Raman mineral-to-matrix ratios correlate with weight percentage mineral-to-matrix ratio determined by in-SEM Raman imaging of bone tissue

Raman imaging combined with scanning electron microscopy (SEM) is a powerful technique that allows for topographical, chemical and structural correlative multi-scale imaging. It provides the perfect tool to determine which of the Raman mineral-to-matrix ratios represent the best parameter to accurately measure the degree of mineralization of the bone matrix using quantitative backscattered electron imaging (qBEI) as the reference methodology. Indeed, previous studies evidenced that the v2PO4 and v4PO4 vibrational modes were less sensitive to laser polarization than the v1PO4. However, using the v2PO4 or v4PO4 requires a longer acquisition time or lower spectral resolution. In the present study, we evaluated the correlation between mineral-to-matrix ratios computed from v1PO4 and v2PO4 in a human bone sample retrieved from orthopaedic surgery during hip replacement and wt% mineral / wt% organic matrix obtained from qBEI using the inLux SEM Raman interface. We reported here that all mineral-to-matrix ratios were significantly linearly correlated with wt% mineral / wt% organic matrix and that v1PO4/CH2 exhibited the strongest correlation coefficient (r=0.880). This study suggests that the v1PO4 is still a valid Raman peak to estimate the mineral-to-matrix ratio in bone samples and can be used to diagnose bone fragility disorders.