A comparison between glass/polyimide and titanium/polyimide microjoint performances in cerebrospinal fluid

Assessment of neural biocompatibility requires that materials be tested with exposure in neural fluids. Laser bonded microjoint samples made from Ti coated glass substrate and polyimide film (GPI) and titanium foil and polyimide film (TIPI) were evaluated for mechanical performance before and after exposure in artificial cerebrospinal fluid (CSF) for two, four, and 12 weeks at 37 degrees C. These samples represent a critical feature, i.e., the microjoint-a major weakness in the bioencapsulation system. Both material systems showed initial degradation up to 4 weeks which then stabilized afterwards and retained similar strength until 12 weeks. The TIPI system appears to exhibit better overall performance with less degradation compared to its as-received strength. The CSF exposed TIPI samples predominantly failed at the interface, while GPI samples had mixed glass and polyimide substrate and interface failure. The amount of glass failure decreases and interface failure increases with increase in CSF exposure time. The failure mechanism of the as-received (not exposed to CSF) GPI samples under tension was predominantly flexure type failure of the glass substrate.