Histological Reaction to Polyimide Films in the Cochlea

The biocompatibility of commercially available polyimides was examined in relation to the sensory and neural structures of the cochlea. Thin films of four different polyimides were prepared as substrates for photolithographically produced scala tympani electrode arrays and implanted in 32 cat cochleae. Following at least three months implantation time, the animals were sacrificed and the cochleae were evaluated histologically for toxicity, differences in the severity of ototoxic effects among the four polyimide groups, and relationships among the different kinds of histopathology secondary to implantation. Findings included the following. Inflammatory reaction to the implants, when present, was generally mild and confined to the immediate vicinity of the implant. Additionally, ototoxic effects were essentially the same across the four groups. Finally, a clear interdependence among the different kinds of cochlear damage secondary to implantation was demonstrated.