Bio-Sourced Organic Materials for Biodegradable Electronics

We study the biopigment eumelanin as a prototype of benign material for sustainable technologies in environmentally benign electronics. The building blocks of eumelanin have several competing polymerization sites. As a result, eumelanin is a chemically disordered (heterogeneous) macromolecule. The chemical disorder leads to polymorphic pi-pi stacked regions in the supramolecular structure, such that eumelanin exhibits structural (and consequently energetic) disorder, at least in the short range. Importantly, hierarchical development characterizes the formation of eumelanin-based materials. Ensembles of oligomers of the two DHI and DHICA building blocks hierarchically build up via π−π stacking with an interplane distance of about 3.4 Å and lateral extension of about 20 Å. Large particles, of 100-200 nm, form from further aggregation, through pi-pi stacking and edge-to-edge H-bonding interactions. Such large particles can be tentatively associated to granules observable by Transmission Electron Microscopy images obtained from Sepia Melanin samples.<br/>Several models have been proposed to describe the transport physics of eumelanin, from the amorphous semiconductor to the mixed ionic-electronic model. Further, transport has not been studied under the lens of eumelanin hierarchical structure and its implications when probed at different lengths.<br/>Such fundamental studies are certainly needed to exploit the full technological potential of eumelanin.<br/>In this contribution, we will focus on unexpected transport mechanisms in printed eumelanin films as affected by the presence of printing additives in ink formulations. Preliminary characterizations suggest unprecedented electrical response (conductivity) in printed eumelanin films , possibly attributable to percolation due to segregation.<br/>Results are promising for large area electronic applications based on abundant biocompatible and biodegradable materials and devices.