Undulatory swimming in fluids with polymer networks

Abstract

The motility behavior of the nematode Caenorhabditis elegans in polymeric\nsolutions of varying concentrations is systematically investigated in\nexperiments using tracking and velocimetry methods. As the polymer\nconcentration is increased, the solution undergoes a transition from the\nsemi-dilute to the concentrated regime, where these rod-like polymers entangle,\nalign, and form networks. Remarkably, we find an enhancement in the nematode's\nswimming speed of approximately 65% in concentrated solutions compared to\nsemi-dilute solutions. Using velocimetry methods, we show that the undulatory\nswimming motion of the nematode induces an anisotropic mechanical response in\nthe fluid. This anisotropy, which arises from the fluid micro-structure, is\nresponsible for the observed increase in swimming speed.\n