Chaotic flows from periodic motions of defects in active nematics

From microtubule-kinesin suspensions to cellular tissues and bacterial colonies, a wide variety of biological and biomaterial systems share the behaviors of active nematics, which couple orientational order to internal force generation. Topological defects in the orientational order play essential roles in driving motion of the surrounding material. I will share recent progress from my research group in understanding the structure and dynamics of these defects. In strongly confined two-dimensional systems, we explore repeating cycles of defect motions that arise spontaneously (in a typically chaotic system) and trace out well-defined braids. Counterintuitively, these periodic motions drive chaotic stirring of the fluid more efficiently than random motions would. Turning to three-dimensional systems, we find so-called twist disclinations—known from the study of liquid crystals—in the cell orientations of tumor tissue from gliomas, a form of brain cancer.