A single sperm cell propels itself by driving undulations in its slender tail, which is known as the flagellum. This undulatory beating is driven by, arguably, the most complex engine known: an intracellular nanomachine called the axoneme. Although much is known about the structure of a flagellum and its axoneme, very little is understood about how the whole propeller operates. Experimentally studying the dynamics of a flagellum or axoneme in a living sperm cell is challenging. We analyze the beating patterns of tethered sperm cells and use fluid mechanics to shed some light on the internal forces and power exerted by the protein motors that power the axoneme. Our investigations also suggest that the flagellum material behaviour could be viscoelastic and that this complex mechanical behaviour could play a fundamentally important role in determining the undulatory beating patterns observed in sperm.
Dr. Prabhakar Ranganathan leads the Complex Fluid Systems research group in the Dept. of Mechanical & Aerospace Engineering at Monash University. He is interested in understanding through modeling, simulations and analysis how micro-scale interactions determine the complex and emergent macroscale behaviour of complex fluid systems. Systems of interest include active systems consisting of self-propelled particles, as exemplified by cilia and flagella driven collectively by protein motors, and suspensions, swarms and tissues of motile microbes, and also passive systems, such as solutions of flexible polymers. The group also works on analytical tools and techniques for designing experiments to test theoretical models and for developing innovative applications of complex fluid systems.