Actin-Based Propulsion: Intriguing Interplay between Material Properties and Growth Processes
Most living cells are able to perform a directed motion, either by swimming in a liquid environment, by crawling on a solid support or by squeezing through a three-dimensional matrix of ﬁbers.
The speed of swimming bacteria can reach up to 100 m s−1, whereas eukaryotic cell crawling can be as fast as 1 m s−1 (Ref.  and references therein). Given their size and speed, the motion of single cells is governed by viscous forces, not inertia; that is, the Reynolds number Re 1.