UC Davis

AbstractIn vitro cell culture models are quickly replacing animal models for drug development, mechanistic studies, and precision medicine. Visual methods are the primary means of studying organ-on-a-chip (OoC) models, but are limited to microscopy and immunofluorescent staining protocols. These techniques expose tissues to an adverse environment outside of an incubator or must be prepared with fluorescent proteins, which may affect the underlying cellular processes. In addition, these quantification approaches are often end-point assessments, limiting the number of measurements from a sample. Impedance-based methods allow for continuous monitoring of the electrical properties of tissues that provide insight into biochemical and cellular mechanisms. Transepithelial electrical resistance (TEER) is a useful metric for quantifying the integrity of an epithelial cell layer (e.g., gut epithelium), but lacks the spatial resolution of the microscopic techniques. This thesis reports on the design and experimental validation of a distributed hardware including a voltage-controlled current source (VCCS) for safe current injection, TEER measurement circuitry to sample the impedance across conductive phantoms, and real-time data conversion for monitoring changes in the system. Tomographic concepts will be adapted from electrical impedance tomography (EIT) systems to realize a distributed TEER device capable of continuous, non-invasive spatial imaging of tissues. Multiplexers will spatially expand the TEER measurement circuitry to detect minor changes in impedance by gathering a representative sample of data from the entire chip. The system is validated using conductive and insulating phantoms in saline tanks with varying size and orientation. Finally, EIT image reconstruction techniques are used for converting the raw data to images with high spatial resolution. This platform should be broadly applicable to real-time monitoring of developing in vitro tissue cultures and spatial detection of barrier disruptions, and can be scaled for studies requiring frequency sweeps or higher resolution images.