in vitro Reactive-Accelerated-Aging (RAA) Assessment of Tissue-Engineered Electronic Nerve Interfaces (TEENI)

A reactive-accelerated-aging (RAA) soak-test has been employed to challenge microfabricated neural interface devices against an aggressive environment that mimics worstcase chronic physiological inflammation. The RAA tests were able to determine the ability of different materials to increase the adhesive strength of the polyimide and platinum-goldplatinum metallization thin-film interface. It was found that a 3-day RAA soak-test at 87 °C in phosphate buffered saline with 10 to 20 mM hydrogen peroxide resulted in adhesive failure of the metal-polyimide interface when titanium was used as the primary adhesion promotor. The addition of hydrogenated amorphous silicon carbide was able to eliminate the onset of adhesive failure of the metal-polyimide interface during 7-day RAA soak tests. However, sporadic cracking of the silicon carbide layer resulted in a minority of broken metal interconnects that resulted in failed electrodes. These tests have demonstrated the ability of RAA soak tests to provide rapid in vitro assessment of microfabricated neural interfaces and thereby reduce the time needed to develop synthetic methods to fabricate chronically reliable devices.