Highly Stretchable, Compliant, Polymeric Microelectrode Arrays for In Vivo Electrophysiological Interfacing

Abstract

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.

Cyber–Physiochemical Interfaces

“…Modification or evaporation of conductive layer on prestretched elastic substrates randomly produces wrinkles which also contribute to stretchability . Using this prestretching method, stretchable polymeric microelectrodes such as the polypyrrole (PPy) electrode were produced with high stretchability (≈100%) . Similar to ancient paper folding art, the origami and kirigami approach was proposed for stretchable electronics with advantages such as high throughput, large deformability, and comparable performance to rigid electronic .…”

“…Copyright 2017, Springer Nature. Polymer electrode image: Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…Their high transconductance facilitates biosignal transduction from the cell to the recording electrode . PPy NWs/PPy film electrode shows a lower impedance than bare Au or PPy/Au electrode, high stretchability (≈100%), and high interfacial adhesion (1.9 MPa) (Figure f) . The polymeric microelectrode arrays are successfully applied in differentiating a normal rat from epileptic rat by in vivo recording electrocorticograph (ECoG) signals and stimulating the rat ischiadic nerve .…”

“…Mechanical mismatching issue is most pronounced, as the majority of well‐developed sensing and data processing components are based on silicon technologies, which are stable but rigid (several GPa and stretchability less than 5%). Human tissues show Young's modulus from tens of kPa to several MPa and stretchability from 10% to 100%, e.g., 0.1–2 MPa and 30–70% strain for the epidermis, 0.5–2.5 kPa and 10% strain for the brain, and tens of kPa and 20–35% strain for the heart . For on‐skin applications, these rigid sensing units failed to realize conformable contacts to the arbitrarily shaped skin with dynamic deformations .…”

A skin-like stretchable colorimetric temperature sensor

“…For instance, high-adhesion stretchable electrodes have been used both for stretchable electrodes and strain sensors to reliably detect electromyography signals and the joint motions [14]. Polymeric microelectrode arrays have been fabricated with high stretchability of 100%, and used for conformally recording the electrocorticography signals from rats in normal and epileptic states [15]. In another example, surface strain redistribution is reported to significantly enhance the sensitivity of fiber-shaped stretchable strain sensors that can be reliably used to monitor the sports activity [16].…”