Cell attachment functionality of bioactive conducting polymers for neural interfaces Rylie A. Green, Nigel H. Lovell, Laura A. Poole-Warren * Graduate School of Biomedical Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia article info Article history: Received 2 February 2009 Accepted 18 March 2009 Available online 16 April 2009 Keywords: Neural interfaces Conducting polymers Bioactivity Laminin peptides abstract Bioactive coatings for neural electrodes that are tailored for cell interactions have the potential to produce superior implants with improved charge transfer capabilities. In this study synthetically produced anionically modified laminin peptides DEDEDYFQRYLI and DCDPGYIGSR were used to dope poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum (Pt) electrodes. Performance of peptide doped films was compared to conventional polymer PEDOT/paratoluene sulfonate (pTS) films using SEM, XPS, cyclic voltammetry, impedance spectroscopy, mechanical hardness and adherence. Bioactivity of incorporated peptides and their affect on cell growth was assessed using a PC12 neurite outgrowth assay. It was demonstrated that large peptide dopants produced softer PEDOT films with a minimal decrease in electrochemical stability, compared to the conventional dopant, pTS. Cell studies revealed that the YFQRYLI ligand retained neurite outgrowth bioactivity when DEDEDYFQRYLI was used as a dopant, but the effect was strongly dependant on initial cell attachment. Alternate peptide dopant, DCDPGYIGSR was found to impart superior cell attachment properties when compared to DEDE- DYFQRYLI, but attachment on both peptide doped polymers could be enhanced by coating with whole native laminin. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Modification of conventional platinum (Pt), gold or iridium oxide electrodes with conducting polymer coatings has the potential to significantly improve the long-term performance of neural implants including the cochlear implant, vision prosthesis, neural regeneration devices and neural recording electrodes [1,2]. Conventional electrode materials are typically fabricated with smooth surfaces that are not conducive to tissue integration. As a result the interface between a metal electrode and neural tissue is associated with a significant fluid gap through which the electrical signal must be transduced. This distance is critical in determining the current amplitude required to activate the neural tissue and the quality of the perceived signal [3,4]. Conducting polymers such as polypyrrole (PPy) and poly- thiophene derivative poly(3,4-ethylene dioxythiophene) (PEDOT) have been used by several research groups to enhance the prop- erties of neural interfaces [5–9]. Conducting polymer coatings have been shown to improve the charge transfer characteristics of conventional metal electrodes and biological assays have shown that cells preferentially adhere to coated electrodes [5,10,11]. The biological interaction has the potential to eliminate the fluid gap through intimate contact between the tissue and electrode. It is hypothesised that controlled interaction between the conducting polymer and surrounding tissue can be achieved through the incorporation of biological molecules tailored to produce a response from specific cell types [2]. Extracellular matrix molecules are known to support cell attach- ment and growth when incorporated into conducting polymers or used as a coating. Molecules that have been implicated in these roles for cell regeneration include laminin, chondroitin sulfates, other proteoglycans and hyaluronic acid (HA) [12–14]. Laminin, a multido- main basement membrane glycoprotein is known to provide a permissive substrate that binds to cell surface receptors and also can function to stimulate neurite extension [15,16]. However, the use of the full multidomain protein or even a single domain bears some disadvantages including the need for isolation and purification, the risk of degradation via immune attack and proteolysis [17]. Only specific sections of the laminin molecule contain the required receptors for cell adherence and studies have shown that partial functions of the large laminin molecule can be imitated by smaller fragmental components with specific functional binding [18]. Inves- tigations by Huber et al. have found that synthetically prepared peptides have a greater stability than native laminin [19]. * Corresponding author. E-mail address: l.poolewarren@unsw.edu.au (L.A. Poole-Warren). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2009.03.043 Biomaterials 30 (2009) 3637–3644