Understanding the origin, nature and degradation of implant debris

Total hip replacements (THRs) are one of the most common and effective surgical procedures, with more than 100,000 procedures performed annually in the UK alone. This intervention is used primarily to alleviate pain and restore functionality, with an implant survival rate that exceeds 90% after at least ten years of follow-up. However, despite these high success rates, 10–15% of implants still fail within 15–20 years, particularly due to tribocorrosion, a combined degradation mechanism involving mechanical wear and electrochemical corrosion. The degradation then leads to the release of metallic debris and ions, triggering complex biological responses that can result in systematic inflammation, implant loosening, osteolysis, and eventual implant failure.
This study investigates the degradation of Low Carbon - Cobalt Chromium Molybdenum (LC-CoCrMo) alloys by examining their tribocorrosion behaviour and microstructural evolution under both macroscale and microscale contact conditions, which have traditionally been studied separately. Uniquely, it establishes a direct link between these contact regimes and the origin and nature of implant wear debris, an aspect that has not been previously reported in the literature.
Using a nanotribometer integrated with electrochemical cells, tribocorrosion experiments
were performed under varying loads (10, 50, 100, and 200 mN) and contact conditions to quantify wear rates and assess surface degradation. Microscale contacts were achieved using a spherical tip of 25 µm diameter, while macroscale tests used a 200 µm diameter tip, enabling comparative evaluation of degradation mechanisms across scales. Furthermore the chemical wear was calculated using a mechanistic approach adapted to account for the specific conditions of small-scale tribocorrosion testing.
Post-test characterisation using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy SEM-EDX, white-light interferometry (WLI), transmission electron microscopy (TEM), and nanoindentation revealed distinct degradation mechanisms across scales.
Different wear regimes were characterised and directly associated with microstructural
evolution under varying local stress conditions. A clear shift in the degradation mechanism was observed from mechanically dominated wear at the microscale to corrosion-driven processes at the macroscale.