Mammalian appendages such as hair, quill and wool have a unique structure 
composed of a cuticle, a cortex and a medulla. The cortex, responsible for the 
mechanical properties of the fibers, is an assemblage of spindle-shaped 
keratinized cells bound together by a lipid/protein sandwich called the cell 
membrane complex. Each cell is itself an assembly of macrofibrils around 300 nm 
in diameter that are paracrystalline arrays of keratin intermediate filaments 
embedded in a sulfur-rich protein matrix. Each macrofibril is also attached to 
its neighbors by a cell membrane complex. In this study, we combined atomic 
force microscopy based nano-indentation with peak-force imaging to study the 
nanomechanical properties of macrofibrils perpendicular to their axis. For 
indentation depths in the 200 to 500 nm range we observed a decrease of the 
dynamic elastic modulus at 1 Hz with increasing depth. This yielded an estimate 
of 1.6GPa for the lateral modulus at 1 Hz of porcupine quill's macrofibrils. 
Using the same data we also estimated the dynamic elastic modulus at 1 Hz of the 
cell membrane complex surrounding each macrofibril, i.e., 13GPa. A similar 
estimate was obtained independently through elastic maps of the macrofibrils 
surface obtained in peak-force mode at 1 kHz. Furthermore, the macrofibrillar 
texture of the cortical cells was clearly identified on the elasticity maps, 
with the boundaries between macrofibrils being 40-50% stiffer than the 
macrofibrils themselves. Elasticity maps after indentation also revealed a local 
increase in dynamic elastic modulus over time indicative of a relaxation induced 
strain hardening that could be explained in term of a α-helix to β-sheet 
transition within the macrofibrils.