Attenuation of sound due to bio-encapsulants in an electronic laryngeal prosthesis

Following total laryngectomy, a person is without voice communication. An electronic laryngeal prosthesis, fully implantable in the neck, would be a desirable means of supplying artificial voice. Such a device must provide a powerful acoustic signal of the correct fundamental frequency for males and females and be rich in harmonic energy. Sound energy must be available to permit a listener to pick up intelligible speech. Such a device places severe demands on any bio-encapsulant: these include provision for an 18 mil displacement of a diaphragm moving at 100 to 200 Hz, excellent fatigue characteristics, hydrolytic and thermal stability, and minimum permeation for water and ionic solutions. This paper describes the application of a polyvinylidene chloride, a segmented copolyether polyurethane, a silicone rubber, and a semi-rigid epoxy--by solvent cast methods--to such a prosthesis. The ability of these materials to pass the sound energy with minimal attenuation was evaluated. Results indicated that the polyurethane coating provided the best compromise between minimum water penetration, maximum flexibility at the implant site, and minimum sound attenuation.