Shape memory thin films of polyurethane: Synthesis,characterization, and recovery behavior

Polyurethane thin films with inherent two phase segregated characters are exceptional candidates for the development of shape memory materials. However, controlling the phase behavior of such complex structures for decoding their recovery behavior still experiences its early stage of development. In this work, polyurethane thin films were synthesized based on two polyols, ester-based polyols (ESP), and ether-based polyols (ETP) together with diphenyl diisocyanate (MDI). The effects of ingredient ratio of PETP (ether-based prepolymer)/PESP (ester-based prepolymer) on the chemical structure and final properties of polyurethanes were studied by the Fourier-transformed infrared spectroscopy (FTIR), the differential scanning calorimetry (DSC), the scanning electron microscopy (SEM), the dynamic mechanical thermal analysis (DMTA), a tensiometer, and the atomic force microscopy (AFM). The shape memory behaviors were explored by the thermomechanical cycles applied by a DMTA device in the controlled force mode. The PU films showed various properties compared with the bulk PU since they formed spherulitic textures with different structures. All the PU films except PU-0 showed high shape recovery ca. 90% in the first cycle with a large glassy storage modulus in the range of 2,800–4,040MPa, and a recovery ratio enhanced by increasing the number of cycle to a maximum of 95%.     

Solvent-free synthesis of Cu-Cu2O nanocomposites via green thermal decomposition route using novel precursor and investigation of its photocatalytic activity

In the present study, Cu-Cu₂O binary nanocomposites were successfully synthesized through a one-pot, cost-effective and green thermal decomposition route using PMP-Cu(II), extracted from pomegranate marc peels (PMP) by Cu(II), as a novel starting reagent for the first time. The morphology, crystalline structure, and composition of as-prepared Cu-Cu₂O nanocomposites were extensively characterized by SEM, XRD, EDS and HRTEM. Effect of reaction parameters such as time, temperature and precursor type on product composition and morphology was evaluated. Moreover, methylene blue (MB) was used as a model of organic dye pollutant and photodegradation experiments were conducted by UV-vis spectrophotometry. The as-synthesized Cu-Cu₂O binary nanocomposites demonstrated their potential as an excellent photocatalyst for degradation of MB under visible-light irradiation and Cu-Cu₂O photocatalyst with higher content of Cu₂O (prepared in air) exhibits the highest photocatalytic efficiency (～99% degradation of MB in <150 min).     

Use of a "composite" vascular access graft in a young child on hemodialysis

Although arterio-venous fistulae (AVF) are currently considered to be the first choice of permanent vascular access for hemodialysis, there are some patients who are not candidates for fistulae and synthetic grafts provide other options. The Thoratec (Vectra) polyurethane vascular access graft is a new prosthetic graft that may be cannulated within days of insertion due to "self-sealing" properties. However, a tendency for kinking at the suture site due to the strong elasticity of this graft, leading to undesirable complications such as thrombosis, have been reported. We describe a surgical modification of the anastomosis by interposing a segment of expanded polytetrafluoroethylene graft (ePTFE, Venaflo) between the native vessels and the polyurethane graft sections in a pediatric patient. This modification may overcome the kinking complication associated with use of the polyurethane graft and the resulting thrombosis.     

Liposome: classification,preparation, and applications

Liposomes, sphere-shaped vesicles consisting of one or more phospholipid bilayers, were first described in the mid-60s. Today, they are a very useful reproduction, reagent, and tool in various scientific disciplines, including mathematics and theoretical physics, biophysics, chemistry, colloid science, biochemistry, and biology. Since then, liposomes have made their way to the market. Among several talented new drug delivery systems, liposomes characterize an advanced technology to deliver active molecules to the site of action, and at present, several formulations are in clinical use. Research on liposome technology has progressed from conventional vesicles to ‘second-generation liposomes’, in which long-circulating liposomes are obtained by modulating the lipid composition, size, and charge of the vesicle. Liposomes with modified surfaces have also been developed using several molecules, such as glycolipids or sialic acid. This paper summarizes exclusively scalable techniques and focuses on strengths, respectively, limitations in respect to industrial applicability and regulatory requirements concerning liposomal drug formulations based on FDA and EMEA documents.     

Nonintrusive characterization of fluidized bed hydrodynamics using vibration signature analysis

There are many techniques to characterize the hydrodynamics of fluidized beds, but new techniques are still needed for more reliable measurement. Bed vibrations were measured by an accelerometer in a gas–solid fluidized bed to characterize the hydrodynamics of the fluidized bed in a nonintrusive manner. Measurements were carried out at different superficial gas velocities and particle sizes. Pressure fluctuations were measured simultaneously. Vibration signals were processed using statistical analysis. For the sake of the evaluation, the vibration technique was used to calculate minimum fluidization velocity. It was shown that minimum fluidization velocity can be determined from the variation of standard deviation, skewness, and kurtosis of vibration signals against superficial gas velocity of the bed. Kurtosis was proved to be a new method of analyzing vibration signals. Results indicate that analyzing the vibration signals can be an effective nonintrusive technique to characterize the hydrodynamics of fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

5-Fluorouracil-loaded poly(vinyl alcohol)/chitosan blend nanofibers: morphology,drug release and cell culture studies

Electrospun polymeric nanofibers as carriers for anticancer drugs have received a great deal of attention to treat tumor cells. This work was aimed to prepare an optimized nanofibrous sample based on poly(vinyl alcohol) (PVA)/chitosan (CS) blend, and then evaluate it containing 5-fluorouracil (5-FU) in terms of morphology, drug release, and cell culture. The electrospinning conditions to produce PVA/CS (50/50) blend nanofibers with an average diameter of approximately 150.8 nm were adjusted as follows: applied voltage 17 kV, needle tip to collector distance 60 cm, and flow rate 0.1 mL/h. The obtained results from Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed that there were no chemical interactions between the polymers and drug during the electrospinning process and the uniform morphology without beads. Moreover, to prolong 5-FU release from the blend nanofibers, three layered samples consisting of PVA/CS blend and poly (ε-caprolactone) (PCL) [PVA/CS-PCL 3-layers] were electrospun. On the other hand, by adding PCL in the PVA/CS blend nanofibers, the samples showed more hydrophobic property. Eventually, thiazolyl blue (MTT) assay along with NIH 3T3 cells culture proved that the sample could kill more than 80% of the cells. This formulation could be a promising candidate for cancer therapy potentially.

     

Self-assembly of nanoparticles to prepare of dendritic AgCl–Ag<Subscript>2</Subscript>S nanocomposites through a simple one-pot hydrothermal approach and its photocatalytic activity

Herein, AgCl–Ag₂S nanocomposites with dendritic morphology were synthesized via a simple one-pot hydrothermal route for the first time. AgNO₃, HCl, and thioacetamide were utilized as starting reagents. The as-prepared AgCl–Ag₂S nanocomposites were extensively characterized by techniques such as X-ray diffraction patterns, scanning electron microscopy, energy dispersive X-ray spectroscopy and diffused reflectance UV–visible spectrum. The results showed that the nanoparticles were self-assembled to prepare AgCl–Ag₂S nanocomposites with dendritic morphology. The efficiency of AgCl–Ag₂S nanocomposites as a photocatalyst for the decolorization of methyl orange (MO) using visible light irradiation has been evaluated. As a result, an enhanced photocatalytic efficiency of AgCl–Ag₂S nanocomposites compared to AgCl nanostructures was obtained due to absorption of wider range of light wavelength by AgCl–Ag₂S nanocomposites.     

Effect of Fe-rich intermetallics on the wear behavior of eutectic Al–Si piston alloy (LM13)

In the present study, the effect of Fe-rich intermetallics has been investigated on the wear behavior of eutectic Al–Si alloy (LM13). Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 18, 51, 74 and 100 N at a constant sliding speed of 0.3 m/s. Addition of 1.2% Fe to the LM13 alloy leads to the formation of the flake like β-intermetallic compounds. These hard compounds initiate micro cracks and can reduce the wear resistance of the alloy. The addition of Mn converts the flake like β-intermetallic compounds to the star-like α-intermetallics and decreases the detrimental effect of iron. Applying high cooling rate during solidification of the alloy containing Fe and Mn, resulted to the formation of finer α-intermetallic compounds and improved the wear behavior of the alloy to a great extent.     

Predicting Transition Velocities from Bubbling to Turbulent Fluidization by S-Statistics on Vibration Signals

Vibration signatures as the representatives of the fluidized bed nonlinear hydrodynamics were measured in a lab-scale fluidized bed of sand particles operated at ambient conditions. The experiments were carried out for three particle sizes, different velocities, and three probe heights. The S-statistic method was applied to the vibration signatures for the chaotic attractor comparison. The measured signatures of two different consecutive velocities in similar conditions were compared based on null hypothesis that they have same origin. According to this method, when the value of S is larger than 3, the null hypothesis is rejected with the confidence level of 95% indicating that the two signals are originated from different hydrodynamics. The results are compared with results obtained from common statistical methods and it is shown that attractor comparison can be a reliable method for detecting regime transition velocity.