Structure‐Property Relationships in Catecholamine Coatings for Broad Surface Functionalization

ABSTRACT The attachment of mussels relies on adhesive proteins rich in 3,4‐dihydroxyphenyl‐L‐alanine (DOPA) residues, which bind to surfaces underwater. Their broad‐spectrum adhesive behavior has inspired the development of many underwater adhesive and coating strategies based on catecholamine polymers (such as polydopamine); however, their complex coating processes and underlying molecular mechanisms (aggregation, deposition, and polymerization) are still not fully understood. Here, we study a set of six catecholamine building blocks to elucidate fundamental structure‐property relationships in mussel‐inspired underwater coatings. This set of molecules produced coatings with significant differences in morphology, conformality, and exposed functional groups at the surface, which are rationalized based on varying key molecular structure parameters. Based on comprehensive spectroscopic and microscopic characterization, we identified norepinephrine as a well‐balanced catecholamine building block for underwater coatings, providing both excellent morphological homogeneity as well as abundant reactive surface groups available for further post‐functionalization. Leveraging this reactivity, we explored polynorepinephrine (PNE) coatings as surface primers for substrate‐agnostic organic and inorganic surface functionalization via solution‐based polymer grafting and electroless deposition metallization processes. This approach produced PNE‐based underwater coatings with custom properties and functionality, including tunable surface chemistry, electrical conductivity, and magnetization, demonstrated on different substrate materials and for applications in wetting, electronics, and microrobotics.