Foreign Body Response Investigated With an Implanted Biosensor by In Situ Electrical Impedance Spectroscopy

One of the principal challenges for the long-term implantation of biosensors is that the normal physiological response of the body creates a fibrotic capsule of scar tissue surrounding the implanted sensor (the foreign body response). This dense, collagenous capsule isolates the device from the local environment, causing a time-dependent degradation of the signal. We utilize this degradation or change to an electrical signal as an indicator of the physiological responses to the implantation of the biomaterial device. We thus track the foreign body response electronically, an important analytical method for our program that aims to reduce the foreign body response. We applied electrical impedance spectroscopy (EIS) to track changes of the electrical signal behavior over time between micro-electrode arrays. We have performed experiments both in vitro and ex ova. In vitro, we used a reservoir of phosphate buffered saline into which selected proteins were introduced that adsorb onto the electrode surface. Three proteins were studied and each was found to affect the EIS results differently. We have investigated the foreign body response ex ova using the chick chorio-allantoic membrane (CAM) model. Following implantation of the electrode array the chick CAM exhibited a response similar to the mammalian foreign body response. We report that the electrical signal degrades with tissue growth during the healing and remodeling following the traumatic implantation of the electrode needle through the ectoderm side of the CAM tissue.