Properties of the Matrix in Keratins

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Abstract
A technique is described for the determination of stress-strain curves of keratin specimens in longitudinal and transverse compression. The testing procedure involves use of a table-model Instron testing machine, modified to improve the linearity of the instrumental characteristic (the compliance of the machine), and to give precision of strain determinations of the order of ±0.1 μm, as measured by the reproducibility of the crosshead position during a stress-strain test. Pro cedures are discussed for the preparation of specimens with near-parallel test faces, generally in the form of cylinders or rectangular parallelepipeds of typical dimensions 200 X 150 X 100 μm. The residual nonparallelism of the specimen causes the low-strain region of the stress-strain curve to be sigmoidal, resulting in an apparently linear, strictly inflexion region. Values of longitudinal and transverse "inflexion" moduli are reported for keratins at various relative humidities. In water, the former vary little from keratin to keratin, while the latter range from ~0.03 G Pa for rhinoceros horn to ~1.0 G Pa for echidna quill.

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