High-Temperature Cross-Linking of Carbon Nanotube Multi-Yarn Using Polyvinylpyrrolidone as a Binding Agent

Carbon nanotube (CNT) multi-yarn was cross-linked together at elevated temperatures using a poly- mer, with the intent of improving their strength and electrical conductivity. They were functionalized using an acid treatment and immersed in a bath of different concentrations (0.5%, 0.1%, and 0.2%) of polyvinylpyrrolidone (PVP). Then they were placed in an oven at various temperatures (180 °C, 200 °C, and 220 °C) in order to cause cross-linking among the carbon nanotube yarns. The phys- ical, chemical, electrical, and mechanical properties of the cross-linked yarns were investigated. The yarns cross-linked at higher temperatures and greater concentrations of PVP had a greater increase in linear mass density, indicating that the cross-linking process had worked as expected. Yarns that were cross-linked at lower temperatures had greater tensile strength and better spe- cific electrical conductivity. Those that were treated with a greater concentration of polymer had a greater ultimate tensile strength. All these results are encouraging first step, but still need further development if CNT yarn is to replace copper wire.

Creep and inverse stress relaxation behaviors of carbon nanotube yarns

Creep, creep recovery and inverse stress relaxation behaviors of carbon nanotube yarns that consisted of 1-, 30-, and 100-yarn(s) were characterized. Primary and secondary creep stages were observed over the duration of 336 h. The primary creep stage lasted for about 4 h at an applied load equal to 75% of the ultimate tensile strength. The total strain in the primary stage was significantly larger in the carbon nanotube multi-yarn than in the carbon nanotube 1-yarn. In the secondary stage, 1-yarn also had a smaller steady state strain rate than the multi-yarn, and it was independent of number of yarns in multi-yarn. Strain response under cyclic creep loading condition was comparable to its counterpart in non-cyclic (i.e., standard) creep test except that strain response during the first cycle was slightly different from the subsequent cycles. Inverse creep (i.e., strain recovery) was observed in the 100-yarn during the cyclic creep tests after the first unloading cycle. Furthermore, inverse stress relaxation of the multi-yarns was characterized. Inverse stress relaxation was larger and for longer duration with the larger number of yarns.

Skin cancer treatment by albumin/5-Fu loaded magnetic nanocomposite spheres in a mouse model

Albumin/drug loaded magnetic nanocomposite spheres were fabricated using an oil-in-oil emulsion/solvent evaporation method, and tested on a mouse model (experimental squamous cell carcinoma) to determine the efficacy of the drug delivery system (DDS) on skin cancer. This novel DDS consists of human serum albumin, poly(lactic-co-glycolic acid) (PLGA), 5-fluorouracil (5-Fu), magnetic nanoparticles (10 nm) and fluorescent labeling molecule (diphenylhexatriene). One of the major purposes of using albumin is that it likely provides internal binding to and retention by the inflammatory tissues to reduce the amount of magnetic nanoparticles needed in the drug loaded microspheres (750–1100 nm). This study is aimed at reducing many negative side effects of conventionally used chemotherapy drugs by localizing the chemotherapy drug, controlling the release of the therapeutic agent and encouraging uptake of the DDS into cancerous cells. A group of mice treated with (1) the magnetic targeted DDS were compared to the other three groups, including, (2) DDS without a magnet, (3) 5-Fu local injection, and (4) untreated groups. The fluorescent tracer was ubiquitously identified inside the tumor tissue, and the DDS/tumor tissue boundary presented a leaky interface. The test results clearly showed that the magnetic targeted DDS exhibited significantly superior therapeutic effects in treating the skin cancer, with the increased efficacy to halt the tumor growth.

Cytotoxicity of release products from magnetic nanocomposites in targeted drug delivery

The efficacy of chemotherapy can be significantly improved if the therapeutic agent remains localized at the afflicted area and released at controlled rates. Such a targeted drug delivery can be achieved using magnetic nanocomposite (MNC), which incorporates drug and magnetic nanoparticles in biodegradable polymer microspheres. Reported here are results from an in vitro study on drug release rate and cytotoxicity of other release products from MNC. The model system contains an anti-cancer chemotherapy agent 5-flurouracil (5-FU) and (Co(0.5)Zn(0.5))Fe(2)O(4) in poly(lactic-co-glycolic acid) (PLGA) matrix produced by an oil/oil emulsion technique. Cell proliferation data indicate a sustained release of 5-FU for mouse macrophage cell eradication, whereas other microsphere components of magnetic nanoparticles and PLGA have little cytotoxic effects.

Dielectric Properties of Electrospun PVP and PAN Nanocomposite Fibers at Various Temperatures

Dielectric properties of electrospun polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) nanocomposite fibers were determined as a function of temperature and concentration in order to explore the possibility of using them as dielectric materials in different industrial applications. Multiwall carbon nanotubes and Ni0.6Zn0.4Fe2O4 (NiZn ferrite) were individually dispersed into the polymeric solutions of PVP and PAN and were then electrospun at various conditions. Thin layers of films were placed between two parallel Al electrode plates of the capacitance bridge prior to the measurements. We determined that nanoscale inclusions and temperature mainly affect the dielectric properties of the nanocomposite fibers. The dielectric studies can provide critical information for many electronic applications, such as loss of a cable insulator, the impedance of a substrate, and the frequency of a dielectric resonator.

A ferrofluid guided system for the rapid separation of the non-magnetic particles in a microfluidic device

A microfluidic device was fabricated via UV lithography technique to separate non-magnetic fluoresbrite carboxy microspheres (approximately 4.5 microm) in the pH 7 ferrofluids made of magnetite nanoparticles (approximately 10 nm). A mixture of microspheres and ferrofluid was injected to a lithographically developed Y shape microfluidic device, and then by applying the external magnet fields (0.45 T), the microspheres were clearly separated into different channels because of the magnetic force acting on those non-magnetic particles. During this study, various pumping speeds and particle concentrations associated with the various distances between the magnet and the microfluidic device were investigated for an efficient separation. This study may be useful for the separation of biological particles, which are very sensitive to pH value of the solutions.

Neutral pH Ferrofluid Fabrication for Biomedical Applications

Ferrofluids are composed of nanoscale magnetic nanoparticles (iron, cobalt, nickel, or their oxides) and strongly polarized in the presence of magnetic field. After coating the surface of these nanoscale particles (∼10nm) by surfactant molecules (e.g., oleic acid, tetramethylammonium hydroxide, citric acid, etc.), they become fully stable and do not aggregate or segregate under the strong magnetic field. Ferrofluids are used for various applications, including medical (cancer detection ∕ curing, pharmaceutical, MRI), ferrofludic seal around the spinning drive shafts, liquid coolant (megaphones and loudspeakers), friction reducer ∕ shock absorber, earthquake, as well as defense, aerospace, grain size measurement and heat transfer. Ferrofluids are produced at extreme high or low pH values in order to prevent agglomeration of the nanoparticles caused by van der Waals and magnetic forces. This limits the application of ferrofluid for various fields because of the oxidation, corrosion as well as harmful effect to body. In this study, magnetite (Fe3O4) nanoparticles (∼10nm) were produced by coprecipitation of iron (II) and iron (III) chloride salts in the presence of ammonium hydroxide, and stabilized using first citric acid at 100°C and a fatty acid at room temperature. Measured pH value of the ferrofluid was 7.0. As is known, magnetite nanoparticles that have excellent magnetic saturation (∼78emu∕g) are desirable for those applications due to the strong ferromagnetic behavior, less sensitivity to oxidation and relatively low toxicity compared to many other magnetic materials (e.g., iron, nickel and cobalt).

Biodegradable Magnetic Nanocomposite Spheres Fabrication by O∕O Emulsion∕Solvent Evaporation Technique for Drug Delivery Purposes

Drug targeting systems are important research areas for many diseases treatments (e.g., cancer, nerve damage, heart and artery, diabetic, eye and other medical treatments). Currently, magnetic field, electric field, ultrasound, temperature, UV light and∕or mechanical force systems are considered more for research and development. Magnetic targeted drug delivery system is usually preferred because targeted systems improve the therapeutic index of drug molecules by minimizing the toxic side effects on healthy cells and tissues. In this study, magnetic nanoparticles (∼10nm) were prepared by a chemical coprecipitation of ferric and ferrous chloride salts in the presence of a strong base (ammonium hydroxide) and used for a drug delivery purposes. An oil-in-oil emulsion∕solvent evaporation technique was chosen for the synthesis of nanocomposite spheres. Percentages of magnetic nanoparticles (%5, %10, %20 and%30) and poly(D,L-lactide-co-glycolide) were combined together to produce nanocomposite particles with diameters of 500nmto1.2micronmeter. The effect of particle concentrations on nanocomposite particle size and distribution and morphology were investigated by using scanning electron microscopy (SEM) and laser light scattering (LLS). Additionally, external magnetic fields with various magnet distance, magnetic field, pump speed and solid contents were applied to the nanocomposite particles in a liquid media to find out the effect of variables for the targeting of drug carrying nanocomposite spheres.