**1. Introduction**

Stainless steel (SS) is a biomaterial that is highly used to manufacture devices that will be in close contact with human tissues for extended periods of time [1–3]. In the field of dentistry, particularly in orthodontics, SS is immensely used to fabricate appliances and devices, such as archwires and brackets, due to its outstanding anticorrosive properties [4–6]. However, since such devices are located within the oral cavity, they are highly susceptible to bacterial adhesion and biofilm formation due to the surface properties of this biomaterial [7–10].

Surface roughness and hydrophobicity are two of the most relevant properties involved in the process of bacterial adhesion and biofilm formation. Surface roughness promotes bacterial adhesion [11] and surface hydrophobicity allows bacterial species to adhere, colonize and grow on a surface [11,12]. Bacterial adhesion to such devices is favored by the fact that SS may have a rough surface; this adhesion will eventually lead to the formation of a mature biofilm that has the potential to cause harmful conditions to surrounding natural tissues, such as dental caries or gingivitis [13,14].

**Citation:** Arango-Santander, S.; Serna, L.; Sanchez-Garzon, J.; Franco, J. Evaluation of *Streptococcus mutans* Adhesion to Stainless Steel Surfaces Modified Using Different Topographies Following a Biomimetic Approach. *Coatings* **2021**, *11*, 829. https://doi.org/10.3390/ coatings11070829

Academic Editor: Jun-Beom Park

Received: 8 June 2021 Accepted: 4 July 2021 Published: 9 July 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Different approaches, especially oral hygiene-related procedures, have been investigated over the years to reduce bacterial adhesion to natural and artificial surfaces [15–17]. Nonetheless, these methods have proven insufficient. An additional approach, known as surface modification, has been reported in the scientific literature in recent years. Surface modification is a vast field that includes many different chemical [18,19] and physical techniques. Topographic modifications at micro and nanometric scales is one of such physical approaches [20].

Physical surface modification techniques are divided into two large areas: top-down techniques, in which nano or microstructures are created from larger structures, and bottom-up techniques, in which larger structures are created from smaller elements [21,22]. Soft lithography belongs to the former and is a set of techniques based on self-assembly and replica molding to create micro and nano structures on the surface of materials [22,23]. Soft lithography is based upon copying and transferring the topography of a master model, which has been traditionally created using photolithography [23], to another surface. However, nature has shown, over thousands of years, that an enormous number of master models are readily available to be used for human strategies. Such inspiration in natural models is known as biomimetics [24,25]. Modified surfaces inspired by animal sources have been previously investigated [24,26], but botanical products have been scarcely used as models to modify the surface of biomaterials. Natural vegetal products, such as the leaves from Taro (*Colocasia esculenta*), Montbretia (*Crocosmia aurea*) and Giant salvinia (*Salvinia molesta*) display particular surface features, including water repellency and self-cleaning abilities, that may be interesting when considering using natural surfaces as models for surface modification [23].

Surface modification to reduce bacterial adhesion has been studied and reported in the scientific literature over the last years. Different authors have demonstrated that bacterial adhesion is reduced to physically modified surfaces [27,28]. Biomimetics has served as inspiration to other authors to emulate natural patterns, like the shark skin, and transfer them to the surface of biomaterials [29], while other investigations have shown that the topography of natural leaves reduces bacterial adhesion on SS and titanium alloy orthodontic wires [30]. However, even though the reported results are highly promising, information on using botanical sources as models to modify the surface of biomaterials is scarce and only a few plants or leaves have been reported.

Therefore, the objective of this work was to modify the surface of SS plates using the topography from three natural leaves and compare the adhesion of *Streptococcus mutans* to such modified surfaces.
