Scanning electron microscopy studies of collagen, mineral and ground substance in human cortical bone

This paper presents scanning electron microscopy (SEM) observations made on the collagen, mineral and ground substance components comprising human cortical bone, which to a very large extent have been made possible by a sample preparation technique which takes advantage of the fracture propagation behavior inherent to the mature, highly heterogeneous, lamellar cortical bone tissue. By varying the extent to which bone samples are decalcified, it is possible to study certain morphological aspects of all these three main components of bone. Collagen features observable at fairly low magnification (approximately 1000x) include collagen bundle orientations with respect to the long axis of bone or of the osteon samples and collagen bundle morphological interrelationships. Much higher magnifications (approximately 20,000x) reveal spherical structures attached to the collagen fibrils which comprise the fiber bundle. Ground substance, yet to be identified biochemically, was noted in so-called interlamellar regions of osteons and of periosteal and endosteal tissue as well as in resting lines, cement lines and hypercalcified rings. It was observed to contain sulfur and to be trypsin soluble, providing evidence for the presence of a noncollagenous protein and of chondroitin sulfate which may be biochemically related in a protein polysaccharide complex. Such conclusion does not, however, preclude the presence of other ground substance components in this observed material. Large concentrations of mineral were noted in the interlamellar region of osteons and of periosteal and endosteal bone. This mineral does not seem to be directly associated with collagen. This study involves the use of scanning electron microscopy in both the secondary and back-scattered electron detection modes and energy dispersive x-ray microanalysis (XMA).