Development of a Bionic Eye – the Diamond Eye
A bionic eye aims to restore sight to those with severe vision loss due to retinal diseases. The retina at the back of the eye contains light sensitive cells called photoreceptors. Photoreceptors converts light into biological signals, which are then transmitted into the brain. However, in some diseases such as retinitis pigmentosa and age-related macular degeneration, the photoreceptors die but the other retinal cells remain intact. A bionic eye replaces the function of the degenerated photoreceptors. Using an electrode array placed next to the retina, a bionic eye sends electrical stimulation to the remaining retinal cells, which then delivers the the information to the brain.
In the past years, Dr Wei Tong has been involved in the development of a bionic eye based on the diamond technologies, the Diamond Eye, together with many other researchers in Melbourne, Australia. These diamond materials are safe and stable, exhibit suitable properties for neural stimulation, and are expected to last long after implantation. Dr Tong’s research experiences cover materials optimisation, device fabrication, animal testing and stimulation strategy development. During her postdoctoral study at NVRI, she developed a technique called calcium imaging to study the spatial response patterns of retinal ganglion cells to electrical stimulation. Using this technique, the team improved design of the devices and developed novel strategies to enhance the stimulation strategy. The Diamond Eye is aimed for restoring high-quality vision to the blind.
Carbon-based Fibre Electrodes for Next Generation Neural Interfaces
Neural interfaces, also called brain-computer interfaces, create links between the nervous system and the outside world. Using implantable microelectrode arrays, these devices can read out and/or write information to the brain by detecting and/or modulating neural activity. Such devices are critical tools in neuroscience research to advance our understanding of neural functions and also in clinical applications for treating neurological disorders and injuries. The next generation of neural interfaces will benefit from closed-loop operation, in which the device records from neurons and uses the recorded information to inform stimulation. However, current technologies have limited functionality and longevity. Existing microelectrodes primarily perform one function, either neural stimulation or recording; and they have very limited lifetime, due to the instability of the electrode materials and the inflammatory tissue response evoked by electrode insertion.
Using carbon, the primary element of biology, Dr Tong and her collaborators have developed different fibre structured electrodes that are suitable to perform multiple functions for an extended period of time. These fibre electrodes are stable, flexible and ultrathin, with cross-section diameters in the range of cellular dimension. The flexibility and small dimension reduces the tissue damage due to electrode insertion, and the small diameter increases the spatial resolution for neural stimulation and recording. Such electrodes will be the core component for the next generation neural interfaces.
Light-responsive Diamond for Neural Stimulation
As neurons are physically electroactive, the application of electrical stimulation has long been proved effective in modulating neuronal activity. Existing devices for delivering electrical stimulation are normally large and complicated, as they have to contain the conductive materials for stimulation, the components for programming electrical stimulation and the cables for connecting the electrode array with an external stimulator. The complex structures bring challenges for device design and fabrication. The bulky devices also have higher risks for adverse outcomes, such as contamination in in vitro research and infection in in vivo and clinical applications.
Dr Tong uses diamond as a transducer that can generate electric fields in response to near-infrared light for the purpose of neural stimulation. In contrast to electrical stimulation, optical signals can be delivered wirelessly with high spatiotemporal resolution. Light with sufficiently long wavelengths and intensity can penetrate deep into tissues, including the ability to penetrate through the skull. Without the necessity of using cables for powering and external communication, the devices that use optical stimulation can be miniaturised. The device fabrication can also be simplified. The light-sensitive diamond, by replacing the conventional electronic devices, is expected to bring benefit to future neural stimulation applications.