Electrochemical characterization and in vivo biocompatibility of a thick-film printed sensor for continuous in vivo monitoring

This paper assessed the material biocompatibility and investigated the temporal modulation in electrochemical performance of printed thick-film electrochemical sensing devices (ESDs) that can serve as the basis of various enzymatic sensor in detecting an electrochemically potent species. The sensors were placed in phosphate buffered saline (PBS), human serum, or implanted subcutaneously in rats, free or in stainless steel cages. The exudate collection allowed the evaluation of inflammatory cell populations, up to 21 days. The ferrous/ferric redox electrode reactions were used to assess the electrode elements performance for up to 49 days. Following testing, scanning electron microscopy (SEM) evaluated cell surface adhesion, while fibrous capsules were examined by histology. It was determined that the exudates leukocyte concentration due to the presence of sensors was comparable to the empty cage controls. For the length of the study, the sensors functionality appeared not to be influenced by the in vivo environment, when tested ex vivo, without the surrounding fibrous capsule. Surface imaging (SEM) indicated temporal focal dissolution of the Ag/AgCl electrodes with no apparent local toxicity. We concluded that the ESDs were biocompatible and their ex vivo functionality was not lost when maintained in vivo for up to 49 days.