molecules Review Gaseous Plastron on Natural and Biomimetic Surfaces for Resisting Marine Biofouling Yujie Cai 1,2, Wei Bing 1,2,*, Chen Chen 3 and Zhaowei Chen 3,* 1 School of Chemistry and Life Science, Changchun University of Technology, 2055 Yanan Street, Changchun 130012, China; [email protected] 2 Advanced Institute of Materials Science, Changchun University of Technology, 2055 Yanan Street, Changchun 130012, China 3 Institute of Food Safety and Environment Monitoring, College of Chemistry, Fuzhou University, Fuzhou 350108, China; [email protected] * Correspondence: [email protected] (W.B.); [email protected] (Z.C.) Abstract: In recent years, various biomimetic materials capable of forming gaseous plastron on their surfaces have been fabricated and widely used in various disciplines and fields. In particular, on submerged surfaces, gaseous plastron has been widely studied for antifouling applications due to its ecological and economic advantages. Gaseous plastron can be formed on the surfaces of various natural living things, including plants, insects, and animals. Gaseous plastron has shown inherent anti-biofouling properties, which has inspired the development of novel theories and strategies toward resisting biofouling formation on different surfaces. In this review, we focused on the research progress of gaseous plastron and its antifouling applications. Keywords: antifouling; gaseous plastron; super-hydrophobic; biomimetic; antibacterial Citation: Cai, Y.; Bing, W.; Chen, C.; Chen, Z. Gaseous Plastron on Natural 1. Introduction and Biomimetic Surfaces for Resisting Marine Biofouling. Molecules 2021, 26, Marine biofouling is widespread in marine environments and the most serious issue 2592. https://doi.org/10.3390/ in the shipping industry [1]. Biofouling generally refers to an undesirable colonization of molecules26092592 organisms on the surface of underwater structures. It begins within minutes of soaking and goes through several stages, including bacterial adaptation, biofilm formation [2], Academic Editor: Teofil Jesionowski and the settlement of larger organisms. Fouling organisms refer to the community of microorganisms, plants, and animals attached to the bottoms of ships, buoys, and all indus- Received: 15 March 2021 trial installations [3]. Defilade organisms are complex communities composed mainly of Accepted: 26 April 2021 stationary organisms, with numerous species, including bacteria, attached diatoms [4], and Published: 29 April 2021 many large algae, as well as a variety of phyla, from protozoa to vertebrates. Subsequently, more complex macroscopic organisms appear on the immersed surfaces, for example, Publisher’s Note: MDPI stays neutral mussels [5], barnacles [6], tubeworms [7], and so on. There are more than 2,000 species of with regard to jurisdictional claims in fouling organisms in the sea environment, the most common of which are algae, hydroids, published maps and institutional affil- barnacles, and oysters. Their adhesion has caused serious harm to marine facilities and iations. ships, and greatly restricts the development of the marine economy. Marine biofouling generally leads to increased sailing resistance and fuel consump- tion, blocking of ocean transport pipelines, and disabled ocean instruments. Efficient antifouling strategies are critical to maintaining operational performance [8], reducing Copyright: © 2021 by the authors. fuel consumption [9] and cleaning costs [10], and decreasing the transfer risk of intrusive Licensee MDPI, Basel, Switzerland. marine species [11]. A series of antifouling technologies have been explored by changing This article is an open access article surface roughness, wettability, and electrical properties, or imitating the natural defenses distributed under the terms and of marine organisms. At present, antifouling strategies mainly focus on non-toxic and conditions of the Creative Commons environmentally friendly technologies [12–14]. Non-toxic antifouling strategies that aim Attribution (CC BY) license (https:// to develop low-adhesion and non-adhesion surfaces are more encouraged, as they exert creativecommons.org/licenses/by/ little environmental risk [12]. As a new non-toxic antifouling strategy, gaseous plastron has 4.0/). Molecules 2021, 26, 2592. https://doi.org/10.3390/molecules26092592 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 16 Molecules 2021, 26, 2592 2 of 16 environmental risk [12]. As a new non-toxic antifouling strategy, gaseous plastron has achievedachieved certaincertain successsuccess withwith aa broad-spectrumbroad-spectrum and and long-lasting long-lasting antifouling antifouling effect effect (Figure (Figure 11).). GaseousGaseous plastron,plastron, alsoalso knownknown asas aa cushioncushion ofof air,air, isis aa thinthin filmfilm ofof airair betweenbetween substratesubstrate andand liquid.liquid. FigureFigure 1.1. Schematic diagram diagram showing showing the the mechanism mechanism responsible responsible for for the the antifouling antifouling of ofgaseous gaseous plastron.plastron. TheThe persistentpersistent underwaterunderwater airair layerlayer hashas evolvedevolved inin manymany aquaticaquatic andand semi-aquaticsemi-aquatic organismsorganisms toto adaptadapt toto underwaterunderwater dragdrag reductionreduction oror underwaterunderwater respiration.respiration. FiveFive criteriacriteria areare requiredrequired for for long-term long-term underwater underwater air retentionair retention [9], namely, [9], namely, hair-like hair structures-like structures [15,16], hydrophobic[15,16], hydrophobic chemistry chemistry [17,18], undercuts,[17,18], undercuts, elasticity elasticity of the structure, of the structure and heterogeneous, and hetero- hydrophilicgeneous hydrophilic tips on superhydrophobic tips on superhydrophobic surface [surface19]. Attachment [19]. Attachment point theory point theory describes de- surfacescribes surface interactions interactions based on based the relativeon the relative contact contact surface surface area [20 area,21] [20 of organisms,21] of organisms at the water/surfaceat the water/surface interface, interface, where the where size differencethe size difference determines determines the strength the of strength the attachment of the point.attachment In contrast point. to In the contrast fluid/solid to the interface,fluid/solid the interface, liquid/air the interface liquid/air does interface not attract does thenot adsorptionattract the adsorption of marine organisms of marine regardlessorganisms of regardless their size of [22 their]. Therefore, size [22]. creating Therefore, biomimetic creating surfacesbiomimetic that surfaces maintain that trapped maintain interfacial trapped air interfacial could lead air to ancould alternative lead to classan alternative of antifouling class coating.of antifouling The earliest coating. research The earliest on gaseous research plastron on gaseous for antifoulingplastron for dates antifouling back to dates a patent back into 1937a patent [23]. in The 1937 effective [23]. The maintenance effective maintenance of gaseous plastronof gaseous is anplastron important is an factor important that determinesfactor that determines its practical its application. practical application. In this review, In this we review will discuss, we will the discuss factors the affecting factors itsaffecting stability, its andstability, how and to obtain how to stable obtain gaseous stable gaseous plastron plastron by virtue by of virtue current of current advanced ad- technologies.vanced technolog Dueies to. theDue advantages to the advantages of broad-spectrum of broad-spectrum and ecological and ecological interest, gaseousinterest, plastron has been gradually used in the field of marine antifouling and preventing bacterial gaseous plastron has been gradually used in the field of marine antifouling and prevent- adhesion, as shown in Figure1. In this review, some natural examples of gaseous plastron ing bacterial adhesion, as shown in Figure 1. In this review, some natural examples of are discussed in detail to explain how organisms can skillfully use bubbles to survive and gaseous plastron are discussed in detail to explain how organisms can skillfully use bub- adapt to the environment from the macro- to the nano- scale, and how we can learn from bles to survive and adapt to the environment from the macro- to the nano- scale, and how such natural processes to design biomimetic artificial antifouling interfaces with similar we can learn from such natural processes to design biomimetic artificial antifouling inter- characteristics via tuning the microstructures and chemical compositions. faces with similar characteristics via tuning the microstructures and chemical composi- 2.tions. Factors Influencing the Formation and Maintenance of Gaseous Plastron When a superhydrophobic coating is immersed in water, it can maintain a layer 2. Factors Influencing the Formation and Maintenance of Gaseous Plastron of trapped air to separate the solid from the surrounding liquid. This air layer, also knownWhen as gaseous a superhydrophobic plastron, has showncoating great is immersed potency inin continuedwater, it can antifouling, maintain corrosiona layer of resistance,trapped air and to separate drag reduction. the solid The from formation the surrounding and durability liquid. of This gaseous air layer, plastron also is known deter- minedas gaseous by many plastron, factors, has including shown thegreat surface potency properties in contin likeued