A freeze fracture technique for examining human hair medulla with Scanning and Transmission Electron Microscopy

Abstract

Examination of hair medulla by transmission electron microscopy (TEM) is difficult because of the keratinous composition of hair and because of sectioning problems that result from insufficient infiltration and nonmiscibility of hair with embedding resins, even those of low viscosity. Although longitudinally cutting or tearing fibers will expose the medulla for embedment or direct viewing, considerable disruption occurs in its structure. Less disruption results from the use of freeze fracture techniques for either transmission or scanning electron microscopy (SEM).Freshly plucked human scalp and beard hairs were submersed in liquid nitrogen for a minimum of three minutes, held at proximal and distal ends with Dumont #10 tweezers, and slowly bent to an arc until the specimens broke at the apex. Customarily, clean bevelled fractures occurred along the tips of the arcs and exposed not only the medulla but also the cortex and cuticle. The fractured specimens were then removed from liquid nitrogen.