Effects of applied load on bone tissue as observed by Raman spectroscopy

The skeleton is certainly essential to our physiology. Yet, surprisingly little is understood about how bone responds when a load is applied. This is particularly true at the ultrastructural. level, where neither the behavior under stress of the collagenous matrix nor that of the calcium phosphate mineral has been explored. Most standard techniques used in the investigation of the biomechanical properties of bone tissue are unable to obtain information at this level. Raman spectroscopy, however, is capable of probing biological specimens at the molecular level, without interference from water or common histological stains. Using this technique, we are able to observe changes in both the mineral and the matrix of bone during and after the application of load. These changes manifest themselves as band shifts in the bone Raman spectrum. We utilize this ability in this study. Two-dimensional Raman imaging is used to investigate the effect of macroscopic fracture on the mineral in sections of femora from 4-month-old and 18-month-old mice. Changes are seen in the mineral around fractured areas that indicate the fracture process may be causing a phase transformation in the bone mineral, similar to the "transformation toughening" process that is observed in many ceramics. We discuss the physiological implications of these results.