenoids, and alkaloids were produced by Spirulinaplatensis, Isochrysisgalbana, and Tetraselmissuecica, whereas tocopherols and carotenoids were produced by the four microalgae, except for phycocyanin and allophycocyanin, which were only produced by S. platensis and Porphyridiumcruentum. The findings demonstrate that the continuous cultivation of microalgae in photobioreactors is a convenient method of efficiently producing antioxidants.