Physical surface and electromechanical properties of doped polypyrrole biomaterials

Conducting polymers doped with biomolecules (biodopants) are becoming more widely evaluated for use as biomaterials. The use of biodopants is intended to enhance the compatibility of the polymers, however their effect on the physical properties of the final composite material has generally been less of a consideration. Here, we have characterised the physical surface properties of polypyrrole substrates doped with extracellular matrix and non-biological molecules using Atomic Force Microscopy (AFM) and Electrochemical AFM (EC-AFM) techniques. The physical parameters of the differently doped films ranged between 5 and 32 nm for the RMS roughness, 30-1000 MPa for the Young's modulus, and 1.6-4.7% for the actuation strain. It was found that irrespective of whether the dopant was biologically derived, the physical properties tended to group together with films having either a low roughness, low modulus and high strain, or vice versa. When compared to our previous study, which investigated these polymers as potential biomaterials for supporting the growth and differentiation of skeletal muscle cells, these two groupings of the parameters correlated with the differing ability of the polypyrrole substrates to support the cells. Thus, in addition to the chemical advantage gained from using biodopants, the resulting physical properties of the polymer material should also be considered in their design as biomaterials for tissue engineering applications.