Unraveling the influence of substrate on the growth rate, morphology and covalent structure of surface adherent polydopamine films

Polydopamine (PDA), also known as synthetic melanin, is widely used as a biomimetic anchoring layer for the modification of various solid substrates. PDA is utilized for a wide range of biomedical, sensing and tribological applications, even though the polymer's precise covalent structure has not been completely revealed yet. Even more, it is not evident to which extent the chemical nature of the substrate, on which the layer is formed, influences and predetermines the covalent structure of resulting PDA. In this contribution, we have studied the growth of PDA using various surface-sensitive techniques such as spectroscopic ellipsometry, atomic force microscopy and X-ray photoelectron spectroscopy. We supplemented grazing angle attenuated total reflection FTIR spectroscopy with multivariate statistical analysis to further gain analytical power. We have particularly focused on the effects of polymerization time and substrate on the PDA structure. We found notable differences in the chemical composition of PDA formed on gold and on surfaces terminated with oxides/reactive hydroxides such as silicon and N-dopped-TiO2 in the early stages of the layer formation. At the later stages of layer formation, a merely unified chemical structure was observed independently on the type of substrate.

Automated summary

This study investigated the growth of polydopamine on different substrates and found that the chemical nature of the substrate influences the structure of the resulting polydopamine in the early stages of layer formation. However, a unified chemical structure was observed at later stages of layer formation regardless of the substrate type. Various surface-sensitive techniques were utilized in this research to analyze the effects of polymerization time and substrate on polydopamine structure.