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Mossel, W.p.
12-08-1997, 09:15 PM
Dear readers,
On October 24 I posted 4 question about the E-modulus of human skin. Under
the questions a summary of the replies. Thanks very much for the help.

>I am developing a model for skin friction. In the model the modulus of
>elasticity (Young's modulus) of the skin is present. The value of the
>E-modulus of skin was earlier discussed on this list by means of a question
>of Lenny Tsap. I got from him a summary of the answers being:

>>In the book Handbook of Human Tolerance by McElhaney et al there is a page
>> on the mechanical properties of skin. They present data by various age
>> ranges. Note that the units are not correct engineering units, and should
>> be multiplied by gravity.
>> AGE Modulus of Elasticity (kg/mm^2)
>>
>> 7 months - 3 years 2.9
>> 15 years - 30 years 6.7
>> 30 years - 50 years 8.1
>> 50 years - 80 years 11.0
>>
>>This data was taken from the following reference, which seems like it would
>>be difficult to get.

>>Rollhauser, H. Tensile strength human skin. Excerpts from Anatomical
>>Institute, Marburg-Lahn, Germany, pp. 341-346, 1950.<

>I am looking for answers on the following questions:
>1. In which volume of Handbook of Human Tolerance by McElhaney is the
> above mentioned page and which number page is it?
>2. Has anybody ever seen that 6 pages of Rollhauser? If so, where? Or has
> anybody a photocopy of that pages?
>3. Is anything know about the way the modulus of elasticity of skin in vivo
> can be measured?
>4. Why is a gap present between 3 and 15 years in the values of the
E-modulus?

On the questions 1, 2 and 4 I got no replies.
On question 3 or relatated to question 3 the following replies were given:

Paul Bourassa :
I have interest in biomechanics and I am from a mechanical engineering
background. It looks to me that you couls measure the Elastic modulus in
vivo or on any specimen with ultrasonic transducers.With ultrasonic
transducers, you can measure the time elapsed between a pulse transmitted
at one location and the same pulse received at a second location. The time
elapsed divided by the distance between the emitter and the receiving
transducer gives the sound velocity. For elastic bodies, there is a
relationship beyween the sound velocity in a material and the modulus of
elasticity. c=sqrt(E/rho) where c is the sound velocity in a rod and rho is
the mass density. For example, for steel, rho is about 7500 kg/m3 and E is
about 200,000 MPA or 200,000,000,000 N/m2 which gives c= about 5200 m/s
Therefore, measuring the sound velocity gives a good clue to the value of
the elastic modulus.
I have simplified every thing quite a bit, because the skin some kind of
viscoelastic material, and more of a composite material than a homogeneous
and linear elastic material. Furthermore, there are other kinds of waves
transmitted through materials like shear waves which have a lower velocity,
but which are also linked to the modulus of elasticity.
The firms involved in the production of ultrasonic transducers could give
you the particular relationships for each of their transducers.
----------------------------------------
Douglas Chang :
You should check out the classic biomechanics papers:
2. Lanir Y; Fung YC.
Two-dimensional mechanical properties of rabbit skin. I. Experimental
system.
Journal of Biomechanics, 1974 Jan, 7(1):29-34.
1. Lanir Y; Fung YC.
Two-dimensional mechanical properties of rabbit skin. II. Experimental
results.
Journal of Biomechanics, 1974 Mar, 7(2):171-82.
Since that time there are literally hundreds of papers on the biomechanics
of skin, from the fields of plastic surgery, dermatology, forensics,
pathology, biomaterials and biomechanics. Try a Medline search.
For example:
42. Potts RO; Chrisman DA Jr; Buras EM Jr.
The dynamic mechanical properties of human skin in vivo.
Journal of Biomechanics, 1983, 16(6):365-72.
Some exciting recent work on in vivo properties are being pursued by:
1. Sanders JE; Garbini JL; Leschen JM; Allen MS; Jorgensen JE.
A bidirectional load applicator for the investigation of skin
response to
mechanical stress.
Ieee Transactions on Biomedical Engineering, 1997 Apr, 44(4):290-6.
also check out:
2. Sanders JE; Goldstein BS; Leotta DF.
Skin response to mechanical stress: adaptation rather than breakdown--a
review of the literature.
Journal of Rehabilitation Research and Development, 1995 Oct, 32(3):214-2
---------------------------------------
Partap Singh Khalsa :
You may also wish to check out a recent paper by Pete Grigg which measured
some of the moduli of rat hairy skin [Grigg P (1996) Stretch sensitivity of
mechanoreceptor neurons in rat hairy skin. J Neurophysiol. 76:2886-2895].
He found that the material properties of rat skin were non-linear and at
least orthotropic, if not fully anisotropic. I'd suspect that human skin
material properties are similar in composition. In any case, using a single
modulus to represent skin will be quite inaccurate over a broad range of
physiological deformations.
---------------------------
Michael S. Sacks :
There is quite a large literature (clinical) regarding non-invasive
methods to test the mechanical and other properties of the of the skin.
There are several review books, as well as work by several
biomechanically-oriented researches. Look in particular to the work by
Brian Finlay published in the Journal of Biomechanics, which developed a
torsional device. Be forwarned that the level of technology is not
high.
--------------------------------------
JE Sanders :
FYI. We have a paper coming out in the Journal of Rehabilitation
Research and Development reporting experimental data on coefficient of
friction measurements between skin and prosthetic interface materials
as well as socks.
--------------------------------------
Bill Vannah :
Manschot & Brakkee (J. Biomechanics; 19:511-539), in-vivo
testing of human skin should be more readily available, and
might be a good starting point.
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Matt Warner :
Hello, my name is Matt Warner, I'm a post-grad at bath university. I'm
studying the poroelastic behaviour of soft biological tissues, mostly
cartilage, I don't know how relavent this is but the following paper
contains several references to material properties of skin:
Mak, AF, Huang, L, and Wang, Q, (1994). A biphasic poroelastic analysis of
the flow dependant subcutaneous tissue pressure and compaction due to
epidermal loading: issues in pressure sore. J Biomech Eng, vol.116,
pp.421-429.
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"All spelling errors due to line noise"
Kind regards, Vriendelijke groet, Grusze
Wim Mossel

a.k.a. w.p.mossel@io.tudelft.nl
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