Growing interest in developing devices that can be implantable or wearable requires the identification of suitable materials for the components of these devices. Electrochemical supercapacitors are not the exception in this trend, and identifying electrode materials that can be not only suitable for the capacitive device but also biocompatible at the same time is important. In addition, it would be advantageous if physiological fluids could be used instead of more conventional (and often

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... ve) electrolytes for implantable or wearable supercapacitors. In this study, we assess the biocompatibility of films of anodized TiO 2 nanotubes subjected to the subsequent annealing in Ar atmosphere and evaluate their capacitive performance in a physiological liquid. A biocompatibility test tracking cell proliferation on TiO 2 nanotube electrodes and electrochemical tests in 0.01 M phosphate-buffered saline solution are discussed. It is expected that the study will stimulate further developments in this area.