Effects of tissue age on bone tissue material composition and nanomechanical properties in the rat cortex

Abstract

While osteoporosis is known to alter bone tissue composition, the effects of such compositional changes on tissue material properties have not yet been examined. The natural gradient in tissue mineral content arising from skeletal appositional growth provides a basic model for investigation of relationships between tissue composition and mechanical properties. The purpose of this study was to examine the effects of tissue age on bone tissue composition and nanomechanical properties. The nanomechanical properties and composition of regions of differing tissue age were characterized in the femoral cortices of growing rats using nanoindentation and Raman spectroscopy. In addition, spatial maps of the properties of periosteal tissue were examined to investigate in detail the spatial gradients in the properties of newly formed tissue. Newly formed tissue (0–4 d) was 84% less stiff and had 79% lower mineral:matrix ratio than older intracortical (15–70 d) tissue. Tissue modulus, hardness, mineral:matrix ratio, and carbonate:phosphate ratio increased sharply with distance from the periosteum and attained the modulus and mineral content of intracortical tissue within four days of formation. The mineral:matrix ratio explained 54% and 62% of the variation in tissue indentation modulus and hardness, respectively. Our data demonstrate significant variations in tissue mechanical properties with tissue age and relate mechanical properties to composition at the microscale.

Raman Assessment of Bone Quality

“…The main advantages of Raman spectroscopy include its applicability to fresh tissue [24,74] and higher spatial resolution (with sampling volumes of 1 lm 3 or less) [25]. Raman spectroscopy can also be used with fixed and embedded specimens [32,80] and also to fluorescently labeled and stained specimens [21,52,75], although heavy staining may facilitate burning [50]. When combined with mechanical loading regimes, Raman spectroscopy correlates chemical information with bone failure responses at the ultrastructural level [15].…”

“…Raman mineral-to-matrix ratios have not been calibrated with measured materials such as the ash weight of bone. Nevertheless, these ratios can be used to assess compositional trends in a series of related specimens such as the increased age-related mineralization trends observed in mouse calvarial tissues [73] and rat cortical bone [21]. Matrix bands based on methylene side chains (CH 2 at 1450 cm À1 ) [69,80,82] [3,43,82].…”

Whole Bone Mechanics and Bone Quality

“…Similar to other natural materials, bone tissue is spatially heterogeneous in material properties and composition [36,50]. Osteoporotic tissue exhibits reduced spatial variation in compositional measures [96,102], but a direct link to fracture remains to be established.…”

Age‐related changes in organization and content of the collagen matrix in rabbit cortical bone

“…Several parameters related to the composition are commonly calculated from the absorption spectrum, for example, mineral-to-matrix and carbonateto-phosphate ratio. 9,11,17,18 Additionally, studies in demineralized bone have been used to estimate collagen content from the amide I band. 19 Furthermore, FTIR analysis techniques have also been developed to analyze minor compounds in the samples.…”