The integration of electronics with the human body has fascinated scientists and science fiction fans alike for many decades now. They are enthralled by the bionic organ, an organ made of human tissue with an abiotic (nonliving) element. However, electronics are made from silver and other metals that are toxic to cells and can cause them to die. Researchers are trying to find a way to work around this compatibility problem and incorporate electronics into the body so that the transition from cell to metal is seamless. The cells and the abiotic molecules would be right next to each other with no space between the two. Current methods are complex and have yet to yield a true bionic organ: either the cells are inactive or the electronic component is not functioning. Manu Mannoor, a Princeton graduate student with the Mechanical and Aerospace Engineering (MAE) department, took a novel approach to solving this problem when he constructed a completely functioning bionic ear.

The Bionic Ear

Mannoor’s bionic ear is like any other ear, except for the fact that it does not listen to sound waves. Instead, the ear “listens” to radio waves. The eardrum and cochlea are replaced by a coil made of silver in the bionic ear. The coil acts as an antenna that picks up radio waves. The signal from the radio waves is then transmitted through a wire that comes out the other side of the ear.

Not only is the bionic ear the first functioning bionic organ, but it is also the first to be created using a 3D printer. 3D printing first begins with the computer-assisted design (CAD). The CAD is just a computer-simulated object that one can adjust and design on a computer. Mannoor and his team loaded a design of an ear and then modified it to include their electronic component of an antenna. They also labeled which parts were made of different materials; the ear itself is composed of cells, but the antenna is made of silver and coated with silicon. The silicon neutralizes the toxicity of the silver, and provides structural support for the ear.

After all the modifications to the CAD are complete, the software then splits the 3D design into near microscopic layers from the bottom-up. The design is now ready to print. The printer operates by aligning a syringe containing the printing material along an x-y-z coordinate system. With each layer, the z component shifts up. The syringe dispenses a select amount of material at the specified coordinate according to the software. Progress can be monitored on the computer and when a new material is reached, the syringe is just replaced with another containing the appropriate substance.

After printing, the bionic ear must be incubated and cultured for seventy days because the cells have not fully “settled” yet—the cells don’t interact with each other like they do in a tissue or an organ. While in incubation, the cells begin to secrete an extracellular matrix, which gives structural support and promotes interaction between neighboring cells. The ear has now become a tissue. Several tests are run to ensure the validity of the ear: are the cells active? Does it have the correct shape and hardness? The functionality of the antenna—whether it picked up radio waves and how well it transmitted the signals—must be tested as well. Mannoor’s bionic ear was validated and fully functional. For the first time, a bionic organ was successfully created.

While much of the buzz has focused on the use of the 3D printer, Mannoor emphasizes that “the 3D printer was just a tool” to achieve the integration between electronics and the human body. He wants the focus to be the big picture of intertwining electronics with biology. 3D printing provides a resourceful method in attaining that goal, but a question arises: in what other ways can we integrate electronics with the human body?

The Future of Integration

The possibilities that accompany an organ with electronic components are endless. An organ can either be replaced or enhanced. Scientists have already created an electronic nose, and there is now a prosthetic leg that can be controlled by the brain with wires that are attached to nerve endings in the leg. But Mannoor would still like to see a biological component with cells and tissue in addition to the electronic ones.

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knee
Attached sensors show the applied pressure on the knee’s menisci through an embedded display.

According to Mannoor, “If it’s completely abiotic, it still doesn’t do the entire functionality, it’s not a replacement organ. I still believe it’s better to have a bionic organ with a biological component and then integrate electronics that are not invasive and are not harmful, only beneficial.” In Mannoor’s vision, the electronics would only be enhancing the original biological functions of the body.

Mannoor elaborates upon this idea with knee meniscus surgery as an example. Mannoor still advocates for the original surgery, which replaces the tissue, but would also use an embedded display on the knee. The display would be connected to a sensor, which “would measure the pressure on the meniscus. Stress sensors on bones can then tell you about your movement to prevent injury.” The display would indicate when you are putting too much pressure on the knee. With an ordinary surgery, there is always the possibility of tearing the meniscus. But now with the electronic component, you could possibly prevent future injuries.

The concept of enhanced functionality with electronics has intrigued many, including Princeton students. After the bionic ear, at least four undergraduates have joined research teams within the MAE department. Mannoor and other MAE research groups are interested in finding more ways to integrate electronics and the human body. As more research is done and more innovative approaches taken, the day when everyone can have a bionic organ is not far away.

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