Seminar - Physics Department
Patterns of topological defects in soft optical materials and in cells monolayers
Francesca Serra, Johns Hopkins University
Category: Condensed Matter Seminar
Refreshments at 11:15am
Topological defects in soft materials are of special interest for their optical and elastic properties. To control and manipulate them, we use topographical cues patterned on the bounding surfaces. For example, we control large-scale arrays of umbilical defects in liquid crystals by combining an external electric field and micro-patterned substrates. By controlling the spacing between the surface features, we can create multiple patterns on the same sample by changing the frequency of the applied field. This tunable structure can then be used as a switchable diffraction grating or as a tool for the creation of ordered arrays of colloidal particles. Monolayers of living cells also show liquid crystal-like order and form topological defects, which are responsible in regulating important mechanisms such as cell apoptosis and extrusion. By patterning the substrate we can induce the formation of topological defects at specific locations. This allows us to create arbitrary defects, including those with integer topological charge, which are not typically observed in cells monolayers. We compare the behavior of fibroblasts and epithelial cells on such patterns, characterizing the degree of alignment and the variation of cell density near the topological defects. By varying the size of the surface features, we can also obtain an estimate of physical parameters such as the size of the defect core.