Material Composition and Implantation Site Affect in vivo Device Degradation Rate

Tissue engineering requires biomedical devices that stabilize wounds, then degrade as tissue regenerates. However, published material degradation rates are often conflicting. Incorporating monitoring functionality into implanted devices allows real-time assessment of degradation and failure, but requires contrast agents, as most biomedical devices are composed of polymeric materials invisible to medical imaging modalities. Computed tomography (CT)-visible radiopaque composites were created from 5-20wt% tantalum oxide (TaOx) nanoparticles in polymers with distinct degradation profiles: polycaprolactone (PCL), poly(lactide-co-glycolide) (PLGA) 85:15 and PLGA 50:50, representing slow, medium and fast degrading materials respectively. Radiopaque phantoms, mimicking biomedical devices, were implanted into mice intramuscularly or intraperitoneally, and monitored via CT over 20 weeks. Changes in phantom volume, including collapse and swelling, were visualized. Phantom degradation profile was dictated by polymer matrix, regardless of nanoparticle addition. Foreign body response was dependent on implant site and degradation kinetics were significantly affected in middegrading materials, transitioning from linear degradation intramuscularly to exponential degradation intraperitoneally, due to differences in inflammatory responses and fluid flow. Nanoparticle excretion via liver and spleen lagged polymer degradation, requiring modulation of nanoparticle clearance. Tracking real time device behavior advances the new era of personalized medicine, allowing individualized treatment plans to biomedical devices.