Juliano E. Oliveira

Structural and Morphological Characterization of Micro and Nanofibers Produced by Electrospinning and Solution Blow Spinning: A Comparative Study

Nonwoven mats of poly(lactic acid) (PLA), poly(ethylene oxide) (PEO), and poly(e-caprolactone) (PCL) were prepared at a nano- and submicron scale by solution blow spinning (SBS) and electrospinning in order to compare crystalline structure and morphology developed by both processes during fiber formation. Polymer solutions were characterized by rheometry and tensiometry. Spun fibers were characterized by several analytical steps. SEM analyses showed that both solution blow spun and electrospun fibers had similar morphology. Absence of residual solvents and characteristic infrared bands in the solution blow spun fibers for PLA, PCL, and PEO was confirmed by FTIR studies. XRD diffraction patterns for solution blow spun and electrospun mats revealed some differences related to distinct mechanisms of fiber formation developed by each process. Significant differences in thermal behavior by DSC were observed between cast films of PLA, PCL, and PEO and their corresponding spun nanofibers. Furthermore, the average contact angles for spun PLA and PCL were higher than for electrospun mats, whereas it was slightly lower for PEO. When comparing electrospun and solution blow spun fibers, it was possible to verify that fiber morphology and physical properties depended both on the spinning technique and type of polymer.

Development of poly(lactic acid) nanostructured membranes for the controlled delivery of progesterone to livestock animals

Solution blow spinning (SBS) is a novel technology feasible to produce nanostructured polymeric membranes loaded with active agents. In the present study, nanofibrous mats of poly(lactic acid) (PLA) loaded with progesterone (P4) were produced by SBS at different P4 concentrations. The spun membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The in vitro releasing of P4 was evaluated using high-performance liquid chromatography (HPLC). Interactions between progesterone and PLA were confirmed by rheological measurements of the PLA/P4 solutions and in the spun mats by microscopy (SEM), thermal (DSC) and spectral (FTIR) analyses. SEM micrographs provided evidences of a smooth and homogeneous structure for nanostructured membranes without progesterone crystals on fiber surface. FTIR spectroscopy indicated miscibility and interaction between the ester of PLA and the ketone groups of the P4 in the nanofibers. X-ray analysis indicated that the size of PLA crystallites increased with progesterone content. Finally, by in vitro release experiments it was possible to observe that the progesterone releasing follows nearly first-order kinetics, probably due to the diffusion of hormone into PLA nanofibers.

Poly(lactic acid)/Carbon Nanotube Fibers as Novel Platforms for Glucose Biosensors

The focus of this paper is the development and investigation of properties of new nanostructured architecture for biosensors applications. Highly porous nanocomposite fibers were developed for use as active materials in biosensors. The nanocomposites comprised poly(lactic acid)(PLA)/multi-walled carbon nanotube (MWCNT) fibers obtained via solution-blow spinning onto indium tin oxide (ITO) electrodes. The electrocatalytic properties of nanocomposite-modified ITO electrodes were investigated toward hydrogen peroxide (H2O2) detection. We investigated the effect of carbon nanotube concentration and the time deposition of fibers on the sensors properties, viz., sensitivity and limit of detection. Cyclic voltammetry experiments revealed that the nanocomposite-modified electrodes displayed enhanced activity in the electrochemical reduction of H2O2, which offers a number of attractive features to be explored in development of an amperometric biosensor. Glucose oxidase (GOD) was further immobilized by drop coating on an optimized ITO electrode covered by poly(lactic acid)/carbon nanotube nanofibrous mats. The optimum biosensor response was linear up to 800 mM of glucose with a sensitivity of 358 nA·mM−1 and a Michaelis-Menten constant (KM) of 4.3 mM. These results demonstrate that the solution blow spun nanocomposite fibers have great potential for application as amperometric biosensors due to their high surface to volume ratio, high porosity and permeability of the substrate. The latter features may significantly enhance the field of glucose biosensors.

Evaluation of Hemagglutination Activity of Chitosan Nanoparticles Using Human Erythrocytes

Chitosan is a polysaccharide composed of randomly distributed chains of β-(1-4) D-glucosamine and N-acetyl-D-glucosamine. This compound is obtained by partial or total deacetylation of chitin in acidic solution. The chitosan-based hemostatic agents have been gaining much attention in the management of bleeding. The aim of this study was to evaluate in vitro hemagglutination activity of chitosan nanoparticles using human erythrocytes. The preparation of nanoparticles was achieved by ionotropic gelification technique followed by neutralization with NaOH 1 mol/L−1. The hemagglutination activity was performed on a solution of 2% erythrocytes (pH 7.4 on PBS) collected from five healthy volunteers. The hemolysis determination was made by spectrophotometric analysis. Chitosan nanoparticle solutions without NaOH addition changed the reddish colour of the wells into brown, suggesting an oxidative reaction of hemoglobin and possible cell lysis. All neutralized solutions of chitosan nanoparticles presented positive haemagglutination, without any change in reaction color. Chitosan nanoparticles presented hemolytic activity ranging from 186.20 to 223.12%, while neutralized solutions ranged from 2.56 to 72.54%, comparing to distilled water. Results highlight the need for development of new routes of synthesis of chitosan nanoparticles within human physiologic pH.

Sensor Array for Water Analysis Based on Interdigitated Electrodes Modified With Fiber Films of Poly(Lactic Acid)/Multiwalled Carbon Nanotubes

A disposable low cost and simple flow-cell electronic tongue for water analysis is described. A sensor array is used that is comprised of six interdigitated microelectrodes coated with nanofiber films of poly(lactic acid)/mutliwalled carbon nanotube (MWCNT) composites. Fiber films are deposited directly on the interdigitated electrodes surface by solution blow spinning. Fiber film thickness is varied by using different deposition times (1, 3, and 15 min). Analysis of scanning electron microscopy and transmission electron microscopy micrographs indicates that average fiber diameters are 400 nm for neat poly lactic acid (PLA) and 200 nm for the PLA/MWCNT composite. The MWCNT is poorly dispersed in the PLA fiber matrix and formed aggregates interspersed throughout the fiber length. There are also MWCNTs exposed or partially exposed at the fiber surface. Fiber films containing MWCNT (1%) give the highest dc conductivity values and the most linear I-V profiles at room temperature. Sensor arrays with thin fiber film coatings (1 min deposition time) provide the best result for discriminating potable water samples using principal component analysis (PCA). The flow-cell electronic tongue coupled with PCA is used to discriminate potable water samples from non-potable water contaminated with metals or traces of pesticides.

Solution blow spun nanocomposites of poly(lactic acid)/cellulose nanocrystals from Eucalyptus kraft pulp

Cellulose nanocrystals (CNCs) were extracted from Eucalyptus kraft pulp by sulfuric acid hydrolysis, and esterified with maleic anhydride (CNCMA). The incorporation of sulfate ester groups on the cellulose surface resulted in higher stability of the nanoparticles in aqueous suspensions and lower thermal stability. Then, PLA/CNC and PLA/CNCMA nanocomposites were successfully obtained by solution blow spinning (SBS) using dimethyl carbonate (DMC) as solvent. CNC and CNCMA indicated to be acting both as nucleating agents or growth inhibitors of PLA crystal and tends to favor the formation of PLA crystals of higher stability. A fraction of the nanocrystals indicate to be exposed on the surface of the PLA fibers, since the hydrophilicity of the composite films increased significantly. Such composites may have potential application as filtering membranes or adsorbents.

An electronic tongue based on conducting electrospun nanofibers for detecting tetracycline in milk samples

The development of novel and portable chemical sensors aimed at the food industry is of prime importance for food safety issues, and nanomaterial science can greatly contribute to this task. In this context, a careful choice of the sensing material is essential for achieving high performance sensor arrays, such as those employed in nanostructured electronic tongues (e-tongues). In the current work, an impedimetric e-tongue based on gold interdigitated microelectrodes (IDEs) modified with polyamide 6/polyaniline (PA6/PANI) electrospun nanofibers was developed, characterized and used to detect tetracycline (TC) residue in fat and skimmed milk samples. By analyzing the electrical resistance data collected by the e-tongue, which were treated by Principal Component Analysis (PCA), the e-tongue was able to identify the presence of TC residues (from 1 to 300 ppb) in fat and skimmed milk samples. The results obtained demonstrate the ability of the approach of modifying IDEs with conducting electrospun nanofibers to be used as sensing units in the e-tongue, aiming to analyze complex matrices such as milk without any prior pre-treatment.

Obtenção de micro e nanofibras de PVC pela técnica de Fiação por Sopro em Solução

We obtained PVC micro- and nanofibers by Solution Blow Spinning, a recently developed technique capable of producing polymeric micro- and nanostructures with high speed as compared to other techniques such as electrospinning. The PVC fibers produced had an average diameter ranging from 217 nm to 2.5 µm, depending on the experimental conditions. We evaluated the effects of processing conditions and polymer concentration in solution had the most significant effect in fiber diameter. It was also observed that the thermal stability of the fibers was unaffected when compared to PVC films and powder.

Impact of different silkworm dietary supplements on its silk performance

This study aims to evaluate the effect of silkworm larva (Bombyx mori) diet supplementation with two amino acids (threonine and valine) on the cocoon production and on the structural and mechanical properties of the silk produced. Negligible morphological differences were observed in the silk fiber threads from silkworm larvae supplemented with the tested amino acids. Higher production (yield) of silk was obtained using threonine in the diet of the silkworm. The treatments with threonine have increased the limit of proportionality, tensile strength, toughness, and maximum deformation of the thread of silk fibers. No significant increment in these properties was observed due to the increase in the threonine content. The treatments with valine led to lower increase in tensile strength and toughness. The real density of the silk has decreased with the use of supplements. The present study contributes to engineering of advanced silk materials, which should be attractive candidates for multipurpose applications.

Métodos de reforço microestrutural da hidroxiapatita

Hydroxyapatite (HAp) is a calcium phosphate of chemical formula Ca10(PO4)6(OH)2, with a molar ratio of Ca /P equal to 1.67. This material has a great importance in bioceramics technology, being the main mineral phase constituent in human teeth and bones. It is used as a substitute for damaged hard tissues, coating of orthopedic prostheses and implants and bone tissue repair. However, low mechanical strength and high brittleness makes its use restricted to low mechanic strength areas. One way of improving these properties is to combine HAp with other materials such as zirconia, alumina, mullite, titanium, bioglass and ions in order to join desirable properties of both materials. This review aims to describe the properties resulting from the formation of different ions and materials. It was observed that most of the approaches currently used for mechanical reinforcement are effective in improving fracture toughness and flexural strength and hardness.It was also found that the effect of titanium ions on such the mechanical behavior of HAp composite materials has not been completely elucidated. The improvement of the mechanical behavior due to the addition of reinforcement is dependent on factors such as sintering temperature, amount of reinforcement used, absence of undesirable structural changes, as well as presence of other phases that are deleterious to the ultimate properties of produced materials.