Encapsulation of electronic components for a retinal prosthesis

Abstract

Long-term success of an implantable retinal prosthesis depends on the ability to hermetically seal sensitive electronics from a saline environment with an encapsulant material. Furthermore, the retinal implant project's proposed laser-driven prosthesis requires that the encapsulation material be transparent. The device itself has two components that must protrude out of the encapsulation material. The first is an electrode array on a polyimide strip. The second is a platinum return wire. Difficulty in finding encapsulation materials has arisen from saline leakage at the interface of the encapsulant and these two protruding components. This thesis addresses the pursuit of materials and bonding strategies suitable to protect the device in chronic submersion. An electrode array lying on a polyimide layer sits flat against the ganglion cells within the eye. Precise stimulation requires that current does not flow between the individual electrode contacts. The array must be tested under chronic saline submersion to ensure that each electrode remains electrically isolated by the polyimide. The electronics package will be supported in the eye by a modified intraocular platform, similar to a device typically used in human cataract surgery. The lens is created by photolithography, a rapid prototyping technique. This platform must conform to surgical needs and structural integrity required by the device. The primary goal of this thesis is to find a flexible transparent encapsulant material. This material must undergo long term leakage tests to ensure that it will be reliable in protecting the microelectronics mounted on the platform before being considered for use. The secondary goal of the thesis is testing of the polyimide electrode array itself to determine its ability to resist saline leaks.