Probing Pre-failure Molecular Deformation in Cortical Bone with Fluorescent Dyes

Abstract

To reduce bone fracture incidence, gaining knowledge on the underlying bone damage mechanisms is essential. Although several mechanisms have been proposed on different length scales, the pre-failure deformation processes of bone are still not completely understood. We previously reported an opaque process zone feature in bone under tensile loading which colocalizes with high-strain regions. Unlike the classical damage which can be stained in the unloaded state, the process zone can be stained only when the sample is loaded. In this study, a wide range of fluorescent dyes with different molecular weights (MW) and charges were used to probe the size and charge properties of the structural features leading to process zone emergence. We found none of these fluorescent dyes tested were able to stain the process zone once the loading was removed. All of the negativelycharged dyes with MW less than 70 kDa stained the process zone, while the positively- or neutrally-charged dyes did not, except for the one with smallest MW tested (380 Da) in group of the positively charged dyes. Therefore, we proposed that certain molecular groups with positive charge in bone were exposed during process zone emergence under loading.