ABSTRACT
Motility is a fundamental property of cells and bacteria. Unicellular organisms constantly move in search for food; eggs would not be fertilised in the absence of sperm cell motion; macrophages move to infection sites; broblast cells motion allows the remodelling of connective tissues and the rebuilding of damaged structures. Cell motion also plays an important role in cancer with the formation of metastases. Cells and bacteria can swim when they are propelled by the beating of cilia or agellae or by the polymerisation of an actin gel. They can also crawl inside the extracellular matrix or on surfaces. The crawling motion of cells requires a deformation of the cytoskeleton and occurs in several steps: protrusion in which new cytoskeleton polymerises in front of the cell leading edge, adhesion of the cell on the substrate that allows momentum transfer and depolymerisation and contraction of the rear of the cell in which the adhesion sites are broken and the rear parts of the cytoplasm are dragged forward.
