The moment a foreign material is implanted into living tissue, the inflammatory response reacts to protect the host from infection. In many cases this response results in failure of the implant. A hallmark of the early inflammatory response is the production of reactive oxidative species (ROS) from activated macrophages. These ROS are highly unstable molecules that play a key role in degrading pathogens and foreign materials. When macrophages are unable to degrade foreign materials such as many synthetic biomaterials, it leads to continued macrophage activation and ROS production, a local excess of which can damage lipids, proteins, DNA, and lead to altered local tissue composition. The superoxide anion radical (O2-) is the primary species of the ROS, a hallmark of the inflammatory response and we believe a sentinel marker for chronic inflammation.

We hypothesize that the acute inflammatory response can be manipulated by sensing ROS production and delivering anti inflammatory cytokines that will down regulate their production. To begin testing this hypothesis we have developed a probe to sense real time production of ROS. The probe was fabricated by combining a silver-silver chloride reference electrode and platinum anode coiled around a plastic core. Upon polarization at 650 mV, hydrogen peroxide is oxidized at the platinum surface and the current generated is correlated to concentration. Coating the platinum surface with superoxide dismutase (SOD) provides the ability to catalyze the dismutation reaction of O2- with the release of oxygen and hydrogen peroxide. Hydrogen peroxide is oxidized and the current generated allows us to determine O2- concentration.

Once the sensor was fabricated, a series of in-vitro tests were performed to examine sensor performance, response time, and sensitivity. We first obtained a standard curve for hydrogen peroxide using an un-coated probe. Next, the SOD coated probe was tested by generating O2- in a reaction of xanthine oxidase and xanthine salt. The probes exhibited increased current output in response to increased concentrations of xanthine salt in solution, indicating that the sensor was catalyzing the dismutation of O2- into oxygen and hydrogen peroxide and oxidizing hydrogen peroxide at the platinum surface. Sensor response time to increased O2- production is real-time for all practical purposes and the sensor currently responds in the range of 1 mmol to 10 mmol O2-.

Initially the ROS sensor will act as a research tool to better understand ROS production in vitro and how ROS can be used as a sentinel measurement for inflammatory response. In the future, we envision such a device to be used in concert with local drug delivery strategies to engineer host reponse for various implant applications.