Fabrication and characterization of gold nanoparticle-doped electrospun PCL/chitosan nanofibrous scaffolds for nerve tissue engineering

In the field of nerve tissue engineering, nanofibrous scaffolds could be a promising candidate when they are incorporated with electrical cues. Unique physico-chemical properties of gold nanoparticles (AuNPs) make them an appropriate component for increasing the conductivity of scaffolds to enhance the electrical signal transfer between neural cells. The aim of this study was fabrication of AuNPs-doped nanofibrous scaffolds for peripheral nerve tissue engineering. Polycaprolactone (PCL)/chitosan mixtures with different concentrations of chitosan (0.5, 1 and 1.5) were electrospun to obtain nanofibrous scaffolds. AuNPs were synthesized by the reduction of HAuCl₄ using chitosan as a reducing/stabilizing agent. A uniform distribution of AuNPs with spherical shape was achieved throughout the PCL/chitosan matrix. The UV–Vis spectrum revealed that the amount of gold ions absorbed by nanofibrous scaffolds is in direct relationship with their chitosan content. Evaluation of electrical property showed that inclusion of AuNPs significantly enhanced the conductivity of scaffolds. Finally, after 5 days of culture, biological response of Schwann cells on the AuNPs-doped scaffolds was superior to that on as-prepared scaffolds in terms of improved cell attachment and higher proliferation. It can be concluded that the prepared AuNPs-doped scaffolds can be used to promote peripheral nerve regeneration.

Open image in new window

     

Synthesis and photocatalytic studies of TiO2-clinoptilolite on spent caustic wastewater treatment

Mixed spent caustic is an industrial wastewater that is generated from oil refineries and olefin units. In this investigation, the TiO₂ film was loaded with Clinoptilolite for preparing TiO₂-clinoptilolite photocatalyst. In order to characterize the surface of composite and its microstructure, scanning electron microscopy (SEM) and powder x-ray diffraction (XRD) have been used. Subsequently, this photocatalyst is utilized for the degradation of spent caustic wastewater to determine the photocatalytic efficiency of TiO₂-clinophotocatalyst. Then the photocatalytic degradation of chemical oxygen demand (COD) in spent caustic wastewater has been modeled using the design of experiment method. This procedure was performed in two ways: in the presence of an oxidant agent (H₂O₂) and by minimizing the amount of oxidant. The results show that the maximum degradation efficiency of TiO₂-clinophotocatalyst is 74.3% and 77.3% under the condition of applying limitation and without concerning limitation for the presence of oxidant, respectively.     

Immobilisation of phytase producing Gluconacetobacter with bacterial cellulose nano‐fibres and promotion of enzyme activities by magnetite nanoparticles

The isolated Gluconacetobacter sp. with accession number: {"type":"entrez-nucleotide","attrs":{"text":"KY996741","term_id":"1315565261"}}KY996741 was assayed for evaluation of phytase activity. It could solubilise sodium phytate in the absence of soluble phosphate with the cells; however, the enzyme was not seen in cell free extract, to the best of their knowledge the intracellular phytase activities of Gluconacetobacter sp. was not reported previously. Also, the potential of in situ immobilisation of cells produced enzyme (/phytase producing bacteria) in bacterial cellulose was investigated and was studied by SEM and AFM. The results showed that the immobilised probiotic cells had the best activity of 1229 U/ml. The optimum temperature of the immobilised enzyme activity was at 45°C (5969 U/ml) and the immobilised phytase maintained 64% of its activities after two repeated cycles. The enzyme needs mild conditions for its activity and has a short life time and low stability and lost activities from 1229 to 500 U/ml during 30 days. However, it was showed that the addition of 1 ppm nano‐ferric oxide particles could promote the phytase activities of immobilised cell from 500 U/ml to >1500 U/ml. This immobilised phytase producing cells on bacterial cellulose can be useful as food and/feed supplement for phytin removal.Inspec keywords: enzymes, microorganisms, cellular biophysics, biochemistry, molecular biophysics, nanofibres, scanning electron microscopy, atomic force microscopy, nanoparticlesOther keywords: phytase producing Gluconacetobacter immobilisation, bacterial cellulose nano‐fibres, enzyme activities promotion, magnetite nanoparticles, accession number {"type":"entrez-nucleotide","attrs":{"text":"KY996741","term_id":"1315565261"}}KY996741, intracellular phytase activity, sodium phytate, cell free extract, SEM, AFM, probiotic cells, nano‐ferric oxide particles, phytin removal, time 30 day     

Mechanical modeling of silk fibroin/TiO2 and silk fibroin/fluoridated TiO2 nanocomposite scaffolds for bone tissue engineering

Biocompatible and biodegradable three-dimensional scaffolds are commonly porous which serve to provide suitable microenvironments for mechanical supporting and optimal cell growth. Silk fibroin (SF) is a natural and biomedical polymer with appropriate and improvable mechanical properties. Making a composite with a bioceramicas reinforcement is a general strategy to prepare a scaffold for hard tissue engineering applications. In the present study, SF was separately combined with titanium dioxide (TiO₂) and fluoridated titanium dioxide nanoparticles (TiO₂-F) as bioceramic reinforcements for bone tissue engineering purposes. At the first step, SF was extracted from Bombyx mori cocoons. Then, TiO₂ nanoparticles were fluoridated by hydrofluoric acid. Afterward, SF/TiO₂ and SF/TiO₂-F nanocomposite scaffolds were prepared by freeze-drying method to obtain a porous microstructure. Both SF/TiO₂ and SF/TiO₂-F scaffolds contained 0, 5, 10, 15 and 20 wt% nanoparticles. To evaluate the efficacy of nanoparticles addition on the mechanical properties of the prepared scaffolds, their compressive properties were assayed. Likewise, the pores morphology and microstructure of the scaffolds were investigated using scanning electron microscopy. In addition, the porosity and density of the scaffolds were measured according to the Archimedes’ principle. Afterward, compressive modulus and microstructure of the prepared scaffolds were evaluated and modeled by Gibson–Ashby’s mechanical models. The results revealed that the compressive modulus predicted by the mechanical model exactly corresponds to the experimental one. The modeling approved the honeycomb structure of the prepared scaffolds which possess interconnected pores.

     

Photocatalytic degradation of dimethyl sulphoxide by CdS/TiO2 core/shell catalyst: A novel measurement method

In the present research, the photocatalytic degradation of dimethyl sulphoxide (DMSO) by means of CdS/TiO₂ core/shell nanocomposite was investigated and modelled for the direct measurement of degradation rate. Instead of common measurement methods, liquid freezing point measurement was used in order to determine the rate of DMSO decomposition. To model the photocatalytic behaviour, two empirical-statistical equations based on photocatalytic retention time, amount of catalyst and pollutant were introduced. The effect of parameters such as retention time, amount of catalyst and pollutant were studied by statistical methods. The design of experiments, acquisition and optimization of statistical models was performed by response surface methodology (RSM) through central composite design (CCD). The rates of disappearance fitted the Langmuir-Hinshelwood kinetics model and the parameter k was determined to be up to 0.0105 per minute for a low concentration and 0.0073 per minute for a high concentration of DMSO. In addition, more than 85% degradation of 1% DMSO was attained by 8% catalyst in 150 minutes. Finally, the accuracy and consistency of the statistical models was verified by the HPLC method and ~ ± 2.7% difference was observed. The other results indicate that the CdS/TiO₂ nano photocatalyst can efficiently remove dimethyl sulphoxide from wastewater under visible light irradiation.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

A low-power and robust quaternary SRAM cell for nanoelectronics

This paper presents an efficient and low-power quaternary static random-access memory (SRAM) cell based on a new quaternary inverter. For implementation, carbon nanotube field-effect transistors (CNTFETs) are used. Stacked CNTFETs are appropriately used in the proposed design to achieve a considerably low static power dissipation. The proposed SRAM has a more significant static noise margin due to its single quaternary digit line, and it is appropriate for MVL SRAM design as there are more than two stable states. The simulation results using Synopsys HSPICE with 32 nm Stanford comprehensive CNTFET model demonstrate the correct and robust operation of the proposed designs even in the presence of major process variations. In addition, the proposed SRAM cell is applied in a 4?×?4 SRAM array structure to demonstrate the efficiency of the proposed SRAM. The results indicate that the proposed design significantly lowers the power consumption and provides comparable static noise margins compared to the other state-of-the-art CNTFET-based circuits.

     

High-Stability Platinum Nano-Electrocatalyst Synthesized by Cyclic Voltammetry for Oxygen Reduction Reaction

Cyclic voltammetry as a simple electrochemical deposition method was developed in order to prepare a platinum nano-electrocatalyst for oxygen reduction reaction (ORR) in low-temperature fuel cell systems. The morphology of the prepared platinum was evaluated by scanning electron microscopy and energy dispersive x-ray analysis. The effects of platinum concentration in electrodeposition solution and scan numbers of cyclic voltammetry (scan rate: 50 m V s^?1, between 1.489 and ??0.311 versus reversible hydrogen electrode) on the performance of prepared electrocatalysts for ORR were studied. The fabricated electrodes were evaluated by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed that the optimum conditions for the preparation of electrocatalysts were 2E?3 M H₂PtCl₆ and 30 scan numbers. The optimized electrode showed high stability after 1200 cycles.     

Effect of reinforcement type on high velocity impact response of GRP plates using a sharp tip projectile

High velocity impact performance of glass reinforced polyester (GRP) resin composite plates with different type of reinforcement was investigated. The projectile used was a sharp tipped (30°) conical head with total length of 30 mm and shank length of 15 mm with weight of 9.74 g. Five different types of E-glass fiber reinforcement were used, including chopped strand mat (CSM), plain weave, satin weave, unidirectional and cross-ply unidirectional fiber reinforcements. A smooth barrel gas gun was used to conduct high velocity impact tests in the velocity range of 80–160 m/s. Composite plates with size of 15 cm × 15 cm were prepared in 3 and 6 mm thickness. Results showed higher ballistic limit velocity (velocity at which samples fully penetrated the target plates with zero residual velocity) for 3 mm GRP plates with cross-ply unidirectional reinforcement followed by unidirectional reinforcement and plain weave, the plates with satin weave and CSM reinforcements were almost in same level. The thicker specimens (6 mm), plates with plain weave reinforcement showed better ballistic performance towards sharp tipped conical projectile impact, followed by cross-ply unidirectional, satin weave, unidirectional and CSM reinforced plates. Experimentally determined ballistic limit velocity for all specimens correlate well with estimated ballistic limit values obtained in full perforation tests. Damage assessment conducted on all specimens indicated fiber tension and shear failure for thin-walled and sever delamination for the thick-walled specimens as the dominant failure modes.     

Stochastic extinction and the selection of the transmission mode in microparasites.

Stochastic fluctuations in the transmission process of microparasites generate a risk of parasite extinction that cannot be assessed by deterministic models, especially in host populations of small size. While this risk of extinction represents a strong selection pressure for microparasites, it is usually not clearly separated from the deterministic ones. We suggest here that this stochastic selection pressure can affect the selection of the transmission mode of microparasites. To avoid extinction, parasites should maximize their inter-population transmission to ensure frequent reintroductions. Since the types of contacts may differ if congeners belong to the same or distinct populations, strains that are mainly transmitted through inter-population contacts might be selected. To examine this assumption, we analyse the issue of the competition between two strains differing in their transmission mode using a stochastic metapopulation model in which hosts may display different behaviours inside and outside their populations. We show that stochastic selection pressures may drive parasite evolution towards a transmission mode that maximizes the persistence of the parasite. We study the conditions under which stochastic selection pressures may surpass the deterministic ones. Our results are illustrated by the cases of feline immunodeficiency virus in cats and of sexually transmitted diseases in mammals.