Octopus Arm Structure:
Inspiration for Novel Robotics
Michael Stella
Faculty Advisor:
Biology
Dr. William M. Kier
Graduate Mentor:
Ted Uyeno
Background
Internal skeletons consist of stiff elements connected to muscle.
muscle.
External skeletons have a hard outer plate material connected to muscle.
Hydrostatic skeletons make use of water’s incompressibility, featuring
featuring a
sealed internal cavity full of water much like a hydraulic system.
system.
Hydrostatic Skeleton
Octopus arms do not conform precisely to any of these categories
because they have no stiff elements and no internal cavity. Instead,
Instead,
they rely on muscle itself as the hydrostatic ‘fluid’ and are termed
termed
‘muscular hydrostats.’ Human tongues also use this principle.
Sea Anemone
This special system allows the octopus arm to bend, twist,
lengthen, and shorten, and stiffen without joints.
Current robotic arms rely on stiff elements, which are ideal for
Connective
precise, repetitive movement in open areas but are ineffective in
in
confined or obstructed spaces and changing tasks. They must also
Tissue
be equipped with multiple grasping tools to be able to pick up a
(Force Transmission in
range of objects.
Torsion)
A robotic arm modeled after that of an octopus would be much
more versatile in terms of possible environments in which it could
could
Transverse
be used. It could also perform multiple tasks without modification
modification
because it would be able to simply wrap around or attach to
Muscle
diverse objects. In a project supported by the Defense Advanced
(Elongation, Bending
Research Projects Agency, Dr. Kier is collaborating with robotics
robotics
Support)
engineers to develop such an arm.
Longitudinal
Although basic descriptions of octopus arm morphology are
available, a detailed analysis of the muscle and connective tissue
tissue is
Muscle
lacking.
(Shortening, Bending)
Furthermore, most of the literature comes from studies using only
only
one species of octopus, assuming that results can be applied to
Axial Nerve Cord
other species.
My task was to study the structure of arms from three species ofOblique Muscles
octopus (Octopus
(Octopus briareus,
briareus, short arms, Octopus bimaculoides,
bimaculoides,
(Torsion)
intermediate length arms, and Octopus digueti,
digueti, long arms) in an
attempt to identify differences and similarities between them.
Connective
Kier, 2003
External Skeleton
There are three major classes of skeletal systems.
Internal Skeleton
Tissue
(Force Transmission in
Torsion)
Octopus bimaculoides Arm Transverse Section
Results
The arrangement of muscle and connective tissue is similar in all
all three species.
Handedness of the oblique muscle layers on one side of the arm alternates
alternates in all three species.
An oblique muscle on one side of the arm is opposite in handedness
handedness to its pair on the opposite side in
all three species.
For instance, if the external oblique runs in a rightright-handed helix, the medial oblique is leftleft-handed and the inner
oblique is right handed.
If the external oblique on the near side of an arm is rightright-handed, the external oblique on the far side is leftleft-handed.
This seems to indicate that the fibers of the external oblique on
on one side are linked to the fibers of the medial
oblique on the far side.
The purpose of the inner oblique layer and the mechanism by which
which it changes handedness are still unclear and
must be investigated further.
A
B
C
The angles the oblique layers make with the long axis of the arm is approximately the same in O.
briareus and O. digueti.
digueti. The external and medial layers have similar angles, but the inner
inner oblique layer’s
angle is significantly smaller.
External Oblique
Longitudinal
Transverse
Average Angle Made with Long Axis by Oblique Layer
70
Medial
Oblique
Angle (Degrees)
60
50
40
O. briareus
Medial
Oblique
Transverse
O.digueti
30
Internal
Oblique
20
10
0
external
medial
Oblique Layer
internal
A
B
C
Summary
Octopus arms consist of a densely packed array of
muscle and connective tissue.
Ian Walker,Clemson University, Christopher Rahn, Pennsylvania State University
The outermost layer is circular and runs about the
perimeter of the arm perpendicular to the long axis of
the arm.
The next layers are oblique and longitudinal, followed
by another oblique and another longitudinal layer.
Medial to those layers is a third, inner oblique layer and
transversely oriented muscle layer.
Torsional or twisting force is provided by the oblique
muscle layers, which wrap around the arm helically
and transmit force from one side of the arm to the
other via a collagen crossed-fiber array.
The arrangement of the muscle provides force for
both support and movement, allowing elongation,
shortening, bending, and twisting.
Principles of octopus arm structure and function are
being incorporated into the design of robotic devices.
The images to the right are of a prototype arm
moving in ways no conventional robotic arm can.
Robotic Arm Incorporating Principles
Derived from Octopus Arms