3D-Printed Microneedles Open Ears to New Treatments
The inner ear is one of the body’s most protected organs. Surrounded nearly on all sides by one of the hardest bones in the body, it's also shielded from substances in nearby blood vessels by a barrier similar to the blood-brain barrier.
Because of these obstacles, delivering drugs to the inner ear is a huge challenge. But with promising gene therapies and other drugs for hearing loss in development, it’s one that’s becoming increasingly imperative to solve.
Microneedles that may safely deliver drugs to the largely inaccessible inner ear are being developed by researchers at Columbia University's medical and engineering schools. Pictured on the left are 3D-printed microneedles designed to pierce the round window membrane of the human ear. On the right, the hole created by the microneedle. Images: Jeffrey Kysar and Anil Lalwani / Columbia University.
3D-printed microneedles that pierce a tiny membrane separating the inner and middle ear may be one answer. Developed by the research groups of Jeffrey Kysar, PhD, at Columbia Engineering and Anil Lalwani, MD, at Columbia University Vagelos College of Physicians and Surgeons, the microneedle is ultra-sharp. The microneedle shaft has the thickness of a human hair, and the microneedle tip has a radius less than 1% of a human hair's thickness.
This ultra-sharp tip introduces a minimal degree of damage in the tissue as it pierces the tiny membrane because it pushes aside—rather than cuts—the membrane’s structural fibers.
In their latest studies, Kysar and Lalwani found that a single perforation in the membrane of guinea pigs let drugs delivered to the middle ear quickly diffuse into the inner ear. Perforations begin to heal over 24–48 hours, with complete closure by one week, and hearing returns to normal within a day.
They showed that the 3D-printed microneedles also can create precise perforations in thicker human membranes without traveling too far into the inner ear and damaging intracochlear structures (which lie only a millimeter behind the membrane).
The round window is one of two openings into the cochlea from the middle ear. In humans, the elliptical window is approximately 2 mm long and covered with a thin membrane. Diagram from Getty Images.
The next step—hollow microneedles—will explore the potential use of microneedles as tools for direct injection of therapy.
“Despite high rates of inner ear diseases, including hearing loss and balance disorders, we have very few treatments,” Lalwani says. “Microneedles should provide a safe and effective means of intracochlear drug delivery, which will have significant impact for the diagnosis, treatment, and prevention of auditory and vestibular disorders.”
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Jeffrey Kysar, PhD, is professor and chair of mechanical engineering at Columbia University’s Fu Foundation School of Engineering and Applied Science and a professor of otolaryngology/head & neck surgery at Columbia University Vagelos College of Physicians and Surgeons.
Anil Lalwani, MD, is professor of otolaryngology/head & neck surgery at Columbia University Vagelos College of Physicians and Surgeons.
The research appears in two papers published online in November in the journal Otology & Neurotology:
- “3D-Printed Microneedles Create Precise Perforations in Human Round Window Membrane in Situ.” Other authors: Harry Chiang, Michelle Yu, Aykut Aksit, Wenbin Wang, and Sagit Stern-Shavit, all of Columbia University, and
- “Anatomical and Functional Consequences of Microneedle Perforation of Round Window Membrane.” Other authors: Michelle Yu, Daniel N. Arteaga, Aykut Aksit, Harry Chiang, and Elizabeth S. Olson, all of Columbia Univerisity.
The research was funded by the National Institutes of Health (grant R01DC014547).
Anil Lalwani is on the Medical Advisory Board of Advanced Bionics.