Spontaneous self-wrapping in chiral active polymers

Several animals, such as pangolins and armadillos, utilize rolling-up strategies to form self-wrapped configurations for defense against predators. Similarly, snakes and worms use these techniques to regulate body temperature and prevent desiccation. On a smaller scale, DNA wraps around proteins to form nucleosomes, which coil into chromatin structures, and proteins fold into coiled configurations. This study investigates this wrapping behavior by experimentally studying an active chain made of chiral active vibrobots, mimicking the aforementioned biologically inspired behavior. These vibrobots are an example of chiral active granular particles that move autonomously when placed on a vibrating plate. Self-wrapped configurations are observed when each fundamental polymer unit is chiral or, in other words, is characterized by the breaking of body rotational symmetry, leading to circular motion. This results in a spontaneous transition from unfolded to folded configurations uniquely induced by chiral activity. This phenomenon lacks an equilibrium counterpart and challenges current theories of equilibrium polymer physics, giving rise to anomalous Flory exponents. The discovery paves the way for developing innovative strategies for designing robots that can self-organize in rolled or unrolled configurations, with potential applications in swarm robotics.