Microelectrode arrays (MEAs) are designed to monitor and/or stimulate extracellularly neuronal activity. However, the biomechanical and structural mismatch between current MEAs and neural tissues remains a challenge for neural interfaces. This article describes a material strategy to prepare neural electrodes with improved mechanical compliance that relies on thin metal film electrodes embedded in polymeric substrates. The electrode impedance of micro-electrodes on polymer is comparable to that of MEA on glass substrates. Furthermore, MEAs on plastic can be flexed and rolled offering improved structural interface with brain and nerves in vivo.MEAs on elastomer can be stretched reversibly and provide in vitro unique platforms to simultaneously investigate the electrophysiological of neural cells and tissues to mechanical stimulation. Adding mechanical compliance to MEAs is a promising vehicle for robust and reliable neural interfaces.
Rationally designed sinusoidal gold nanobelts are fabricated as stretchable electrodes, and they do not show obvious change of resistance under large deformation after 10,000 cyclic stretching/relaxing processes. As a proof of concept, they are successfully used to record intracranial electroencephalogram or electrocorticogram signals from rats.
Polymeric microelectrode arrays (MEAs) are emerging as a new generation of biointegrated microelectrodes to transduce original electrochemical signals in living tissues to external electrical circuits, and vice versa. So far, the challenge of stretchable polymeric MEAs lies in the competition between high stretchability and good electrode-substrate adhesion. The larger the stretchability, the easier the delamination of electrodes from the substrate due to the mismatch in their Young's modulus. In this work, polypyrrole (PPy) electrode materials are designed, with PPy nanowires integrated on the high conductive PPy electrode arrays. By utilizing this electrode material, for the first time, stretchable polymeric MEAs are fabricated with both high stretchability (≈100%) and good electrode-substrate adhesion (1.9 MPa). In addition, low Young's modulus (450 kPa), excellent recycling stability (10 000 cycles of stretch), and high conductivity of the MEAs are also achieved. As a proof of concept, the as-prepared polymeric MEAs are successfully used for conformally recording the electrocorticograph signals from rats in normal and epileptic states, respectively. Further, these polymeric MEAs are also successful in stimulating the ischiadic nerve of the rat. This strategy provides a new perspective to the highly stretchable and mechanically stable polymeric MEAs, which are vital for compliant neural electrodes.
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