SEM images of wool fiber cross sections etched by means of protease digestion

Abstract

To identify some fine histological features of wool fiber cross-sections by scanning electron microscopy (SEM), the preparation method by the differential dissolution of section with a proteolytic enzyme was investigated. Wool fibers were embedded in epoxy resin and were sectioned into about 25μm thickness. The resultant sections were mounted on the SEM sample stage and were surface etched by enzyme (Savinase : Nobozymes Japan industry) solution followed by SEM observation. By using this method for preparing specimens, this differential digestion of components revealed the relatively distinct histological structure of the fiber in the SEM images with good resolution, where the cystine-poor endocuticle, cell membranes, nuclear remnants, and intermacrofibrillar material of the intact wool cross-sections were partially dissolved away. For the wool fiber oxidized under aqueous acidic conditions with Caro's salt, especially, the macrofibrils were observed in an electron scattering zone (concave circular structure) at the center of each one over the orthocortex, but not over the paracortex. Because of this differentiation, it was possible to distinctly discriminate between the ortho- and pracortex cell types of the fiber. In addition, this method will undoubtedly be valuable for assessing the extent of damage in fiber resulting from various physical and chemical treatments.