Optical characterization of the nanoscale organization of mineral deposits on silk films.

The alignment of deposited minerals in tissues such as bone and teeth plays a critical role in the mechanical properties of these tissues. Therefore, assessment of features that are characteristic of aligned biominerals could aid in the development of novel biomaterials and engineered tissues that can be used to replace damaged or defective human tissues. In this study, we demonstrate that light scattering spectroscopy can serve as a useful tool for the noninvasive characterization of mineralization on aligned organic substrates. Specifically, we used silk films with oriented and nonoriented secondary structures as a protein matrix for control of mineralization. The mineral deposits displayed self-affine fractal morphologies with the oriented films yielding a significantly higher Hurst parameter, which in turn suggests higher levels of fractal organization. In addition, the value of the upper bound of fractal correlation lengths was significantly smaller for the oriented than for the nonoriented films and correlated well with the size of the corresponding nanocrystalline mineral beads identified by scanning electron microscope imaging.