Composition and mechanics of cement lines in cortical bone

Healthy bone tissue is fracture-resistant. To a large part this property stems from bones complex hierarchical structure providing several toughening mechanisms. One of these mechanisms is the deflection of propagating cracks along curved interfaces, deflecting the cracks from the main failure direction increasing the length cracks need to travel, before a bone fails. These interfaces are called cement lines and they are located at the outer boundary of osteons, cylindrical structural elements within bone with diameters on the order of several 100 m. While, the effect is known, the mechanical properties of cement lines enabling it, have so far not been systematically studied and remain largely unknown. Within this project we will apply state-of-the-art technologies to determine the mechanical properties, and the composition of cement lines. In particular, we aim to perform combined compositional and micromechanical analysis on bone samples. For this purpose we will use bone material from the femoral neck of human donors that have been previously healthy or suffered a low trauma femoral neck fracture (osteoporosis). This will not only allow us to obtain information of the mechanical properties of cement lines as a function of their composition and tissue age, but also correlate the data to donor age, medical condition and history. As we suspect specific compositional (and mechanical) changes with age and medical condition, we will also attempt to modify cement line samples in vitro, as well as model systems, and investigate the influence of these modifications on their mechanics. In summary, the properties of cement lines are heavily understudied, yet they are an important locus for fracture resistance in bone. We follow an innovative approach to fill this gap and to further our understanding of bone fracture mechanics.