Bioerodible Polypyrrole
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Bioerodible Polypyrrole Alexander Zelikin1, Venkatram Shastri1,*, David Lynn1, Jian Farhadi2, Ivan Martin2, Robert Langer1 1 Department of Chemical Engineering, Massachusetts Institute of Technology, 45 Carleton St., E25-342, Cambridge, MA, 02139, USA, 2 Department of Surgery, Research Division, Kantonsspital Basel, Basel, Switzerland 4031 * Corresponding author: [email protected] ABSTRACT Conductive polymers such as polypyrrole (Ppy) are potentially useful as an active interface for altering cellular processes and function. Their utilization in medically related applications however have been substantially held back by their non-degradable nature. Herein we report a novel approach to creation of bioerodible polypyrroles via modification of pyrrole beta-carbon with an ionizable moiety. It has been shown that the erosion rate of acid-bearing derivative of polypyrrole increases with pH, which is consistent with the pH dependent ionization of carboxylic acid group. The novel paradigm proposed for the creation of bioerodible polypyrroles allows for simple and efficient control over the erosion rate of the substrate independent of the polymer chain length, via the choice of the terminal ionizable group and its concentration along the polymer backbone. INTRODUCTION Since the discovery that doped polyacetylene can exhibit electrical conductivity as high as copper [1], several polymers have been shown to exhibit electrical conductivity under appropriate doped conditions. Among these the poly(heterocyclics) namely poly(thiophene) and poly(pyrrole) (Ppy) have been explored extensively in various biomedical applications ranging from biosensors [2-4] and gene chips to substrates for cell culture [5]. In recent years it has been shown that electrical stimulation of cells adhered to Ppy substrate can enhance cell differentiation [6,7]. Ppy has also been shown to possess excellent long-term in vivo biocompatibility in rats [6]. The utility of Ppy in biomedical applications will therefore significantly benefit from the development of bioerodible analogs. One approach to the creation of a biodegradable polymer would be to link oligomers of Ppy (4-10 repeat units) via hydrolyzable linkages such as ester, amide or anhydride. This approach has been shown to be feasible in the polythiophene system [9, 10]. Our attempts to apply analogous synthetic strategy to pyrrole derivatives were met with failure due to the side reactions accompanying the pyrrole chemistry. It occurred to us that an alternative to degradation via hydrolysis of the polymer backbone could be erosion of the polymer via solubilization of conductive oligomers as shown schematically in Scheme 1. We further hypothesized that this could be achieved by introducing side chains bearing an ionizable group such as carboxylic acid in the pyrrole ring via the βposition. A key advantage of this novel paradigm is that the erosion behavior of the polymer may be controlled by two different approaches namely: (1) copolymerizing of derivatized pyrrole GG2.7.1
with underivatized
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