Date Published: January 04, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Jordi Cools, Qianru Jin, Eugene Yoon, Diego Alba Burbano, Zhenxiang Luo, Dieter Cuypers, Geert Callewaert, Dries Braeken, David H. Gracias.
Microelectrode arrays (MEAs) have proved to be useful tools for characterizing electrically active cells such as cardiomyocytes and neurons. While there exist a number of integrated electronic chips for recording from small populations or even single cells, they rely primarily on the interface between the cells and 2D flat electrodes. Here, an approach that utilizes residual stress‐based self‐folding to create individually addressable multielectrode interfaces that wrap around the cell in 3D and function as an electrical shell‐like recording device is described. These devices are optically transparent, allowing for simultaneous fluorescence imaging. Cell viability is maintained during and after electrode wrapping around the cel and chemicals can diffuse into and out of the self‐folding devices. It is further shown that 3D spatiotemporal recordings are possible and that the action potentials recorded from cultured neonatal rat ventricular cardiomyocytes display significantly higher signal‐to‐noise ratios in comparison with signals recorded with planar extracellular electrodes. It is anticipated that this device can provide the foundation for the development of new‐generation MEAs where dynamic electrode–cell interfacing and recording substitutes the traditional method using static electrodes.
Microelectrode arrays (MEAs) are the preferred method for long‐term studies of electrophysiological phenomena, and have been successfully applied in fundamental neuroscience, drug discovery, safety pharmacology, and neuroprosthetics.1, 2, 3, 4 In contrast to the well‐established patch‐clamp technique,5 MEAs provide high‐throughput by allowing bidirectional and noninvasive interfacing with a large number of cells in parallel. The most common MEAs are the commercially available “passive” systems, where relatively large metal electrodes are connected to external recording and stimulation units. State‐of‐the‐art MEAs that utilize on‐chip multiplexing architectures provided by integrated circuit (IC) or complementary metal‐oxide‐semiconductor (CMOS) technology can comprise up to 60 000 electrodes enabling highly parallel electrophysiological recordings at subcellular resolution.4, 6, 7, 8, 9 Regardless of the technology, a common goal is to maximize cell–electrode adhesion and electrical coupling in order to achieve high signal quality. Strategies include selective coating of the electrodes using adhesive biomolecules,10 conductive polymers,11, 12 or carbon nanomaterials.13, 14, 15, 16, 17
In summary, a novel and first‐of‐its‐kind multielectrode shell chip has been developed with self‐folding electrodes that bridges the gap from 2D planar recordings to more complex 3D interfacing, allowing parallel readout of all cardinal points of electrogenic cells with higher signal‐to‐noise ratios. The fabrication is done using conventional cleanroom technology allowing cost‐effective, wafer‐level‐based batch processing and future integration with CMOS modules for switching and signal processing. As demonstrated, this device can provide the foundation for the development of new‐generation MEAs where dynamic electrode–cell interfacing and recording substitutes the traditional method using static electrodes. Accordingly, future research effort will have to focus on the next major step of combining these cell‐sized multielectrode shells with microelectromechanical systems (MEMS) in order to have precise control over their position and force, ultimately acting as impactive or even ingressive end effectors. Also the integration of microfluidic layers can be of great interest, which is currently in the scope of our future research and development activities. Finally, by scaling electrode density, highly parallel 3D spatiotemporal electrical maps could be recorded from few or potentially individual cells with micrometer‐scale resolution which would advance our understanding of cellular function, heterogeneity, and response times.
Cell Culture: Neonatal rat ventricular cardiomyocytes were harvested from 2 d old Wistar rats. Animals were handled in accordance with international (EU Directive 86/609/EEC) and national laws governing the protection of animals used for experimental purposes, minimizing distress during procedures. The use of animals and procedures was approved by the Ethical Committee for Animal Welfare (ECD, Ethische commissie Dierenwelzijn) of KULeuven and Imec. The extracted ventricles were washed in Hank’s balanced salt solution (HBSS), followed by overnight incubation at 4 °C in 0.05% trypsin. Next, the tissue was dissociated by adding collagenase for 15 min at 37 °C. Cells were separated through trituration and centrifugation and added to primary cardiomyocyte medium, after which they were pre‐plated to allow for selective attachment of remaining fibroblasts. After counting and a final centrifugation step, a desired concentration of cardiomyocytes was added to cell culture medium and seeded on the substrate.
The authors declare no conflict of interest.