People who have hearing loss because of inner ear damage or from a poorly functioning auditory nerve are not helped by cochlear and middle ear implants. Auditory brainstem implants (ABI), which bypass most of the hearing system and send signals directly to the auditory brainstem, are the best option for such patients. But currently these devices rely on rigid components that do not fit perfectly with each patient’s unique anatomy. This may be one of the reasons that ABIs end up being largely ineffective in many patients.
Now, a team at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland, working with teams at Massachusetts Eye and Ear and Harvard Medical School, has created a flexible auditory brainstem implant that overcomes the serious limitations that stiff devices suffer from.
The device can be placed in intimate proximity with the auditory brainstem, with the exposed thin-film electrodes hugging the tissue and allowing for clean passage of targeted electric signals.
Prototypes of the device, which has a surface area of 0.25 mm2, have already been tested in mice, whose anatomy is an order of magnitude smaller than ours, and they functioned well for over a month of trials. Larger versions, suitable for humans, were created and implanted into cadavers to evaluate whether they can soon be tested in real patients. Moreover, in testing, the researchers believe they see signs that the new approach will lead to a much wider perceived dynamic range of sound, resulting in outcomes that are much better than those with existing ABIs.
An important core achievement of this research was the development of an array of flexible platinum electrodes, encased in silicone, that maintain the properties of the metal they’re made of. Platinum is non-ferrous, so can be used within an MRI machine, and it is biocompatible and already used in many medical applications. To make it flexible, though, the team etched extremely fine patterns into the platinum using micron-scale manufacturing techniques. This was inspired by Japanese kirigami paper-cutting techniques, and the same approach should be useful for designing flexible implants that have to be positioned near very fragile and sensitive tissues.
Here’s an EPFL video showing off the new soft implant technology:
Study in Science Translational Medicine: Microstructured thin-film electrode technology enables proof of concept of scalable, soft auditory brainstem implants