Artificial replacement joints are well known for their tendency to fail and to require replacement after a number of years. Artificial spinal discs particularly suffer from the fact that replacing them is unusually difficult, so developing a material that can withstand decades of use has been a major research goal. Some years ago diamond-like carbon (DLC) was a promising coating for joint implants, but it failed spectacularly as it eventually chipped off from the implants and caused all sorts of problems.
Researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa) have been researching DLC to try to figure out what happened eventually identifying the bonding layer that was used to hold the DLC as the actual culprit. The silicon within this layer degraded leading to implant failure, but the same team has now developed a bonding agent made out of tantalum, a highly corrosion-resistant metal, that should hold on for a lifetime.
This coating was tested in a so-called total disc replacement – a mobile disc implant. We simulated 100 million cycles, i.e. about 100 years of movement in a specially designed joint simulator. The small intervertebral disc implant held out, remaining fully operational with no abrasion or corrosion. The new bonding agent is soon also to be used in combination with DLC coatings for other joints. “The intervertebral disc is the most awkward joint in terms of implants. Because tantalum has performed so well, the DLC project can now be applied to other joints,” says [Dr. Kerstin Thorwarth, Nanoscale Materials Science, Empa].