The mimicry of the underwater mussel adhesion strategy for the development of innovative and versatile dip-coating technologies is exemplified by the introduction of polydopamine (PDA) as a highly adhesive biomaterial for surface functionalization and coating, incorporating the key catechol and amine functionalities of byssal proteins and produced by the oxidative polymerization of dopamine under alkaline conditions.1 Despite unabated interest and an ever expanding use for various surface functionalization applications, PDA-based technologies suffer from some limitations that have prompted intense studies toward novel mussel-inspired surface chemistry.2 They are related to: a) the intrinsic toxicity of the precursor dopamine; b) the use of an alkaline pH; c) the need for high dopamine concentrations (10 mM), and d) difficulties to control film thickness and properties due to the slow kinetics of autoxidation.3 A possible means of bypassing limitations inherent to the autoxidation protocol relies on use of enzymes like tyrosinase, which can be exploited to modulate catecholamine oxidation at pH values around neutrality, and were thus proposed as a practical and convenient ways of obtaining nanometer-thick and uniform films with diverse functionalities.4,5
Herein, we report the tyrosinase-catalyzed polymerization of tyramine as a mild, versatile and efficient procedure for the development of adhesive PDA-type films (ψ-PDA) that could be obtained at neutral pH (i.e. 6.8) and at much lower substrate concentration (e.g. 1 mM) compared to the standard autoxidative PDA coating protocol (typically 10 mM of dopamine).6 ψ-PDA films display structural and physicochemical properties similar to those of PDA films and similar, or even better, antioxidant activity. Finally, the possibility of using tyramine together with confined tyrosinase to achieve site-specific polymerization and/or film deposition is assessed against dopamine. The rationale of the experiments is to prevent the uncontrolled autoxidative deposition of black precipitate, a major drawback of PDA coating technology which may interfere with specific applications. ψ-PDA deposition by tyrosinase-catalyzed tyramine oxidation is thus proposed as a controllable and low-waste technology for selective surface functionalization and coating or for clean eumelanin particle production.
References
[1] Ryu J.H.; Messersnith P.B.; Lee H. ACS Appl. Mater. Interfaces, 2018, 10, 7523-7540.
[2] Lee B.P.; Messersmith P.B.; Israelachvili J.N.; Waite J.H. Annu. Rev. Mater. Res., 41 (2011), 99-132.
[3] Ball V.; Del Frari D.; Toniazzo V.; Runch D. J. Colloid Interface Sci., 386 (2012), 366-372.
[4] Kim J. Y.; Kim, W.I.; Youn W.; Seo J.; Kim B.J.; Lee J.K.; Choi I.S. Nanoscale, 10 (2018), 13351-13355.
[5] Zhong Q.Z.; Richardson J.J.; Li S.; Zhang W.; Ju Y.; Li J.; Pan S.; Chen J.; Caruso F. Angew. Chem. Int. Ed.2019 10.1002/anie.201913509.
[6] Alfieri M.L.; Panzella L.; Youri A.; Napolitano A.; Ball V.; d’Ischia M. Int. J. Mol. Sci. 2020, 21, 4873.
