Introduction: Novel high-density flexible electrodes yield high-quality signals with minimal injury to the brain. This technology suggests the possibility of minimally invasive implantation (MII) techniques. While proof of principle studies have been pursued in cadaveric monkey specimens, the feasibility and potential applications of MII in humans has not been addressed.
Methods: Mock-up flexible electrodes were implanted through minimally invasive cranial openings in cadaveric models of the pediatric (fresh frozen canine) and adult (alcohol-fixed human) head. A range of clinically relevant sizes of polyimide substrate (25µm thick Kapton) without embedded electronics were used to examine implantation techniques. The utility of endoscopic assistance was also examined.
Results: MII techniques yielded successful implantation of flexible electrode substrates. Within the 4mm subdural space, the implant could be safely unfurled over the cortical surface under endoscopic visualization. Smaller implants were placed with greater ease and success due to decreased adhesion between layers and to the overlying dura. Larger implants required greater countertraction for deployment. Hysteresis of the substrate served as an additional challenge for deployment. No visible gross cortical damage was apparent following removal.
Conclusions: MII of flexible electrode substrates is feasible without injury to the cortex. Sufficient subdural space, countertraction, and visualization are key requirements for successful implantation. Confirmation of electrode integrity post-implantation is needed to determine the clinical applicability of presented techniques. These results have direct implications for emerging technologies employing chronic implants and brain-computer interface (BCI) electrodes. Potential indications include interhemispheric implants, temporal implants with minimal temporalis dissection, and intraventricular hippocampal surface implants. Existing challenges and future directions are discussed.
Patient Care: Novel flexible electronics have the potential of being implanted in a minimally invasive manner. In our experiments performed in both canine and human cadaveric specimens, we have determined the requirements and limitations of implanting such devices through a burr hole or keyhole craniotomy. These insights not only allow us to assess the feasibility of such methods, but also allow us to focus our attention on areas of research that may improve current materials, instrumentation, and techniques. At the same time, we discuss potential clinical indications for minimally invasive implantation of flexible electronics.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Understand the techniques used for MII of a flexible substrate.
2) Identify the challenges involved in MII of flexible electrodes in the subdural space.
3) Discuss the potential applications of MII techniques.
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