The mussel living in the sea produces and secretes adhesive proteins, and attaches firmly to the solid surface even in strong waves and impacts. Mussel adhesive proteins (MAPs) are classified using the word fp, which is an abbreviation of Foot Protein, to distinguish between types and properties. The reason for this name is that the MAPs are secreted from the feet of the mussel. There are a total of six MAPs found so far. Among these, the types of MAPs directly involved in adhesion and coating were studied as fp-1, fp-3, and fp-5. Among them, fp-3 and fp-5 have been reported as proteins present at the adhesion interface that directly interacts with the surface when adhering to the underwater ground. In the amino acid composition of the MAPs, the DOPA ratio was 20 mol% for fp-3 and 28 mol% for fp-5. It is known that dopamine content is higher than that of other components such as glycine, asparagine, tryptophan and lysine, and the DOPA plays a major role in the adhesion of mussels. Unlike ordinary adhesives, the MAPs have strong adhesion in underwater environments, and are known to have strong adhesion on most surfaces, not only on polytetrafluoroethylene but also on metal, non-metal, and organic or inorganic substances. Therefore, studies on adhesion mechanisms of MAPs have been actively conducted. However, in order to obtain 1 gram of MAPs from commercial mussel in nature, 10,000 mussels are needed, moreover the price is too high. For this reason, application studies have been made on surface modification using polydopamine or polynorepinephrine, which mimic chemical functional groups involved in the adhesion of mussels, rather than natural extraction.
In this study, the PU nanofibers web prepared by electrospinning was coated with polydopamine to examine how the surface was modified. The PU nanofibers web is a nonwoven fabric in which nanofibers filaments of 500 nm or less can be laminated to form an ultra-thin and ultra-light weight material. Compared to other fibers, it is a material with a small diameter, a very high surface area to volume ratio, and a very high porosity. In addition to the advantages of the PU nanofibers web, polydopamine mimicking the mussel protein was coated in aqueous solution to improve functional properties of the PU nanofibers web. Firstly, to check whether the coating was well done, the SEM images were taken to observe the morphology of the surface and the pores. Secondly, the XPS analysis was used to confirm the functional groups of polyurethane and polydopamine. In addition, the water vapour permeability, air permeability and tensile properties were measured to investigate the changes in physical properties before and after polydopamine coating. In particular, the UV blocking performance and antimicrobial activity were further analyzed to examine whether polydopamine can play a role in improving the performance of PU nanofibers web. From the results, it was found that polydopamine is a desirable candidate as a functional finishing agent to improve the UV blocking performance and antimicrobial activity of the PU nanofibers web. Therefore, the PU nanofibers web coated with polydopamine is expected to be used as a substitute for high functional Gore-Tex membrane.