X-ray pole figure analysis of apatite crystals and collagen molecules in bone

X-ray pole figure analysis was performed on apatite (AP) crystals in bone mineral and collagen molecules in the bone matrix. For AP in bone mineral, the (0002) plane (c-axis) and {21 (3) over bar 0} plane were examined. The diffraction peaks from both planes were well isolated from other diffraction peaks in the bone. To investigate the orientation of collagen molecules in the bone matrix, demineralized bone by EDTA treatment was used. For collagen, the diffraction peak from about the 0.3 nm period along the helix axis of the collagen molecule was investigated. The c-axis of AP and the helical axis of the collagen molecule have strongly preferred orientations in a direction parallel to the bone axis. The c-axis of AP has an appreciable pole density peak in the radial and tangential direction of the bone, whereas collagen molecules were almost uniaxially oriented in the bone axis direction though having an appreciable distribution. This suggests that there are more than two types of morphology in the AP particle in bone mineral: one with the c-axis almost parallel to the bone axis and the other in which the c-axis is oriented almost perpendicular to the bone axis. The {21 (3) over bar 0} plane has isolated peaks of pole density in pole figures in both radial and tangential directions. On the basis of the classification of orientation for elongated polyethylene, the main portion of AP particles in bone is concluded to be biaxially oriented.