Effect of fixation and embedding on Raman spectroscopic analysis of bone tissue

Raman spectroscopy provides valuable information on the physicochemical properties of hard tissues. While the technique can analyze tissues in their native state, analysis of fixed, embedded, and sectioned specimens may be necessary on certain occasions. The information on the effects of fixatives and embedding media on Raman spectral properties is limited. We examined the effect of ethanol and glycerol as fixatives and a variety of embedding media (Araldite, Eponate, Technovit, glycol methacrylate, polymethyl methacrylate, and LR white) on Raman spectral properties (mineralization, crystallinity, and carbonation) measured from the cortical bone of mouse humeri. Humeri were fixed in ethanol or glycerol, followed by embedding in one of the media. Nonfixed, freeze-dried, and fixed but not embedded sections were also examined. Periosteal, endosteal, and midosteal regions of the intracortical envelope were analyzed. Raman spectra of fixative solutions and embedding media were also recorded separately in order to examine the specifics of overlap between spectra. We found significant effects of fixation, embedding, and anatomical location on Raman spectral properties. The interference of ethanol with tissue seemed to be relatively less pronounced than that of glycerol. However, there was no single combination of fixation and embedding that left Raman spectral parameters unaltered. We conclude that careful selection of a fixation and embedding combination should be made based on the parameter of interest and the type of tissue. It may be necessary to process multiple samples from the tissue, each using a combination appropriate for the Raman parameter in question.