PRESS
Biomimetic Ratchets
The
creeping,
crawling,
and slithering
gaits of
worms, snails,
and snakes
show how
organisms
are able
to adapt
to and exploit
certain environmental
and ecological
niches. Because
these gaits
involve the
continuous
interaction
of long flexible
bodies with
a solid substrate,
they are
qualitatively
different
from the
more commonly
studied modes
of animal
locomotion
such as walking,
swimming,
and flying
(1). In these
gaits, periodic
pulses of
muscular
defor mation
are rectified
by one or
more symmetry-breaking
mechanisms,
just as in
a mechanical
ratchet.
Inspired
by these
locomotory
behaviors,
we study
the motion
of a lubricated
rod of a
hydrogel
on a soft
substrate.
We show that
it is possible
to mimic
observed
biological
gaits by
vibrating
the substrate
and by using
a variety
of mechanisms
to break
longitudinal
and lateral
symmetry.
Our simple
theory and
experiments
provide a
unified view
of the creeping,
undulating,
and inchworming
gaits observed
in limbless
locomotion
on land,
all of which
originate
as symmetry-breaking
bifurcations
of a simple
base state
associated
with periodic
longitudinal
oscillations
of a slender
gel.
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