Abstract
Microfabrication technology for cortical interfaces has advanced rapidly over the past few decades for electrophysiological studies and neuroprosthetic devices offering the precise recording and stimulation of neural activity in the cortex. While various cortical microelectrode arrays have been extensively and successfully demonstrated in animal and clinical studies, there remains room for further improvement of the probe structure, materials, and fabrication technology, particularly for high-fidelity recording in chronic implantation. A variety of non-conventional probes featuring unique characteristics in their designs, materials and fabrication methods have been proposed to address the limitations of the conventional standard shank-type (“Utah-” or “Michigan-” type) devices. Such non-conventional probes include multi-sided arrays to avoid shielding and increase recording volumes, mesh- or thread-like arrays for minimized glial scarring and immune response, tube-type or cylindrical probes for three-dimensional (3D) recording and multi-modality, folded arrays for high conformability and 3D recording, self-softening or self-deployable probes for minimized tissue damage and extensions of the recording sites beyond gliosis, nanostructured probes to reduce the immune response, and cone-shaped electrodes for promoting tissue ingrowth and long-term recording stability. Herein, the recent progress with reference to the many different types of non-conventional arrays is reviewed while highlighting the challenges to be addressed and the microfabrication techniques necessary to implement such features.
Highlights
Microfabrication technologies for neural recording have rapidly advanced over the past few decades in terms of spatial resolution [1,2,3,4,5], topological precision [6], manufacturability [7,8,9,10,11], and multi-functionality [12,13,14,15,16]
Microelectromechanical systems (MEMS) have enabled the fabrication of high-density cortical microelectrode arrays potentially capable of integration with electronics [17,18,19,20,21,22,23,24,25], optic interfaces [26,27,28,29,30,31,32,33,34], and microfluidic channels [35,36,37,38,39,40,41,42,43,44,45], serving as a standard methodology for a wide range of in vivo electrophysiological studies and neural prosthetic devices [46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76]
Various types of flexible cortical electrode arrays have been demonstrated based on biocompatible polymers such as polyimide, silicone elastomers, parylene or liquid crystal polymers (LCPs) [88,89,90,91]
Summary
Microfabrication technologies for neural recording have rapidly advanced over the past few decades in terms of spatial resolution [1,2,3,4,5], topological precision [6], manufacturability [7,8,9,10,11], and multi-functionality [12,13,14,15,16]. While a number of review papers have thoroughly discussed the design, fabrication, and testing results of conventional microelectrode arrays for the cortex [193,194,195,196,197,198,199,200,201,202,203,204,205,206,207], there are no review articles, to the best of our knowledge, focusing on these types of non-conventional cortical probes containing special geometric features to overcome the various challenges that could not be resolved. We aim to highlight the challenges to be addressed and the microfabrication techniques required to implement them for each specific structure in the following sub-chapters
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