Figure 2.

Key material characteristics of neural recording implants. (A) Electrical properties. The example shows a neural recording probe (upper) with ITO (white) /ITO-PEDOT:PSS (blue) microelectrodes. The added PEDOT:PSS has been proved to improve electrochemical impedance (lower left) and charge storage capacity (lower right) due to the increased surface roughness (reprinted with permission from Yang et al., 2017). (B) Biocompatibility. The example shows the neuronal preservation and the severity of astrogliosis (left) around implanted SU-8 devices (right) (reprinted with permission from Márton et al., 2020). (C) Stability. The example shows an electrode array made of mechanically and chemically stable, boron-doped polycrystalline diamond (BDD) (upper). Morphological response of rat cortical neurons on the Parylene C and microcrystalline diamond (MCD) substrates (lower) appeared similarly to the control substrate (reprinted with permission from Fan et al., 2020). (D) Biodegradability and bioresorbability. The example indicates patterned molybdenum (Mo) electrodes on the resorbable substrate (PLLA/PCL) (reprinted with permission from Xu et al., 2019). (E) Mechanical properties. The example shows a mechanically flexible neural implant consisting of soft platinum-silicone composited electrodes (upper right) and micro-cracked gold film (lower right) interconnect on a silicone substrate (reprinted with permission from Minev et al., 2015). (F) Optical transparency. The example shows a transparent ITO ECoG implant combined with optical stimulation (reprinted with permission from Kwon et al., 2013).