August 30, 2012, Accutek Engineering Team
By: Maciej Jakucki, Senior Project Engineer
The FDA recommends testing Intervertebral Body Fusion Devices (IBFD) in many different configurations and evaluates each device on a case by case basis. One of the guidance document recommendations is to perform wear testing that analyzes particulate generation. There are specific wear standards that require the use of multi-axis equipment and can take months to complete. Full blown wear testing may or may not be required for your device, depending on your intended use and design.
However, since ASTM F2077-11 dynamic tests are typically performed prior to a specific wear test, there are additional options for characterizing wear in parallel with other tests. If your device is being loaded, wear debris and particulate is often generated, especially if there are articulating components or different materials in contact with each other (PEEK/titanium or ceramics). By testing your device dynamically in a saline or bovine serum solution, you can capture the particulate or debris. The particulate can then be analyzed further using a SEM (Scanning Electron Microscope) to determine the size, morphology and chemical composition of the particles.
Imagine your device releasing wear debris in the human body. Would you rather have small particulate that is round and smooth or a large particle that is jagged and rough? The answer is actually neither, both are undesirable in their own ways. Performing SEM analysis on the released particulate will characterize microscopic details, such as overall size, shape, and distribution, as well as provide a particle count. Additionally, with EDX (Electron Dispersion X-ray) Spectroscopy analysis , the material compositions and chemistry of the particulate can be determined so that you can distinguish between your various materials.
Mass Loss Analysis is also typically performed on the dynamic tests which can give you an idea of how much mass your device is losing (or gaining in certain circumstances). The parts are cleaned and weighed prior to testing, and then cleaned and weighed in the same manner during and/or after the test. If the wear rates are low, then you may want to perform a mass analysis using the SEM to get further quantifiable mass data.