Towards a biocompatible conductive network for cell sensing [electronic resource]
Keywords: Chemical Engineering.

In the recent decade, increasing numbers of electroactive materials incorporated into biomaterials have surfaced. Researchers believe that the mechanical and electronic properties of these electroactive materials can provide benefits to tissue scaffolds, stem cell differentiation, as well as stimulation of nerve and cardiac cells. We believe that incorporating these materials may also be used to investigate changes in the biomechanical and biophysical properties of cells. Investigating cell mechanics can provide better understanding of human disease on the cellular level. Thus, creating tools to characterize physical forces and mechanics of cells can not only help differentiate cancer cells from their healthy counterparts but also provide a greater understanding of cancer cell characteristics. Technologies that currently focus on measuring single cell traction forces include systems that are composed of either elastomeric pillars of polydimethylsiloxane (PDMS) or silicon nanowire forests. However, few have tried to combine electroactive materials with biomaterials for applications to study the mechanics of cells. Our study utilizes single-walled carbon nanotubes (SWNTs) as electronic materials for cell force sensors, investigates factors that affect biocompatibility of these materials, and provides a proof of concept device design that when optimized, could be used to investigate cell mechanics. SWNTs have shown great promise for use in organic electronic applications including thin film transistors, conducting electrodes, and biosensors. Additionally, previous studies found applications for SWNTs in bio-electronic devices such as drug delivery carriers and scaffolds for tissue engineering. While studies have shown the use of surfaces covalently functionalized with primary amines to selectively adsorb semiconducting SWNTs, these processes can be environmentally unstable and unreliable. Here we report the ability to modify substrates with physisorbed polymers as a rapid biomaterials-based approach for the formation of SWNT networks. Rapid surface modification is achieved by adsorption of poly(L-lysine) (PLL), which is frequently used in biological applications. We detail a rapid and facile method for depositing SWNTs suspended in N-methylpyrrolidinone onto various substrate materials using the amine-rich PLL. SWNT adsorption and alignment were characterized by atomic force microscopy while electrical properties were characterized by 2-terminal resistance measurements. To explore the biocompatibility of these SWNT networks, we investigated 3T3 fibroblast cell growth and the C2C12 myoblasts differentiation. After analyzing mitochondrial dehydrogenase activity and Live/Dead fluorescence cell staining, we found that SWNTs absorbed on PLL treated substrates exhibited enhanced biocompatibility compared to SWNT networks fabricated using alternative methods such as drop casting. These results suggest that PLL films can promote formation of biocompatible SWNT networks for biomedical applications. Furthermore, we have explored a number of device architectures that have evolved to improve device sensitivity. These include SWNT networks on PLL treated substrates, SWNT networks on polystyrene bead layers, and free-floating SWNT films on PDMS micropillars. A micromanipulator was used to mimic similar magnitudes of force that a cell would exert to obtain the device's electrical sensitivity. With further device optimization, we believe it will be possible to utilize these devices to translate the cell forces applied on the conductive layer into changes in electrical signal, therefore providing a device architecture that may have applications in studying cell mechanics and cancer cell diagnostics.