Close to twenty years ago, I remember writing about the big news at that time—that Dr. Charles Vacanti of the University of Massachusetts, with the assistance of other researchers including Dr. Linda Griffith-Cima from Massachusetts Institute of Technology (MIT), had created a scaffold, seeded it with cells, and grew a human ear on the back of a mouse.
The Vacanti mouse, or earmouse as it was called, featured an ear-shaped cartilage structure grown by seeding cow cartilage cells into a biodegradable earshaped mold that was then implanted under the skin of a nude mouse. Over three months, the mouse grew extra blood vessels that nourished the cow cartilage cells that grew and infiltrated into the biodegradable scaffolding in the shape of a human ear.
The study was inspired by the fact that total ear reconstruction was very challenging for plastic surgeons due to the complex structure of the ear. Vacanti saw the need for developing techniques for attaching ears in children who had external ear deformities or had lost ears due to traumatic accidents. It was designed to serves as a model for tissue engineering but was never meant to actually be implanted in a human.
In August 1997, the groundbreaking research was published in the journal, Plastic and Reconstructive Surgery, and the startling photo of one small mouse with a human ear growing on its back flashed around the world, creating excitement and controversy. All it took was years of research, many tries with control groups of nude mice, and several weeks of in vitro and in vivo incubation to generate new tissue.
How times have changed. I thought about the earmouse story I covered many years ago, when in May I read about a team of scientists at Princeton University who were exploring ways to merge electronics with tissue. They used 3D printing of cells and nanoparticles followed by cell culture to combine a small coil antenna with cartilage, creating what they call a “bionic ear” that can hear radio frequencies far beyond the range of normal human capability. The ear looks like a very pink natural external ear, but with an embedded electronic coil.
While there are usually there are mechanical and thermal challenges in interfacing electronic materials with biological materials, the Princeton researchers said that their new approach is to build and grow the biology using 3D printing, or additive manufacturing, to interweave tissue with electronics. This allowed them to combine the antenna electronics with tissue within the complex topology of a human ear. They used a standard 3D printer to combine a matrix of hydrogel and calf cells with silver nanoparticles forming an antenna. The calf cells later develop into cartilage.
The finished ear consists of a coiled antenna inside a cartilage structure. Two wires lead from the base of the ear and wind around a helical “cochlea,” which can connect to electrodes. Although the researchers say that further work and extensive testing would need to be done before the technology could be used on a patient, the ear, in principle, could be used to restore or enhance human hearing. They say electrical signals produced by the ear could be connected to a patient’s nerve endings, similar to a hearing aid. The current system receives radio waves, but they plan to incorporate electronic sensors in further studies to enable the ear to register acoustic sounds.
Now, remember Linda Griffith-Cima, whom I mentioned earlier? In 1995, at the time of her work on the earmouse project, she was married to Michael Cima, now the MIT Sumitomo Electric Industries Professor of Engineering. He and Emanuel Sachs, a professor of mechanical engineering, created and patented one of the first practical 3D printers, and gave the name three dimensional printing to the process. What a small world!
For more research being done on replacement ears, read this month’s Global Innovations article.
Beth G. Sisk
Editor
