Microdevices for Continuous Sized Based Sorting by AC Dielectrophoresis

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this project, various microfluidic devices are designed for microparticles and cells separation. The dominant regions of dielectrophoresis among other AC Electrokinetic transport mechanisms are predicted. Flow behaviors of particles for each design parameter are modeled and simulated using COMSOL Multiphysics 4.3a software. Lab-on-a-chip devices having a Ti interdigitated electrode layer on a glass substrate and a PDMS microchannel are fabricated to investigate the most effective design solution for separating particles based on their sizes. Polystyrene particles with different diameters of 3.2 μm and 9.8 μm are used in our experiments and experiments with circulating tumor cells (CTCs) are in progress

On the second-order temperature jump coefficient of a dilute gas

We use LVDSMC simulations to calculate the second-order temperature jump coefficient for a dilute gas whose temperature is governed by the Poisson equation with a constant forcing term. Both the hard sphere gas and the BGK model of the Boltzmann equation are considered. Our results show that the temperature jump coefficient is different from the well known linear and steady case where the temperature is governed by the homogeneous heat conduction (Laplace) equation

Atomic Force Microscopy Characterization of Collagen ‘Nanostraws’ in Human Costal Cartilage

Costal cartilage, a type of hyaline cartilage that bridges the bony ribs and sternum, is relatively understudied compared to the load bearing cartilages. Deformities of costal cartilage can result in deformation of the chest wall, where the sternum is largely pushed toward or away from the spine, pectus excavatum and pectus carinatum, respectively, with each condition having significant clinical impact. In the absence of extensive literature describing morphological features of costal cartilage, we characterized a sample from the costal margin immunohistologically and through atomic force microscopy. We had previously observed the presence of collagen ‘nanostraws’ running the length of costal cartilage. Hypothesizing that these structures may be responsible for fluid flow within this thick, avascular tissue, and prior to microfluidic analysis, we estimated the diameters and measured Young\u27s modulus of elasticity of the collagen nanostraws. We found significant differences in results between treatment type and fixation. Significant differences in nanostraw elasticity and diameter obviously affect nano-fluidic transport calculations, and therefore, we consider these results of importance to the scientific community relying upon measurements in the nanoscale

Micro-Electro-Mechanical-Systems (MEMS) and Fluid Flows

The micromachining technology that emerged in the late 1980s can provide micron-sized sensors and actuators. These micro transducers are able to be integrated with signal conditioning and processing circuitry to form micro-electro-mechanical-systems (MEMS) that can perform real-time distributed control. This capability opens up a new territory for flow control research. On the other hand, surface effects dominate the fluid flowing through these miniature mechanical devices because of the large surface-to-volume ratio in micron-scale configurations. We need to reexamine the surface forces in the momentum equation. Owing to their smallness, gas flows experience large Knudsen numbers, and therefore boundary conditions need to be modified. Besides being an enabling technology, MEMS also provide many challenges for fundamental flow-science research

Boundary conditions at a fluid - solid interface

We study the boundary conditions at a fluid-solid interface using molecular dynamics simulations covering a broad range of fluid-solid interactions and fluid densities, and both simple and chain-molecule fluids. The slip length is shown to be independent of the type of flow, but rather is related to the fluid organization near the solid, as governed by the fluid-solid molecular interactions.Comment: REVtex, to appear in Physical Review Letter

Decorin Expression, Straw-Like Structure, and Differentiation of Human Costal Cartilage

Costal cartilage is much understudied compared with the load-bearing cartilages. Abnormally grown costal cartilages are associated with the inherited chest wall deformities pectus excavatum and pectus carinatum resulting in sunken and pigeon chests, respectively. A lack of understanding of the ultrastructural and molecular biology of costal cartilage is a major confounder in predicting causes and outcomes of these disorders. This study analyzed the structure of marginal human costal cartilage (ribs 6-10) through scanning electron and atomic force microscopes and identified the presence of straw-like structures running longitudinally. We also demonstrated that chondrocytes tend to occur singly or as doublets and that centrally located cells produce high levels of aggrecan compared with more peripherally located cells measured using immunohistochemistry. Gene expression from mRNA extracted from cartilage showed high levels of decorin expression, likely associated with the large, complex tubular structures running through this cartilage type. COL2A1, ACAN, and TIMP1 also showed higher levels of expression compared with ACTB. Analysis of gene expression ratios demonstrate that costal cartilage is under differentiated compared with published ratios for articular cartilage, likely due to the vastly different biomechanical environments of each cartilage type. Further studies need to establish whether findings described here from the costal margins are significantly different than the cartilage of the true ribs and how these values change with age

Linear stability analysis of miscible two-fluid flow in a channel with velocity slip at the walls

The linear stability characteristics of pressure-driven miscible two-fluid flow with same density and varying viscosities in a channel with velocity slip at the wall are examined.Aprominent feature of the instability is that only a band ofwave numbers is unstable whatever the Reynolds number is, whereas shorter wavelengths and smaller wave numbers are observed to be stable. The stability characteristics are different from both the limiting cases of interface dominated flows and continuously stratified flows in a channel with velocity slip at the wall. The flow system is destabilizing when a more viscous fluid occupies the region closer to the wall with slip. For this configuration a new mode of instability, namely the overlap mode, appears for high mass diffusivity of the two fluids. This mode arises due to the overlap of critical layer of dominant instability with the mixed layer of varying viscosity. The critical layer contains a location in the flowdomain atwhich the base flowvelocity equals the phase speed of themost unstable disturbance. Such amode also occurs in the corresponding flow in a rigid channel, but absent in either of the above limiting cases of flow in a channel with slip. The flow is unstable at low Reynolds numbers for a wide range of wave numbers for low mass diffusivity, mimicking the interfacial instability of the immiscible flows. A configuration with less viscous fluid adjacent to the wall is more stable at moderate miscibility and this is also in contrast with the result for the limiting case of interface dominated flows in a channel with slip, where the above configuration ismore unstable. It is possible to achieve stabilization or destabilization of miscible two-fluid flow in a channel with wall slip by appropriately choosing the viscosity of the fluid layer adjacent to the wall. In addition, the velocity slip at the wall has a dual role in the stability of flow system and the trend is influenced by the location of the mixed layer, the location of more viscous fluid and the mass diffusivity of the two fluids. It is well known that creating a viscosity contrast in a particularway in a rigid channel delays the occurrence of turbulence in a rigid channel. The results of the present study show that the flow system can be either stabilized or destabilized by designing the walls of the channel as hydrophobic surfaces, modeled by velocity slip at the walls. The study provides another effective strategy to control the flow syste

Study of pulsatile pressure-driven electroosmotic flows through an elliptic cylindrical microchannel with the Navier slip condition

This paper aims to study an unsteady electric field-driven and pulsatile pressure-driven flow of a Newtonian fluid in an elliptic cylindrical microchannel with Navier boundary wall slip. The governing equations of the slip flow and distributions of electric potential and charge densities are the modified Navier-Stokes equations, the Poisson equation and the Nernst-Planck equations, respectively. Analytical and numerical analyses based on the Mathieu and modified Mathieu equations are performed to investigate the interplaying effects of pulsatile pressure gradients and the slip lengths on the electroosmotic flow