Three-dimensional hydrogel cultures for modeling changes in tissue impedance around microfabricated neural probes

One limitation to the use of neuroprosthestic devices for chronic application, in the treatment of disease, is the reactive cell responses that occur surrounding the device after insertion. These cell and tissue responses result in increases in device impedance and failure of the device to interact with target populations of neurons. However, few tools are available to assess which components of the reactive response contribute most to changes in tissue impedance. An in vitro culture system has been developed that is capable of assessing individual components of the reactive response. The system utilizes alginate cell encapsulation to construct three-dimensional architectures that approach the cell densities found in rat cortex. The system was constructed around neuroNexus acute probes with on-board circuitry capable of monitoring the electrical properties of the surrounding tissue. This study demonstrates the utility of the system by demonstrating that differences in cell density within the three-dimensional alginate constructs result in differences in resistance and capacitance as measured by electrochemical impedance spectroscopy. We propose that this system can be used to model components of the reactive responses in brain tissue, and that the measurements recorded in vitro are comparable to measurements recorded in vivo.