Editorial Cite This: ACS Appl. Mater. Interfaces 2018, 10, 7521−7522
www.acsami.org
Ten Years of Polydopamine: Current Status and Future Directions his issue of ACS Applied Materials & Interfaces features a Forum entitled 10 Years of Polydopamine: Current Status and Future Directions. Polydopamine is the first surface chemistry that can functionalize surfaces of any materials and was introduced in 2007.1 For its simplicity in surface modifications and versatility in surface chemistry, polydopamine has emerged as one of the most powerful tools for broad applications in the biomedical, energy, consumer, industrial, military, and other sectors. Research topics in this forum reflect fundamentals and applications in broad areas: control of polydopamine formation kinetics, structural analysis of polydopamine, energy storage, bone regeneration, marine biofouling, photonic materials, drug release, mechanically robust hydrogels, cancer nanomedicine, reactive oxygen species (ROS) detoxification, and air/water interface films. This Forum features a collection of reviews and research articles authored by leaders in the field of polydopamine chemistry and materials science. It provides a useful collection of articles that allow readers to quickly gain an overview of the past, current, and future research trends, with a focus on applications. In “Boric Acid as an Efficient Agent for the control of Polydopamine Self-Assembly and Surface Properties”, Schneider et al. present a novel approach to control polymerization kinetics of dopamine. Addition of boric acid to the dopamine solution at a stoichiometric ratio of above three forms strong complex with catechol that can largely attenuate spontaneous oxidation of dopamine. This offers a convenient tool in production of a stable suspension of polydopamine as well as user-friendly control of polydopamine growth on solid surfaces. Alfieri’s group performed interesting polydopamine coating experiments. Surfaces can be functionalized by polydopamine layer when dopamine is dissolved, but the investigators found no polydopamine layer formation when 5,6-dihydroxyindole (DHI) is dissolved. It has been known that DHI is the essential intermediate for polydopamine coatings and DHI-based oligomers. Thus, this study importantly suggests that polydopamine films might have an alternative pathway to exhibit polydopamine’s unique surface coating capability. The authors claimed that conventional DHI-oligomers are not a responsible factor in coating. Rather, catecholquinone-amine species are important. Polydopamine coatings have also contributed to the enhancement of the energy storage device field. Jeong et al. reported about “Mussel-inspired Coating and Adhesion for Rechargeable Batteries: A Review”. Polydopamine can be a part of compartments such as electrode active materials and electrolyte additives. Through the uniform coating of polydopamine, a cell compartment can be protected from unwanted side reactions during battery operation. Furthermore, the electrolyte wettability of electrode materials can be largely increased by polydopamine coatings. Polydopamine can also serve as radical/side-product scavenging additives. By adjusting polydopamine coating, the rate and cycling performance of lithium ion battery systems are significantly improved. The
T
© 2018 American Chemical Society
aforementioned multiple effects derived by mussel-inspired polydopamine coating can be continuously considered as an effective and attractive materials for various energy storage devices. Kwon et al. showed that the adhesive properties of polydopamine are texture-dependent. This is the first report of changes in adhesive forces of polydopamine dependent upon surface morphology. Specifically, the adhesion ability was strongly related to root-mean-square (RMS) roughness and gradient of polydopamine layers, and the elasticity of interfacing materials. Importantly, the investigators performed adhesion experiments both in air and aqueous conditions. Marine biofouling, which increases hydrodynamic drag of submerged substrates, causes additional fuel consumption and, in turn, more greenhouse gas emission. Kim et al. reported a versatile method to reduce marine antifouling on various surfaces using mussel-inspired polydopamine coating and catechol conjugated poly(ethylene glycol) (PEG). Multilayered PEG films were fabricated (∼5 nm) with cross-linking of catechol moieties on both polydopamine coating and PEGcatechol through Fe3+-catechol coordination reactions. These films show great antifouling effect to diatom adhesion for 4 weeks. In “Electrospun Silk Fibroin Nanofibrous Scaffolds with Two-Stage Hydroxyapatite Functionalization for Enhancing the Osteogenic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells,” Ko et al. reported the development of a functional electrospun silk fibroin nanofibrous scaffold functionalized with hydroxyapatite particles. The hydroxyapatite particles were incorporated into silk fibroin scaffolds and then immobilized onto nanofibrous scaffolds via polydopamine coating chemistry. This hydroxyapatite-functionalization improved mechanical properties of scaffolds and was capable of providing bonelike microenvironments. This study indicates that the virtually any inorganic material surfaces can be functionalized to provide platforms for osteogenesis of stem cells. Kohri et al. reported fabrication of angle-independent, threedimensional colloidal photonic materials using poly(styrenedivinylbenzene) as the inner core onto which polydopamine was coated. These colloidal photonic materials display various colors ranging from blue, green, to red depending on the size of particles. The photonic structure is stable in solvent immersions because of polydopamine’s adhesive properties. The investigators demonstrated preparations of flexible fibers with microfluidic emulsification and solvent diffusion. Moreno-Villaécija et al. reported that bis-catechol monomers with different polarity (nordihydroguaiaretic acid (NDGA) and N′-(3,4-dihydroxybenzylidene)-3,4-dihydroxybenzohydrazide (BHZ)) were polymerized on surfaces mesoporous silica nanoparticles (MSNs). They formed stable and low-toxic Special Issue: 10 Years of Polydopamine: Current Status and Future Directions Published: March 7, 2018 7521
DOI: 10.1021/acsami.8b02929 ACS Appl. Mater. Interfaces 2018, 10, 7521−7522
ACS Applied Materials & Interfaces
Editorial
Polydopamine has been known to form a spontaneous air/ water interfacial film. Im et al. reported that catechol conjugated heparin and chitosan mixture also generates air/ water interfacial film. Furthermore, the investigators demonstrated that the film can be a useful protective biomaterial. The film is named “BiFACIAL (Biomimetic Freestanding Anisotropic Catechol-Interfaces with Asymmetrically Layered) film, which can serve as a versatile extracellular matrix substitute. We take this opportunity to thank all of the authors for contributing to the Forum, and to the reviewers who provided critical comments necessary to improve the papers before publication. It is hoped that this series of articles will foster new fundamental and applications-focused research in the field of polydopamine chemistry and materials science.
coatings that can be applied for drug release applications. Particularly, the catechol coating on the MSNs controlled the release rate of the loaded model drugs. Although most model drug molecules were released for 2 days from uncoated MSNs, the MSN coated with BHZ (RhB@MSN@pBHZ) exhibited a slow release of the payload. Another study related to drug-controlled releases from polydopamine layer was reported by Yang et al. entitled “Polydopamine Modified TiO2 Nanotube Arrays for LongTerm Controlled Elution of Bivalirudin and Improved Hemocompatibility”. A unique feature of this study is that the initial burst release of drugs was prevented by polydopamine cap coatings to TiO2 nanotubes. This study also demonstrated increases in loading capacity of drugs. The investigators used bivalirudin, an anticoagulant drug, to improve hemocompatibility of the TiO2 nanotubes. In “High Strength Astringent Hydrogels Using Protein as the Building Block for Physically Cross-linked Multi-Network”, Xu et al. utilized a polydopamine derivative called tannic acid (TA), which contains pyrogallol (2,3,4-trihydroxybenzene) moieties. The bovine serum albumin (BSA) and poly(vinyl alcohol) (PVA) solution formed noncovalent networks by a freeze−thawing method. Subsequently, TA was added to crosslink between BSAs and PVAs, establishing secondary noncovalent networks. TA-PVA/BSA composite hydrogel was a pure physical gel. However, the gel exhibited ultrahigh tensile strength up to ∼9.5 MPa. Moreover, its mechanical strength was further improved by prestretching. The use of polydopamine derivative demonstrated a new method to design hydrogels with high mechanical strength. Rahim’s research group reported interesting new method of surface chemistry using catechin, a derivative of dopamine. Catechin contains a catechol and other phenolic moieties that are abundant in green tea extract. Interestingly, the iron source is from rusted nails. The iron-mediated, catechol-Fe-catechol provide good platform for surface functionalization. The authors named the system a multiligand metal-phenolic network (MPN). The muliligand MPN exhibits lower Young’s modulus (∼50%), faster disassembly kinetics(∼50%), and stable dispersions compared to conventional MPN systems, giving insight into tuning the properties of MPNs with the choice of phenolic ligand and source of the metal. Mrówczyński reported a comprehensive overview of synthesis and applications of nanomaterials functionalized by polydopamine coatings for cancer therapy. The article summaries the latest advances in theranostic nanomaterials that are functionalized by polydopamine for imagings or drug loadings. First, the formation of polydopamine in forms of various nanostructures onto nanoparticles, hollow spheres, nanorods, or micelles is discussed. Subsequently, methods for polydopamine coating to incorporate targeting ligands or cancer drugs to achieve multifunctionality is comprehensively demonstrated. Finally, an emerging field of polydopamine for photothermal cancer therapy is introduced. Armada-Moreira et al. reported a novel application of polydopamine for preventing from ecitotoxicity and a neurodegenerative disease. Facile coating capability of polydopamine enables platinum nanoparticles to scavenge reactive oxygen species and ammonia that causes brain excitotoxicity and neurological disease. Microreactors loaded with platinum and assembled layers of polydopamine, poly(L-lysine), and poly(methacrylic acid) revealed potent therapeutic efficacy upon neuroblastoma.
■
Kirk S. Schanze, Editor in Chief Haeshin Lee, Forum guest editor Phillip B. Messersmith, Forum guest editor AUTHOR INFORMATION
ORCID
Kirk S. Schanze: 0000-0003-3342-4080 Haeshin Lee: 0000-0003-3961-9727 Phillip B. Messersmith: 0000-0002-1197-333X Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
■
REFERENCES
(1) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-inspired surface chemistry for multifunctional coatings. Science 2007, 318, 426−430.
7522
DOI: 10.1021/acsami.8b02929 ACS Appl. Mater. Interfaces 2018, 10, 7521−7522
