www.afm-journal.de FULL PAPER © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 www.MaterialsViews.com wileyonlinelibrary.com Damia Mawad,* Elise Stewart, David L. Officer, Tony Romeo, Pawel Wagner, Klaudia Wagner, and Gordon G. Wallace* 1. Introduction Conducting polymers (CPs) are impacting on a wide variety of bioapplications such as neural interfaces, [1] biosensors, [2] and as drug delivery, [3] bioerodible [4] or biodegradable platforms. [5] In particular, CPs have exciting potential as scaffolds for tissue engineering, typically applied in regenerative medicine applica- tions. [6] Regenerative medicine holds the promise of treating or curing a wide range of conditions such as burned skin, [7] dam- aged muscle tissue [8] and spinal cord injury. [9] The optimal physical and biological characteristics of a scaf- fold for tissue engineering include tissue-like mechanical prop- erties, a hydrated environment, biocompatibility (preferably A Single Component Conducting Polymer Hydrogel as a Scaffold for Tissue Engineering enhancing cell growth) and biodegrad- ability or bio-erodibility. Many of these characteristics are found in hydrogels rendering them excellent candidates for tissue scaffolds. [10,11] However, scaffolds for muscle and nerve cell regeneration would also benefit from electrical conduc- tivity, which has been shown to provide enhanced cell growth and differentia- tion. [12,13] Electrically conductive hydrogels (ECHs) could fulfill this role. Largely, how- ever, ECHs are polymeric composites fab- ricated from two components; a hydrogel component that provides a highly hydrated environment and a CP component that provides electrical conductivity. Gilmore et al. [14] were the first to report the fabrica- tion of such a composite, a material based on polypyrrole directly electropolymerised on a preformed polyacrylamide hydrogel. Since this proof of principle, ECHs have been the subject of growing attention and a variety of composite hydrogels have been developed. [15] Table 1 lists examples of ECHs com- posites for which conductivity has been reported to date. [16–24] While there is no defined level of conduc- tivity required for tissue engineering scaffolds, it can be seen that all these materials exhibit, at best, moderate conductivities. As stated by Bendrea et al., [25] despite the low conductivity, CP-based materials should still be able to pass the low currents that are potentially required for cell stimulation (in the range of 10 to 100 μA [26] ). Although these composite ECHs have been promoted as suitable tissue scaffolds, they have a series of limitations. The reported conductivities were not measured at physiological pH (7.4) or physiological temperature (37 °C); for instance, the con- ductivity of polyaniline (PANI) would significantly drop at physi- ological pH because it turns back to its neutral state. As the CP is typically physically entrapped in the hydrogel matrix, it can leach out as the hydrogel network swells [27] leading to a drop in the conductivity of the system as well as possible toxic side effects. In cases where the CP is ionically bound to the non-conductive polymeric component, for instance PANI polycation with the residual acrylic acid units in polyacrylamide, the ionic interaction dissociates as the hydrogel swells at physiological pH due to the neutralization of the PANI chains. [18] The development of a single component non-hybrid conduc- tive hydrogel could overcome the aforementioned limitations. Conducting polymers (CPs) have exciting potential as scaffolds for tissue engineering, typically applied in regenerative medicine applications. In particular, the electrical properties of CPs has been shown to enhance nerve and muscle cell growth and regeneration. Hydrogels are particularly suit- able candidates as scaffolds for tissue engineering because of their hydrated nature, their biocompatibility, and their tissue-like mechanical properties. This study reports the development of the first single component CP hydrogel that is shown to combine both electro-properties and hydrogel character- istics. Poly(3-thiopheneacetic acid) hydrogels were fabricated by covalently crosslinking the polymer with 1,1 ′-carbonyldiimidazole (CDI). Their swelling behavior was assessed and shown to display remarkable swelling capabilities (swelling ratios up to 850%). The mechanical properties of the networks were characterized as a function of the crosslinking density and were found to be comparable to those of muscle tissue. Hydrogels were found to be elec- troactive and conductive at physiological pH. Fibroblast and myoblast cells cultured on the hydrogel substrates were shown to adhere and proliferate. This is the first time that the potential of a single component CP hydrogel has been demonstrated for cell growth, opening the way for the development of new tissue engineering scaffolds. DOI: 10.1002/adfm.201102373 Dr. D. Mawad, Dr. E. Stewart, Prof. D. L. Officer, T. Romeo, Dr. P. Wagner, Dr. K. Wagner, Prof. G. G. Wallace ARC Centre of Excellence for Electromaterials Science Intelligent Polymer Research Institute University of Wollongong Wollongong, NSW, Australia E-mail: damia.mawad@unswalumni.com; gwallace@uow.edu.au Adv. Funct. Mater. 2012, DOI: 10.1002/adfm.201102373