Implants That Last A Lifetime?
Researchers in Switzerland say they have coupled advanced coating and bonding agents to build joint replacement implants that should last a person’s lifetime.
The joint implant surface made at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) is called diamond-like carbon (DLC), a superhard material that is extremely resistant to abrasive wear. Such coatings have been used on implants before, but previous attempts have seen the material bonded to the rest of the device with compounds that quickly corroded.
Hip implants with DLC coatings were surgically installed between 1993 and 1995. About 50 percent of these failed within 8.5 years. Later investigation found that corrosion in the bonding layer—made of silicon— caused the DLC coating to delaminate. The exposed surface triggered wear in the joint and subsequent bone loss.
Now the Swiss team has used a rare, dense nonreactive metal called tantalum as the bonding layer instead of silicon. The element doesn’t react with body fluids, doesn’t trigger an immune response and is already used in orthopaedic implants.
They coated an intervertebral disc implant with the two materials and put it in a machine that mimics the wear and tear it would experience in a person’s body.
The implant experienced no abrasion or corrosion after being subjected to 100 million cycles, around what is expected from 100 years of use.
"Our aim was to find a bonding agent which does not corrode and which lasts a lifetime in the body," said Kerstin Thorwarth, a materials scientist at the lab. "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."
All images courtesy EMPA.