RESUMO

The development of dressings based on electrospun membranes with polymers and plant extracts is an interesting approach to skin regeneration, providing elements to prevent contamination and a matrix that accelerates the healing process. We developed a membrane composed of polyvinylpyrrolidone (PVP), gel and Aloe vera peel extract via the electrospinning technique. Additionally, an optimal ratio of PVP/Av gel/Av skin extract was determined to facilitate membrane formation. Electrospun membranes were obtained with fiber diameters of 1403 ± 57.4 nm for the PVP and 189.2 ± 11.4 nm for PVP/Av gel/Av peel extract, confirming that the use of extracts generally reduced the fiber diameter. The incorporation of gel and peel extract of Aloe vera into the electrospun membrane was analyzed via FTIR and UV-Vis spectroscopies. FTIR revealed the presence of functional groups associated with phenolic compounds such as aloin, aloe-emodin, emodin and aloesin, which was confirmed by UV-Vis, revealing absorption bands corresponding to aloin, phenols and carbonyl groups. This finding provides evidence of the effective integration and prevalence of bioactive compounds of a phenolic and polysaccharide nature from the gel and the Av skin extract in the electrospun fibers, resulting in an advanced membrane that could improve and accelerate the healing process and protect the wound from bacterial infections.

RESUMO

Microorganisms showed unique mechanisms to resist and detoxify harmful metals in response to pollution. This study shows the relationship between presence of heavy metals and plant growth regulator compounds. Additionally, the responses of Rhodotorula mucilaginosa YR29 isolated from the rhizosphere of Prosopis sp. growing in a polluted mine jal in Mexico are presented. This research carries out a phenotypic characterization of R. mucilaginosa to identify response mechanisms to metals and confirm its potential as a bioremediation agent. Firstly, Plant Growth-Promoting (PGP) compounds were assayed using the Chrome Azurol S (CAS) medium and the Salkowski method. In addition, to clarify its heavy metal tolerance mechanisms, several techniques were performed, such as optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) supplemented with assorted detectors. Scanning transmission electron microscopy (STEM) was used for elementary mapping of the cell. Finally, yeast viability after all treatments was confirmed by confocal laser scanning microscopy (CLSM). The results have suggested that R. mucilaginosa could be a PGP yeast capable of triggering Pb2+ biosorption (representing 22.93% of the total cell surface area, the heavy metal is encapsulated between the cell wall and the microcapsule), and Pb2+ bioaccumulation (representing 11% of the total weight located in the vacuole). Based on these results, R. mucilaginosa as a bioremediation agent and its wide range of useful mechanisms for ecological purposes are highlighted.

Assuntos

Chumbo , Rhodotorula , Vacúolos , Biodegradação Ambiental

RESUMO

The development of composite materials with thermo-optical properties based on smart polymeric systems and nanostructures have been extensively studied. Due to the fact of its ability to self-assemble into a structure that generates a significant change in the refractive index, one of most attractive thermo-responsive polymers is poly(N-isopropylacrylamide) (PNIPAM), as well as its derivatives such as multiblock copolymers. In this work, symmetric triblock copolymers of polyacrylamide (PAM) and PNIPAM (PAMx-b-PNIPAMy-b-PAMx) with different block lengths were prepared by reversible addition-fragmentation chain-transfer polymerization (RAFT). The ABA sequence of these triblock copolymers was obtained in only two steps using a symmetrical trithiocarbonate as a transfer agent. The copolymers were combined with gold nanoparticles (AuNPs) to prepare nanocomposite materials with tunable optical properties. The results show that copolymers behave differently in solution due to the fact of variations in their composition. Therefore, they have a different impact on the nanoparticle formation process. Likewise, as expected, an increase in the length of the PNIPAM block promotes a better thermo-optical response.

RESUMO

The modulation of nanoparticles' size, shape, and dispersion by polymers has attracted particular attention in different fields. Nevertheless, there is a lack of information regarding the use of charged macromolecules as assistants in the nanostructures' nucleation and growth processes. Prompted by this, the in situ synthesis of gold nanoparticles (AuNPs) aided by hydrolyzed polyacrylamides (HPAM), with different chemical structures, was developed. In contrast to the conventional synthesis of nanostructures assisted by polyacrylamide, here, the polymerization, hydrolysis, and nanostructure formation processes were carried out simultaneously in the same milieu. Likewise, the growing chains acted as a template for the nanoparticles' growth, so their conformations and chemical structure, especially the amount of charges along the chain, played an important role in the AuNPs' morphology, size, and some of the final composite features. The nanocomposite was thoroughly characterized with appropriate techniques, including ATR-FTIR, GPC, UV-Vis, and SEM.

RESUMO

In this work, the influence of carbon nanotubes (CNTs) content on the mechanical and electrical properties of four series of polymeric matrix were made and their cytotoxicity on cells was evaluated to consider their use as a possible artificial muscle. For that, polymer composite yarns were electrospun using polymeric solutions at 10 wt.%. of poly(styrene-co-acrylonitrile) P(S:AN) and P(S:AN-acrylic acid) P(S:AN-AA) at several monomeric concentrations, namely 0:100, 20:80, 40:60, 50:50 (wt.%:wt.%), and 1 wt.% of AA. Carbon nanotubes (CNTs) were added to the polymeric solutions at two concentrations, 0.5 and 1.0 wt.%. PMCs yarns were collected using a blade collector. Mechanical and electrical properties of polymeric yarns indicated a dependence of CNTs content into yarns. Three areas could be found in fibers: CNTs bundles zones, distributed and aligned CNTs zones, and polymer-only zones. PMCs yarns with 0.5 wt.% CNTs concentration were found with a homogenous nanotube dispersion and axial alignment in polymeric yarn, ensuring load transfer on the polymeric matrix to CNTs, increasing the elastic modulus up to 27 MPa, and a maximum electrical current of 1.8 mA due to a good polymer-nanotube interaction.

RESUMO

In this study, tomato plants were grown in vitro with and without incorporation of TiO2 nanoparticles in Murashige and Skoog (MS) growth medium. The aim of this study was to describe the morphological (area and roundness cell) and mechanical (Young's Modulus) change in the different tissue of tomato root, epidermis (Ep), parenchyma (Pa), and vascular bundles (Vb), when the whole plant was exposed to TiO2 nanoparticles (TiO2 NPs). light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), wavelength dispersive X-ray fluorescence (WDXRF) techniques were used to identify changes into the root cells when TiO2 NPs were incorporated. TiO2 NPs incorporation produces changes in the area, roundness, and Young's Modulus of the tomato root. When tomato root is exposed to TiO2 NPs, the Ep and Vb area size decreases from 260.92 µm2 to 160.71 µm2 and, 103.08 µm2 to 52.13 µm2, respectively, compared with the control area, while in Pa tissue the area size was increased considerably from 337.72 mm2 to 892.96 mm2. Cellular roundness was evident in tomato root that was exposed to TiO2 NPs in the Ep (0.49 to 0.67), Pa (0.63 to 0.79), and Vb (0.76 to 0.71) area zones. Young's Modulus in Pa zone showed a rigid mechanical behavior when tomato root is exposed to TiO2 NPs (0.48 to 4.98 MPa control and TiO2 NPs, respectively). Meanwhile, Ep and Vb were softer than the control sample (13.9 to 1.06 MPa and 6.37 to 4.41 MPa respectively). This means that the Pa zone was stiffer than Ep and Vb when the root is exposed to TiO2 NPs. Furthermore, TiO2 NPs were internalized in the root tissue of tomato, accumulating mainly in the cell wall and intercellular spaces, with a wide distribution throughout the tissue, as seen in TEM.

RESUMO

The preparation of ultra-thin semi-transparent solar cells with potential applications in windows or transparent roofs entails several challenges due to the very small thickness of the layers involved. In particular, problems related to undesired inter-diffusion or inhomogeneities originated by incomplete coverage of the growing surfaces must be prevented. In this paper, undoped SnO2, CdS, and CdTe thin films with thickness suitable for use in ultra-thin solar cells were deposited with a radiofrequency (RF) magnetron sputtering technique onto conductive glass. Preparation conditions were found for depositing the individual layers with good surface coverage, absence of pin holes and with a relatively small growth rate adapted for the control of very small thickness. After a careful growth calibration procedure, heterostructured solar cells devices were fabricated. The influence of an additional undoped SnO2 buffer layer deposited between the conductive glass and the CdS window was studied. The incorporation of this layer led to an enhancement of both short circuit current and open circuit voltage (by 19 and 32%, respectively) without appreciable changes of other parameters. After the analysis of the cell parameters extracted from the current-voltage (I-V) curves, possible origins of these effects were found to be: Passivation effects of the SnO2/CdS interface, blocking of impurities diffusion or improvement of the band alignment.