Recent Developments in Biomimetic Antifouling Materials: A Review

Abstract

The term 'biomimetic' might be applied to any material or process that in some way reproduces, mimics, or is otherwise inspired by nature. Also variously termed bionic, bioinspired, biological design, or even green design, the idea of adapting or taking inspiration from a natural solution to solve a modern engineering problem has been of scientific interest since it was first proposed in the 1960s. Since then, the concept that natural materials and nature can provide inspiration for incredible breakthroughs and developments in terms of new technologies and entirely new approaches to solving technological problems has become widely accepted. This is very much evident in the fields of materials science, surface science, and coatings. In this review, we survey recent developments (primarily those within the last decade) in biomimetic approaches to antifouling, self-cleaning, or anti-biofilm technologies. We find that this field continues to mature, and emerging novel, biomimetic technologies are present at multiple stages in the development pipeline, with some becoming commercially available. However, we also note that the rate of commercialization of these technologies appears slow compared to the significant research output within the field.

Keywords: antifouling; biofilm; biofouling; bioinspired; biomimetic; self-cleaning.

Figure 1

(a) An analysis of articles that feature biomimetic or bioinspired antifouling research published per year for the years 2000 until end of 2019 and (b) breakdown of source journals by primary field. The search was conducted in April 2020 using both SCOPUS and Web of Science, with the criteria “(biomim * OR bioinsp *) AND (antifoul * OR biofoul *)”. This search shows the increase in the number of publications on biomimetics and antifouling research from a low baseline in 2000 to a greater publication rate in recent years, with almost half of all results returned having been published in the past four years (2016–2019).

Figure 2

A generalised overview of some of the antifouling strategies that can involve biomimetic aspects or can be inspired by analogous strategies in the natural world. Different strategies can of course be combined, and indeed in many cases can perhaps lead to more efficient or effective fouling control.

Figure 3

(a) An example of an individual marine mussel (centre, Mytilus sp.) attached and anchored to a substrate with surrounding (byssus) threads (arrowed, A, top left), and (b) a backscattered electron micrograph showing an individual byssus thread in detail (arrowed, A: scale bar = 1 mm) and the accompanying adhesive attachment pad (dark approximately circular region within rectangle, B). In this case, the byssus thread is attached to another bivalve species with a surface texture (the vertical lines within image (b)). The extent of the adhesive spreading of the attachment pad is of interest, and the strength of attachment of mussel species makes them particularly prolific biofouling organisms in aquatic environments worldwide. Image (a) by Brocken Inaglory from Wikimedia Commons, licensed under CC BY-SA 3.0.

Figure 4

Crustaceans continue to be a source of inspiration in the search for new antifouling strategies and other technologies such as nanostructured composites. Here, electron microscopy images of the surface of the carapace of the marine decapod crustacean Cancer pagurus (a), also showing laminar structure in cross-section (c, scale bar = 200 µm) show the presence of micro-topographic features presented to any colonising organisms (epibionts). Many of the upper and under surfaces of C. pagurus are covered in these micro-scale spines (microtrichia), approximately some 5 to 20 microns in length (d, scale bar = 20 µm). These surfaces do sustain some colonisation (in this case, benthic diatoms species) (b, scale bar = 50 µm); however, the role and extent of any natural antifouling provided by these surface structures against larger epibionts (particularly other calcareous colonising species such as polychaetes) are not yet fully understood. Image (a) by Matthieu Sontag from Wikimedia Commons, licensed under CC BY-SA 4.0.

Figure 5

The shape and structure of dermal denticles from the small catshark, Scyliorhinus canicula (examined using electron microscopy). ((a,b) scale bar = 500 µm) Variations in the shape of dermal denticles observed from skin samples in different body locations in one individual specimen of this species. Similar structures to the microscopic ridges on the surface of individual denticles (as indicated by arrows in (b), scale bar = 500 µm) are thought to be responsible for drag reduction in sharks. It is interesting to observe the degree of overlap between denticles (inset (c), scale bar = 500 µm) and how the denticles extend and completely envelope the shark, including the trailing edges of fin surfaces (d), scale bar = 1 m)m. The role these structures play in both drag reduction and in antifouling is still of keen research interest. An interesting observation from close examination of denticle surfaces in S. canicula is that the upper surface of individual denticles are often scarred and grooved with microscopic ridges (e), scale bar = 10 µm) perhaps from contact with other sharks or other behaviours that remove attached organisms, although fouling may be observed in some regions (f) scale bar = 50 µm.