The bionic ear - or cochlear implant - is one of the most commonly used bionic body parts. It has returned some level of hearing to tens of thousands of people around the world.
Sounds create vibrations in the ear which are picked up by thousands of tiny hairs in the cochlea. The tiny movements are converted to electrical signals which are sent to the brain, but if the hairs are damaged it results in hearing loss.
Cochlear implants deliver electrical signals directly to the brain. A microphone is attached to the outside of the head and converts sounds to electrical signals. These pass down a thin wire which is threading into the cochlea. Electrodes at the end deliver the signal directly to the auditory nerve.
Each implant costs about £16,500 ($26,000; 20,000 euros) before the added expense of surgery and rehabilitation. Recently, patients have been fitted with a single implant which can restore hearing to both ears.