This project represents an ongoing collaboration between teams at two institutions. As people live longer, blindness caused by degenerative diseases of the retina such as macular degeneration or retinitis pigmentosa is today a major disability among the aging in the developed world. These types of "neural" blindness cannot currently be medically treated in any satisfactory manner. There is now compelling experimental evidence in humans that even when such diseases cause a loss of photoreceptors (i.e., rod and cone cells in the retina), electrical stimulation of the remaining retinal neurons that survive this loss can be used to bypass the damaged tissue and deliver visual information to the brain. This is essentially the same concept that supported the development of the cochlear prosthesis, which has been a fabulous success, restoring hearing to many tens of thousands of deaf patients. The PIs and their respective teams have been working for over 20 years toward the goal of developing a retinal prosthesis to restore truly useful vision to patients in an analogous manner. With prior funding from a number of agencies including NSF, they have created enabling technology for a miniaturized high-density implantable wirelessly-driven neuro-prosthesis package with over 200 individually-addressable channels, which is over three times the inputs and outputs in any current commercially available neurostimulator. The field's ability to create complex integrated circuitry for neurostimulation and/or recording has outpaced the development of long-term implantable packaging, microelectrode array, and assembly technology. If optimized, those technologies would make possible new devices that interface with hundreds of neural tissue sites simultaneously. This is the PI's aim in the current project. The funding will complement existing grants to the PIs and their collaborators, and will allow them to complete development of a new 200+ channel co-fired ceramic signal feed-through disc, to optimize the micro-fabrication process for high-density microelectrode arrays that interface with neural tissue, and to improve the bonding and interconnection processes required to assemble the implant package.
Broader Impacts: The 200+ channel wirelessly-driven implant that will constitute the primary project outcome will have over three times the number of individually-addressable stimulating electrodes now available from any group. This funding will further allow the PI to ready devices for later pre-clinical testing (with anticipated follow-on support from the VA). Project results will be widely disseminated in publications, and by distributing sample devices within the rehabilitation R&D community. The device which is the focus of this project will also be useful in a myriad other future chronically implantable prosthetics, palliative devices, and human-computer interface devices.
The purpose of this research was to develop a high-density visual prosthesis to restore useful vision to patients who are severely blind due to degenerative retinal diseases. The conditions we hope to treat are age-related macular degeneration, which is the leading cause of blindness in the developed world, and retinitis pigmentosa, which is the leading cause of inherited blindness and affects more than 100,000 Americans. The principle on which the Boston device operates is as follows. A camera mounted on a specially-prepared pair of glasses worn by the patient captures the scene in the wearer's environment. A portable controller then processes these images and transmits them to the implant, which is attached behind the patient's eye. The implant, in turn, electrically stimulates 'pixels' in the device's electrode array, which is surgically placed beneath the retina. As a result of this stimulation, user can perceive and experience the stimulated images in their mind, and thus, we bypass the patient's diseased light-sensitive cells. Our high-density device contains more than four times the number of 'pixels' than the closest commercially-available retinal stimulator system, which we believe will improve the patients' perceptions and their user experience - and hence, their quality of life and functional independence. In the course of this effort, we designed and extensively bench-tested a highly configurable, high-density neuro-stimulator ASIC in both wired and wireless configurations. This >256 channel device is appropriate for chronic implantation with our proven, minimally-invasive sub-retinal surgical implantation techniques, and its sophisticated LSK reverse telemetry features will enable optimization of stimuli for each patient. Extensive safety features have been implemented in our chip; driving software, GUI development, and image processing algorithms for the external system are under development, as we prepare for upcoming, separately funded pilot human trials of our retinal prosthesis. My team also presented some of our testing results at an invited talk at the 2012 IEEE Engineering in Medicine and Biology Conference. In the area of component fabrication, my colleagues and I developed high-density hermetic co-fired ceramic feedthroughs, and the means to join these assemblies to laser-welded titanium packages. Additionally, flexible, micro-fabricated 256 channel multi-electrode arrays were fabricated at our off-site laboratory at the NSF-funded Cornell NanoScale Science and Technology Facility in Ithaca, NY. Our engineering team and technician at MIT constructed working prototypes of the complete, packaged HD retinal neurostimulator, including a radio frequency coil to receive power and data signals from the external controller, the multi-electrode arrays, and the hermetically packaged HD stimulator units. The complete devices, shown on a model in the attached photo, also had suture arms to facilitate surgical attachment of the stimulator package to the back of the eye. The completed prosthesis shown represents the culmination of the engineering efforts under this award, and my team and I are grateful for the support which made it possible and that will pave the pay for separately-funded clinical trials of the device to come.