Bone mineral crystal size and organization vary across mature rat bone cortex

Abstract

The macro- and micro-features of bone can be assessed by using imaging methods. However, nano- and molecular features require more detailed characterization, such as use of e.g., vibrational spectroscopy and X-ray scattering. Nano- and molecular features also affect the mechanical competence of bone tissue. The aim of the present study was to reveal the effects of mineralization and its alterations on the mineral crystal scale, by investigating the spatial variation of molecular composition and mineral crystal structure across the cross-section of femur diaphyses in young rats, and healthy and osteoporotic mature rats (N=5). Fourier transform infrared spectroscopy and scanning small- and wide-angle X-ray scattering (SAXS/WAXS) techniques with high spatial resolution were used at identical locations over the whole cross-section. This allowed quantification of point-by-point information about the spatial distribution of mineral crystal volume. All measured parameters (crystal dimensions, degree of orientation and predominant orientation) varied across the cortex. Specifically, the crystal dimensions were lower in the central cortex than in the endosteal and periosteal regions. Mineral crystal orientation followed the cortical circumference in the periosteal and endosteal regions, but was less well-oriented in the central regions. Central cortex is formed rapidly during development through endochondral ossification. Since rats possess no osteonal remodeling, this bone remains (until old age). Significant linear correlations were observed between the dimensional and organizational parameters, e.g., between crystal length and degree of orientation (R(2)=0.83, p<0.001). Application of SAXS/WAXS provides valuable information on bone nanostructure and its constituents, effects of diseases and, prospectively, mechanical competence.

Compressive loading of the murine tibia reveals site-specific micro-scale differences in adaptation and maturation rates of bone

“…This heterogeneity is reflected in the distribution of bone mineral density, mineral crystal composition and direction, and collagen maturity [7–9]. Thus, the material properties depend on the relative composition of the bone matrix components, and the interaction between them, which subsequently affect the structural properties.…”

Small-angle X-ray scattering tensor tomography: model of the three-dimensional reciprocal-space map, reconstruction algorithm and angular sampling requirements

“…The threedimensional reciprocal-space map comprises information on the main orientation of the nanostructure for different q ranges and also its degree of orientation. The reciprocal-space map could further be used as input for fitting the underlying nanostructure, similarly to what has been done on twodimensional SAXS data, for example to retrieve size parameters of the mineralized platelets in bone (Fratzl et al, 2005;Turunen et al, 2016).…”

The Ultrastructure of Bone and Its Relevance to Mechanical Properties

“…the residual crystals viewed in TEM appear to be flake-like, with thickness of about 5 nm and maximum lateral dimensions of 20-50 nm [18]. Wide-angle X-ray scattering shows that the crystals are elongated along their crystallographic c-axis, with a length/width ratio of ∼3 [19]. The flat surfaces of the flakes are formed by the 1010 face of the apatite crystal [20], so that the c-axis must lie in the plane of the flakes.…”