X-ray Pole Figure Analysis of Apatite Crystals and Collagen Molecules in Bone

Abstract

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 {2130} 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 {2130} 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.

X-ray diffraction as a promising tool to characterize bone nanocomposites

“…These mineral crystals are located within the gap-overlap region of staggered patterned collagen fibers and are found to grow with a specific crystalline orientation. The crystallographic c-axis of a mineral crystal coincides with the axis of symmetry parallel to the long dimension of the crystal; it is normal to the (002) lattice plane and has a strong preferred orientation parallel to the long axes of the collagen fibers [14,15]. The mineral crystals also grow outside the collagen fibers.…”

“…The mineral crystals grow with the crystallographic c-axes parallel to the long axes of collagen fibers [14,15]. The presence of such mineral crystals within the fibers had inspired many researchers to directly apply the principles of composite theories to bone.…”

“…Because of their non-destructive and non-invasive properties, x-rays are widely used to study crystalline materials, but are rarely applied to biological tissue like bone. Despite a long history of attempts on the ultrastructural characterization of bone [14,15,41,43,45,[48][49][50][51][52], there are only few reports on the change in lattice parameters with simultaneous loading of bone specimens, which is discussed in the following section.…”

“…When there is preferred orientation of the crystals and the region of interest is aligned to that direction, it is preferable to consider the lattice plane corresponding to that direction. For instance, a (00 l) plane representing the c-axis (longitudinal) orientation of the crystals is widely used in the case of hexagonal crystal system like bone to analyze the deformation and orientation characteristics [14]. However, if the crystals are randomly oriented, the region of interest is not aligned to the preferred orientation, or the x-ray exposure is too short, the diffracted intensity becomes weak and the diffraction profile may lack distinct peaks.…”

Orientation and deformation of mineral crystals in tooth surfaces

“…tissue (Sasaki and Sudoh, 1997). The HAp crystal orientations at tooth surfaces were obtained in the present study.…”