Tunable Interface of Polymeric Composite of Electroactive P3HT-MWCNT Thin Film for Bioelectronics Applications

One of the main challenges in bioelectronics concerns the development of materials able to respond to external stimuli and that are compatible with excitable tissues. In the last decades, conductive polymers (CPs) have been widely studied and developed as electroactive materials for applications in interfacing with biological systems. Their conductive properties allow cells or tissues growth upon stimulation, and their “soft” nature allows to form a better biotic-abiotic interface and reduce the mechanical mismatch between material and cells thanks to the elasticity of polymeric films that is similar to biological tissues [1]. CPs’ physical and iontronic-electronic properties can be optimized through the formation of composites enriched with carbon nanotubes or graphene in order to improve electron transport capacity, decrease impedance and increase flexibility. Their biocompatibility can be improved using functionalization methods with biologically active molecules [2] even if the influence of blending agents is still under investigation. The precise control of CP films nano-topography may have interesting effects for biointerfacing and improving the cell-chip coupling for cell activity recording and stimulation, acting on protein adsorption and cell adhesion.<br/>In this work, we report on how to obtain stable electroactive nanocomposite dispersion using semiconducting regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT), with different percentages in weight of multi-walled carbon nanotubes (MWCNT) and how to deposit to form homogeneous thin films. Their morphologies have been investigated by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the attention has been focused on the “cushion” effect due to the presence of the filler in the polymeric matrix that allow an interesting modification in mechanical properties (Young’s Modulus), analyzed by nanoindentation with atomic force microscopy (AFM), and the formation of a “softer” interface. Considering the central role of extracellular matrix protein in cell adhesion, their interactions at the interface with our systems were investigated by means of quartz crystal microbalance with dissipation monitoring (QCM-D). Noteworthy, it has been found that thanks to the larger available surface area of the blend thin film that act like a sponge, proteins are adsorbed in a very different way with respect to the bare semiconducting P3HT. Indeed, both the adsorption kinetics and the adsorbed mass are increased for each extracellular matrix proteins. The biocompatibility of the systems with different cell lines has been investigated as well as the effect on cell metabolism. Moreover, the effect of the systems on the variation of the distance between cell and electrode has been analyzed by focused ion beam - scanning electron microscopy (FIB-SEM). The realization of this nanostructured bioelectronic interface represents an example of 2.5D cell culture and promotes the optimization of the cell-chip coupling by tuning the cleft between the membrane of the cell and the electrode, also acting on the formation of the extracellular matrix protein coating that helps cells attach to, and communicate with, nearby cells, and plays an important role in cell growth, cell movement, and other cell functions.<br/><br/>[1] Malliaras, G. Biochimica et Biophysica Acta 1830, (2013), 4286–4287.<br/>[2] Scarpa, G. et al. Macromol. Biosci. 10, (2010), 378–383.