Biodegradable polymers have played an important role in the delivery of drugs in a controlled and targeted manner. Polylactic-co-glycolic acid (PLGA) is one of the extensively researched synthetic biodegradable polymers due to its favorable properties. It is also known as a 'Smart Polymer' due to its stimuli sensitive behavior. A wide range of PLGA-based drug delivery systems have been reported for the treatment or diagnosis of various diseases and disorders. The present review provides an overview of the chemistry, physicochemical properties, biodegradation behavior, evaluation parameters and applications of PLGA in drug delivery. Different drug-polymer combinations developed into drug delivery or carrier systems are enumerated and discussed.

No abstract

A comprehensive three‐dimensional fully coupled thermo‐electro‐mechanical finite element framework is developed for modeling spark plasma sintering (SPS). The finite element model is applied to the simulation of spark plasma processing with four different tooling sizes and various temperature regimes. The comparison of modeling and experimental results shows that the model is reliable for qualitative predictions of the densification behavior and of the grain growth in powder specimens subjected to SPS with a given temperature regime. The conducted modeling indicates the possibility of changing the heating pattern of the specimen (warmer central areas of the specimen's volume and cooler outside areas or vice versa) depending on the size of the tooling. High heating rates and large specimen sizes elevate the temperature and, in turn, material structure gradients during SPS processing. The obtained results suggest that the industrial implementation of SPS techniques should be based on the predictive capability of reliable modeling approaches.

No abstracts.

Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2787972͔ Nanothermite materials are comprised of a physical mixture of inorganic fuel and oxidizer nanoparticles. Nonhomogenous distribution of fuel and oxidizer has been observed in the microstructures. 1 This produces random hot spot density distribution and decreases the propagation speed of the combustion wave front. It is, therefore, important to achieve homogenous mixing of the oxidizer and fuel components for faster reaction kinetics. This can be achieved by selfassembly of fuel around the solid oxidizer. Enhancement in the combustion wave speed has already been reported for composites containing porous oxidizers and fuel nanoparticles, 2,3 and also for electrostatically charged selfassembled composites. 4 Recently, we reported that higher combustion wave speeds were achieved for the composites of ordered porous Fe 2 O 3 oxidizer and Al nanoparticles 5 as compared with the one containing porous oxidizer with no ordering of the pores and Al nanoparticles. We have also reported the composite of CuO nanorods and Al nanoparticles exhibiting a combustion wave speed of 1500Ϯ 100 m / s, which enhances to 2200 m / s for the self-assembled composites. 6-8 Interestingly, these higher combustion wave speeds are comparable to the lower end values of the detonation velocities ͑e.g., 2000 m / s for hydrocarbon/alkylene-air mixtures, 9 1500-2700 m / s for metallic azides and fulminates, 10 and about 3000 m / s for ammonium nitrate fuel oil͒ for explosives. 11 In conventional explosives, the gases produced during the chemical reaction develop turbulence due to a combined effect of high pressure and rapid shearing of molecular layers generating a shock wave. In a process called deflagration-todetonation transition ͑DDT͒, the wave propagates in the reactive medium creating localized high pressure at the hot spots and, after a certain run-up distance, rapid deflagration can transition to full detonation. 9 This distance depends on the dimensions of the shock tube and also the level of confinement. 9 In the case of low density superthermites, as the adiabatic reaction temperatures are several thousand degrees, the reaction products can volatilize rapidly 12 resulting in an increased level of turbulence and high localized pressures. Because of the low density and multiphase nature of reaction materials, the corresponding Chapman-Jouguet ͑CJ͒ pressure can be much lower ...

No abstract

No abstract

Scalability experiments on the spark plasma sintering (SPS) of similarly shaped alumina specimens of the four different sizes are conducted. The utilized experimental methodology, based on the principle of rigorous proportionality of all the specimen and tooling dimensions, employs two different SPS devices of different scales. The processed specimens are characterized in terms of relative density and grain‐pore structure. Overall, SPS shows good scalability potential within a single SPS device, but indicates substantial structure changes when switching between different SPS devices. Despite deviations in some cases, by and large, the experimental results obtained for different tooling sizes and temperature regimes are rather similar for specimens processed by the same SPS device. The obtained density and grain size spatial distributions are relatively uniform. High final densities with moderate grain growth are common. At the same time, due to the demonstrated possibility of a significant size impact in case of high heating rates and large specimen sizes, as well as the demonstrated differences of the processing outcomes based on different SPS devices, the predictive capability of reliable modeling approaches is of great importance for the industrial implementation of SPS techniques.