March 2018 New Electronics
As part of the UK’s Healthcare Technologies strategy, the Engineering and Physical Sciences Research Council launched a competition in 2016 to identify promising research projects addressing challenging issues. Among the eight winners, announced in 2017, was Dr Rylie Green of Imperial College London. Dr Green’s efforts centre on implantable polymer bioelectronics for devices such as bionic eyes and cochlear implants. Her aim is to create a soft and flexible conducting polymer.
“Cochlear implants currently have 22 channels of stimulation – a limitation caused by the fact they are made from metals,” Dr Green said. “Metal conducts electricity using electrons, while the body uses ions. The material we’re using can conduct electricity using both. “Metal limits size,” she continued. “You can’t make the device smaller without compromising safety and you can’t push more current through the metal as it could cause unwanted chemical reactions, such as changing the pH in the tissue.”
The polymeric material allows current to be pushed into the body at a ‘faster rate, more efficiently and at a lower voltage’, lowering the risk of electrical changes or degradation significantly. “This provides better perception of sound for a cochlear implant patient, or allows someone with a bionic eye to see not just with 40 or 60 points of light – which is the current limitation of metal electrodes – but with hundreds and thousands of points of light.”
Dr Green’s other challenge was to develop a polymer which could be accepted by the body. This involved modifying the properties of conductive polymers to create a soft interface that interacts more readily and reduces the foreign body response. According to Dr Green, this has been accomplished by hybridising a conductive polymer with hydrogels and elastomers. The bionic eye developed by Dr Green comprises a camera, fitted to sunglasses, connected to a processor that converts the analogue signal into a digital format that is then delivered into the body. The electronic package sits behind the ear under the skin. An electrode lead is inserted into the eyeball, where it can stimulate cells to create a perception of vision. A chip interprets the information received.