A biomimetic approach to organic semiconductor-cell interfaces

In order to engineer different surface anisotropies and topographies adequate to guide biological cells outgrowth on top of WGOFET devices [1] and to establish a controlled mechanism of ion percolation at the organic semiconductor/electrolyte interface we investigated two different biomimetic capping layer: a naturally-derived biopolymer such as keratin and an organic material, the T4-lysine (T4Lys). Biocompatibility and cellular outgrows on top of both biomimetic layers were already studied and reported in literature. [2][3] Electrode integration in keratin thin-film systems allows to study the biopolymer electrical properties for the first time. Reversible binding and extraction of ions from the film volume was observed using cyclic voltammetry outperformed inside an environmental chamber with controlled relative humidity monitored with a traceable hygrometer. The addition of biocompatible additive such as glutaraldehyde to the pristine chemical recipe leads to the insolubility of the keratin active layer which can be then exposed to highly humid environment such as cell culture environments. Instead, T4Lys were introduced as valuable multifunctional platforms for neural cells growth and interfacing due to neuron affinity promoted by lysine linkage. This biomimetic layer exhibits fluorescence combined to humidity-activated ionic conduction and electronic transport. The photogenerated charge in the T4Lys-based biomimetic layer can be used to modulate the cellular membrane potential to at least the action potential threshold, thus triggering neuronal firing. We already tested the cellular behavior on top of T4Lys using P3HT as reference material to tune the photoexcitation power. Cellular activity induced by low power photostimulation on top of the two organic materials showed a similar behavior in term of extracellular signals. To test the two proposed biomimetic layers, we elected n-type WGOFET platforms based on PDI derivatives, named PDIF-CN2 and PDI8-CN2. [4] Comparable state-of-the-art p-type semiconductors mobility values were achieved (~10-3 cm2/Vs). The strategy of applying a biometic capping layer transparent to ions on top of the exposed active layer organic material can offer stealth skills to cells together to the preservation of capacitive coupling at the semiconductor transistor channel/biological environment interface that control the drain-source currents. [1] S. Toffanin et al., J.Mater.Chem.B 1 (2013) 3850-3859; [2] Posati et al., Macromol. Mater. Eng. 2018, 303, 1700653; [3] Bonetti et al., Adv. Healthcare Mater. 2015, 4, 1190-1202; [4] X. Zhanet al., Adv.Mater.23 (2011) 268-284.