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PhonoGraft: 3D Printed Tympanic Membrane Graft

Regenerative medicine approach stimulates the self-healing properties of the tympanic membrane to permanently repair perforations

Perforations of the tympanic membrane or “eardrum,” the thin membrane that conducts sound in the ear, can result in severe hearing loss and recurring infections. Worldwide, tympanic membrane perforations occur in about 30 million people, with about four million people in North America and the European Union alone, due to blast and other traumatic injuries, chronic ear infections, and abnormal, noncancerous skin growth behind the eardrum. When these perforations do not heal on their own, they become chronic and require reconstructive “tympanoplasty” to repair these defects. However, commonly used graft materials, including temporalis fascia grafts harvested from tissue beneath the skin that covers the temples, do not ensure full mending. Hence, patients often require revision surgeries and are at risk for long-term hearing loss. 

Eardrum perforations are affecting millions worldwide. The multidisciplinary PhonoGraft team discusses how their new biomimetic technology enables the permanent repair of perforations, and what motivates them to bring it to the market. Credit: Wyss Institute at Harvard University 

Engineering a permanent regenerative medicine solution

PhonoGraft: 3D Printed Tympanic Membrane Graft
This graphic shows how the PhonoGraft (in blue) leads to functional and morphological regeneration of the tympanic membrane, whereas, in contrast, autologous fascia grafts often only allow imperfect mending in patients that frequently require revision surgeries. The PhonoGraft is a 3D-printed biomimetic membrane that is fabricated in different sizes to accommodate different ear sizes. Illustrations by Shawna Snyder

A multidisciplinary team of material scientists and ENT clinicians led by Gliklich Healthcare Innovation Postdoctoral Research Fellow Nicole Black and Core Faculty member Jennifer Lewis at the Wyss Institute, and Aaron Remenschneider and Elliott Kozin at Massachusetts Eye and Ear in Boston has developed an easy-to-use, biomimetic device, termed PhonoGraft. PhonoGraft is a biomimetic graft that has the potential to enable better and longer-lasting tympanic membrane reconstruction than typically used fascia grafts. These grafts, which are manufactured from biodegradable elastomers in the form of biomimetic circular and radial scaffolds to accommodate different ear sizes, function like the native eardrum.

By mimicking the native tympanic membrane, the PhonoGraft effectively conducts sound and promotes remodeling processes in which native tympanic tissue and vasculature grow into the graft, as the graft material slowly biodegrades. This results in tympanic membrane regeneration inside the ear that recapitulates key properties of the original tympanic membrane, including the conduction of sound across a broad range of frequencies important for human hearing, and normal barrier functions against pathogens.

PhonoGraft promotes tympanic membrane regeneration by combining biodegradability with its biomimetic architecture composed of circular and radial features. This graft conducts sound well at both low and high frequencies, thus restoring function far better than autologous tissue grafts, which are currently used. Moreover, we expect that the PhonoGraft will improve patient healing and hearing outcomes, thereby reducing the need for revision surgeries.

Nicole Black
PhonoGraft: 3D Printed Tympanic Membrane Graft
This composite image shows the noninvasive process by which the PhonoGraft is installed through the ear canal. The existing method involves making an incision behind the ear, which is far more invasive. Credit: Illustrations by Shawna Snyder

Preclinical validation

The team has validated PhonoGraft in preclinical in vivo studies using a chinchilla model whose tympanic membrane size and hearing range are akin to humans. PhonoGraft enabled remodeling of native tissue in animals with chronic perforations, including neovasculaturization, as it slowly degrades. By contrast, autologous tissue grafts, which were used as controls in the same study, do not remodel or degrade. Importantly, PhonoGraft restores hearing far more effectively than control grafts, as determined by auditory tests that measure the ability of sound to reach the cochlea, the anatomical structure in the inner ear that produces nerve impulses in response to sound vibrations, as well as to the brain.

The Wyss Institute is currently de-risking this technology and is seeking industrial partners to assist with commercialization and funding efforts.

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