Browsing by Subject "microspheres"
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Item Characterization of Thermal Properties of Depleted Uranium Metal Microspheres(2012-07-16) Humrickhouse, Carissa JoyNuclear fuel comes in many forms; oxide fuel is the most commonly used in current reactor systems while metal fuel is a promising fuel type for future reactors due to neutronic performance and increased thermal conductivity. As a key heat transfer parameter, thermal conductivity describes the heat transport properties of a material based upon the density, specific heat, and thermal diffusivity. A material?s ability to transport thermal energy through its structure is a measurable property known as thermal diffusivity; the units for thermal diffusivity are given in area per unit time (e.g., m2/s). Current measurement methods for thermal diffusivity include LASER (or light) Flash Analysis and the hot-wire method. This study examines an approach that combines these previous two methods to characterize the diffusivity of a packed bed of microspheres of depleted uranium (DU) metal, which have a nominal diameter of 250 micrometers. The new apparatus is designated as the Crucible Heater Test Assembly (CHTA), and it induces a radial transient across a packed sample of microspheres then monitors the temperature profile using an array of thermocouples located at different distances from the source of the thermal transient. From the thermocouple data and an accurate time log, the thermal diffusivity of the sample may be calculated. Results indicate that DU microspheres have very low thermal conductivity, relative to solid uranium metal, and rapidly form an oxidation layer. At 500?C, the thermal conductivity of the DU microspheres was 0.431 ? 13% W/m-K compared to approximately 32 W/m-K for solid uranium metal. Characterization of the developed apparatus revealed a method that may be useful for measuring the thermal diffusivity of powders and liquids.Item Synthesis and Characterization of Novel Fluorescent Injectable Micro-Carriers for Tissue Regeneration(2014-04-28) Arora, AkshiSpecific problem: Our previous study showed that the nanofibrous poly-l-lactic acid (NF-PLLA) microspheres are excellent cell carriers for tissue regeneration. However, these injectable microspheres are not fluorescent biomaterials. Incorporation of fluorescent chromophore into NF-PLLA microspheres will allow imaging for proper delivery of scaffold at the specified site and monitor time related degradation in the scaffold, and tissue regeneration by live fluorescent imaging, without the need of sacrificing the animals or undertaking elaborate histological procedures. To date, there is no report on the synthesis of fluorescent PLLA. In this research, we aim to develop an injectable fluorescent PLLA scaffold for tissue regeneration by using Eosin Y (EY) fluorophore as initiator. Method: The fluorescent polymer (PLLA-EY) was synthesized by ring-opening polymerization (ROP) of l-lactide by bulk polymerization method using stannous octoate Sn(Oct)_(2) catalyst and EY fluorophore initiator, at four different monomer/initiator (M/I) molar ratios (20:1,100:1,200:1,400:1). The PLLA-EY polymer was characterized by FT-IR, UV-visible spectrophotometry and molecular weight (MW). The smooth walled (SW) and nanofibrous (NF) microspheres were fabricated from PLLA-EY 200:1 and 400:1 from methods previously described. These were characterized by SEM, confocal, in vitro biodegradation in PBS (pH change and SEM) and cytotoxicity testing (MTS assay) on dental pulp stem cells (DPSCs). Results: EY initiator generated free radicals causing ROP of l-lactide and incorporation of EY in the PLLA polymer chain. FT-IR and UV-vis spectra confirmed incorporation of EY in the polymer. Increasing the M/I ratio increased MW of PLLA-EY polymer. Microspheres formed from PLLA-EY were auto-fluorescent and increasing the polymer MW resulted in more well-defined nanofibers. Both short term (7d) and long term (21d) cytotoxicity results confirmed non-toxicity of the fluorescent polymer to DPSCs. NF microspheres formed small aggregates with cellular extensions between the DPSCs. Biodegradation of NF microspheres was not seen until 6 weeks in PBS solution under SEM. Conclusion: Fluorescent PLLA-EY polymer and its microparticles can be manufactured, and appear to be very promising candidates for dental pulp regeneration. Future studies should evaluate the ability to track the polymer and their microparticles in vivo, and their ability to accommodate cell adhesion, proliferation, differentiation and in vivo implantation.