Spectral contents readout of birefringent sensors

The objective of the research performed was to establish the feasibility of using spectral contents analysis to measure accurately, strains and retardation in birefringent sensors, and more generally, on transparent materials

Digital image correlation based internal friction characterization in granular materials

Based on the realization that Newtonian fluids have the unique property to redirect the forces applied to them in a perpendicular direction, a new apparatus, called the Granular Friction Analyzer (GFA), and the related GFA index, were proposed for characterizing the internal friction and related flow behavior of granular materials under uniaxial compression loading. The calculation of the GFA index is based on the integration of the internal pressure distribution along the cylinder wall, within which the granular material is being uniaxially compressed by a piston. In this paper an optical granular friction analyzer (O-GFA) is presented, where a digital image correlation (DIC) method is utilized to assess the cylinder strains used to calculate the internal pressure distribution. The main advantage of using the DIC method is that the starting point (piston-powder contact point) and the length of the integration considering the edge effects can be defined. By using the DIC full-field, instead of a few points strain measurements, a 2% improvement of the GFA indexʼs accuracy has been achieved and its robustness with respect to the number of points has been demonstrated. Using the parametric error analysis it has been shown that most of the observed total error (7.5%) arises from the DIC-method-based measurements of the strains, which can be improved by higher-resolution cameras and DIC algorithms for the strain evaluation. Additionally, it was shown that the GFA index can be used for determining the well-known Janssen model parameters. The latter was demonstrated experimentally, by testing three SS 316 L granular material samples with different mean particle sizes. The results confirm that the mean particle size regulates the internal friction of granular materials

Enhanced cell adhesion and alignment on micro-wavy patterned surfaces.

Various micropatterns have been fabricated and used to regulate cell adhesion, morphology and function. Micropatterns created by standard photolithography process are usually rectangular channels with sharp corners (microgrooves) which provide limited control over cells and are not favorable for cell-cell interaction and communication. This paper proposes a new micropattern with smooth wavy surfaces (micro-waves) to control the position and orientation of cells. To characterize cell growth and responses on the micro-patterned substrates, bovine aortic endothelial cells were seeded onto surfaces with micro-grooves and micro-waves for 24 h. As a result, the cells on the micro-wavy pattern appeared to have a lower death rate and better alignment compared to those on the micro-grooved pattern. In addition, flow-induced shear stress was applied to examine the adhesion strength of cells on the micro-wavy pattern. Results showed that cells adhered to the wavy surface displayed both improved alignment and adhesion strength compared to those on the flat surface. The combination of increased alignment, lower death rate and enhanced adhesion strength of cells on the micro-wavy patterns will offer advantages in potential applications for cell phenotype, proliferation and tissue engineering

Alignment of BAOECs on 20 µm micro-wavy substrates after 24 h incubation.

<p>(A–C) Histograms of cell number, alignment angle, and cell location on 20 µm wavy surfaces (n = 100). Error bars, SEM.</p

Microfluidic based testing device.

<p>(A) Sketch of the microfluidic device; (B) Image of the microfluidic device.</p

Cell distribution at the initial seeding.

<p>(A) Microscope image of cells on a wavy surface with 20 µm spacing and 6.6 µm height; (B) The number of endothelial cells at different wave locations.</p

Illustration of the fabrication process of microwavy patterns.

<p>(A–D) Uniaxial stretching of PDMS films at various mechanical stretch settings to generate microwavy patterns.</p

Shear flow testing via a microfluidic based testing platform.

<p>(A) Shear stress of 1 dyn/cm² was applied for 12 min; (B) Diagram represents shear stress level applied, 2 min at 0.25 dyn/cm², 2 min at 0.5 dyn/cm², 2 min at 1 dyn/cm², 2 min at 2.5 dyn/cm², 2 min at 5 dyn/cm², 2 min at 10 dyn/cm². Data presented as mean ± SEM (n = 3).</p