Online Measurement System for Dynamic Flow Bioreactors to Study Barrier Integrity of hiPSC-Based Blood-Brain Barrier In Vitro Models

Electrochemical impedance spectroscopy (EIS) is a noninvasive, reliable, and efficient method to analyze the barrier integrity of in vitro tissue models. This well-established tool is used most widely to quantify the transendothelial/epithelial resistance (TEER) of Transwell-based models cultured under static conditions. However, dynamic culture in bioreactors can achieve advanced cell culture conditions that mimic a more tissue-specific environment and stimulation. This requires the development of culture systems that also allow for the assessment of barrier integrity under dynamic conditions. Here, we present a bioreactor system that is capable of the automated, continuous, and non-invasive online monitoring of cellular barrier integrity during dynamic culture. Polydimethylsiloxane (PDMS) casting and 3D printing were used for the fabrication of the bioreactors. Additionally, attachable electrodes based on titanium nitride (TiN)-coated steel tubes were developed to perform EIS measurements. In order to test the monitored bioreactor system, blood-brain barrier (BBB) in vitro models derived from human-induced pluripotent stem cells (hiPSC) were cultured for up to 7 days. We applied equivalent electrical circuit fitting to quantify the electrical parameters of the cell layer and observed that TEER gradually decreased over time from 2513 O·cm2 to 285 O·cm2, as also specified in the static control culture. Our versatile system offers the possibility to be used for various dynamic tissue cultures that require a non-invasive monitoring system for barrier integrity.