Nano-mechanical properties of composite biomaterials are governed by the morphological features and chemical distribution of heterogeneous multiple subunits. However, very little is known about such structure-function correlation at the nanoscale. We have used wool fibers as a model of composite biomaterials for such study. Wool fibers provide an ideal two component cylindrical model for such study as their ultrastructure and chemical composition have been well characterized, they have a core cellular component surrounded by an outer cell layer. The core is 16-40 micron in diameter and rich in axially aligned keratin microfibrils. Outer cells have multiple laminar layers, 60-600 nm thick and are distinctly rich in disulfide bonds. In this study, we have used an atomic force microscope (AFM) to examine the micromechanical properties of the different structural components using complementary techniques of nano-indentation and force-volume imaging. AFM images of transverse sections of wool fibers were obtained in ambient environment (Figure 1).

The exo-cuticle showed a significantly higher mechanical stiffness than the internal cellular core region (Figure 2).