Pentaerythritol-DOPA (PE-DOPA): A tetra-catechol derivative for versatile hydrophilic nanocoatings

Pentaerythritol (PE) was modified with 3,4-dihydroxy-L-phenylalanine (L-DOPA) to produce a tetra(catecholamine) tetra-ester derivative (PE-DOPA). Subsequently, PE-DOPA was used to dip-coat glass, stainless steel (SS) and various plastics under alkaline conditions and formed a poly(PE-DOPA) surface coating ranging in thickness between 1.0–3.0 nm on glass and 9.0–12.0 nm on SS, as estimated by X-ray photoelectron spectroscopy (XPS). The as-coated poly(PE-DOPA) showed increased hydrophilicity compared to the bare substrate, as demonstrated by water contact angle (WCA) measurements, whilst subsequent thermal annealing of poly(PE-DOPA) coatings on glass and SS at 120 °C for 6 h reversed the as-coated hydrophilicity through an indole ring formation reaction. The molecular structure of the poly(PE-DOPA) coating was investigated by adsorption studies, suggesting monolayer formation on glass and multilayer on SS. Surface modification of plastic substrates (e.g. Nylon, polyester, polyolefines, PTFE) was also confirmed at the molecular level by XPS and at bulk properties level by WCA. PTFE was the only plastic substrate that didn't show any altering of its bulk hydrophilicity. Lastly, the fabrication of multilayer structures where poly(PE-DOPA) was coated by bovine serum albumin (BSA) allowed for a first assessment of poly(PE-DOPA) affinity for BSA and the associated possibility of tailoring poly(PE-DOPA) response.