23.8: Summary

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In this TLP the elastic properties of biological materials were studied. You will have learnt that few biological materials exhibit Hookean behaviour either because they do not have linear stress-strain curves, or because they do not have reversible stress-strain curves.

Many biomaterials show J-shaped curves and the reasons why these arise were discussed, in terms of material structure. The S-shaped curve has been covered, and concepts such as the entropy spring introduced in The Stiffness of Rubber TLP have been revised. You will have seen that S-shaped stress-strain curves lead to elastic instabilities such as aneurysms, and that this can be demonstrated experimentally, using cylindrical balloons.

Horse hair, human hair and spider silk are examples of materials which show viscoelasticity and tensile tests were carried out on human hair and horse hair. You should now be aware of the structure of hair and spider silk and the reasons for their low coefficient of restitution.

Going further

Books

S Vogel, Comparative Biomechanics: Life’s Physical World, Princeton University Press, 2003.
JE Gordon, The Science of Structures and Materials, Scientific American Books, 1988.
JFV Vincent, Structural Biomaterials, Princeton University Press, 1990.

Websites

Mechanical properties of keratin
A site maintained by Richard Bonser about the mechanical properties of keratin, with particular reference to the mechanical properties of feathers.
Silk biomechanics
An article on the American Museum of Natural History website.