Compositional differences among undamaged, strained, and failed regions of bone using Raman spectroscopy

Understanding compositional changes that occur when bone fails may help predict fracture risk. Compositional differences that arise among failed, strained, and undamaged regions of bone can be determined using Raman spectroscopy and double-notch specimens. A double-notch specimen is a rectangular bone beam that has identical, rounded notches milled equidistant from each end. When subjected to a four-point bend test, maximum strains occur at the roots of the notches, and eventually the bone fractures at one of the notches. Because both notches experience the same force, when one notch breaks, the other is 'frozen' in the state directly preceding fracture. Spectra taken at the roots of both the unbroken and fractured notches can measure changes in tissue that occur prior to and after bone failure, respectively. Phosphate center of gravities (CGs) were calculated and compared among three regions: control, strained (root of unbroken notch), and failed (root of fractured notch). In comparison to control regions, the phosphate CGs near the unbroken notch showed a shift toward higher wavenumbers ( > 0.5 cm^-1), with the shift being concentrated at the comers of the notch. The tissue in the failed region appears to have relaxed, and showed a shift toward higher wavenumbers (> 0.5 cm^-1) only near the edge of the fracture.