Diamond-like carbon (DLC) coatings are commonly used in medical implants to greatly improve their resistance to environmental factors. Though impressively strong and impermeable, DLC will often break off from the implants to become a nuisance within the body. Now scientists at Empa, a Swiss research institution, have discovered why that happens and what can be done to prevent the chipping.
“When two materials are placed in contact with each other, the result is a reaction layer at the interface between them, which is only several atomic layers thick. Thus a new material is formed, which we investigated now for the first time”, explains Roland Hauert of Empa’s “Nanoscale Materials Science” laboratory.
His team showed that the so far barely considered reaction layer, which is not always completely corrosion resistant, is responsible for the detachment of the DLC layer. On the one hand, stress corrosion cracking occurred in the reaction layer. The mechanical load in conjunction with the penetration of body fluids led to slow-growing cracks, which in turn caused the DLC substrate to detach little by little.
In other cases, crevice corrosion was responsible for the damage. Over time, an aggressive, acidic medium develops in fine crevices and slowly dissolves the reaction layer or the additional adhesive layer, likewise leading to detachment.
But the Empa team didn’t stop there; together with their industry partners Synthes and Ionbond, they developed a corrosion-resistant intermediate layer at the interface to the DLC layer. What’s more, the researchers also developed a process that can determine a crack’s growth rate under conditions similar to those experienced in the human body as well as the dissolution rate of the reaction layer in cases of crevice corrosion.
Full story from Empa: Nanocorrosion causes implants to fail…