Welcome to the NOVA module
Our group is a part of the NIH SPARC HORNET (Human Open Research Neural Engineering Technologies) mechanism, an initiative for open-architecture, open-source implantable neuromodulation systems. We are a collaborative team from the University of Michigan (Ann Arbor, Michigan), and the COSMIIC project based out of Case Western Reserve University (Cleveland, Ohio).We were funded to develop a high-channel count, implantable sensing device adapted from Network Neural Prosthesis (NNP) (Makowski et al., 2021) under an open-source framework. This 64-channel module includes existing and new circuit elements to the NNP, as well as a novel titanium package.
Scroll through this page for a tour of the NOVA device, and visit our GitHub repository where the most up to date design files are posted.
A miniature titanium package (35x28x44mm) was designed with 64 hard-wired sensing channels. This package was designed with titanium for biocompatibility and ease of welding. The titanium package has a top and bottom enclosure with a lid-through cap to seal the enclosure. The 64 hard-wired channels exit the device out of the top enclosure through eight, 8-channel feedthroughs. These feedthroughs are soldered directly to a flexible printed circuit board (PCB).
(Left: 64 sensing leads hand-soldered onto PCB, Right: PCB folded and weld band preparation)
Titanium caps cover these feedthroughs so the sensing channels exit the device through durable wire bundles. Power and communication network connections exit the device out the lidthrough through 2-channel feedthroughs. These connections are also hand-soldered to the PCB. We have contracted Ardiem Medical Inc. to form a custom molded header around these network connections.
(Left: power and communication network connections soldered to a flex portion of the PCB, Right: fully assembled titanium package with welded lidthrough).
All pictures show successful welds completed at Ardiem Medical Inc. The unit shown above passed final helium checks at less than 1×10-9 leak rate. Mechanical testing of sensing leads is in progress. Drawings and design files for all titanium parts and feed throughs are uploaded to our GitHub. To fabricate the package parts, .drwsw files for the top, bottom enclosures, and lidthrough were sent to Fathom for fabrication.
(Left: top side of the populated rigid-flex circuit board housing a microcontroller and power management circuitry, Right: bottom side of PCB housing a 64-channel array for sensing leads and an Intan 64-channel amplifier)
We have also completed development of the 64-channel electronics and preliminary electrical testing. The top of the PCB houses a microcontroller unit (MCU) and power management circuitry. A low-power STM32 microcontroller from the A5 series (STM32U5A5QJI6Q) was chosen with extra RAM for temporary data storage on a micro BGA footprint. Extra NVM (8Mb) was added for parameter storage to allow for on-board decoding. The top side also houses the 64-channel feedthrough array where leads are to be hardwired into. Slotted cutouts around each 8-channel cluster in the array were added to allow for flexibility when hand-soldering each lead to the board (we found that they were very delicate during assembly).
This design isolates analog and digital signals to protect against contamination. The bottom side houses an RDH2164 Intan amplifier connecting to the 64 sensing channels. Diodes were added to the PCB on each channel to protect against electrostatic discharge during implant. Extra capacitors were also added on each channel to allow MRI compatibility. SPI protocol is used for communication between the MCU and the Intan, sampling signals at up to 20kHz. The MCU will also be programmed to operate in direct memory access mode with frequent sleep periods to achieve lower power consumption. The board is powered on the FESCAN network or 5V DC for debugging.
Preliminary electrical testing on the 64-channel electronics has also been completed. Current leakage was measured from each of the 64-channel feedthroughs while the device was powered on the FESCAN network with a 500kHz 3.3V square wave. The average current leakage from all channels was 1.2µA with a standard deviation of 0.6µA. This is well within the 60606-1 touch current allowable leakage in normal conditions of 100uA. Functional electrical testing is ongoing to evaluate simultaneous sensing across all 64-channels sampled at 1kHz and 2kHz, as well as subsets of channels at 10kHz and 20kHz.
Altium designs, Gerbers, SPICE simulations, and BOM files for PCB fabrication and assembly are uploaded on our GitHub, along with a list of vendors and manufacturers.