Is polyazulene cytocompatible? The synthesis method matters

Polyazulene is an underrated conductive polymer characterized by its unique building blocks involving a fused-ring structure with an intrinsic dipole moment. It has been studied with a focus on the development of organic electronics, such as photovoltaic cells. However, the biological properties of polyazulene have not been reported to date. This study, the first of its kind, not only describes the properties of electrochemically and chemically synthesised polyazulenes and so-called true polyazulene, but also characterises their cytocompatibility. The physico-chemical properties of polyazulene powders and films were characterized by FTIR, Raman and UV-Vis spectroscopy, profilometry, scanning electron microscopy, voltammetry, van der Pauw conductivity measurement, and thermogravimetric analysis. Their cytocompatibility was explored using NIH/3T3 mouse embryonic fibroblasts, HaCaT human keratinocytes, and ES R1 mouse embryonic stem cells. Our results indicate that the tested polyazulenes exhibit an overall favourable short-term in vitro cytocompatibility with limitations varying according to the synthesis method and conditions. Electrochemically synthesized polyazulene formed continuous films with moderate conductivity under optimized deposition conditions, whereas chemically prepared films were inhomogeneous for reliable conductivity measurements. These differences in conductivity therefore primarily reflect variation in film morphology and deposition conditions rather than intrinsic bulk electronic properties of the respective polyazulene types.