Substrates with patterned topography reveal metastasis of human cancer cells.

In this study, we aimed at studying the effects of engineered and patterned substrates on the migration characteristics of mammalian cancer cell lines. On the shallow topographical patterns, cells from different histological origins showed different migration speed and directionality. We also observed that cells from the same origin showed distinctive behaviour, suggesting these substrate topographies could distinguish cancer subtypes. To eliminate the influence of genetic background, we examined two isogenic subpopulations of ovarian cancer cell lines for their different metastatic activities. While these cell lines showed indistinguishable migration characteristics on a flat substrate, their motilities on the patterned substrates were highly different, suggesting that cancer cells' motilities on these substrates varied in a metastasis-dependent manner. While cells with different metastatic activities showed similar morphology and focal adhesion distribution on flat surface, vinculin aggregated into single cytoplasmic foci in metastatic cells cultured on the engineered substrates. This implies that the topographical patterns on the substrates induced vinculin redistribution in cancer cells with a higher invasive activity. The fabricated platforms with topographical patterns offer a novel in vitro technique for metastasis assessment. Moreover, such platforms could potentially provide the opportunity to sort cells in different metastatic states using advanced pattern designs and features.

A Unidirectional Cell Switching Gate by Engineering Grating Length and Bending Angle.

On a microgrooved substrate, cells migrate along the pattern, and at random positions, reverse their directions. Here, we demonstrate that these reversals can be controlled by introducing discontinuities to the pattern. On "V-shaped grating patterns", mouse osteogenic progenitor MC3T3-E1 cells reversed predominately at the bends and the ends. The patterns were engineered in a way that the combined effects of angle- and length-dependence could be examined in addition to their individual effects. Results show that when the bend was placed closer to one end, migration behaviour of cells depends on their direction of approach. At an obtuse bend (135°), more cells reversed when approaching from the long segment than from the short segment. But at an acute bend (45°), this relationship was reversed. Based on this anisotropic behaviour, the designed patterns effectively allowed cells to move in one direction but blocked migrations in the opposing direction. This study demonstrates that by the strategic placement of bends and ends on grating patterns, we can engineer effective unidirectional switching gates that can control the movement of adherent cells. The knowledge developed in this study could be utilised in future cell sorting or filtering platforms without the need for chemotaxis or microfluidic control.

Apodization of terahertz Bragg gratings in subwavelength polymer fiber.

We report on an apodization scheme for terahertz fiber Bragg gratings. The grating consists of only 90 ablated notches on two opposite sides of a subwavelength polymer fiber. The grating strength can be effectively tuned by controlling the longitudinal shift between the two-sided notches, and apodization can be achieved by applying an envelope profile. Side lobe suppression of 14 dB was experimentally observed when compared with an unapodized grating.

Terahertz filter with tailored passband using multiple phase shifted fiber Bragg gratings.

Transmission filters for the terahertz domain having a shaped bandpass have been modeled and demonstrated. The filter designs were based on the desired filter type and bandwidth, and implemented by cascading quarter wave phase shifted fiber Bragg gratings written in Topas polymer subwavelength fiber. As an example, a 5-pole Chebyshev filter with <3 GHz bandwidth was designed and fabricated. Experimental and simulated results are in good agreement.

Characterization and modeling of Bragg gratings written in polymer fiber for use as filters in the THz region.

We demonstrate fiber Bragg gratings written in polymer fiber for use in the THz window for the first time. A KrF excimer laser operating at 248 nm was used to inscribe notch-type gratings in single component Topas subwavelength fiber. A transmission loss at the centre wavelength of the grating of 60 dB is observed in short gratings containing only 192 notches. Experimental results and modeling are presented. The gratings are expected to find use in THz signal filtering and chemical or biosensing applications.