Interview conducted by April Cashin-Garbutt, BA Hons (Cantab)
Please can you give a brief introduction to the history of bionic devices?
Bionic devices are implants which replace biological functions which have been lost due to nerve damage. They use electrical signals to stimulate the remaining nerve cells following disease or injury. Although the term bionic was only coined in the late 1950s, the earliest bionic devices were cardiac pacemakers, developed in the early 1900s. However the first commercial implantable units were not available until the 1950s.
The next most notable bionic device was the cochlear implant to stimulate hearing, and the first device was made commercially available in 1972. Currently, the bionic eye is under development with several groups across the globe seeking to provide a viable device for enabling sight impaired patients to perceive light.
What are bionic devices currently used for?
Pacemakers were the first bionic device types but have been expanded to include not only cardiac pacemakers, but also urinary and diaphragm pacing devices. Similarly implantable electrodes have been used for functional electrical stimulation, encompassing a range of devices which enable movement of muscles in patients with nerve damage, such as paraplegics. These devices perform functions which can include limb movement, sphincter and erectile control.
The more widely recognised bionic devices are the cochlear implant and the bionic eye. Actively stimulated nerve guides for repairing nerve injury and stimulated wound healing electrodes may also be considered bionic devices.
What are the limitations of current bionic devices?
Current bionic devices typically use metal electrodes to stimulate the nerve cells. While these electrodes have been sufficient for the past few decades and in devices which are implanted for only a few years, these metal electrodes are now becoming a limitation. As the miniaturisation of electronics continues to allow us to reduce the size of implants and offer patients devices with more functionality, there is a need to create smaller, more densely packed electrodes. At these sub-micron sizes, metal electrodes cannot be safely used for multiple decades, as is now required by cochlear implant patients who receive devices as children. As a result there is significant interest in new electrode materials.
I have been investigating conducting polymers for this purpose for the last 10 years. Over this time I have developed a number of electrically conductive materials which can improve on the performance of conventional metallic electrodes. However, since these materials are still recognised by the human body as foreign, they still suffer from a process known as fibrous encapsulation, where the body produces scar-like cells which surround and wall off the implant. An optimal implant will form an intimate connection with the surrounding cells, without inciting growth of scar tissue.
You have recently received a Ramaciotti Development grant entitled, "Living electrodes: Bridging the bionic interface.” Please can you explain how you are going to use this grant?
I was awarded the Ramaciotti grant to develop a new electrode material system which will combine both electroactive materials and nerve cells to form this intimate connection between the device and tissue. This approach uses the knowledge from both bionic device research and tissue engineering, which is more commonly used to replace bulk tissue types as a result of injury.
The implant coating will be developed such that it has cells encapsulated within the electroactive material. It is expected that these cells will branch out to integrate with the surrounding tissue, forming an intimate connection and preventing scar tissue growth.
How will these bionic devices “talk” to the nervous system?
The cell laden coating will allow much smaller, safer electrical stimuli to be used to activate the nerve cells. When the cells within the coating are stimulated they can communicate the stimulation to the damaged tissue using synaptic connections. These connections are the natural method of charge transfer within the human body, and considered to be superior to the electron charging required to stimulate tissue with metallic electrodes. It is expected that this more natural form of communication will be beneficial to the long-term safety and efficacy of bionic devices.
What impact do you think this work will have?
I expect that this work will provide a new technology platform for developing bionic devices with improved functionality. By minimising scar tissue growth and enhancing device integration it is likely that devices with many more electrodes can be developed. The potential of such devices is in improving patient outcomes, such as better hearing for cochlear implant users and improved sight for bionic eye recipients.
Do you think this technology will have applications across a multitude of bionic devices?
This technology will have application across all bionic devices and across a wider range of implants including brain-machine interfaces, nerve grafts and gene therapy – essentially in any implant where electrical interfaces are desirable.
How do you think the future of bionic devices will develop?
I think the future of bionic devices is very exciting. As we continue to push the boundaries of technological capabilities we are finding that it is possible to create very small, functional devices. The progress in making these devices biomimetic through tissue engineering is also creating new opportunities for replacing the function of tissue types we have previously thought too complex or irreparable. I expect that bionic whole organs, hybridizing the natural tissue with synthetic electronic elements is a very real prospect for the future.
Where can readers find more information?
For further information on the Ramaciotti Awards: http://www.perpetual.com.au/ramaciotti/
About Dr Rylie Green
Rylie is a researcher in the Graduate School of Biomedical Engineering, University of New South Wales. She actively researches new materials which will improve the function of bionic implants including the cochlear implant and bionic eye.
Rylie’s research has been focused on developing plastics which conduct electricity and can communicate directly with the body’s nerves.
Rylie completed a Bachelor of Mechatronic Engineering, a Masters of Biomedical Engineering and a PhD at the University of New South Wales, where she now leads her own research group.