Optimizing Microfluidic Design for Cell Separation

To evaluate the performance of various designs of crossflow filtration microfluidic devices, blood flow was modeled using computational fluid dynamics software (COMSOL Multiphysics). Velocity profiles were generated and used to analyze four critical design parameters: pillar size, pillar shape, gap size, and wall length. These parameters were optimized to yield greatest flow from an unfiltered main channel into two filtered side channels of the device, thereby maximizing filtration capacity. Devices containing pillars of 10 µm diameter yielded a significantly greater filtration capacity than devices with pillars of 20 µm diameter. Flow patterns from the main channel to the side channels were not significantly affected when circular, octagonal, and hexagonal pillars were compared; however, use of triangular and square pillars caused a reduction in side channel flow rates. Side channel velocities consistently improved as gap sizes were increased from 3.0 µm to 8.0 µm; however, 3.5 µm gaps were included in the final design for the purpose of separating red and white blood cells. Backflow prevention walls were placed at bends in the device and were systematically lengthened until all backflow was eliminated. Following optimization of the microfluidic device, two prototypes were prepared: a polydimethylsiloxane (PDMS) device with glass backing and a silicon device with PDMS backing. The filtration capacity of these devices were tested using polystyrene microspheres with sizes corresponding to those of red and white blood cells. In both prototypes, between 73 and 75% of small microspheres were consistently filtered into the side channels. Silicon-PDMS devices demonstrated better retention of large microspheres in the main channel and less microsphere agglomeration than did PDMS-glass devices. The benefits of silicon-PDMS devices, however, came at the cost of a difficult fabrication process

Rheological properties of poly(lactic acid) based nanocomposites: Effects of different organoclay modifiers and compatibilizers

Poly(lactic acid) (PLA) nanocomposites containing five types of organically modified, layered silicates and two elastomeric compatibilizers, namely ethylene-glycidyl methacrylate (E-GMA) and ethylene-butyl acrylate-maleic anhydride (E-BA-MAH), were prepared using a twin screw extruder. The morphologies of the nanocomposites were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the rheological properties of the melts were measured using small-amplitude oscillatory shear. XRD revealed that the addition of E-GMA to the binary nanocomposites resulted in higher compatibility between the organoclay nanoplatelets and the polymer matrix. TEM showed that all of the nanocomposites contained mixed dispersed structures, involving tactoids of various sizes, as well as intercalated and exfoliated organoclay layers. Rheological properties were found to be affected by the differences in the compatibility between the organoclays and the polymer matrix, and by the addition of the compatibilizer. Organoclay types that resulted in high level of dispersion exhibited higher values of complex viscosity compared to that of neat PLA. The addition of E-GMA introduced a solid-like rheological behavior at low frequencies. All of the nanocomposites had similar rheological behavior at high frequencies. (C) 2015 Wiley Periodicals, Inc

Hydrogen Peroxide Stability in Silica Hydrogels

Hydrogen peroxide (H₂O₂) entrapment in silica hydrogels has potential to be used in various industrially important applications to increase H₂O₂ stability. In this study, optimum conditions for hydrogel formation and H₂O₂ stability were determined by varying the sodium content and initial H₂O₂ concentration. Higher retention and better stability of H₂O₂ were achieved with hydrogels at room temperature at low sodium concentration. Retention values of 89% were obtained with initial H₂O₂ concentrations up to 10 wt %. H₂O₂ decomposition in hydrogels followed a first-order reaction. Hydrogels were characterized by measuring their surface area, pore size, and pore size distribution by Brunauer–Emmett–Teller analysis and scanning electron microscopy. Mesoporous (3–24 nm) hydrogels with high surface area (1000–1400 m²/g) were obtained. In addition, the melting point of the entrapped H₂O₂-water mixture in the hydrogels was studied by low temperature differential scanning calorimetry