Improvement of the biocompatibility and potential stability of chronically implanted electrodes incorporating coating cell membranes.

The development of chronically implanted electrodes attracts much attention since these electrodes are much favorable for monitoring changes of neurotransmitters in brain science. The research of this field mainly was only focused on chemical modification to improve the potential stability, less on the biocompatibility. In this work, at the first time, we proposed the concept of cell-membrane electrodes based on a basic hypothesis using animal's self-cell membrane to reduce animal exclusiveness (hyperacute rejection and chronic rejection). As a proof of concept, we first studied cell-membrane reference electrodes for chronically implanted electrodes. Red cell membrane (RCM) was extracted from the rat's blood and coated on the chemically modified Ag/AgCl electrodes. It was found that ionic liquid (IL), 1-butyl-2, 3-dimethylimidazolium hexafluorophosphate (BDMI) showed a good performance rather than Nafion used as coating film for protection of silver chloride on Ag wire and support of the cell-membrane. Electrochemical impedance spectra supported that charge transfer resistance nearly kept constant before and after the electrodes were implanted into the rat's brain tissues for 28 days. Immunohistochemical analysis of the implant sites in rat's brain tissues indicated that the extent of glial scarring arising from the Ag/AgCl/BDMI/RCM electrodes was smaller than that of both Ag/AgCl/Nafion electrodes and Ag/AgCl/Nafion/RCM electrodes after 28 days of implantation. The RCM-coated Ag/AgCl/IL electrodes showed a relatively potential stability compared with that of RCM-noncoated Ag/AgCl/IL electrodes after 28 days of implantation. Additionally, the current-voltage curve demonstrated that the RCM-coated electrodes can be used as polarized electrodes. This work demonstrated that the RCM which was coated on the Ag/AgCl/IL electrodes can much improve the biocompatibility and potential stability of the RCM-noncoated Ag/AgCl/IL electrodes implanted in rat brain. The cell-membrane coated electrodes will serve as a lighthouse in guiding the design of chronically implanted electrodes for in vivo electrochemical detection.