Cleanroom-Free Microfluidic Chips with Capacitively Coupled 3D Liquid-Metal Electrodes as a Platform Technology for Controlled Electrical Field Stimulation of 2D and 3D Cell Cultures.

Abstract

Existing in vitro electrical stimulation platforms are limited by cleanroom-dependent fabrication, direct electrode-electrolyte contact that generates cytotoxic byproducts, and poor compatibility with 3D culture systems. This study reports a modular, cleanroom-free workflow for fabricating polydimethylsiloxane (PDMS) microfluidic chips with capacitively coupled 3D liquid metal (EGaIn) electrodes using digital light processing (DLP)-printed molds. The process achieves sub-day turnaround at electrode resolutions of ∼200 µm, which extends to ∼25 µm via a hybrid DLP/two-photon polymerization approach. A ∼150 µm PDMS dielectric barrier isolates the electrodes from the culture medium to eliminate faradaic reactions. COMSOL and ANSYS HFSS simulations show uniform electric fields of 27-108 V/m (three-channel chip) and (1.72-2.63) × 103 V/m (five-channel chip) across the culture chamber. Platform performance was validated across multiple cell types and culture formats. Stimulus-evoked calcium signaling was demonstrated in 50B11 dorsal root ganglion neurons (2D and 3D collagen) and in primary cortical neurons. Daily stimulation (∼4.68 × 103 V/m, 60 kHz) of OCY454 osteocytes in 3D collagen resulted in an 8-fold increase in cell proliferation (compared to 2-fold in controls) and a significant reduction in sclerostin expression. An automated pipeline combining Cellpose segmentation with hierarchical clustering identified three distinct cell subpopulations based on their calcium signaling dynamics. These results establish a customizable, cleanroom-free platform for delivering quantified 3D electrical fields to diverse cell cultures.