Rewiring Organs
Researchers at MIT are reviving paralyzed organs by means of a living implant that uses rewired nerves. This represents a new step in medicine, in which the patient’s own tissue becomes the hardware.
Numerous conditions cause nerve damage that result in organs no longer being able to function normally, or at all. Spinal cord injuries, for example, can render the bladder nonfunctional. Crohn’s disease can stop intestines from moving food along. Certain procedures can save lives but sometimes result in nerve damage that affects various bodily functions.
There may be hope on the horizon.
In a study published in Nature Communications, researchers from MIT introduced a novel myoneural actuator (MNA), that can restore movement in static organs. The MNA, when implanted, reprograms living muscles into fatigue resistant computer-controlled motors.
Not only does the system have the potential to restore function, but, according to the research team, it may be able to do so in a way that is safer and simpler than existing technology.
Addressing Previous Challenges
The MIT study confronts several challenges that previous researchers have struggled with when trying to restore function to paralyzed organs.
Some studies have focused on creating muscle tissue in the laboratory, cell by cell. But the process is extremely time consuming, and the technology is nowhere near ready for use in humans.
Some other previous efforts have tried to insert miniaturized actuators into the body. But those actuators themselves present an array of problems. They’re difficult to miniaturize, for example. Once implanted, they’re not very efficient, and they fatigue quickly. It’s very challenging to design a fatigue resistant technology that communicates with the nervous system.
A Novel Approach
The researchers at MIT have built an interface that leverages natural pathways used by the nervous system. According to Hugh Herr, the senior author of the study and a professor of media arts and sciences at the MIT Media Lab, their system enables the transmission of sensory feedback to the brain while leveraging those pathways so that the organs can be seamlessly controlled.
The MIT study focused on repurposing existing muscle within the body. The result is a living implant that uses rewired sensory nerves to revive the static organs. Researchers believe that this may represent a new genre of medicine, using the patient’s own tissue as hardware.
Says researcher Hyungeun Song, “We engineered existing muscles to become an actuator, or motor, that reinstates motion in organs.”
One of the challenges in the study was creating an actuator that would interface with the nervous system, allowing it to work properly, but also could not be overridden by the brain.
Says researcher Guillermo Herrera-Arcos, “You don’t want the brain to consciously control the muscle actuator because you want the actuator to automatically control an organ, like the heart.”
Using a computer controlled muscle to move the organ could not only ensure the organ functioned automatically, but would also bypass damaged brain pathways.
The study rerouted motor signals through sensory fibers, in order to make a computer, rather than the brain, the muscle’s new “command center.”
The scientists weren’t sure, at the beginning of the study, if it would be possible to fluidly fuse sensory nerves with muscle, a necessary step in their plan. However, when the researchers replaced motor nerves with sensory nerves in rodent muscle, the sensory nerves re-innervated the muscles and formed functional synapses.
Says Herrera-Arcos, “It’s a tremendous discovery.”
Beyond Fatigue Resistance
In addition to enabling the use of a digital controller, the sensory neurons also helped the muscles to become more resistant to fatigue. In fact, the rodent muscle in the study was 260 percent more fatigue resistant than the native muscles.
According to the researchers, this came down to the size of the axons. Motor neuron axons come in a variety of sizes. When a motor nerve is electrically stimulated, the largest ones fire first, which results in quick fatigue and exhaustion. Sensory axons, on the other hand, are more uniform in size, so the signal is broadcast more evenly across the muscle fibers, which helps the muscle to resist fatigue.
The new system developed by the researchers is a biohybrid motor called a myoneural actuator. And the results are promising.
Researchers wrapped the actuator around a paralyzed intestine in a rodent, and found that the actuator reinstated the organ’s squeezing motion. In another experiment designed to mimic residual muscle in human lower limb amputations, researchers successfully controlled rodent calf muscles using their system.
The MNA system also transmitted sensory signals to the brain. According to researcher Song, this result suggests that the team’s novel technology could be used to seamlessly link organs to the brain.
Song says, “We might be able to make a paralyzed stomach relay hunger.”
Next Steps
There are, of course, many steps between the team’s breakthrough and bringing the MNA to clinic.The system will have to undergo trials with larger animal models, and then human trials.
But if successful, the system could provide a safer route toward reviving static organs. For one thing, implanting the MNA could be done through a surgery that is already routine. The researchers believe that their system might also be both simpler and safer than existing mechanical devices or organ transplants, as they will be using the body’s own tissue rather than implanting a foreign object.
Researcher Herrera-Arcos says, “Today’s solutions are mostly synthetic: pacemakers and other mechanical assist devices. A living muscle actuator implanted alongside a weakened organ would be part of the body itself. That is a category of medicine different from anything seen in clinic.”
Researcher Song sees a multitude of possible uses for the technology, including restoring tactile feedback to people with skin grafts or who use prostheses. Song also sees the possibility for using MNA systems to improve virtual reality systems.
“The idea is that, if we couple the MNA system to skin and muscles, a person could feel what their virtual avatar is touching even though their real body isn’t moving.”
Researcher Herrera-Arcos adds, “Our research is on the brink of giving new life to various parts and extensions of the body. It’s exciting to think that our system could enhance human potential in ways that once only belonged to the realm of science fiction.”