(33) Insertion Method for Flexible Implantable Arrays without a Stiffener

Introduction: A primary challenge subcortical neural implants face is the surgical approach and insertion of the arrays, especially for flexible polymer-based arrays. A variety of methods have been used to facilitate this with temporary stiffeners. Our group has developed and promulgated the use of a silicon stiffener temporarily attached to our flexible polymer arrays over the last decade. Other approaches for temporary support structures include needles. Both of these approaches introduce additional complexity for both engineering and building the neural interface as well as the surgical approach. As an example, the stiffener temporarily displaces some additional brain tissue which may have lasting effects on post-implant recovery. Here, we present a much simplified approach that eliminates need for stiffeners. This is achieved by using an insertion tool which introduces an ultrasonic vibration along the electrode array during implantation, allowing a flexible polymer probe to be implanted without a stiffener.

Methods: A commercially-available ultrasonic transducer and insertion tool (Actuated Medical) has previously been demonstrated to reduce insertion force on rigid electrode arrays. Here, we utilized that same setup and attached our flexible polymer electrode array. By aligning the probe perpendicular to the insertion surface and applying ultrasonic vibrations, we were able to insert the electrode arrays without a stiffener. We performed a study across power, speed, and type of array to isolate and optimize insertion parameters. Using this data, we then worked with collaborators to perform the same study in a small number of rats.

Results: Our results in a controlled environment using agarose models have shown that ultrasonic vibration works well to reduce the insertion force required to implant our single-shank flexible neural arrays with very repeatable results and high yield. These probes were repeatedly removed and inserted into the same gel with near 100% success. Translating this effort to the operating room on rats showed success after repeated insertions but introduced new challenges including adjusting for brain movement (respiratory and cardiac movement), fluid changes (saline flushing and evaporation), that will be addressed by performing additional animal studies.

Conclusion: Our group has provided electrode arrays to a variety of research groups utilizing a temporarily attached silicon stiffener with a dissolvable adhesive. The new stiffener-less insertion method shown here will reduce surgical effort and complexity, reduce surgical time, potentially reduce tissue damage which may also result in quicker recovery times. Additionally, post-processing finished electrode arrays will be much simpler, reducing costs, production time, and improving yield.