Nanopatterned Nafion Microelectrode Arrays for In Vitro Cardiac Electrophysiology

Abstract

In this study, nanopatterned Nafion microelectrode arrays for in vitro cardiac electrophysiology are reported. With the aim of defining sophisticated Nafion nanostructures with highly ionic conductivity, fabrication parameters such as Nafion concentration and curing temperature are optimized. By increasing curing temperature and Nafion concentration, the replication fidelity of Nafion nanopatterns when copied from a polydimethylsiloxane master mold are controlled. It is also found that cross‐sectional morphology and ion current density of nanopatterned Nafion strongly depends on the fabrication parameters. To investigate this dependency, current‐voltage analysis is conducted using organic electrochemical transistors overlaid with patterned Nafion substrates. Nanopatterned Nafion is found to allow higher ion current densities than unpatterned surfaces. Furthermore, higher curing temperatures are found to render Nafion layers with higher ion/electrical transfer properties. To optimize nanopattern dimensions, electrical current flows, and film uniformity, a final configuration consisting of 5% nanopatterned Nafion cured at 65 °C is chosen. Microelectrode arrays (MEAs) are then covered with optimized Nafion nanopatterns and used for electrophysiological analysis of two types of induced pluripotent stem cell‐derived cardiomyocytes (iPSCs‐CMs). These data highlight the suitability of nanopatterned Nafion, combined with MEAs, for enhancing the cellular environment of iPSC‐CMs for use in electrophysiological analysis in vitro.

Fabrication of Micro‐ and Nanopatterned Nafion Thin Films with Tunable Mechanical and Electrical Properties Using Thermal Evaporation‐Induced Capillary Force Lithography

“…This may be attributed to SO 3  functional groups in Nafion molecules tightly interacting with one another in thermal conditions via hydrogen bonding. In addition, according to previous literature, [ 6 ] 20% Nafion showed broad amorphous regions in the XRD spectrum, implying that 5% Nafion is more crystalized and hard relative to the 20% Nafion. As a result, the mechanical properties of the Nafion patterns could be controlled via fabrication parameters for further applications.…”

“…[ 34 ] Patterned Nafion films have also been successfully integrated with microelectrode arrays for analyzing the electrophysiological function of cardiomyocytes and neurons differentiated from human induced pluripotent stem cells. [ 5,6 ] To measure and characterize the electrochemical activity of micro‐ and nanopatterned Nafion thin films that were fabricated using a variety of parameters (concentration, curing temperature), electrodes were overlaid and integrated with micro‐ and nanomolded Nafion. Total impedance was influenced in the high frequency regimes by Ohmic behavior, while the impedance at lower frequencies is dominated by ion conductance ( Figure B).…”

“…Nafion has been widely applied in proton exchange membranes and biointerfaces over the past couple of decades. [ 1–6 ] Nafion is ion‐permeable and consists of a hydrophilic sulfonic group and a hydrophobic polyfluoroethylene backbone. Previous findings show that material processing and fabrication conditions play an important role in regulating the characteristics of the produced Nafion.…”

“…For example, while other polymers are typically unable to transmit electrical signals, Nafion's ion permeability allows for its integration in microelectrode arrays that are then able to obtain electrophysiological recordings of excitable cells, such as cardiomyocytes and neurons that are cultured on these films. [ 5,6,24 ]…”

“…[ 25 ] Recently, our group has demonstrated that Nafion films can be patterned at micro‐ and nanoscale via a rapid prototyping and drying process. [ 5,6,24 ] However, these Nafion patterns fabricated by solution casting were found to encounter critical issues with pattern fidelity. Specifically, after fabrication, the Nafion patterns tended to shrink significantly due to solvent evaporation, and differences in the evaporation rates at the center and at the edges of the mold‐substrate interface induced patterning nonuniformity over the entire substrate area.…”