It is well accepted that a major cause for osteolysis and orthopaedic implant failure is the build-up of wear debris during the articulation of artificial joints. This is particularly the case for metal on polymer implants and has led to the use of alternate bearing surface materials, such as metal alloys, ceramics and novel polymeric combinations. It is for this reason that controlling bodies such as the FDA require standard wear and fatigue tests to measure expected wear volumes and characterise the generated wear debris. Continuum Blue offers orthopaedic companies particle analysis services to analyze & characterize wear debris from implant studies according to ASTM F1877 & ISO 17853 standards.
SEM & TEM Particle Analysis
An implant, such as a total disc replacement (TDR) or total hip replacement (THR), is loaded in a simulator designed to apply loads and motions in accordance with the relevant standard, such as ASTM F2423. The implant is then tested to several millions of wear cycles in a lubricant, such as bovine serum or phosphate buffered saline. The mass loss of the implant component/s is measured as a function of wear cycles and the serum or saline is sampled for wear particle analysis.
Once the particles are isolated from the serum using acid, basic or enzymatic digestion methods, they are sequentially filtered through typically 10, 1 and 0.1 micron membrane filters. This is sufficient for polymer particles, but analysis of ceramic and metallic particles which are very small requires filtration through finer membrane filters (0.015 micron) or deposition on grids.
Particles captured on the membrane filters or grids are imaged using a scanning electron microscope (SEM) or transmission electron microscope (TEM) at the relevant magnifications. A number of images are taken from each filter/grid and then processed using image analysis software so that particles can be detected and characterised
The results collected in this systematic way enable the characterisation of the particles generated by the simulated test. Particle size and distribution can then be determined. Additional results of the analysed wear debris can be generated such as:
- Particle count & distribution per ml
- Particle geometry (roundness, aspect ratio & form factor)
- Compositional analysis using energy dispersive x-ray (EDX) or Fourier transform Infrared (FTIR)