The effect of long-term implantation on metabolically active devices is of utmost importance for not only the success of implanted glucose sensors used in diabetic therapy, but also for the development of artificial tissues and encapsulated cell devices. Such devices are dependent on the constant, predictable supply of metabolites from the local vasculature. Long-term implantation leads to the formation of a foreign body capsule whose purpose is the protection of the host and isolation of the foreign material from local tissue resources. While this encapsulation is successful in protecting tissues from invading agents, metabolite flow continues, albeit at greatly reduced levels. The understanding of this encapsulation process is critical for the design and successful implementation of active implants dependent on metabolite supply.

The project goal is to utilize implantable wireless telemeters designed and manufactured by Glysens, Inc. to understand changes in oxygen levels of the surrounding subcutaneous tissues over the course of implantation in pigs. This is performed in three distinct, yet interrelated parts, namely: the analysis of oxygen signals collected from the long-term implantation of telemeters, the histological analysis of serial tissue samples collected from regions adjacent to the telemeter-like shams over the course of implantation, and the investigation of an accurate model for the dynamics of metabolite supply to implanted devices over the long-term.

Oxygen signals collected from sensors implanted into the subcutaneous tissues of pigs were found to contain several salient features. First, a long-term trend exhibiting exponential decay properties was discovered and is attributed to the impedance of mass transfer by the formation of a thick, avascular, fibrous foreign body capsule. The existence of such a capsule is demonstrated via histological examinations, and its impact on mass transfer of oxygen from the underlying vasculature to implant surface is investigated utilizing analytical and numerical methods. Second, a dominant frequency with a period of oscillation of 7–14 days was found for most of the signals examined. A model is proposed detailing the critical components of such an oscillations and how they might correlate with specific stages of the wound healing response.

The successful completion of this project provide a better understanding of the tissue changes that occur during the foreign body reaction, and the findings will be of direct benefit to the implant and device community allowing for better design parameters and device performance.