Assessment of the biocompatibility of photosensitive polyimide for implantable medical device use

Polyimides have been widely used for biosensor encapsulation and more recently as substrates for neural implants. They have excellent thermal stability, high chemical resistance, and can be prepared as thin, flexible films. Photosensitive polyimides present similar physical properties to polyimides, and have the advantage that they can be photo-lithographically patterned. However, to date little data on their biocompatibility has been reported. Two commercially available polyimides (PI) and one photo-sensitive polyimide (PSPI) were evaluated in vitro using the ISO 10993 standard on biocompatibility. The materials were Dupont Kapton foil HN, HD Microsystem PI2611, and Fujifilm Durimide 7020 (PSPI). PI2611 and Durimide 7020 were spin-coated on silicon wafers, cured at temperatures ranging from 150 to 450 degrees C, and sterilized by autoclave. All materials were evaluated using a scanning electron microscope pre- and postcell culture. Cell viability was determined by an MTS assay. Their mechanical properties and stability during cell culture as a function of time and environment were investigated by nanoindentation. The MTS results show that PSPI is noncytotoxic compared with the negative control of polyethylene and the conventional PIs tested. Fibroblast adhesion, morphology, and spreading were good and better on the PSPI substrate than on the PI2611. Schwann cell appearance was similar on each of the PIs and the PSPI tested. The results suggest that PSPIs may have potential use for biological microsystem and neuroprosthetic applications.