Bone Mineral as Seen in the Scanning and Transmission Electron Microscopes

Abstract

Transverse sections of bovine tibial bone have been investigated in both the SEM and TEM. SEM photographs of Collagenase etched surfaces reveal the mineral hydroxyapatite component as small spheroidal particles ∼ 10 nm across which are fused together to form spheroidal units ∼ 100 nm across. These 100 nm units aggregate to form a continuous mineral phase with holes or gaps (typically ∼ 200 nm across) through which collagen fibres pass in vivo. TEM photographs of untreated thin sections confirm the existence of these spheroidal units but additionally reveal rod shaped mineral particles (typically ∼ 10 nm by 100 nm). Both these morphological forms give electron diffraction patterns consistent with a poorly crystalline hydroxyapatite. Therefore, it is suggested that bone consists of a continuous fused spheroidal mineral component interpenetrated by collagen fibres which are closely associated with a second distinct morphological form in the shape of rod like mineral particles.