  Taking inspiration from the crawling motion of biological cells on a
substrate, we consider a physical model of self-propulsion where the
spatio-temporal driving can involve both, a mechanical actuation by active
force couples, and a chemical actuation through controlled mass turnover. We
show that the competition and cooperation between these two modalities of
active driving can drastically broaden the performance repertoire of the
crawler. When the material turnover is slow and the mechanical driving
dominates, we find that the highest velocity at a given energetic cost is
reached when actuation takes the form of an active force configuration
propagating as a traveling wave. As the rate of material turnover increases,
and the chemical driving starts to dominate the mechanical one, such a
peristalsis-type control progressively loses its efficacy, yielding to a
standing wave type driving which involves an interplay between the mechanical
and chemical actuation. Our analysis suggests a new paradigm for the optimal
design of crawling biomimetic robots where the conventional purely mechanical
driving through distributed force actuators is complemented by a distributed
chemical control of the material remodeling inside the force-transmitting
machinery.
