POLYMERIC PROTECTION OF IMPLANTABLE MICRO-ELECTRONICS

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Our long-term objective is the development of technology suitable for the packaging of chronically implantable micro-electronic integrated circuits. Integrated circuits, (micro-transducers) are needed to provide sensing and control functions to further the development of implantable electronic systems. Presently devices exists which could be used for implantable neuroprostheses, including auditory, bladder, diaphramatic, and cardiac (pacemaker) prosthetic devices, upper and lower extremity functional-neuromuscular-stimulation systems, cranial pressure monitors, blood ion and gas sensors, and implantable drug delivery systems for use with hypotension controlling drugs and insulin. During the past decade, the design of implantable electronic systems which incorporate subminiature integrated- circuit sensors and transducers has been seriously limited by the absence of packaging technologies suitable for the protection of the electronic devices from the physiological environment. The significance of limited sizes makes pacemaker packaging technology inapplicable. The present proposal incorporates basic studies which will identify materials and technologies capable of protecting chronically implanted I.C. transducers for periods of years, even decades, and is aimed at: 1. Determining the corrosion-control capabilities of polydimethylsiloxanes and polyimides used for the protection of implanted micro-electronic assemblies. Material parameters such as adhesion, hardness, permeability, elongation, and ear resistance will be correlated with performance. 2. Evaluating the effectiveness of surface preparation techniques including priming, cleaning, etching, and vacuum bake-out in reducing metallization corrosion through the reduction of electrical leakage currents. 3. Defining constraints affecting the selection and development of polymeric encapsulants for moisture protection of complete implantable devices in-vitro and in-vivo. Evaluation of encapsulation systems will be made with due regard for the special problems of output leads and biocompatibility. 4. Testing the modified materials on a sensor currently under development in our laboratory. This will be accomplished by designing and fabricating a subminiature interface from the I.C. to a miniature flexible electrical cable.