Multimodal Evaluation of the Spatio-Temporal Variations of Periprosthetic Bone Properties

Titanium implants are widely used in dental and orthopedic surgery. However, implant failures still occur because of a lack of implant stability. The biomechanical properties of bone tissue located around the implant need to be assessed to better understand the osseointegration phenomena and anticipate implant failure. The aim of this study was to explore the spatio-temporal variation of the microscopic elastic properties of newly formed bone tissue close to an implant. Eight coin-shaped Ti6Al4V implants were inserted into rabbit tibiae for 7 and 13 weeks using an in vivo model allowing the distinction between mature and newly formed bone in a standardized configuration. Nanoindentation and micro-Brillouin scattering measurements were carried out in similar locations to measure the indentation modulus and the wave velocity, from which relative variations of bone mass density were extracted.The indentation modulus, the wave velocity and mass density were found to be higher i) in newly formed bone tissue located close to the implant surface, compared to mature cortical bone tissue, and ii) after longer healing time, consistently with an increased mineralization. Within the bone chamber, the spatial distribution of elastic properties was more heterogeneous for shorter healing durations. After 7 weeks of healing, bone tissue in the bone chamber close to the implant surface was 12.3 % denser than bone tissue further away. Bone tissue close to the chamber edge was 16.8 % denser than in its center. These results suggest a bone spreading pathway along tissue maturation, which is confirmed by histology and consistent with contact osteogenesis phenomena.