Silastic with polyacrylic acid filler: swelling properties, biocompatibility and potential use in cochlear implants

We present a new hygroscopic implant material which consists of high-molecular-weight polyacrylic acid (PAA) as a filler in a Silastic R matrix. The mixture swells upon immersion in bodily fluids; the degree of swelling depends on the ratio of PAA to Silastic and allows the design of implants that will achieve their final shape and size only after the implantation procedure. In vivo and in vitro biocompatibility tests reveal no adverse cellular or tissue responses. In cochlear implant development the material has been experimentally incorporated into intracochlear electrode arrays which curl after insertion, and in bacteriostatic devices for electrode fixation.