Reactive-Accelerated-Aging Testing of Thinned Tissue-Engineered Electronic Nerve Interfaces

Tissue responses can cause a significant reduction in the performance of microelectrode-based devices implanted into neural tissue. Since the reduction of the thickness of implants has been shown to reduce tissue response, in this work we report on our effects to reduce the thickness of our tissue-engineered-electronic-nerve-interface (TEENI) devices and characterize their long-term reliability in a harsh environment. We were able to reduce the thickness of the TEENI threads that are to be located in nerve tissue from ~10 μm to ~2.5 μm in total thickness. To maintain the handleability needed during the assembly of the TEENI device into the hydrogel-based scaffold, we maintained full thickness elsewhere in the TEENI device and added support rails. During longitudinal reactive-accelerated-aging (RAA) experiments performed over 6 days and at 67°C, which corresponds to ~48 days in tissue, we observed that some channels maintain a stable impedance and others do not. Although analyses performed using a scanning electron microscope could clearly reveal delamination in some channels that exhibited large changes in impedance, it did not always correlate. Some channels with significant changes in impedance did not exhibit any observable delamination. Additional work is needed to study the relationship between changes in impedance and structural changes in the device, with the goal of improving device design to achieve longer-lasting devices.