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.
14 May 2016 - 17 May 2016