Neuralace: manufacture, parylene-C coating, and mechanical properties.

Abstract

<i>Objective.</i>This study investigates the mechanical properties of the Neuralace, a novel ultra-thin, high-channel-count mesh-type subdural electrode array, to characterize its mechanical compatibility with neural tissue (i.e., the forces exerted onto the brain upon conformation) for chronic brain-computer interface (BCI) applications.<i>Approach.</i>A full-factorial design of experiments was used to assess the effects of geometrical variations, orientation, and polymeric encapsulation on the stiffness of silicon-based Neuralace structures. A custom low-force four-point bending setup was developed to measure flexural stiffness in a physiologically relevant displacement range.<i>Main results.</i>The stiffness values of Neuralace structures ranged from 2.99 N m^-1to 7.21 N m^-1, depending on the cell-wall thickness (CWT) of the lace, orientation, and parylene-C (PPXC) encapsulation. Orientation and CWT had the largest impact on the stiffness of the structures, while the effects of PPXC encapsulation were statistically significant but more subtle. The stiffest Neuralace configuration is expected to exert forces approximately 10-100 times lower than commercially available subdural implants would when conforming to the brain's topology (considering a 60 mm radius of the gyrus).<i>Significance.</i>Subdural electrode arrays have traditionally been used for epilepsy monitoring and surgical planning. These arrays are now transitioning from short-term implantation in epilepsy monitoring to long-term use in BCIs, which requires consideration of the foreign body response to ensure long-term durability and functionality. Biocompatibility challenges, such as fibrotic encapsulation and reactive astrogliosis, highlight the need for conformal subdural implant designs that minimize mechanical stress on neural tissue. This study establishes a rigorous and reproducible framework for mechanical characterization of conformable neural implants and demonstrates the feasibility of tuning design parameters to reduce implant-induced mechanical stress on cortical tissue. The results support future development of chronic BCI-compatible subdural electrodes with improved biocompatibility through mechanical design.