Quantifying fibronectin adhesion with nanoscale spatial resolution on glycosaminoglycan doped polypyrrole using Atomic Force Microscopy

Background: The interaction of ECM proteins is critical in determining the performance of materials used in biomedical applications such as tissue regeneration, implantable bionics and biosensing. Methods: To improve our understanding of ECM protein-conducting polymer interactions, we have used Atomic Force Microscopy (AFM) to elucidate the interactions of fibronectin (FN) on polypyrrole (PPy) doped with different glycosaminoglycans. Results: We were able to classify four main types of FN interactions, including those related to 1) non-specific adhesion, 2) protein unfolding and subsequent unbinding from the surface, 3) desorption and 4) interactions with no adhesion. FN adhesion on PPy/hyaluronic acid showed a significantly lower density of surface adhesion with the adhesion restricted to nodule structures, as opposed to their peripheries, of the polymer morphology. In contrast, PPy/chondroitin sulfate showed a significantly higher density of surface adhesion to the point where the distribution of adhesion effectively masked the topography. Through conductive AFM imaging, we found that the conductive regions correlated with regions of FN adhesion. Conclusions: Given that the conductivity requires doping of the polymer, these findings suggest that FN adhesion is mediated by interactions with chondroitin sulfate and hyaluronic add at the polymer surface and may be indicative of specific interactions due to contributions from electrostatic attraction between the FN and sulfate/anionic groups of the dopants. General significance: This study demonstrates the ability of AFM to resolve the protein-conducting polymer interactions at the molecular and nanoscale level, which will be important for interfacing these polymer materials with biological systems. This article is part of a Special Issue entitled Organic Bioelectronics - Novel Applications in Biomedicine. (C) 2013 Elsevier B.V. All rights reserved.