Drawing inspiration from nature to develop anti-fouling coatings: the development of biomimetic polymer surfaces and their effect on bacterial fouling

Abstract

The development of self-cleaning biomimetic surfaces has the potential to be of great benefit to human health, in addition to reducing the economic burden on industries worldwide. Consequently, this study developed a biomimetic wax surface using a moulding technique which emulated the topography of the self-cleaning Gladiolus hybridus (Gladioli) leaf. A comparison of topographies was performed for unmodified wax surfaces (control), biomimetic wax surfaces, and Gladioli leaves using optical profilometry and scanning electron microscopy. The results demonstrated that the biomimetic wax surface and Gladioli leaf had extremely similar surface roughness parameters, but the water contact angle of the Gladioli leaf was significantly higher than the replicated biomimetic surface. The self-cleaning properties of the biomimetic and control surfaces were compared by measuring their propensity to repel Escherichia coli and Listeria monocytogenes attachment, adhesion, and retention in mono- and co-culture conditions. When the bacterial assays were carried out in monoculture, the biomimetic surfaces retained fewer bacteria than the control surfaces. However, when using co-cultures of the bacterial species, only following the retention assays were the bacterial numbers reduced on the biomimetic surfaces. The results demonstrate that such surfaces may be effective in reducing biofouling if used in the appropriate medical, marine, and industrial scenarios. This study provides valuable insight into the antifouling physical and chemical control mechanisms found in plants, which are particularly appealing for engineering purposes.

A comparison of vegetable leaves and replicated biomimetic surfaces on the binding of Escherichia coli and Listeria monocytogenes

“…To fabricate biomimetic replicates, several biological samples of the same leaf type were mounted with double-sided tape on a smooth surface and an addition-cured silicone duplicating system (Shera Duo-Sil H, Shera GmbH & Co. KG, Germany) was poured on the adaxial surfaces of the leaves in order to produce a negative mould. Dental wax (Kemdent Eco dental wax, UK) was then poured onto the negative mould, creating a positive wax surface for each leaf (McClements et al, 2021). A 15 mm diameter steel hole punch was used to create equally sized coupons.…”

“…The surface-energy components of the leaves and replicates were calculated according to the work by van Oss and colleagues (van Oss, 1995), which considers the contact angles of three test liquids including water to estimate the interfacial free energy ( G iwi ). The contact angles of each surface were determined using a drop goniometer (GH11 model, Krüss, France) and a PC-based data analysis system as described in McClements et al (2021). The interfacial free energy was used as a measure of the hydrophobicity of a surface where greater (negative) G iwi values correspond to more hydrophobic surfaces.…”

“…Appropriate dilutions in sterile distilled water were performed to obtain an OD of 0.5 at 540 nm, corresponding to 5.5 × 10 8 E. coli or L. monocytogenes colony forming units (CFU)/mL. The biomimetic coupons and the fresh leaves were analysed for attachment (by spray plus wash), adhesion (by spray), and retention (by 1-h static incubation) assays with monocultures of the selected bacteria (McClements et al, 2021;Rajab et al, 2018). Before being used, the leaves were also cut into 15 mm diameter circles, washed with sterile distilled water and air-dried in a class 2 flow hood for 1 h. For attachment and adhesion assays, replicates of biomimetic surfaces and original leaves were attached to a vertical stainless steel tray and the bacterial suspension was sprayed (Spraycraft Universal Air Propellant, Shesto, UK) over the surfaces for 10 s. Immediately after spraying, the surfaces were divided into two sets (n = 3 each), one was laid horizontally and left to dry (adhesion assay) and the other was rinsed using a water spray bottle (attachment assay).…”

“…However, there has been an increasing interest in reproducing the surface properties of biomimetic surfaces using simpler methodologies. These have included reproducing the leaves of lotus and rice on gold surfaces using polydimethylsiloxane (PDMS), and then chemically modifying them with alkanethiol (Zhao et al, 2010), recreating two bamboo varieties and Gi0nkgo biloba using a PDMS replicating protocol (Legrand et al, 2021), reproducing the morphology and wettability of water bamboo leaves using PDMS (Guan et al, 2015), and replicating the surface of the Gladiolus hybridus (Gladioli) leaf using silicone material to create a negative mould of the leaf surface, followed by using dental wax to produce a biomimetic surface (McClements et al, 2021).…”

“…botrytis (Cauliflower), and Allium ampeloprasu (Leek) -using a casting technique. Negative silicone moulds of the leaves surfaces were manufactured and dental wax was used to create the biomimetic surfaces because it is a low-cost, easily mouldable material, and mimics the crystalline hydrocarbons found on several hydrophobic leaves (McClements et al, 2021). The biomimetic wax surfaces were then compared with the original leaves and flat wax surface (control) to determine the effectiveness of plant-based surfaces in counteracting bacterial attachment, adhesion and retention.…”