# Micro-Fabrication of Components for a High-Density Sub-Retinal Visual Prosthesis
###### Abstract  
We present a retrospective of unique micro-fabrication problems and solutions that were encountered through over 10 years of retinal prosthesis product development, first for the Boston Retinal Implant Project initiated at the Massachusetts Institute of Technology and at Harvard Medical School's teaching hospital, the Massachusetts Eye and Ear--and later at the startup company Bionic Eye Technologies, by some of the same personnel. These efforts culminated in the fabrication and assembly of 256+ channel visual prosthesis devices having flexible multi-electrode arrays that were successfully implanted sub-retinally in mini-pig animal models as part of our pre-clinical testing program. We report on the processing of the flexible multi-layered, planar and penetrating high-density electrode arrays, surgical tools for sub-retinal implantation, and other parts such as coil supports that facilitated the implantation of the peri-ocular device components. We begin with an overview of the implantable portion of our visual prosthesis system design, and describe in detail the micro-fabrication methods for creating the parts of our system that were assembled outside of our hermetically-sealed electronics package. We also note the unique surgical challenges that sub-retinal implantation of our micro-fabricated components presented, and how some of those issues were addressed through design, materials selection, and fabrication approaches. microfabrication; visual; prosthesis; vision; electrode; neurostimulator; wireless; high-density; retina; neurostimulation +
Footnote †: journal: Micro-Fabrication  
0000-0001-5895-2233-1111/00/00/00001-5895-2233-111/00/00001-5895-2233-111/00/00001-5895-2233-11/00/00001-5895-2233-11/000001-5895-2233-111/000001-5895-  
In recent years, the visual prosthetic community of researchers and commercial entities has expanded to well over 20 groups worldwide [4; 6; 7; 8; 9; 10; 11; 12; 13; 14]. Remarkable strides have been made toward the restoration of useful vision to severely blind patients by several teams, including recent promising results by the Pixium company in subjects with macular degeneration [15]. Collectively, the results to date are encouraging, but the field as a whole falls shy of the goal of creating natural, high quality vision that could justify the risks of surgery and the high cost of the devices. These issues among others have led in part to modest market penetration by existing prosthetic devices that have obtained regulatory approval, and even to the closure of some companies that produced them. The need to achieve higher quality of restored vision has motivated us, as well as other teams, to develop more advanced, high-density devices and to seek to introduce stimuli to the target tissue with closer apposition of the stimulating electrodes. In this regard, the approach of our team has been to further develop penetrating sub-retinal electrodes as we prepared devices for pre-clinical testing, and we are now striving to demonstrate the potential advantages of such a design over the planar electrodes that have been a standard for use by many groups. The focus of this report is on the micro-fabrication methods that have been used to create the implantable components of our sub-retinal prostheses that lie outside of the electronics package. We address in detail the creation of an electrode array that is introduced into the sub-retinal space using an _ab externo_ (\"from the outside\") surgical approach, and the means to facilitate the implantation of these flexible arrays through a flap created in the sclera. More recently, this effort has included the addition of flexible structures that incorporate penetrating electrodes, which we have successfully implanted using the same techniques as the planar arrays [16; 17].