Recent advances in silicon-based neural microelectrodes and microsystems: a review

Developments in neurotechnology are recently driven by newly national and international brain research initiatives worldwide. The challenging goal of understanding how the human brain works requires a vast amount of information gained by neural sensors. Microelectrodes implanted in the central nervous system are extensively used to record electric activity inside the brain tissue. More recently, deep-brain stimulation in Parkinson disease proved the feasibility of such electrodes in human medical treatments as well. To add novel sensor or even actuator functions to these microelectrodes, limitations of recent fabrication technologies have to be considered. To date, silicon microtechnology offered the highest potential to meet the demands of neural applications regarding multiple functions integrated on a single implantable microsystem. Besides reproducibility and low variability of silicon-based microelectrodes, combination of various functionalities like standard electrophysiology, integrated signal processing, local drug delivery, neurochemical detection and optogenetic stimulation is also possible using these microsystems. This ability makes silicon microelectrodes good candidates to provide high-resolution recording and stimulation in the electric, fluidic, chemical or optical domain in more complex neurophysiological experiments in the future. The aim of this review is to give an overview on various aspects of silicon-based implantable neural microelectrodes and microsystems developed in the last decade. Microfabrication approaches of 2-D and 3-D arrays are summarized. Features of the latest active microelectrodes including CMOS signal processing circuitry are compared. Integration methods of convection enhanced drug delivery functions for local administration of pharmacons are demonstrated. Performance of recent silicon-based chemical sensors for the detection of neurotransmitters is also studied. An analysis on the latest developments in silicon-based optrodes for optogenetic and thermogenetic stimulation is also included in this paper. Microelectrode-tissue interaction is described through the evaluation of recent experimental studies on in vitro and in vivo biocompatibility. (C) 2015 Elsevier B.V. All rights reserved.