Thanks to their customary use in engagement rings, diamonds have come to represent a lifelong commitment 'til death do us part.' As researchers at Case Western Reserve University (Cleveland) are discovering, however, diamonds may provide a similarly long commitment in the body in the form of an implantable diamond-coated flexible electrode designed to last a lifetime.

"There are several very attractive engineering properties for the use of diamond as an electrode in general, and especially for an implantable electrode," says Heidi Martin, a professor of chemical engineering at Case Western leading the research. "If you're thinking of making an implant out of something that will last forever, that's very appealing because you don't want to do surgery several times because the material goes bad."

Deterioration of quality, performance, or physical structure of an implanted device over time is an ongoing problem, according to Martin. In the case of platinum electrodes used in neurostimulation, for example, data has shown material degradation and the presence of platinum chloride in nearby tissue, she says. Diamond, in contrast, is known for being chemically robust and stable; it won't corrode in the body over time.

In addition to forming more-durable neurological electrodes, diamond demonstrates potential for improving sensing electrodes. Its basic electrochemical properties and wide operating range could enable the detection of chemicals that were previously undetectable. "For instance, we have some data that we can detect a specific neuromodulator that people couldn't see before because it oxidizes at too high of a potential for other electrodes to sense," Martin says. "The role of this neuromodulator could now be explored electrochemically."

Diamond may also help overcome obstacles in chemical sensing. "One of the common interferences you get with biosensors is the presence of oxygen in the tissue," Martin adds. "[Conventional] metal electrodes will reduce the oxygen and create a signal that will interfere with whatever you're trying to measure." Because a diamond electrode greatly inhibits the electrochemical reduction of oxygen, it could minimize interference.

But despite these numerous biomedical benefits, the abrasive and tough nature of diamond does not lend itself to abundant use in applications requiring contact with the body's soft tissue. With this in mind, Martin and Chris Zorman, a professor of electrical engineering and computer science, are exploring a diamond-on-polymer electrode construction that capitalizes on only the desirable qualities of diamond by placing it solely at the biological interface.

To achieve this design, the researchers grow diamond at extremely high temperatures--around 800° to 900°C--on a silicon-based substrate. They then configure the backplane of the electrode, the electrical contacts, and other components on top of the diamond. Once this step is completed at room temperature, the team releases the diamond film from the silicon substrate and transfers it to a polynorbornene (PNB) polymer, yielding an electrode that features diamond only at the desired interface.

Although the scientists are optimistic about the viability of the diamond-on-polymer electrode, they are still conducting fundamental research and optimizing the structure. Martin anticipates that they may be able to move into clinical trials in three to five years. "This particular architecture will allow us to make a diamond electrode that is truly implantable for long-term use," she says. "Consequently, the diamond electrode could be a superior long-term implant, replacing other carbon- or metal-based electrodes."