In 2014, the bioelectrics team was tasked with exploring the neural probe technical space and identifying paths of interest. A neural probe is a microelectrode (a small, electrically conductive structure) used either for sensing (to record changing voltage potentials created by neurons firing), or for stimulation (to trigger neural activity). We wanted to understand the direction(s) this technology could take in the next five to 10 years, and we also wanted to identify potential synergistic couplings with existing GE businesses or GE Global Research technological capabilities.
In this Invention Factory video produced by Vice, Jeff Ashe and I describe the probes we developed.
Early on, it became clear from speaking with top neurosurgeons that the structural dimensions of the probe could have a large impact on the success of an implant. Narrower probes appeared to cause less tissue damage and remained functional for longer durations of implantation. The team realized that we might be able to harness existing GE process knowledge in an adjacent technical space to build a neural probe in a novel way.
By using proprietary material alloys and techniques previously developed in the GRC Cleanroom to build the MEMS (Microelectromechanical System) Microswitch, our team was able to fabricate a long, narrow (2 millimeters x 30 microns) gold alloy probe in a very short time. The process of developing a design concept, planning the process flow, and executing the build in the cleanroom took a total of 4 weeks, at the end of which we had our first neural probe prototypes.
Using a Dynamic Mechanical Analyzer, the team confirmed that the gold alloy was stiff enough to resist deflection upon insertion into tissue, and that the material was not so brittle that fracture was a concern. Our next step was to prepare for functional electrical testing. Long flexible leads were attached with anisotropic conductive film, and a 4 micron parylene dielectric coating was applied to the entire assembly. A 355nm UV laser then selectively ablated the parylene coating on the very tip of the probes, ensuring that this region would be the only electrically functional region.
Finally, we conducted pre-clinical testing of the probes to evaluate electrical performance. We observed an excellent signal-to-noise ratio, which allowed for clear oscilloscope imaging of neural spike waveforms. The team was very encouraged with the results of this test, as the signal recording results were comparable with previously tested neural probes of larger width. These wider probes cause more tissue disruption, and thus may not remain effective for as long as our narrower prototypes. These efforts are part of the many activities necessary before the probes are evaluated further through clinical research in humans.
Our team was especially grateful for the strong efforts of the GRC cleanroom processing team; their work allowed us to follow an accelerated development timeline that allowed for device design, construction, and pre-clinical evaluation to be rapidly completed. This work has resulted in an NIH grant application (submitted along with our partners) to continue pre-clinical work, with our eventual longer term goal being testing and use in humans.