In Situ Mechanical Behavior of Regenerating Rat Calvaria Bones Under Tensile Load via Synchrotron Diffraction Characterization

In recent years, research in bone surgery has focused on developing tissue engineering strategies to accelerate bone regeneration. The major challenge of these researches is to repair large bone defects where innovative implants (biomaterials) have been developed to fill and heal the latter. However, the mechanical behavior recovering of the newly formed bone, as the regeneration process takes place, remains still poorly understood. This work aims at mechanically characterize the bone regeneration process in the tissue engineering frameworks related to bone substitute isolated implantation. This study highlights the distribution of mechanical stresses induced by the healing process and the evolution of minerals crystallographic texture along with regeneration through mechanical behavior mapping in various regeneration levels by means of rat calvarias samples harvested at different regeneration stages until complete reconstruction. In situ tensile testing under WAXS/SAXS synchrotron µ-beam have been achieved to spatially resolve the elastic strain/stress response of mineral crystals and collagen fibers of bone architecture, respectively. Results are then correlated with the microbiological processes through histological and micro-tomography observations.Results indicate that the evolution of the mechanical response of healed bone tissue inside the initial defect at different regeneration stage is expressed by a randomly distributed mineralization followed by a mineral density reorganization along with crystal platelets reorientation in the newly formed bone matrix during bone reconstruction. Observations also show that such a sequence is strongly affected by the implant nature resulting in significant differences in regenerated tissue quality and healing rate