  Micro/nano-scale propulsion has attracted considerable recent attention due
to its promise for biomedical applications such as targeted drug delivery. In
this paper, we report on a new experimental design and theoretical modelling of
high-speed fuel-free magnetically-driven propellers which exploit the
flexibility of nanowires for propulsion. These readily prepared nanomotors
display both high dimensional propulsion velocities (up to ~ 21 micrometer per
second) and dimensionless speeds (in body lengths per revolution) when compared
with natural microorganisms and other artificial propellers. Their propulsion
characteristics are studied theoretically using an elastohydrodynamic model
which takes into account the elasticity of the nanowire and its hydrodynamic
interaction with the fluid medium. The critical role of flexibility in this
mode of propulsion is illustrated by simple physical arguments, and is
quantitatively investigated with the help of an asymptotic analysis for
small-amplitude swimming. The theoretical predictions are then compared with
experimental measurements and we obtain good agreement. Finally, we demonstrate
the operation of these nanomotors in a real biological environment (human
serum), emphasizing the robustness of their propulsion performance and their
promise for biomedical applications.
