A cure for hearing loss? Researchers have created 3D printed custom-designed prosthetic replacements for damaged parts of the middle ear.
Researchers using CT scans and 3D printing have created accurate, custom-designed prosthetic replacements for damaged parts of the middle ear. The technique has the potential to improve a surgical procedure that often fails because of incorrectly sized prosthetic implants.
Hearing works partly through the transmission of vibrations from the ear drum to the cochlea, the sensory organ of hearing, via three tiny bones in the middle ear known as ossicles. Ossicular conductive hearing loss occurs when the ossicles are damaged, such as from trauma or infection.
To remedy conductive hearing loss, patients can undergo surgical reconstruction. It requires prostheses made from stainless steel struts and ceramic cups. The surgery involves tailoring a prosthesis for each patient in the operating room. Unfortunately, this technique has a high failure rate.
“The ossicles are very small structures, and one reason the surgery has a high failure rate is thought to be due to incorrect sizing of the prostheses,” says study author Jeffrey D. Hirsch, M.D., assistant professor of radiology at the University of Maryland School of Medicine (UMSOM) in Baltimore.
“If you could custom-design a prosthesis with a more exact fit, then the procedure should have a higher rate of success.”
To this end, Dr. Hirsch and colleagues looked at 3D printing as a way to create customized prostheses for patients with conductive hearing loss.
For their studies, the team removed the middle linking bone in the ossicular chain from three human cadavers. They then imaged the structures with CT.
Next, they used an SLA (stereolithographic) 3D printer to create prostheses to restore continuity for each of the middle ears. Each of the prostheses had unique measurements.
When four surgeons performed insertion of each prosthesis into each middle ear, they did so without knowing about the bone from — and for which — each was made. The researchers then asked the surgeons to match each prosthesis to its correct source.
All four surgeons were able to correctly match the prosthesis model to its intended temporal bone — the bone containing the middle and inner parts of the ear. The chances of this occurring randomly are 1 in 1,296, according to Dr. Hirsch.
“This study highlights the core strength of 3D printing — the ability to very accurately reproduce anatomic relationships in space to a sub-millimeter level,” Dr. Hirsch said. “With these models, it’s almost a snap fit.”
The results suggest that commercially available CT scanners can detect significant anatomic differences in normal human middle ear ossicles. Moreover, it’s possible to accurately recreate these differences with current 3D printing technology. More significantly, surgeons are able to detect these differences, which should not only increase the likelihood of a proper fit, but also decrease surgical time.
The next step in the research is to create prostheses out of biocompatible materials. The team are also exploring a different approach that would combine the 3D printed prostheses with stem cells.
“Instead of making the middle ear prosthesis solid, you could perforate it to be a lattice that allows stem cells to grow onto it,” says Dr. Hirsch. “The stem cells would mature into bone and become a permanent fix for patients with hearing loss.”