Brillouin–Raman microspectroscopy for the morpho-mechanical imaging of human lamellar bone

Abstract

Bone has a sophisticated architecture characterized by a hierarchical organization, starting at the sub-micrometre level. Thus, the analysis of mechanical and structural properties at this scale is essential to understand the relationship between its physiology, physical properties, and chemical composition. Here, we unveil the potential of Brillouin–Raman microspectroscopy, an emerging correlative optical approach that can simultaneously assess bone mechanics and chemistry with micrometric resolution. Correlative hyperspectral imaging, performed on a human diaphyseal ring, reveals a complex microarchitecture that is reflected in extremely rich and informative spectra. An innovative method for mechanical properties analysis is proposed, mapping the intermixing of soft and hard tissue areas, and revealing the co-existence of regions involved in remodelling processes, nutrient transportation, and structural support. The mineralized regions appear elastically inhomogeneous, resembling the pattern of the osteons’ lamellae, whilst Raman and Energy Dispersive X-rays images through Scanning Electron Microscopy show an overall uniform distribution of the mineral content, suggesting that other structural factors are responsible for lamellar micromechanical heterogeneity. These results, besides giving an important insight into cortical bone tissue properties, highlight the potential of the Brillouin and Raman microspectroscopy to access the origin of anisotropic mechanical properties, almost ubiquitous also in other biological tissues.