Implants: When technology makes sense – quite literally

Disease, injury, or a condition you were born with – reasons why some people must live without one or several of their five senses. Fortunately, there are many modern sensory aids that help replace one sense with another, which is especially the case when it comes to vision and hearing. Given technology’s advancements, can artificial or biological implants someday soon be a viable alternative?

The idea here is not only to replace senses but also to restore or maintain them if there is only a partial inability or if an acute sensory loss is imminent. Ideally, we would be able to regenerate damaged nerve fibers that connect a sensory organ to the brain. Unfortunately, regenerative medicine is not ready to accomplish this at this juncture.

Current approaches are merely aimed at bridging severe nerve damage between the limbs and the brain. Medical specialists use nerve fibers from elsewhere in a patient’s body to maintain limb function and to prevent paralysis. One side effect is that the sense of touch would be restored. However, this approach would only be successful if the sensory organs themselves are intact and merely the connection to the brain is damaged.

Could artificial implants that directly connect with the sensory organs be the solution? They might be in some cases. A first step would then be to maintain sensory functions that are in danger of loss or deterioration. Implandata Ophthalmic Products GmbH is taking this approach with eyemate: "Eyemate is a proprietary implant that facilitates remote monitoring and management of glaucoma patients," Max Ostermeier, CEO and co-founder of Implandata Ophthalmic Products GmbH, explains in a MEDICA-tradefair.com interview.

Glaucoma causes elevated intraocular pressure. If left untreated, it damages the optic nerve and ultimately leads to permanent vision loss. The decrease in vision is usually peripheral and gradual over time. For several years, mini glaucoma shunts have facilitated drainage of aqueous humor in the eye, lowering the eye pressure in the process. However, patients may still need continuous monitoring of their intraocular pressure. This is currently done by physicians at their office, which means you merely get a snapshot into the disease progression.

The eyemate system features a micro-sensor that is implanted in the eye and measures the intraocular pressure continuously. Patients use the company's proprietary handheld device to make measurements on their own. The device then transmits the data to a secure database, allowing the eye doctor to monitor the condition remotely. Eyemate is implanted during cataract or glaucoma surgery. Implandata’s next project is an injectable intraocular pressure sensor.

Implants can also help when a sense has already been lost or is compromised. The Argus II implant from Second Sight Medical is a great example of this. The system comprises glasses with a build-in camera. The signals are sent to an electrode array implanted on the patient’s retinal surface. The array stimulates the optic nerve and allows people who are blind due to retinitis pigmentosa to see shapes and contrasting light and dark patterned images again. By now, Argus II has been replaced by the Orion system, a brain implant with electrodes that can deliver an image to the visual part of the brain. An early feasibility study of the Orion Cortical Visual Prosthesis is underway in the U.S.

For years, a similar concept comes into play to help patients with hearing loss. A cochlear implant is an electronic device that is embedded in the cochlea where it electrically stimulates the auditory nerves. Unfortunately, today's cochlear implants have a major drawback: "Implant wearers (thus) can find it difficult to distinguish between pitches, which means they have a harder time understanding spoken language, and this often also affects their enjoyment of music," Prof. Tobias Moser explains in a MEDICA-tradefair.com interview.

The electric current spreads widely along the human cochlea, thus stimulating many nerve cells at the same time. Moser and his "OptoHear" project team want to solve this problem with optical fibers, since "light can be more easily focused and spatially confined, certain regions in the cochlea can be stimulated better with light versus electrical pulses."

Nerve cells are not light-sensitive by nature and must therefore be genetically adapted, meaning the researchers' first step is to develop a successful gene therapy. It should prompt the formation of new pores in the nerve cells that open when light hits. This excites the nerve fiber and sends an impulse to the brain. The method is currently still being explored in animal research. According to Moser, the first optical cochlear implant could be available as early as the late 2020s.

These are just some examples of implants that protect, restore, or replace our senses. However, these implants are not nearly an adequate substitute for the natural organ - the applied technologies are not yet ready to do this and the stimulation of the nerves is still too rudimentary. Ideally, the affected sensory organs would be fully restored versus having to replace them with technology.

Biotechnology and regenerative medicine are still in their infancy in this setting. It is impossible to say whether we will someday be able to grow entire new sensory organs in the lab or produce them using 3D printing. A first step would certainly be to regenerate nerve fibers, a process that no longer relies on the transplantation of cells from a patient's own tissue but prompts the regrowth of new nerve fibers inside or outside the body. Only time will tell when research makes breakthroughs and creates the respective life-changing organ replacements.