Real-time Microdamage and Strain Detection during Micromechanical Testing of Single Trabeculae

Research in bone diseases like osteoporosis is motivated by its immense social impact and health care costs. While there are numerous studies about the influence of bone mineral density and microarchitectural properties on the mechanical properties of trabecular bone, little is known about the influence of bone matrix material properties. In this communication, we present novel ways for combining mechanical testing of single trabeculae with imaging on both the microand nanoscale to further investigate these material properties. Our results indicate microdamage in an ellipsoid zone on the tension side of the trabeculae tested in three-point bending. We estimated the highest tensile strains in this region to be about 3.5%. Quantitatively global whitening versus distance curves correlate well with retrieved force-distance data. Scanning electron microscopy investigations of the microdamaged and optically whitened zones suggest that damage formation happens primarily in the bone and not on the surface. In addition to whitening/microdamage assessment on the microscale, we used atomic force microscopy together with a custom made three-point bending device and a region based digital image correlation tool to obtain quantitative local surface displacements on the bending side of single trabeculae. We found that bone deformation is heterogeneous with different surface domains shearing off each other. The two novel methods presented make it possible to investigate the dynamics of plasticity and failure of bone both on the microand on the nanoscale.