People get hearing loss in many ways, from aging to damage caused by long-term exposure to noise, infection or accidents. Some are born. In addition, many different parts of the ear may need to be healed to solve the problem. In some cases, this is possible, albeit difficult.

In many cases, the fine hairs in the cochlea (part of the inner ear)-which enable the brain to recognize sounds as electrical impulses-are damaged. In other cases, the tympanic membrane has been perforated. Two different research teams have found solutions.

Yunming Wang of Huazhong University of Science and Technology in China and his colleagues focused on repairing the damaged cochlea and developed a prototype implantable device that converts sound waves into matched electrical signals when placed in a model ear. At the same time, scientists at Harvard University focused on repairing the damaged tympanic membrane and developed the PhonoGraft device, a 3D printed biocompatible graft implant to promote the healing process of tympanic membrane perforation.

There is no way to eliminate the damage to the inner ear hair cells. Therefore, current treatment is limited to cochlear implants and hearing aids. Unfortunately, such devices require an external power source and it is often difficult to amplify speech well or accurately enough to be understood by the user. Hearing aids that do not require batteries can solve these shortcomings. Chinese scientists have designed such devices. It simulates healthy cochlear hair and successfully converts noise into electrical signals of the brain as a recognizable sound without external power supply.

To achieve this goal, scientists have created a material that uses compression and friction. These materials have piezoelectric and triboelectric properties. Piezoelectric materials are self-powered and become charged when compressed by the pressure accompanying sound waves. When these sound waves move, the triboelectric material generates friction and static electricity. They used the new piezoelectric triboelectric sponge material to make a prototype acoustic sensing device that provides high efficiency and sensitivity over a wide range of audio frequencies.

How the team made the materials:

To test the membrane, the scientists sandwiched it between two thin metal grids and sonicated it. The vibrating membrane generates electric current through the piezoelectric effect, and the nanoparticles bounce back from their cavity walls, generating triboelectric charges.

The effect of bouncing particles increases the total electrical output of the material by 55% (compared to the piezoelectric itself). As a result, the frequency produced by the membrane is in the sound range of most adults (170 Hz).

Then, the team conducted a second experiment. They implanted the device into the model ears and played music, recorded the electrical output and converted it into a new audio file. The recording display is very similar to the original song file. This proves that self-powered devices are sensitive to a wide range of acoustics and should be able to pick up most sounds and sounds within the range of human hearing.

Perforated tympanic membrane, scientifically called tympanic membrane, is very difficult to repair. Unfortunately, they can be painful and cause hearing loss. The thin circular tissue conducts sound by responding to sound wave vibrations and converting that movement into electrical signals that the brain can interpret. It can also act as a protective barrier against invading pathogens, making it vulnerable to chronic infections, which can damage fragile tissues. Other methods of membrane perforation include trauma, explosions, and loud noises.

The eardrum has extraordinary self-healing ability, but many perforations still need help in the healing process. The surgeon can repair the hole through a reconstruction "tympanoplasty" procedure involving tissue grafts collected from the patient. However, failure usually ensues, so revision surgery is required. In addition, the structure of the patient-derived tissue graft does not match the structure of the normal tympanic membrane, resulting in imperfect sound conductivity.

The PhonoGraft technology of the Harvard team is a regenerative medicine solution for this situation. This is a 3D printed implant that can promote natural cell regeneration and repair damage; it provides a scaffold for body cell regeneration and hearing restoration. It works very well in experiments and has entered commercial production.

Elliott Kozin, an ear surgeon, an ear doctor and neurologist at MEE, and an assistant professor at HMS, said:

"In the past ten years, ear surgery has made a lot of progress. An important development is the development of endoscopic surgery, which allows us to treat patients directly through the ear canal, avoiding skin incisions and behind-the-ear drills in many cases. Hole. This method combined with Lewis Lab’s innovation allows us to imagine, design, and ultimately manufacture a device that may one day improve the outcome of eardrum surgery."

The PhonoGraft implant imitates the complex shape of the natural tympanic membrane with a pattern of "spokes" like a bicycle wheel. It is made of synthetic polymer-based 3D printing ink specially developed for this product.

Jennifer Lewis, co-inventor of PhonoGraft, said:

"When I learned that the native tympanic membrane is composed of a web-like radial and concentric structure, I was really excited because it builds on the early work in our laboratory. We first demonstrated the printing of a 3D spider web-like structure."

"In order to create a real regenerative graft, imitating the circular and radial collagen pattern of the tympanic membrane, it guides cell migration because they deposit new collagen fibers in the same pattern while matching the acoustic and mechanical properties of the natural tympanic membrane. A huge challenge. These grafts must be 3D printed to truly reproduce these complex features and functions."

Dr. Nicole Black, also co-inventor of PhonoGraft, added:

"It soon discovered that we must invent a new'ink' for soft tissue repair. Our goal is a biodegradable programmable ink that can be used to control the graft structure across multiple length scales, and ultimately be able to produce A regenerative graft with a natural tympanic membrane sound-conducting structure. To achieve this goal, we have developed a synthetic polymer-based ink system that can be aligned during the 3D printing process."

The researchers implanted the prototype of the device into the eardrums of the Chinchilla animal model because their ears are very similar to human ears in terms of hearing range and size. More importantly, this surgery is less invasive than myringoplasty because it can be inserted through the ear canal, which must be performed through an incision behind the ear.

MEE ear surgeon Aaron Remenschneider said:

"Three months after implanting our optimized graft into Chinchilla’s ears, we had a truly pleasant moment. Hearing tests showed that sound conduction was completely restored, which was a big obstacle. Then we used an endoscopy The mirror saw the ear canal for the first time. All we saw was the ghost of our graft being replaced by new tissue-a beautifully reconstructed tympanic membrane with a radial circular pattern. The different cell types of the tympanic membrane and blood support The vascular system is arranged along patterned polymer fibers and integrated into functional tissues. In addition, no signs of infection can be seen in the reconstructed tympanic membrane."

The Wyss Institute at Harvard University established a start-up company called Beacon Bio to bring this invention to the market. Then, the company was acquired by Desktop Health. Now, its founders are working hard to get FDA approval. Other similar implants, such as ClearDrum in Australia, are also under development.