Abstract

Locomotion at the micron scale is at the root of many fundamental processes in Biology. These include the immune system response, the migration of metastatic tumour cells, and sperm cells successfully swimming their way by beating a flagellum until they reach and fertilise an egg cell. Besides their biological interest, motile cells provide a template for the bio-inspired design of micro-meter-scale, self-sufficient machines capable of executing controlled motion. We will report on some of our recent studies on swimming micro-motility by shape control, discussing general principles first, and then a concrete case study. General principles are obtained by regarding locomotion as a control problem: we will highlight some conceptual principles that may inspire the design of engineered bio-inspired devices. The case study concerns the protist Euglena gracilis, which is capable of moving either by beating a flagellum, or by executing dramatic shape changes. These are accomplished thanks to a complex structure (pellicle) underlying the plasma membrane, made of interlocking proteinaceous strips, microtubules, and molecular motors. We study the mechanisms by which the sliding of pellicle strips leads to shape control and locomotion, by means of both theory and experiments. A new concept of surface with programmable shape emerges from these studies.