Octopus shows the way

Published in   JFWTC in house Journal Vol.1 Issue 1 2005


Biological species are a perennial source of inspiration to scientists and engineers: be it  developing  a new material , fabricating a smart device or  designing a  more versatile robot.

Prof Binyamin Hochner, a biologist at Hebrew University in Jerusalem,  Albert H. Titus assistant professor in electrical engg.dept.  at the State University of New York,  Buffalo and Eric Baer Professor in Polymer science at the  Case western University have one thing in common: all three are totally captivated by  the Octopus.

An octopus, of course  has several fascinating  features.   To begin with it is a truly blue  blooded animal because  copper rich hemocyanin flows  through its veins. Anatomically it is a mass of soft flesh with no internal  skeleton.  It manages to keep its eight long dangling  arms  free from entanglement.  It can regrow  an arm if one is  severed.  At times  it resorts to  this trick willingly to escape from  a fearsome predator.  It has other escape modes too: several hidden sacks of  thick blackish ink  which  can be  sprayed  to confound enemies Its  specialized skin cells are capable of  color changing as well as  reflection and refraction  of light. Octopus uses this in multiple ways :  to camouflage themselves with the ambience, to  communicate with other octopuses, or as a warning signal.

Binyamin Hochner, heading the Octopus lab  at Hebrew University in Jerusalem is eager to learn a few things from the octopus  to design the  next generation  robots with flexible arms. It is the neurophysiology of the  arm that  amazes Hochner’s  group. Not only the  arm has seemingly infinite degrees of freedom, it can almost do the great Indian rope trick. For example, when in demand, the soft supple  arm  can turn into  a segmented semirgid structure. 

So how does the Octopus do it ? The answer lies in  the structural features of the arm which anatomically falls in the class of muscular hydrostat, a hydrostatic system where the fluid ( water)  is within muscle cells.  Since water is incompressible, contraction of the muscles in one dimension causes expansion of the hydrostat in an orthogonal direction. The production of movement and force is dictated by the constant-volume constraint in these structures.  Elephant trunks and tongues are other examples of a muscular hydrostat.  

The muscles themselves are special and made up of  longitudinal,  transverse  and helical  fibres.  A fibre reinforced   hydro or organo gel composite is the  closest approach to a muscular hydrostat. Karra from the dept. of Computer science and applied mathematics is working with  the team  trying to unravel the complex  biomechanics and movement control strategies by developing a physical 3D dynamic arm model and simulations.  

Titus, the Optical engineer at the State University of New York  finds  the octopus eye to be  an amazing organ.  The most  unique being.

Octopus eye is fitted with a biological lens that rolls  in and out  of the socket to focus close up, and distant objects respectively.  Titus has an NSF funded research project  to  replicate an octopus retina in a silicon chip,    Titus has  built into his  O-retina chip  the capability to distinguish objects on the basis of brightness, size, orientation and shape.  Titus hopes to incorporate polarized vision as well as edge recognition in future versions. Polarized vision   enables  the octopus to spot  otherwise transparent prey such as jellyfish.  Edge detection is  a data compression feature very special to biological eyes. Edge information usually is sufficient for detecting and tracking objects.  In robots, this chip could thus allow for faster processing of visual data. O- retina chips will be low in power consumption because  it uses analog circuitry. Ideal for  autonomous robots or other devices that need to work overtime.

Eric Baer and his team  are  trying to mimic  the focusing power of the octopus eye. The octopus eye,can focus light five times more strongly than a human eye s. Many biological lenses consist of several nanolayers  and form a smooth gradient that helps to focus light.  Baer’s team picked two commonly available polymers:  poly (methylmethacrylate) and poly(styrene-co-acrylonitrile). These polymers have different refractive indices (1.4893 and 1.5700 respectively),  By varying the number of polymer nanolayers in each film, the researchers varied the final resultant  refractive index.   One such set when  rolled  into a sphere  had a focusing ability equivalent to that of the octopus eye. Baer is optimistic, that  this paves the way for  designing lenses with almost any desired focusing power. He has already made for  himself a pair of reading glasses.

Courtsey : National Geographic News   February 9, 2005  Optical Engineering  August 2003  and Nature Dec. 7, 2004