Alignment and controlled formation of topological defects in living fibroblast cells by liquid crystals*

Arrays of living tissue-forming cells behave as orientationally ordered active nematics and create topological defects of strength +1/2 and -1/2. These defects play an important role in compressive-dilative stresses in tissues and facilitate effects such as apoptosis and cell migration. The challenge is to design orientational patterns of cells with predetermined spatial locations of topological defects in them. We propose an approach to control the alignment of human dermal fibroblast (HDF) cells by substrates with photoaligned liquid crystal polymers (LCPs). With a plasmonic metamask alignment method, we patterned the director orientation of the LCPs with topological defects of integer (+1, -1) and semi-integer (+1/2, -1/2) strength. Combination of polarized, phase contrast and fluorescent microscopies proves that the HDF cells align along the patterned director of the LCP substrate. The patterns cause a modulation of cell density, as the cells accumulate near the cores of the defects with positive topological charge. The approach could be used to control the locations of defect formation in tissues of living cells and potentially control the extrusion of undesirable cells.