Stress-actuated partially flexible microelectrode arrays for activity recording in 3D neuronal cultures

Microelectrode arrays (MEAs) are instrumental in monitoring electrogenic cell populations, such as neuronal cultures, allowing high precision measurements of electrical activity. Although three-dimensional neuronal cultures replicate the behavior of in vivo systems better than two-dimensional models, conventional planar MEAs are not well suited to capture activity within such networks. Novel MEA geometries can overcome this difficulty, but often at the cost of increased fabrication complexity. Here, we used the stress mismatch between thin film layers to fabricate MEAs with vertical electrodes, using methods compatible with established microfabrication protocols. A micrometric SiO₂ hinge enables control over the bending angle of flexible polyimide structures with embedded electrodes. The performance of the patterned electrodes was assessed before and after stress actuation, through impedance measurements, voltage noise mapping, and neuronal activity recordings. 3D MEAs with 30 × 30 μm² electrodes showed an impedance of 0.96 ± 0.07 MΩ per electrode and detected neuronal activity spikes with amplitudes as high as 400 μV. These results demonstrate the potential of the developed methods to provide a scalable approach to fabricate 3D MEAs, enabling enhanced recording capabilities for in vitro neuronal cultures.