Almost ten years ago, Lee et al. [13] formulated a universal adhesive coating based on observation of the strong attachment by mussels through their byssal threads to virtually all types of inorganic and organic surfaces. The amino acid compositions of the mussel foot proteins that generate the attachment are rich in catechol and amine groups. [13][14][15] These groups associate under marine conditions, forming strong covalent and noncovalent interactions with substrates. [13] This led to the idea that both catechol and amine groups were crucial in forming robust, wide spectrum adhesive nanolayers [16,17] and consequently dopamine was conceived as a powerful building block for spontaneous deposition of thin polymer films. The dopamine monomer is deposited onto unadulterated surfaces through self-assembly and oxidative cross-linking from mild pH aqueous solution in a rapid reaction. This results in a durable, nanoscale, conformal, and hydrophilic coating that can be readily modified to introduce specific surface chemistries for a particular application. [18][19][20][21][22] These bioinspired, polydopamine materials are chemically and structurally indistinguishable from eumelanins found in the human body, [23,24] providing excellent biocompatibility. Additionally, polydopamine has broad electromagnetic absorption and excellent photothermal energy conversion [25] as well as having ionic-electronic hybrid conductivity. [26] Along with the excellent coating performance, these properties provide a vast array of potential applications for polydopamine materials.In this article, we explain what is known about polydopamine and related catecholamine coatings; their formation, the adhesion mechanism, and their physicochemical properties and we also review the applications of these materials (Figure 1). Since 2011, there have been a number of reviews on this subject matter, including general reviews on the physicochemical properties of polydopamine coatings [11,20,[27][28][29] and their applications. [20,27,30] There are also a number of more specific reviews on the chemical synthesis and modulation of polycatecholamine coatings, [31] the biomedical applications of these coatings, [8,[32][33][34] their electronic properties, [26,35] the use of polydopamine to make films at fluid interfaces, [36] in hierarchically constructed particles, [33] and capsules, [30] exploitation of polycatecholamine coatings in membrane filtration, [37] polydopamine-derived carbon materials, [38] and the use of coordination chemistry in catechol-based materials. [39] Nonetheless, this area of research is growing so rapidly [25,27] that many recent Polydopamine and related polycatecholamines can be easily deposited onto almost any surface from mild, aqueous solution. This results in durable, nanoscale coatings that exhibit high biocompatibility and have useful chemical and electronic properties. Additionally, these materials can be readily chemically and physically modified, and consequently, they are used extensively for surface modification. This ...
