Novel inner-ear drug delivery system offers hope for hearing disorder


Scientists at the Charles Stark Draper Laboratory have recently designed and tested a simplified micropump and used it to demonstrate the flow of fluid in and out of the device, to store drug in a reservoir on board, and the infusion of drug into the cochlea (auditory portion of the inner ear). Scientists are now aiming to miniaturize the electronics, so the device can fit into the bony space behind the ear.

Patients of tinnitus and other hearing disorders have no proved treatment options. Since the inner ear is one of the most inaccessible places in the human body with a bony membrane-lined labyrinth measuring only a few cubic millimeters here. In fact, these tight quarters make surgery impossible. “We can operate in the heart, in the brain, even inside the eye, the only place where we can’t operate in a functioning organ is the inner ear,” says Robert Jackler, a Stanford University School of Medicine otologist–neurotologist who specializes in complex ear diseases.

Moreover, the tiny space has also dissatisfied most research attempts to develop and deliver drugs to treat hearing disorders, developed by aging or exposure to loud noises. Tiny amounts of fluid are needed, with even more finely tuned quantities of drugs, that attempts to dispense medication over long periods of time have failed. “We’ve tried directed medication when treating hearing disorders but the way we do it today is very imprecise and poorly calibrated,” Jackler says.

Two systems, in particular, are gaining a lot of attention: one that infuses a little polymer matrix with drugs to stop relentless ringing in the ears and one that uses a miniscule pump to deliver the goods to damaged cilia (hair cells) that cause hearing loss.

Precision drug delivery is crucial, so one of the main challenges is engineering the matrix so that it releases its payload gradually, in a pulsating fashion. “The classic problem is how to get a local delivery source that distributes over a long period of time,” Borenstein says. “We want our device to be able to treat a problem for months if needed.” The idea is for a person suffering from a balance disorder or tinnitus, for example, to carry a wireless remote control with them and simply tap a button to release a therapeutic drug whenever the symptoms—whether disorientation or ringing in the ears—become unbearable.

Until now there has been no effective way to deliver medication to the inner ear, says Jeffrey Borenstein, a senior biomedical engineer at Draper. He and his colleagues have tested their polymer in lab tests thus far and are now exploring ways to trigger chemical compounds to release on demand, using wireless signals.

The Draper scientists are working with biomaterials scientists at the Massachusetts Institute of Technology’s (M.I.T.) Langer Laboratory—headed by bioengineer Robert Langer—to develop the matrix, made of a biodegradable gel that would harmlessly dissolve after use. The polymer might last for weeks or even months, releasing drugs into the inner ear that block the excessive release of certain neurotransmitters associated with tinnitus or calm any hyperactive nerves found in the cochlea.

“Although very few people actually suffer from ringing in the ears to the extent that it keeps them awake at night, tinnitus is a hearing disorder that we don’t really have many solutions for,” Jackler says. As a result sufferers of severe tinnitus are often prescribed antidepressants, which Jackler says do not eliminate the problem but rather help alleviate some of the associated anxiety and depression and help people better cope with their problem.

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