Nanostructured TiN-Coated Electrodes for High-Sensitivity Noninvasive Characterization of in Vitro Tissue Models

Because of a rising use of in vitro models as an alternative to animal models, the precise assessment of tissue-specific parameters of such in vitro test systems has become a critical part of ensuring predictive results. Impedance spectroscopy as a noninvasive method serves as a reliable and efficient tool for quality control because it only minimally interferes with the system during investigation. In this study, we present a refined impedance measurement system using nanostructured titanium nitride (TiN) electrodes. This advanced material was used to investigate tissue maturation and changes in the barrier integrity of an intestinal Transwell-based in vitro model. The reduction of noise facilitated a more detailed data extraction and biological interpretation. Compared to standard stainless steel electrodes, at a typical measurement frequency of 12.5 Hz, the maximum electrode impact on the signal could be reduced from over 75% to less than 5%. This allowed the accurate determination of transepithelial electrical resistance values from Caco-2 in vitro tissue models without a further mathematical analysis based on a computer simulation. The novel design of a 3D-printed measurement attachment equipped with nanostructured TiN electrodes was used to continuously monitor the barrier integrity of the Caco-2 cells during a permeability assay. Moreover, because of low process temperatures, the TiN coatings for enhanced impedance measurement sensitivity could also be deposited onto several other materials, e.g., commercially available cell culture equipment such as standard disposable multiwell plate dishes. In conclusion, we developed a novel method to improve the electrode properties for impedance spectroscopy, which can be easily implemented into standardized end-point measurement to qualify a variety of in vitro test systems.