irMass TransferDuring the Pre-Usage Dehydration of PolyvinylAlcohol Hydrogel Wound Dressings: Mass transfer during pre-usage dehydration of PVPhydrogels

Nowadays, hydrogels are widely used as wound dressings in biomedicalapplications. Similar to other types of the moist (wet) wound dressings, it isnecessary to have sufficient information about their dehydration kinetics during thepre-usage period (e.g. storage duration) and also the wound healing process. In thiswork, hydrogel wound dressings based on polyvinyl alcohol were prepared bycyclic freezing-thawing method and their dehydration process investigated byexperimental and mathematical methods. The dehydration tests were performed atatmospheric pressure at 37 °C, using hydrogels containing initial water content of70, 80 and 90 wt% and thickness of 1, 3 and 4 mm. The dehydration kinetics of eachhydrogel was determined by plotting the relative water loss (ratio of water loss toinitial water content) versus time. The obtained results showed that the dehydrationrate has inverse dependency to the thickness of wound dressing. On the other hand,the initial water content of the wound dressing has not significant effect on itsdehydration rate. To compare the obtained results with theoretical data, themathematical modeling on the basis of diffusion mechanism was developed topredict the dehydration process of the wound dressings. The results obtained fromthe mathematical modeling were in agreement with the experimental results showingthat the main phenomenon governing the dehydration of the wound dressings is thediffusion

Effect of Nanoclay on Mechanical Properties and Ablation Behavior of a Nitrile-Based Heat Insulator

Thermal insulation of rocket motor chamber is one of the most important functions of elastomeric ablative material. Combustion of solid rocket motor propellant produces turbulent media containing gases with a velocity more than 1000 m/s, temperature and pressure more than 3000°C and 10 MPa, respectively,which destroys all metallic alloys. Elastomeric nanocomposite heat insulators are more attractive subjects in comparison to their non-elastomeric counterparts, due to their excellent thermal stresses and larger deformation bearing capacity. Nitrile rubber with high thermal properties is a proper candidate in such applications. Development in ablation performance of these heat shields is considered as an important challenge nowadays. A few works have been recently carried out using organoclay to enhancethe ablation and mechanical properties of heat insulators. In this work, an elastomeric heat insulator with superior ablative and mechanical properties was presented using nanotechnology. The results showed that an elastomeric nanocomposite heat insulator containing 15 wt% organoclay exhibits superior characteristics compared to its composite counterpart such as: 46% more tensile strength, 60% more elongationat-break, 1.7 times higher modulus (at 100% strain), 62% higher “insulating index number” and 36% lower mass ablation and erosion rates under a standard test with a heat flux of 2500 kW/m2 for 15 s

VVertical Electrospinning of UHMWPE/ZnO Nanocomposite Fibers at High Temperature

UHMWPE, as a thermoplastic polymer and especially in the form of high performance fiber, has attracted much interest due to its exceptional tribological and mechanical properties. In this work, electrospinning process, known as a versatile, low cost, highly efficient and suitable technique for continuous production of fine fibers in micron or nanometer scale is employed to fabricate the UHMWPE/ZnO nanocomposite fibers. Electrospinning of UHMWPE has some inherently serious problems and limitations, due to its poor solubility in common solvents and low electrical conductivity of its solution. The most important issue is the necessity of maintaining the system temperature sufficiently high to prevent temperature depression and solution gelation during spinning. Fabrication of UHMWPE/ZnO nanocomposite fibers, containing 2.5, 5 and 7.5 wt% of ZnO nanoparticle, was carried out by self-modified vertical electrospinning at high temperature. An electrospinning system was first equipped with an infrared emitter (IR heaters) and then the conditions for fabrication of bead-free uniform UHMWPE fibers with an average diameter of 1.8±0.25mm were implemented. Under the acquired conditions, uniform and bead-free UHMWPE/ZnO nanocomposite fibers containing various percentages of ZnO nanoparticles were also successfully produced. UHMWPE/ZnO nanocomposite fibers exhibited much higher average diameter proportional to added percentage of nanoparticles. The morphology and the quality of nanoparticles dispersion within nanocomposite fibers were evaluated using field emission scanning electron microscopy (FESEM) equipped with EDAX mapping spectra. The results showed a well dispersed morphology, which was attributed to good compatibility between the ZnO nanoparticles, solvent and UHMWPE matrix

Thermal Protection Performance of Phase Changing Material Based on Polyethylene Glycol

Phase change materials (PCM) are substances with a high heat of fusion which, through melting and solidifying at certain temperatures, are capable to store or release a large amount of energy. This phenomenon can be utilized in designing heat protective materials as well as in thermal energy storage systems. One of the approaches to avoid materials leaching from a structure, where PCMs are incorporated, is to blend them with suitable polymers. To have a proper blend it is necessary to choose a compatible polymer with a PCM. It is important to assess the optimized concentration of PCM in polymer matrix and the phase structure and morphology of the blend, which causes the best heat protection. In this work, the influence of polyethylene glycol (PEG) as PCMs in epoxy resin matrix on heat protection was investigated. A special performance test was designed to study timetemperature behavior of the prepared samples and DSC and SEM tests to observe the melting point, heat of fusion and morphology of the samples. The results indicated that increases in PCM content led to better heat protection and the best concentration for PEG was found to be 60% wt. Time-temperature curves show that increases of temperature for PCM samples is very slow compared with net epoxy sample. PCM samples curves show plateau in melting region. In this region, they show nearly 15°C temperature lower than a net epoxy sample. The plateau region makes a delay time in temperature increment, which is about 22 min for PEG samples compared with a net epoxy

Synthesis of Plate-Like Nanoalumina and Its Effect on Gas Permeability of Carbon Fiber Epoxy Composite

In recent years considerable efforts have been made to develop gas impermeable polymer systems. Compared with metal system counterparts they have advantages such as low density and production costs. The most important challenge in development of impermeable polymer systems is to reduce their gas permeability by proper selection of system composition and process conditions. In this work, nanoparticles were initially synthesized using Al (NO3)3•9H2O and sodium dodecyl sulfate as a structure-directing agent via hydrothermal method and a plate-like structure was characterized by FESEM and EDAX analyses. In the second step, epoxy/plate-like nanoalumina nanocomposites and epoxy-carbon fiber composites containing 1, 2.5, and 5 wt% nanoalumina were prepared. The effect of nanoparticle loading level on permeability of nitrogen, argon, and carbon dioxide in epoxy/plate-like nanoalumina nanocomposites was investigated. It was observed that the permeability of epoxy/plate-like nanoalumina nanocomposites toward nitrogen, argon, and carbon dioxide gases reduced 83%, 74%, and 50%, respectively. It was deduced that the permeability reduction was clearly associated with the diameter of gas molecules. Generally speaking, the results showed that the incorporation of plate-like nanoalumina particles significantly reduced the gas permeability. Also, carbon dioxide gas permeability of carbon fiber epoxy composites containing plate-like nanoalumina was investigated to show the effect of ingredients on the gas permeability of the system. The results indicated that carbon dioxide gas permeability of epoxy carbon fiber composite containing 5 wt% of plate-like nanoalumina was totally reduced 84%

Correction: A Biosynthetic Nerve Guide Conduit Based on Silk/SWNT/Fibronectin Nanocomposite for Peripheral Nerve Regeneration

As a contribution to the functionality of nerve guide conduits (NGCs) in nerve tissue engineering, here we report a conduit processing technique through introduction and evaluation of topographical, physical and chemical cues. Porous structure of NGCs based on freeze-dried silk/single walled carbon nanotubes (SF/SWNTs) has shown a uniform chemical and physical structure with suitable electrical conductivity. Moreover, fibronectin (FN) containing nanofibers within the structure of SF/SWNT conduits produced through electrospinning process have shown aligned fashion with appropriate porosity and diameter. Moreover, fibronectin remained its bioactivity and influenced the adhesion and growth of U373 cell lines. The conduits were then implanted to 10 mm left sciatic nerve defects in rats. The histological assessment has shown that nerve regeneration has taken places in proximal region of implanted nerve after 5 weeks following surgery. Furthermore, nerve conduction velocities (NCV) and more myelinated axons were observed in SF/SWNT and SF/SWNT/FN groups after 5 weeks post implantation, indicating a functional recovery for the injured nerves. With immunohistochemistry, the higher S-100 expression of Schwann cells in SF/SWNT/FN conduits in comparison to other groups was confirmed. In conclusion, an oriented conduit of biocompatible SF/SWNT/FN has been fabricated with acceptable structure that is particularly applicable in nerve grafts

Schematic representation of rolling up protocol for NGC preparartion.

<p>1) Porous SF/SWNT substrates prepared by freeze-drying. 2) Aligned FN containing nanofibers prepared by electrospinning on freeze-dried substrate. 3) Rolling up the complex together by manually manipulation of a flat-tweezer. 4) A tubular NGC with internal aligned nanofibers coated by porous Silk/SWNT substrate.</p

Inclusive observation after 5

<p>a) Defected sciatic nerve without NGC (control group), b) Implanted SF/SWNT conduit, c) Implanted SF/SWNT/FN conduit.</p