Development of polymer-coated paramagnetic Implants for biomedical oximetry Applications

Abstract

There are a variety of methods available for measuring and mapping of oxygen concentration in biological tissues. The particulate-based, electron paramagnetic resonance (EPR) oximetry is a powerful technology that allows non-invasive and repetitive monitoring of oxygenation in tissues. Lithium naphthalocyanine (LiNc) forms highly stable paramagnetic crystals which can be used for high resolution oximetry in tissues. To show efficient biocompatibility, long-term in vivo stability and responsiveness of LiNc oximetry probes, as well as for making the probes surgically implantable/ retrievable, we coated LiNc microcrystals with Teflon AF 2400 (TAF) polymeric materials. EPR linewidths of polymer-coated LiNc probes under anoxic conditions as well as at varying partial pressures of oxygen (pO2) did not show appreciable change relative to uncoated LiNc particulates, yet the linewidth of coated LiNc crystals was linearly dependent on varying pO2. The coated implantable probes responded to changes in pO2 quickly and reproducibly, enabling dynamic measurements of oxygenation in real time. The implants were unaffected by biological oxidoreductants. The oxygen sensitivity and stability of the coated LiNc was demonstrated in vivo in mice for more than two months. Thus, new TAF polymer-coated LiNc crystals are potential candidates for future in vivo studies including clinical trials for oxygen measurements in pathophysiological tissues.