Smart Surface Chemistries of Conducting Polymers: for Guiding Cell Behavior in Polymeric Microsystems

In this thesis we investigate post-polymerization covalent modifications of poly(3,4-dioxythiophene (PEDOT)-type conducting polymers. The aim of the modifications is to gain specific control of the interaction between the material and living mammalian cells. The use of “click-chemistry” to modify an azide-modified PEDOT, poly(3,4-(1-azidomethylethylene)-dioxythiophene) (PEDOT-N₃), is studied in detail, and found to be a valuable approach. This is concluded, as we are able to obtain delicate control of cellular adhesion, by covalently attaching appropriate bio-functional molecules onto PEDOT-N₃ thin film substrates.
Complementing these findings, we introduce a novel technique for fabricating surface chemical gradients on PEDOT-N₃ substrates. The technique is based on applying “electro-click chemistry” to locally induce covalent modifications. Further supplementing these results, we develop a straightforward and in-expensive method for patterning conducting polymer thin films into microelectrodes, without losing control of the surface chemistry of the samples. On the contrary, the method provides direct control of the surface chemistry of both the fabricated micro-electrodes and the gaps between them. The method is based on locally removing PEDOTtype polymers to expose underlying non-conducting functional polymer substrates. Thereby, multifunctional substrates are obtained. By applying this method, we are able to fabricate allpolymer micro-systems with multiple types of localized functional (bio)-chemistries.
In the course of our studies, we find that PEDOT-N₃ thin films undergo a significant yet reversible swelling when exposed to dimethyl-sulfoxide (DMSO). This swelling is found to be of practical use for controlling the reaction density and depth. This, for example, enables the fabrication of dense poly-ethylene-glycol-coatings of the conducting polymer substrates. These coatings render the substrates resistant to protein adsorption. Hence, the choice of solvent is found to be a key parameter for achieving functional post-polymerization modifications of PEDOT-N₃.
The methods developed in this thesis are highly generic, and can therefore be applied for fabricating a diversity of microsystems based on conducting polymers, with multiple types of localized and highly bio-specific surfaces chemistries.