Dynamic Raman spectroscopy of mineralized tissue.

Abstract

Bone is a complex biomaterial comprised of mineral particles in an organic matrix. The chemical structure and properties of the material strongly influence the mechanical properties of bone, including disease states such as osteoporosis. Bulk measurements of the chemical composition (including x-ray densitometry) do not adequately predict bone quality and mechanical properties. A technique is needed to probe the chemical changes in bone during mechanical loading. The technique must provide detailed chemical information at high spatial and temporal resolution. An appropriate technique, dynamic Raman spectroscopy, has been widely used for the study of synthetic materials including polymers and ceramics. Bone presents some unique challenges to the direct application of dynamic spectroscopy using existing methods. These challenges have now been overcome. A system is described to collect high-resolution spectra with the needed spatial resolution in less than 2 seconds. This is appropriate for both mechanical loading experiments and high-speed Raman imaging. System performance is demonstrated on specimens including polypropylene and whole bone. Spectral changes are seen at physiological loads that reflect distortion of both the mineral lattice and the collagen structure.