Raman spectroscopic detection of changes in bioapatite in mouse femora as a function of age and in vitro fluoride treatment

Laser Raman microprobe spectroscopy, which characterizes the molecular stru cture of a mineral, was used to analyze microscopically small regions of bi oapatite in mouse femora in order to study the effect of mouse age and in v itro fluoride treatment on the bone mineral (i.e., mineral identity and deg ree of crystallinity). Both femora that had and those that had not undergon e in vitro NaF treatment underwent point analysis of 1 mum spots in the cen ter of the compact bone's cross-section. The Raman spectra of bones treated with fluoride showed a peak up-shift of the PO, vibration mode from 961 to 964 Delta cm(-1) indicating a conversion from a carbonated hydroxylapatiti c to a carbonated fluorapatitic mineral phase.; The spectral band width of the 961 Delta cm(-1) PO4 vibration in femora of 4-, 10-, and 24-week-old mi ce showed that aging, as well as in vitro treatment with 1.5 M NaF for 12 h ours, significantly increases the degree of crystallinity of the bioapatite . In vitro fluoridation of 10-week-old mouse femora increased the bioapatit e's degree of crystallinity to about the same degree as did aging to 24 wee ks. Four-point bending tests indicated that the age-related increase in cry stallinity of untreated bones was associated with decreased deformation to failure, i.e., in creased brittleness. In contrast, the increased crystalli nity following fluoridation of 10-week-old bones was associated with increa sed deformation, i.e., increased ductility, perhaps due to the altered mine ral composition. This study shows that the laser Raman microprobe readily d etects the conversion of carbonated hydroxylapatite to carbonated fluorapat ite, as well as changes in crystallinity of either mineral phase, in micros copically small regions of a bone sample.