Now Hear This: Process Can Customize Ear Implants

Late-night infomercials and full-page magazine ads tout the benefits of hearing aids that either look like Bluetooth headsets or fit inside the ear and can’t be seen at all. But neither has the capability of devices being developed by Drs. Roger Narayan and Yuan-Shin Lee, which are crafted to replicate the function of the bones in the middle ear. The innovative process the two researchers use could also customize hearing implants for individuals.

The bones of the middle ear—scientifically known as ossicles and commonly referred to as the hammer, anvil, and stirrup—sometimes break down because of age, illness, or injury. “Other bones can be reformed after a trauma,” says Narayan, a physician and professor in the Department of Biomedical Engineering. “But the repair process for ossicles is limited.” Other attempts to replicate ossicles have been prone to infection or degradation, and they didn’t always meet individual needs. So Narayan designed an implant that resembles a thumbtack—a flat head atop a narrow shaft—to fill in where nature fails. Small spikes on the head of the device help promote cell growth so it can attach to the ear drum.

Using a process called two-photon polymerization, Narayan directs pulses of a laser at a hybrid ceramic-polymer resin. Each pulse lasts a quadrillionth of a second and can be focused on a micron-sized area, creating a reaction in which only that area hardens. The process allows an implant to be built quickly, layer by layer, he says, adding that slight adjustments in the laser’s aim can produce devices to match the anatomy of specific patients.

Lee, a professor in the Fitts Department of Industrial and Systems Engineering, is developing a computer-aided design program for physicians to use MRI or CT scans to provide a guide for the laser to create the custom implants. Narayan and Lee are evaluating the mechanical properties of the devices to optimize their design, and graduate and undergraduate students have constructed an apparatus to examine the devices’ acoustical properties. “The material gives us the elasticity and vibration properties of natural bone,” Lee says.

Laser pulses create a reaction in a hybrid ceramic-polymer resin to allow a middle-ear implant to be built quickly, layer by layer.

The device hasn’t been tested yet in humans, but Narayan points to two advantages that will accelerate deployment once tests are completed. The ceramic-polymer material, often used in reconstructive dentistry, is already approved for clinical use, and the laser process doesn’t require expensive clean rooms for production. “We’re excited about the opportunities this novel prosthesis fabrication technology presents,” he says, “especially for patient-specific prostheses on a small scale.”

 

Dr. Roger Narayan, graduate student Philip Miller and Dr. Yuan-Shin Lee, left to right, examine a positioning system used for microscale processing of medical devices. The system can create custom middle-ear implants, like the one depicted in the illustration below, to combat hearing loss.