Impact of chemical composition on microscale elastic properties of cortical bone - A site-matched FTIR-SAM study

Cortical bone strength is determined by multiple factors. Among them, changes in cortical porosity and elastic properties of the extracellular bone matrix have been suggested to be related to fracture risk. The objective of this ex-vivo study was to assess matrix stiffness and chemical composition by means of site-matched 200-MHz acoustic microscopy and synchrotron radiation based FTIR microscopy in cortical bone samples obtained from the tibia mid-shaft of a representative sample cohort (19 human donors, age range: 69-94 yrs). The microscale stiffness coefficient c₃₃ was compared to characteristic features of the organic and inorganic constituents derived from the FTIR spectrum in site-matched osteonal and interstitial tissue regions. Matrix stiffness c₃₃ ranged from 22.4 GPa to 46.9 GPa (CV: 19%). A subset from 3 donors has been compared with FTIR parameters so far. In these samples, a consistent negative correlations of c₃₃ were observed with mineral-to-matrix ratio (R=-0.44, p<;0.005), collagen cross-linking (R=-0.5, p<;0.005) and carbonate-to-phosphate ratio (R=-0.33, p<;0.005). These findings underline the diagnostic value of elastic properties for the assessment of alterations in the organic tissue matrix. The former could be assessed by in-vivo US technologies, e.g. axial transmission measurements.