The study of complex suspensions made of particles suspended in a simple fluid has been growing lately, with many opportunities for industry or lab-on-a-chip technology. The macroscopic flow properties of these suspensions depend on the nature of the suspended micro-particles, such as their size or flexibility, and remain poorly understood. These flow properties directly result from the microscopic interaction between the viscous flow and the particles. Researchers from ESPCI Paris collaborated with a team from the University of California San Diego to investigate the dynamics of a microscopic flexible filament in a flow. Their results have been published in the Proceedings of the National Academy of Sciences.