Animal Test Models for Implant-Associated Inflammation and Infections

To evaluate the biocompatibility and inflammatory potential of prospective implant materials a mouse model was established using in vivo imaging to monitor inflammatory responses to individual implants over time. Various inflammation associated products and processes were assayed such as reactive oxygen radicals, proteases produced by immune cells, cell stimulatory signaling molecules and interferon gene activation. These were detected either by biochemical activation of fluorescent molecules or by transgenic animals expressing luciferase to monitor inflammatory interferon-\(\upbeta \) (IFN-\(\upbeta )\) induction. The results showed that inflammatory signals can be detected by in vivo imaging after subcutaneous implantation of biocompatible or immune stimulatory implants. However, there were specific differences depending upon the assay system. The response to inflammatory proteases and cell growth signaling molecules appeared delocalized and was difficult to assign to one of several implants in individual animals. On the other hand, the interferon response was locally focused and was highly specific for pathogens whereas no signal was detected in response to wounding or to biocompatible implant materials. In conclusion, of the various detection systems investigated, the transgenic interferon mouse model could be applied to monitor bacterial implant infections and will be useful to evaluate the efficacy of antimicrobial implant coatings.