Bone Abstracts

Degradable bone implants may provide improved long-term healing, tissue remodeling and quality of life. In order to optimize alloy composition and degradation properties, in-vivo monitoring of the degradation process and its impact on bone formation is essential because degradation progresses differently in-vivo versus in-vitro. We aim to understand how degradation of magnesium alloy implants influences bone remodeling and bone structure using Micro-Computed Tomography (μCT).

Mini-screws composed of three different alloys (Mg2Ag, Mg10Gd, WE43 and titanium) have been implanted into rat femurs. After 3 month the complete femur samples have been excised. μCT scans have been performed (Scanco VivaCT 80, 70 kVp, 114 mAs, 1500 projections/180°, 15.4 μm isotropic voxel size, beam hardening reduction kernel, bone mineral density calibration). For the samples of low degradation, a layering approach has been used to investigate the lamellar changes perpendicular to the implant surface, for those in a further progressed degradation stage, density histograms restricted to volumes of interest around the initial (guessed) implant position were evaluated.

Compared to commonly used Ti-implants, imaging of Mg-alloys in μCT is less affected by metal artefacts and extraction of meaningful density profiles is feasible using μCT. In the scenario of strong degradation and non-uniform progression, the separation of bone and implant material remains a challenging task. A time-lapse in-vivo μCT study can elucidate the progression of the degradation, especially where corrosion is not taking place exclusively at the surface. Because the characterization of the bone-implant interface is very important for the understanding and refinement of degradable implant materials due to its influence on implant fixation, ultra-high resolution imaging should be combined with our μCT data in a hierarchical approach. Also multimodal approaches (spectroscopy, molecular imaging, histology and others) will help to better understand the complex processes involved in bone healing in the presence of degradable implants.