Development of a Hydrogel-Actuated 3D Micro Electrode Array (MEA) for Neural Spheroids and Organoids

Organoids and spheroids are versatile tools in research. Their 3D structure can faithfully replicate the complexity and functionality of human organs and tissues, enabling scientists to study biological phenomena in a dish. Specifically, neural organoids and spheroids offer exciting opportunities for understanding neuronal connectivity and exploring neurological disorders. Electrophysiological recordings play a crucial role in assessing these parameters. While micro electrode arrays (MEAs) are commonly used for such measurements, they are mostly limited to 2D (planar) configurations, which do not fully capture the complexity of three dimensional organoids and spheroids.<br/>In this study, we present an intuitive 3D MEA platform based on shape-morphing bilayers to engulf the spheroid and enable recordings from its entire surface. The first layer forms the microelectrode arrays patterned as a thin metal film embedded in polymers such as polyimide and parylene. The second layer consists of a hydrogel membrane covalently grafted onto the MEA and capable of swelling upon immersion in cell culture medium thereby enabling actuation.<br/>By precisely tuning the hydrogel formulation, bilayer thicknesses, and MEA geometry, we successfully designed 3D MEA platforms that accommodate a wide range of tissue sizes and shapes. One device included 32 electrodes, with a radius of 15 µm, distributed onto 4 bilayers folding with a radius of closure 300 µm. To expedite and guide the design and microfabrication process, we conducted comprehensive mechanical and electrical characterization of each component, and developed accurate in silico finite element models. The shape morphing MEAs interface reliably with commercial MEA readout platforms, requiring no additional instrumentation and minimal training.<br/>We aim to study network patterns collected from the volumetric MEA over neural spheroids and hope to collect valuable insights into the connectivity, health, and functionality of neural organoids.