Navigating conjugated polymer actuated neural probes in a brain phantom

Abstract

Neural probe insertion methods have a direct impact on the longevity of the device in the brain. Initial tissue and vascular damage caused by the probe entering the brain triggers a chronic tissue response that is known to attenuate neural recordings and ultimately encapsulate the probes. Smaller devices have been found to evoke reduced inflammatory response. One way to record from undamaged neural networks may be to position the electrode sites away from the probe. To investigate this approach, we are developing probes with controllably movable electrode projections, which would move outside of the zone that is damaged by the insertion of the larger probe. The objective of this study was to test the capability of conjugated polymer bilayer actuators to actuate neural electrode projections from a probe shank into a transparent brain phantom.Parylene neural probe devices, having five electrode projections with actuating segments and with varying widths (50 -250 µm) and lengths (200 -1000 µm) were fabricated. The electroactive polymer polypyrrole (PPy) was used to bend or flatten the projections. The devices were inserted into the brain phantom using an electronic microdrive while simultaneously activating the actuators. Deflections were quantified based on video images.The electrode projections were successfully controlled to either remain flat or to actuate out-of-plane and into the brain phantom during insertion. The projection width had a significant effect on their ability to deflect within the phantom, with thinner probes deflecting but not the wider ones. Thus, small integrated conjugated polymer actuators may enable multiple neuro-experiments and applications not possible before.

Implantable Neural Probes for Brain-Machine Interfaces ? Current Developments and Future Prospects

“…Perhaps the most important issue facing developers is the biocompatibility and mechanical suitability of implantable neural probes. Advancements in material science and mechanical techniques will aid in developing strategies for minimizing brain scarring while maintaining adequate electrode contact [159160]. Assessments of signal quality and side effects should be performed in both in vitro and in vivo systems (e.g., non-human primates) to determine the practical applications of novel BMI systems prior to use in humans.…”