Polymer Vision

By testing a range of materials, researchers at the University of Alabama, Huntsville, have come up with a set of waterproof coatings that both protect electronic retinal implants and the sensitive eye tissue of the wearer. The research was presented during a session in the Division of Polymer Chemistry on March 30 at the American Chemical Society national meeting in Anaheim.

Retinal implants could help millions of people with ocular disease regain some of their vision, but making a device that can send electrical signals from a camera to an array of electrodes in the eye is no easy task. If a bit of water gets into the electronics, they will short out.

To solve this problem, Carmen Scholz and her colleagues are investigating a wide variety of protective coatings. The catch is that this impermeable material must be perfectly biocompatible.

"We don't want any scar formation," Scholz explained. Even a thin layer of damaged tissue could block the implant's faint electrical signals.

Initially, her team tested two polymers and two other substances by implanting them into pig eyes. Polyethylene glycol and diamond-like carbon performed better than amorphous aluminum oxide or polyvinyl pyrrolidone, which caused severe irritation, Scholz said. Since then, her group has focused on creating block copolymers made of polyethylene glycol and amino acid-based polymers. The researchers have also experimented with polyoxazoline as an alternative to polyethylene glycol.

"The work is wonderful," said Christopher Ober, who led the symposium session in which Scholz spoke. "It certainly shows the importance of polymer chemistry to interface between the material and the biological world."

Ober mentioned that a first-generation retinal implant has been tested in several people. He predicts that someday there will be smart coatings that can repair themselves, perhaps with some help from their surrounding tissue.