Development of biocompatible implants of fusinite for in vivo EPR oximetry

The development of oxygen-sensitive paramagnetic materials is being actively pursued because of their potential applications for in vivo electron paramagnetic resonance (EPR) oximetry. Among these materials, fusinite is of particular interest because of the high sensitivity of the EPR linewidth to the partial pressure pO₂. Although this material has led to a number of very useful results in experimental systems, its potential use in humans is limited by the need to prove that it will not cause deleterious effects. The strategy used in this study to optimize the biocompatibility of the oxygen- sensitive materials was to prepare small silicon implants containing the fusinite. The use of silicon permits the diffusion of oxygen inside the implant while the material does not have contact with the biological environment. Radiosterilization did not affect the pO₂ sensitivity of the material. The feasibility of performing pO₂ measurement was verified in vivo by periodically inducing ischemia in the gastrocnemius muscle of mice over a period of 6 weeks.