The bionic human is nearly a reality. In recent years, scientists have been able to develop everything from bionic eyes to bionic hands. Yet these machines are still largely dependent on the existing human structures to which they connect. If a person's nerve endings are damaged, for instance, the usefulness of these machines becomes limited. Scientists might soon be able to overcome these obstacles, however, as researchers were able to use an implant to deliver gene therapy to the auditory portion of a guinea pig's ear — a treatment that not only caused the animal's auditory nerves to regrow, but improved the human-machine interface in the process.

The implant sends electrical impulses into surrounding cells

In the study, published today in Science Translational Medicine, researchers used an antibiotic treatment to deafen adult guinea pigs. Then, they introduced recombinant DNA — DNA formed in a lab by combining genetic material from various sources  — into the cochlea, the portion of the guinea pigs' ear that transforms vibrations into sound signals. Once the DNA was in place, they implanted the ear with a modified cochlear implant that was able to send short, directed electrical impulses to the surrounding cells, in addition to enhancing the animals' hearing. These impulses are part of a gene therapy technique called "electroporation" that allowed the recombinant DNA to enter the cochlear cells and produce neurotrophins, proteins that cause auditory nerve endings to regenerate.

"Our gene therapy is an example for a successful treatment of a condition that is not even caused by a genetic defect," says Matthias Klugman, a neuroscientist at the University of New South Wales, in Australia, and a co-author of the study. Thanks to the electrical impulses, the cells close to the implant's electrode were able to manufacture a protein that usually stops being produced after adulthood, Klugman explains. This caused the nerve fibers to grow out to those cells, and hence to the electrodes in the implant. This growth, the researchers say, significantly improved the animals' pitch perception and tonal range.

improved pitch perception and tonal range

Unfortunately, the production of neurotrophins only lasted a few months, so the method needs to be improved before it can go on to human trials. But Gary Housley, a co-author and neuroscientist also at the University of New South Wales, said in an email to The Verge that the implant might one day help people "appreciate music and hear in noisy environments."

Housley also said that the technology could be used to improve other medical bionics applications, such as retinal implants and deep brain stimulation, which is used to treat Parkinson's disease. "Deep brain stimulation uses a small array of electrodes very similar to the cochlear implant array," he said, "so we believe that this could be used to introduce different DNA sequences to very discrete regions of the brain to provide directed gene therapy." These human-machine interfaces also rely on the cells and nerve endings that surround them, so being able to deliver gene therapy in a selective and directed manner could lead to big improvements — and much more powerful bionics.