Photosensitive-polyimide based method for fabricating various neural electrode architectures.

An extensive photosensitive-polyimide (PSPI)-based method for designing and fabricating various neural electrode architectures was developed. The method aims to broaden the design flexibility and expand the fabrication capability for neural electrodes to improve the quality of recorded signals and integrate other functions. After characterizing PSPI's properties for micromachining processes, we successfully designed and fabricated various neural electrodes even on a non-flat substrate using only one PSPI as an insulation material and without the time-consuming dry etching processes. The fabricated neural electrodes were an electrocorticogram (ECoG) electrode, a mesh intracortical electrode with a unique lattice-like mesh structure to fixate neural tissue, and a guide cannula electrode with recording microelectrodes placed on the curved surface of a guide cannula as a microdialysis probe. In vivo neural recordings using anesthetized rats demonstrated that these electrodes can be used to record neural activities repeatedly without any breakage and mechanical failures, which potentially promises stable recordings for long periods of time. These successes make us believe that this PSPI-based fabrication is a powerful method, permitting flexible design, and easy optimization of electrode architectures for a variety of electrophysiological experimental research with improved neural recording performance.

Improvement of neuronal cell adhesiveness on parylene with oxygen plasma treatment.

We improved adhesiveness of a neuron-like cell, PC12, on a Parylene-C surface by O(2) plasma treatment which changes the surface from hydrophobic to hydrophilic. Neural cell adhesiveness on the plasma-treated Parylene-C was more than twenty times better compared to non-treated Parylene-C and it was close to that on a conventional polystyrene tissue-culture dish.

Neurite outgrowth of PC12 cells on diX (parylene) family materials.

We investigated neuronal cell differentiation, particularly neurite outgrowth, on the surface of diX H and diX AM using an in vitro examination of a neuron-like rat pheochromocytoma cell line, PC12. diX H and diX AM are in the parylene family of diX C (or Parylene-C), which is widely used as a novel coating material to insulate neural electrodes, and they have been recently commercialized; diX H and diX AM offer different features of biocompatibility. Previously, we found that these new parylene materials have high cell adhesiveness to neuronal cells whereas the adhesiveness of diX C is extremely low. However, their cell differentiation remains unknown although neuronal cell differentiation plays a crucial role in their development and regeneration. This study showed that almost all PC12 cells adhering to the surface of diX AM and diX H were differentiated, but the neurite outgrowth was significantly larger on diX H than that on diX AM and a conventional polystyrene culture dish. The result suggests that diX H may be advantageous as a biocompatible coating material for a scaffold, which can be used on virtually any substrate to get various configurations in neural devices.

Development of a BCI master switch based on single-trial detection of contingent negative variation related potentials.

To control the startup/shutdown of a conventional brain-computer interface (BCI) that is always running for daily use, we proposed and developed a new BCI system called a BCI master switch. We designed it with on/off switching functions by detecting the contingent negative variation (CNV)--related potentials. We chose CNV to improve the single-trial discrimination of user intentions to switch because CNV had a high signal-to-noise ratio and needed high concentration for its elicitation. We also applied a support vector machine (SVM) to improve the single-trial detection of CNV-related potentials. As the best parameters of SVM were estimated and applied, the offline evaluation's best performance achieved a CNV detection rate of 99.3% for the intention to switch and 2.1% for the intention not to switch. Remarkably, this performance was achieved from single-trial detection, imaginary response of user's intention without physical reaction, and the data from only one recording electrode. These results suggest that our proposed BCI system might work as a master switch by single-trial detection.

Comparison of neuronal cell adhesiveness of materials in the diX (Parylene) family.

DiX C (or Parylene-C) has been widely used as a coating material to insulate neural electrodes in recent decades. However, its uses are limited due to its extremely low adhesiveness with neuronal cells. Other functional materials in the diX family, such as diX A, diX AM, and diX H, have been commercialized recently and would offer different features in biocompatibility from diX C. However, their cell adhesiveness remains unknown. In this work, we used an in vitro approach to investigate how the surface of each material in the diX family affects the degree of neuronal cell adhesiveness compared with a conventional culture dish of polystyrene (PS). The neuronal cell adhesiveness on diX AM and diX H was almost equivalent to that for the PS dish, whereas neuronal cells did not settle on the surface of diX C and diX A. Our results suggest that diX AM and diX H could provide another practical feature as a coating material for a scaffold in a substrate with any configuration in neural devices.

A photosensitive polyimide based method for an easy fabrication of multichannel neural electrodes.

To develop practical and inexpensive multichannel neural electrodes, we designed and fabricated photosensitive polyimide based flexible multichannel neural electrodes using MEMS technologies. Compared to a conventional micromachining with non-photosensitive materials, the advantage of applying photosensitive polyimide is the elimination of the dry etching, which involves the complex multilevel processes for controlling the etching conditions to define the outline of the neural electrodes and expose the microelectrodes. Thus, photosensitive polyimide allows more options in optimization of the configuration and size of neural electrodes depending on experimental purposes, and enables fabrication at a lower cost with improvement of process yields.