The Life & Mind Seminar Network

Seminar #71: Histology for Robot Engineers

Posted in Audio / Video, Seminars by Tom Froese on September 17, 2010

Next Monday we will have Nick Hockings present a Life and Mind seminar on:

Histology for Robot Engineers

16:30-18:00
Mon. 19th, Sept. 2010
Fulton Bldg. 109

An analysis of why robots constructed of rigid materials fail as biomimetic systems and as embodiment for lifelike intelligence.

This seminar: Examines histology as materials science underpinning biomechanics. Introduces the concept of ‘material embodiment’. Demonstrates that the body is not an assembly of parts, but a single fibro-elastic continuum, that uses hyper-elastic fiber-gels to achieve low friction dynamics and energy conservation. Presents a series of engineering proposals for how to build soft bodied robots with near human tactile sensation and dynamics.

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Nick will be presenting this seminar at the Italian Institute of Technology, Genova on Wednesday, so all critique and feedback will be greatly appreciated.

All welcome!

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Video and slides of the presentation are now on the Audio/Video page

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5 Responses

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  1. Colin said, on September 17, 2010 at 2:30 pm

    In terms of histology the body is most surely an assembly of parts. Its also a continuum in the way suggested. I don’t think the two are at odds.

    How continuous tissues with adaptive properties arise from sheets of discrete but tightly coupled cells is surely a matter of interest.

    The current findings in materials science are clearly of huge potential.

    But living tissue is still made from components and knowing how those interact surely would bring still more advances in robotics and materials.

  2. Nick said, on September 17, 2010 at 7:27 pm

    Hi Colin,

    Strictly the structures of the body differentiate within the continuum, and can be dissected into parts. By contrast robots conventionally are manufactured as parts which are then fastened to each other to assemble the robot.

    When modeling the body it often helps to treat the parts as distinct, because this makes the model easier to understand, and more tractable.

    When building a robot to provide a biomimetic embodiment for intelligence, the mechanical properties of the robot have a large influence on how similar the passive behaviour of the robot body is to the biological body that it is imitating.

    Those mechanical properties are determined by the materials and geometry of the robot.

    eg iCub has rigid metal structure, actuated by reduction gearboxes driven by electric motors… all made of metal and rigid plastic. Consequently when something unexpectedly collides with it, iCub is essentially rigid, the impact forces are consequently high, and risk of breakage is real.

    By comparison ECCE Robot is compliant, and much less likely to break. ECCE Robot is also an assembly of parts not a continuum. The moving parts of ECCE Robot are separated by air, and have pulleys where sliding contact is necessary. This limits the density with which its actuators can be arranged around its body without interfering with each other.

    If ECCE Robot were given as much muscle mass as a living body, there would be a problem of collisions between the rigid motors and friction where cables cut into other parts.

    Real muscles are packed tightly and slide over each other without significant friction. This is because they form an elastic continuum. In the layer between adjacent muscles there is areolar connective tissue, a hyper-elastic fiber-gel. There is in fact no friction, only a very small amount of hysteresis, because there are no separate surfaces sliding over each other. The areolar tissue is flexing as only a hyper-elastic material can.

    Areolar tissue is hard to appreciate without experience handling it. Preserved anatomy specimens are misleading because preservation vulcanizes the tissue radically altering its mechanical properties. Likewise refridgerated pieces of meat are stiffer than when they are alive. Fresh dissection is the only way to way to observe its behaviour.

    If you get the opportunity to do a dissection, take an anatomy textbook and try to dissect the tendons and liggaments of the hand or knee. What you will find is that there are not distinct boundaries between tendon, ligament, bone, cartilage, and areolar connective tissue. Try also to find the boundary between the dermis and the subcutis.

    Analyse the tissues as a materials scientist. Measure their anisotropy, their elastic modulus and extensibility. Examine the directional arrangement of fibres and their relationship to tissues capable of resisting compression.

    It is not impossible to manufacture robots that have these composite structures. To do so requires the use of hyper-elastic gels and fibres.

    The seminar looks at what the properties of different tissues are, how they relate to biomechanics, and how a robot with the same properties can be built.

  3. Colin said, on September 18, 2010 at 1:16 pm

    Hi Nick –

    Actually I have done some neuro-surgery on live animals (rats) some histology and some imunnohistochemistry and tracer studies. I’m familiar with skeletal muscle and nerve properties, but mainly through instruction rather than experience. The only direct experience I have is with live scalp muscles (in which connective tissue is clearly visible in fact, and must be carefully dealt with), and live hearts and recently deceased animals which I did not dissect because they were shortly stuffed full of fixative.

    But I’m most definitely not claiming expertise in those areas; just a few months experience and some med/pre-med neuroanatomy courses that included muscalature as well.

    I don’t disagree with your aims or anything you say really. My point was that I don’t think you’re being clear conceptually in claiming, or appearing to claim, that animal tissue is a continuum in histological terms. I think of histology as the study of cells, but its the study of tissues as a whole too, I appreciate that.

    Tissues aren’t a homogeneous continuum. However, that’s not all that important to your aims because as you point out, they are *in effect* continuous, for present purposes.

    We cannot make artificial dermis or muscle from artifical cells yet. It might not ever be required.

    But, my point was that making the distinction between what *is* the case in animals (tissues are made of cells and are not super or supra continuous) and what is the case *for present purposes* (they may as well be considered continuous, and probably should be) leaves room for *future* advances beyond even the very impressive work presently underway. Those advances might be, some day, continuous tissues and support substances closer to the biology, and made of cell like entities that interact, and replace e.g. ruffini’s corpuscle equivalents when they break.

    Possibly there will never be an advantage in that. Very possibly we won’t be able to do it.

    But it seems wise to leave room for it.

    The recent advances are obviously extremely significant, and I’m not suggesting they are lacking in some way.

    I just think the limits should be clearly dilineated even in the most pivotal of advances.

    Hope I’ve cleared that up. It’s a trivial quibble maybe in the end. Maybe not. tissues (and as you point out junctres between them) are continuous *for practical purposes at present*

    But strictly, they aren’t. One day that could be important in making a robot that has even greater capability.

  4. Colin said, on September 18, 2010 at 1:20 pm

    also: there’s never *no* friction!

  5. Nick said, on October 3, 2010 at 4:55 am

    Hi Colin,

    The particular tissues you have had experience of happen to be highly cellular. In many other tissues the cells make up only a small fraction of the volume, eg cartilage, fascia, tendons, and areolar tissue.

    The cell membrane is crucial for biochemical separation, but has very little mechanical strength of its own. Plants, fungi, and bacteria have cell walls outside the membrane, which are mechanically robust.

    In animals the cell’s strength depends on the fibers of the cytoskeleton, which connect to membrane proteins, which in turn interact with the extracellular matrix. Mechanically the cells do function as immiscible droplets, but the fibers of the cytoskeleton and of the extracellular matrix form gels, which are often highly anisotropic due to the orientation of the fibers. Thus animal tissues (except blood and bone) are fibro-gel-emulsions. So yes not homogeneous, but mechanically continuous.

    Re Friction Erratum (7/10/10):

    I was using “friction” where “dry friction” is the correct term. “Internal friction” would refer to entropy due to elastic hysteresis plus plastic deformation, so Colin is right the energy loss is still “friction”.

    Friction occurs where two surfaces in contact move relative to each other. Within a continuum undergoing deformation there is elastic resistance and hysteresis, but not friction.

    The soft tissues of the body are hyper elastic, with low elastic modulus (except along the axis of their fibers). Consequently a flattened hysteresis loop on the stress:strain graph gives low energy loss to hysteresis. Areolar tissue is extreme in this property, and behaves analogously to a very good lubricant. It is unlike a lubricant however in that it is a solid gel, not a fluid, hence it is limited to finite shear strain. This is why tendon sheaths are needed.

    Robots that we can build:

    Today we cannot yet make autopoietic robots, and if we did they would arguably be organisms not robots. We can however make the materials to build a robot that provides an accurately biomimetic material embodiment. Such a robot would provide a suitable embodiment for a simulated nervous system.


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