Clicked into Place: Biomimetic Copolymer Adhesive for Covalent Conjugation of Functionalities

Polydopamines (PDA) are a popular class of materials and promising candidates as adhesives for new fastening techniques. PDA layers can be formed on a wide range of substrates in various environments. Here, we present a novel method for functionalizing PDA-based copolymer films by using click chemistry. These copolymers adhere strongly to various surfaces and simultaneously have active groups that allow the attachment of functional groups. We discuss the coupling of two types of chitosan and a rhodamine B dye molecule to the alkyne groups of the copolymers by employing click reactions. Azidopropyl methacrylate (AzMA), methyl methacrylate (MMA), and dopamine methacrylamide (DOMA) are copolymerized and codeposited with (3-aminopropyl)triethoxysilane on silicon wafers, polyethylene (PE), and polytetrafluoroethylene (PTFE). AzMA provides the surfaces with azides for use in click reactions, MMA functions to control the polymer as a nonfunctional diluent, whereas DOMA provides adhesion, as well as cross-linking groups. After codeposition, the dyes are grafted to the copolymer to illustrate the ability of the films to link functional groups covalently. Fourier transform infrared spectroscopy confirms the successful click reaction in solution, and atomic force microscopy shows the surface morphologies following grafting. Fluorescence microscopy provides evidence of successful grafting. As an example of a possible application, layers exhibiting antifouling properties are prepared. Chitosan grafted to PE is tested for antifouling performance. These functionalized layers show nonspecific inhibition of protein adsorption. We find that chitosan can lower the adsorption of fluorescein-labeled bovine serum albumin (BSA) protein by more than 90% for the best performing fluorescein-labeled BSA protein and by more than 90% for the best-performing layer. These results demonstrate the viability of our PDA-based copolymers for surface functionalization through click chemistry grafting at challenging adhesion to surfaces.