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Jun-kyo Suh
09-07-1995, 12:24 AM
Mike;
I think this discussion subject is very interesting and extremely
important. Without putting too much thought on this, a question coming
first into my mind is whether the difference in the deformation between the
tissue surface and the interior structure is due to an experimental
artifact. If you simply grip the tissue surface with a clamp, I am not
quite sure whether we can assume a uniform boundary condition on the cross
section of the tissue at the clamp location. Of course, I think this
argument depends on the tissue thickness.
Could you let us have some quantitative feeling on Lee's experiment? In
addition, did he tell you how much the difference in the surface and
internal deformation was?
My second question is about the definition of surface and internal
deformation. When we deal with a layered fiber composite material
(especially consisting of very compliant, nonhomogenous fibers), the
non-homogenous deformation (not necessarily surface vs. internal) is quite
common. In this case, we can represent the deformation in an average
sense, although there can be microscopically localized large deformation in
the area.

I look forward to further discussions on this subject. It is really a
good subject, Mike!

Best regards,

J.K. 'Francis' Suh, Ph.D.
Assist. Prof.
Dept. of Orthopaedic Surgery
Univ. of Pittsburgh
Pittsburgh, PA 15213
Tel: 412-648-1985
Fax: 412-648-2001
-----------------------------------------

>A few months ago I posted the following message:
>
>J. Michael Lee recently mailed to me the following interesting
>message:
>-------------------------------------------------------------------------
>A couple of years ago we were very interested in whether displacement of
>markers attached to the surface of tissue samples gave accurate reflections of
>internal deformations. We made a micro-tensile tester similar to that
>described in the 70's by Neil Broom and used it to deform uniaxial samples of
>canine pericardium---a tissue which is nearly transparent. This device was
>mounted on a microscope so we could follow internal structure using
>birefringence microscopy. We placed small graphite particles on the tissue
>surface, or glued on small metal flakes. What we discovered was that the
>tissue surface (at least in simple tensile tests) often deforms by quite
>different amounts than does the internal structure. We were very concerned
>about this as you can imagine. I would urge anyone relying on this type of
>system to develop appropriate control experiments to confirm the relationship
>between internal/surface deformation.
>-------------------------------------------------------------------------
>
>I would like to start a discussion on this topic of inter-laminar
>collagen fiber mobility when the tissue is stretched. This result
>could potentially affect much of the biomechanical data collection
>techniques that have been used for decades for soft tissues. Please
>feel free to respond freely with your ideas. As usual, I will attempt
>to put together all the responses into a single file when I feel we
>have exhausted the subject.
>
>As luck would have it, I ran out of time to really moderate this
>discussion. I would like to have another go at it. Please post
>your thoughts on this topic or any other related to the micro-
>mechanical basis of soft tissue mechanical behavior.
>
>Best regards,
>
>Michael Sacks, Ph.D.
>Dept. of Biomedical Eng.
>U. Miami