Electrospun polyamide 6/poly(allylamine hydrochloride) nanofibers functionalized with carbon nanotubes for electrochemical detection of dopamine

The use of nanomaterials as an electroactive medium has improved the performance of bio/chemical sensors, particularly when synergy is reached upon combining distinct materials. In this paper, we report on a novel architecture comprising electrospun polyamide 6/poly(allylamine hydrochloride) (PA6/PAH) nanofibers functionalized with multiwalled carbon nanotubes, used to detect the neurotransmitter dopamine (DA). Miscibility of PA6 and PAH was sufficient to form a single phase material, as indicated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), leading to nanofibers with no beads onto which the nanotubes could adsorb strongly. Differential pulse voltammetry was employed with indium tin oxide (ITO) electrodes coated with the functionalized nanofibers for the selective electrochemical detection of dopamine (DA), with no interference from uric acid (UA) and ascorbic acid (AA) that are normally present in biological fluids. The response was linear for a DA concentration range from 1 to 70 μmol L(-1), with detection limit of 0.15 μmol L(-1) (S/N = 3). The concepts behind the novel architecture to modify electrodes can be potentially harnessed in other electrochemical sensors and biosensors.

Advances in Functional Polymer Nanofibers: From Spinning Fabrication Techniques to Recent Biomedical Applications

Functional polymeric micro-/nanofibers have emerged as promising materials for the construction of structures potentially useful in biomedical fields. Among all kinds of technologies to produce polymer fibers, spinning methods have gained considerable attention. Herein, we provide a recent review on advances in the design of micro- and nanofibrous platforms via spinning techniques for biomedical applications. Specifically, we emphasize electrospinning, solution blow spinning, centrifugal spinning, and microfluidic spinning approaches. We first introduce the fundamentals of these spinning methods and then highlight the potential biomedical applications of such micro- and nanostructured fibers for drug delivery, tissue engineering, regenerative medicine, disease modeling, and sensing/biosensing. Finally, we outline the current challenges and future perspectives of spinning techniques for the practical applications of polymer fibers in the biomedical field.

Nanocomposite PAAm/methyl cellulose/montmorillonite hydrogel: evidence of synergistic effects for the slow release of fertilizers

In this work, we synthesized a novel series of hydrogels composed of polyacrylamide (PAAm), methylcellulose (MC), and calcic montmorillonite (MMt) appropriate for the controlled release of fertilizers, where the components presented a synergistic effect, giving very high fertilizer loading in their structure. The synthesized hydrogel was characterized in relation to morphological, hydrophilic, spectroscopic, structural, thermal, and kinetic properties. After those characterizations, the application potential was verified through sorption and desorption studies of a nitrogenated fertilizer, urea (CO(NH2)2). The swelling degree results showed that the clay loading considerably reduces the water absorption capability; however, the hydrolysis process favored the urea adsorption in the hydrogel nanocomposites, increasing the load content according to the increase of the clay mass. The FTIR spectra indicated that there was incorporation of the clay with the polymeric matrix of the hydrogel and that incorporation increased the water absorption speed (indicated by the kinetic constant k). By an X-ray diffraction technique, good nanodispersion (intercalation) and exfoliation of the clay platelets in the hydrogel matrix were observed. Furthermore, the presence of the montmorillonite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel in different pH ranges. In conclusion, excellent results were obtained for the controlled desorption of urea, highlighting the hydrolyzed hydrogels containing 50% calcic montmorillonite. This system presented the best desorption results, releasing larger amounts of nutrient and almost 200 times slower than pure urea, i.e., without hydrogel. The total values of nutrients present in the system show that this material is potentially viable for application in agriculture as a nutrient carrier vehicle.

Cytotoxicity and expression of genes involved in the cellular stress response and apoptosis in mammalian fibroblast exposed to cotton cellulose nanofibers

Cellulose nanofibers (CNF) have mechanical properties that make them very attractive for applications in the construction of polymeric matrices, drug delivery and tissue engineering. However, little is known about their impact on mammalian cells. The objective of this study was to evaluate the cytotoxicity of CNF and their effect on gene expression of fibroblasts cultured in vitro. The morphology of CNF was analyzed by transmission electron microscopy and the surface charge by Zeta potential. Cell viability was analyzed by flow cytometry assay and gene expression of biomarkers focused on cell stress response such as Heat shock protein 70.1 (HSP70.1) and Peroxiredoxin 1 (PRDX1) and apoptosis as B-cell leukemia (BCL-2) and BCL-2 associated X protein (BAX) by RT-PCR assay. Low concentrations of CNF (0.02-100 μg ml(-1)) did not cause cell death; however, at concentrations above 200 μg ml(-1), the nanofibers significantly decreased cell viability (86.41 ± 5.37%). The exposure to high concentrations of CNF (2000 and 5000 μg ml(-1)) resulted in increased HSP70.1, PRDX1 and BAX gene expression. The current study concludes that, under the conditions tested, high concentrations (2000 and 5000 μg ml(-1)) of CNF cause decreased cell viability and affect the expression of stress- and apoptosis-associated molecular markers.

Preparation of chitosan nanoparticles using methacrylic acid

In this work the preparation of chitosan nanoparticle was investigated using methacrylic acid in different conditions and studied by particle size analyzer, zeta-potential, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM). The particle size was dependent on the chitosan concentration used during the preparation method. Nanoparticles with sizes as small as 60 nm were achieved, that can be extremely important for several applications. The nanoparticles solution was also pH-sensitive, due to swelling and aggregation of the nanoparticles. The nanoparticles obtained presented a very homogeneous morphology showing a quite uniform particles size distribution and a rather spherical shape.

Effect of fiber treatments on tensile and thermal properties of starch/ethylene vinyl alcohol copolymers/coir biocomposites

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber-matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Young's modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.

An artificial taste sensor based on conducting polymers

Pure and composite nanostructured films of conducting polymers were used as individual sensing units constituting an electronic tongue. The use of extremely thin films for signal transduction via impedance spectroscopy measurements in the frequency range 10-1 MHz allows the detection of trace amounts of tastants and inorganic contaminants in liquid systems. In addition, the sensor could detect the suppression of sourness by sweetness displaying similarities with the biological system. Brands of several commercial beverages could be easily distinguished without complex analysis, including the discrimination of waters, tastants and wines.

Solution blow spun PMMA nanofibers wrapped with reduced graphene oxide as an efficient dye adsorbent

Composite nanofiber membranes of PMMA-rGO serve as promising materials for effective adsorption of dye pollutants from contaminated water.

Caracterização química e estrutural de fibra de sisal da variedade Agave sisalana

Nos últimos anos, o interesse pelo uso de fibras naturais em materiais compósitos poliméricos tem aumentado significativamente. Neste trabalho foram investigadas as propriedades, químicas, físicas, térmicas e estruturais da fibra de sisal brasileira da variedade Agave sisalana. Nosso objetivo foi avaliar a qualidade e o desempenho desta fibra para aplicações industriais. Foram realizados ensaios de resistência à tração, análise da composição química, difração de raios X, e estudos por microscopia eletrônica de varredura (MEV) ao longo do comprimento da fibra. A fibra de sisal brasileira apresentou propriedades mecânicas e térmicas dentro da faixa relatada na literatura, mostrando-se adequada para ser utilizada em materiais compósitos poliméricos.

Preparation and characterization of novel micro- and nanocomposite hydrogels containing cellulosic fibrils

The main objective of this article was to report a simple, fast, and low cost strategy for the synthesis of micro- and nanocomposites by adding cellulose nanofibers, obtained by acid hydrolysis, and added to hydrogels as reinforcing agents. Specifically, when cellulose nanofibers were added to hydrogels, morphologic analyses showed significant decreases in pore size and formation of three-dimensional well-oriented porous microstructure. It was also observed that cellulose nanoparticles improved the mechanical and structural network properties without negatively impacting their thermal and hydrophilic properties. The value of maximum compressive stress was 2.1 kPa for the PAAm-MC, and it increased to 4.4 kPa when the cellulose nanofiber was incorporated into the hydrogel. By investigation of XRD patterns, it was found that the incorporation of cellulose nanofiber affected the crystallinity of PAAm-MC hydrogels, thus contributing to improvements in mechanical, structural, and hydrophilic properties of the PAAm-MC hydrogels.

Improving the electrochemical properties of polyamide 6/polyaniline electrospun nanofibers by surface modification with ZnO nanoparticles

ZnO nanoparticles adsorbed onto electrospun nanofiber surfaces improve the electron transfer kinetics and increase the electrode electroactive area. The modified electrodes can be a potential platform for electrochemical applications.

Wearable sensors made with solution-blow spinning poly(lactic acid) for non-enzymatic pesticide detection in agriculture and food safety

On-site monitoring the presence of pesticides on crops and food samples is essential for precision and post-harvest agriculture, which demands nondestructive analytical methods for rapid, low-cost detection that is not achievable with gold standard methods. The synergy between eco-friendly substrates and printed devices may lead to wearable sensors for decentralized analysis of pesticides in precision agriculture. In this paper we report on a wearable non-enzymatic electrochemical sensor capable of detecting carbamate and bipyridinium pesticides on the surface of agricultural and food samples. The low-cost devices (<US$ 0.08 per unit) contained three-electrode systems deposited via screen-printing technology (SPE) on solution-blow spinning mats of poly (lactic acid) (PLA). The flexible PLA/SPE sensors can be used on flat, curved and irregular surfaces of leaves, vegetables and fruits. Detection was performed using differential pulse voltammetry and square wave voltammetry with detection limits of 43 and 57 nM for carbendazim and diquat, respectively. The wearable non-enzymatic sensor can discriminate and quantify carbendazim and diquat on apple and cabbage skins with no interference from other pesticides. The use of such wearable sensors may be extended to other agrochemicals, including with incorporation of active bio (sensing) layers for online monitoring of any type of agricultural products and foods.

Whiskers de fibra de sisal obtidos sob diferentes condições de hidrólise ácida: efeito do tempo e da temperatura de extração

Neste trabalho, os efeitos de diferentes condições de tempo e temperatura usados para a preparação de whiskers de sisal foram investigados com o objetivo de se determinar a influência destes parâmetros experimentais na morfologia, cristalinidade e estabilidade térmica dos materiais preparados. A obtenção dos whiskers deu-se após o pré-branqueamento da fibra de sisal com solução alcalina de peróxido de hidrogênio. A fibra branqueada foi submetida ao processo de hidrólise com solução de ácido sulfúrico 60% (m/m) sob três diferentes condições de temperatura e tempos de extração: 45 °C e 60 minutos (WS45_60); 45 °C e 75 minutos (WS45_75) e 60 °C e 30 minutos (WS60_30). Os whiskers foram caracterizados quanto à morfologia por microscopia eletrônica de transmissão (MET), quanto à cristalinidade (DRX), carga superficial (potencial zeta) , teor de enxofre (análise elementar) e quanto à estabilidade térmica por termogravimetria (TGA). Os resultados mostraram que os whiskers de sisal apresentaram comprimento e diâmetro médios e 210 nm e 5 nm respectivamente. Devido à alta aglomeração dos whiskers, diferenças relativas às características dimensionais não puderam ser determinadas. Os resultados obtidos revelaram uma forte dependência da cristalinidade final dos whiskers com a temperatura e tempo de extração. O uso de temperatura mais alta (60 °C) associado a um menor tempo de extração (30 minutos) resulta em whiskers com boa estabilidade térmica (235 °C), maior cristalinidade e sem o comprometimento da estrutura cristalina da celulose.