3D printable conductive composite inks for the fabrication of biocompatible electrodes in tissue engineering application

Native tissues are affected by the microenvironment surrounding the tissue, including electrical activities. External electrical stimulation, which is used in replicating electrical activities and regulating cell behavior, is mainly applied in neural and cardiac tissues due to their electrophysiological properties. The in vitro cell culture platform with electrodes provides precise control of the stimulation property and eases the observation of the effects on the cells. The frequently used electrodes are metal or carbon rods, but their risk of damaging tissue and their mechanical properties that are largely different from those of native tissues hinder further applications. Biocompatible polymer reinforced with conductive fillers emerges as a potential solution to fabricate the complex structure of the platform and electrode. Conductive polymer can be used as an ink in the extrusion-based printing method, thus enabling the fabrication of volumetric structures. The filler simultaneously alters the electrical and rheological properties of the ink; therefore, the amount of additional compound should be precisely determined regarding printability and conductivity. This review provides an overview on the rheology and conductivity change relative to the concentration of conductive fillers and the applications of printed electrodes. Next, we discuss the future potential use of a cell culture platform with electrodes from in vitro and in vivo perspectives.