Long term in vitro functional stability and recording longevity of fully integrated wireless neural interfaces based on the Utah Slant Electrode Array

Abstract

We evaluate the encapsulation and packaging reliability of a fully integrated wireless neural interface based on a Utah Slant Electrode Array/integrated neural interface-recording version 5 (USEA/INI-R5) system by monitoring the long term in vitro functional stability and recording longevity. The INI encapsulated with 6 µm Parylene-C was immersed in phosphate buffered saline (PBS) for a period of over 276 days (with the monitoring of the functional device still ongoing). The full functionality (wireless radio-frequency power, command and signal transmission) and the ability of the electrodes to record artificial neural signals even after 276 days of PBS soaking with little change (within 14%) in signal/noise amplitude constitute a major milestone in long term stability and allow us to study and evaluate the encapsulation reliability, functional stability and its potential usefulness for a wireless neural interface for future chronic implants.

Figure 1

(a) Schematic, and (b) the photograph of the Utah Slant Electrode Array/integrated neural interface-recording version 5 (USEA/INI-R5) device.

Figure 2

Frequency shift keying (FSK) modulated radio-frequency (RF) spectra transmitted wirelessly from the fully integrated and encapsulated USEA/INI-R5 in phosphate buffered saline (PBS) upon power up, and command telemetry frequency ‘0’ and telemetry frequency ‘4’.

Figure 3

Transmitted wireless RF signal monitored for the telemetry frequency ‘0’ as a function of soak time in PBS (antenna was @ 8 cm from the device). (a) Peak RF signal strengths and the respective frequencies as extracted from the spectra measured using the spectrum analyzer (inset shows few consecutive RF spectra at 20 min. intervals). (b) RF signal strengths and the respective frequencies as monitored on custom-developed wireless receiver board.

Figure 4

Experimental set-up for wireless recording of artificial neural signals in agarose.

Figure 5

In-vitro wirelessly recorded artificial action potentials that were injected from Grass SD-9 stimulator into the agarose dish. Recording is shown from one channel at time t=0, at soak time t=108 days, at soak time t=150 days, at soak time t=211 days and at soak time t=276 days to demonstrate the recording longevity of particular channel in UTAH/INI-R5 device after PBS soaking. Inset shows the recording of the artificial action potentials at t=0, and at soak time t=276 days at different time scale.