# Chitosan-based coatings to prevent Nitratidesulfovibrio vulgaris influenced (bio)corrosion on aluminium alloy

Viktoriia Drebezghova, Cyril Cugnet, Susana C.M. Fernandes, Jean-Charles

Dupin, Marion Guignard, Anthony Ranchou-Peyruse, Magali

Ranchou-Peyruse, Corinne Nardin

► To cite this version:

Viktoriia Drebezghova, Cyril Cugnet, Susana C.M. Fernandes, Jean-Charles Dupin, Marion Guignard, et al.. Chitosan-based coatings to prevent Nitratidesulfovibrio vulgaris influenced (bio)corrosion on aluminium alloy. Colloids and Surfaces B: Biointerfaces, 2025, 253, pp.114751. 10.1016/j.col surfb.2025.114751. hal-05085456

HAL Id: hal-05085456

https://univ-pau.hal.science/hal-05085456v1

Submitted on 26 May 2025

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# Chitosan-based coatings to prevent *Nitratidesulfovibrio vulgaris* influenced (bio)corrosion on aluminium alloy

Viktoriia Drebezghova<sup>a</sup>, Cyril Cugnet<sup>a</sup>, Susana C.M. Fernandes<sup>a</sup>, Jean-Charles Dupin<sup>a</sup>, Marion Guignard<sup>a, b</sup>, Anthony Ranchou-Peyruse<sup>a, b</sup>, Magali Ranchou-Peyruse<sup>b, c</sup>, Corinne Nardin<sup>a, *, c</sup>

## ARTICLE INFO

**Keywords:**

(Bio)corrosion

Sulfate reducing bacteria

Chitosan coating

Silanization

Aluminium alloy

## ABSTRACT

Chitosan, a natural polymer derived from chitin, is widely recognized for its biocompatibility, biodegradability, and in particular antimicrobial properties. This study investigates the effectiveness of chitosan grafted onto aluminium Al 2024 alloy substrates in preventing (bio)corrosion, specifically in the presence of the sulfate-reducing bacterium *Nitratidesulfovibrio vulgaris* (formerly *Desulfovibrio vulgaris*), a model organism for bio-corrosion. Chitosan-based coatings of micrometer thickness were applied using a dip-coating method, which is easy to implement in industrial settings. The coatings were applied to both mirror-polished aluminium substrates, with and without triethoxysilylpropylsuccinic anhydride (TESPSA) for functionalization. Weight loss analysis, profilometry, epifluorescence microscopy, and X-ray photoelectron spectroscopy (XPS) were conducted on the chitosan-coated aluminium alloy before and after microbial incubation. The results showed that chitosan coatings, particularly those functionalized with TESPSA, significantly reduce (bio)corrosion and microbial growth. Notably, the 2 % w/v chitosan coating demonstrated strong adhesion, with less than 5 % detachment under tape tests and no detachment observed after five weeks of exposure to *N. vulgaris*, and substantial (bio)corrosion resistance. Epifluorescence microscopy revealed a nearly tenfold decrease in bacterial coverage compared to the uncoated substrate. XPS showed minimal impact from *N. vulgaris* on the 2 % w/v chitosan-coated aluminium, with a stable C/N ratio of 7.4 +/- 0.2 before and after incubation. Electrochemical corrosion tests indicated that the combination of chitosan coatings and TESPSA functionalization significantly decreases the corrosion rate, despite a minor increase in susceptibility to corrosion. These findings highlight the potential of chitosan-based coatings, especially when paired with surface treatments like TESPSA functionalization, to effectively combat corrosion and (bio)corrosion of aluminum alloys.

## 1. Introduction

Microbially influenced corrosion (MIC), also known as biocorrosion, is a significant area of research due to its deleterious impact in various industries, including oil fields and marine environments [1–4]. MIC can dramatically increase the corrosion rates of metals, leading to structural degradation. It is primarily caused by a variety of microorganisms, including bacteria, archaea, fungi, and algae [5–7]. In anoxic environments, sulfate-reducers play a key role in biocorrosion processes. Multiple parallel reactions usually occur simultaneously in MIC, including those that are purely chemical (e.g. oxidation of iron), those that are chemical but microbially influenced (e.g. chemical corrosion by

microbially produced hydrogen sulfide) and direct withdrawal of electrons from surfaces by bacteria. Foremost among those studied are sulfate-reducing bacteria, which are known to be one of the main corrosive agents in anaerobic aqueous environments [8]. Notably, the bacterial strain *Nitratidesulfovibrio vulgaris* (formerly *Desulfovibrio vulgaris*) is commonly used as a model organism to investigate the bio-corrosion of iron-containing metals, copper and copper-nickel alloy [9–15]. Additionally, the corrosive effects of these microorganisms on aluminum have been demonstrated [16,17]. Some sulfate-reducing bacteria that were previously classified within the same genus *Desulfovibrio* have been associated with human infections (*Desulfovibrio fairfieldensis*, *Pseudodesulfovibrio desulfuricans*, *N. vulgaris*) [18–20].

<footnote><sup>a</sup> Université de Pau et des Pays de l'Adour, CNRS, IPREM, Pau, France</footnote>

<footnote><sup>b</sup> Université de Pau et des Pays de l'Adour, LaTEP, Pau, France</footnote>

<footnote>* Corresponding author.
E-mail address: corinne.nardin@univ-pau.fr (C. Nardin).</footnote>
To combat biocorrosion, polymer coatings have been employed [21–24]. These coatings protect metal surfaces by i) incorporating bio-cides, ii) using quaternary ammonium compounds [25], or iii) utilizing conductive materials [22]. Coatings modified with nanoparticles such as ZnO, CuO, and Ag have also been studied for their protective potential [26–28]. Although natural polymers are less frequently used due to their inferior mechanical strength in comparison to synthetic polymers, they are often blended with synthetic polymers [29], nanoparticles [30,31], or both [32]. Chitosan, a non-toxic, biodegradable and antimicrobial biopolymer, is particularly effective in addressing both corrosion [33–35] and biocorrosion due to its inherent properties and exceptional film-forming and coating abilities [36]. For example, a study by Gu and colleagues demonstrated that chitosan coatings slowed down the biocorrosion of a magnesium alloy [37]. In response to the challenges posed by biocorrosion in several areas, we report here on the investigations conducted using chitosan-based coatings on a model substrate, i. e. Aluminium Al 2024 alloys, which is widely used in the aerospace and fuel storage industries. This alloy’s susceptibility to localized corrosion makes it vulnerable to MIC [38].

In this study, we report on the efficiency against MIC of adherent chitosan coatings processed on aluminium alloy substrates using dip

coating. These coatings, of thickness in the micrometer range, remained remarkably stable even after five weeks of incubation with *N. vulgaris*, as shown through our experimental data. We employed weight loss analysis, epifluorescence microscopy, profilometry, electrochemical characterization and X-ray photoelectron spectroscopy (XPS) to characterize the coatings before and after microbial incubation, demonstrating that both corrosion and biocorrosion were effectively prevented.

## 2. Experimental section

### 2.1. Raw materials and chemicals

The metal substrate selected for this study is the Aluminium Al 2024 alloy, supplied by Goodfellow Cambridge Ltd. (Huntingdon, England) in a sheet of 300 mm x 300 mm x 1.6 mm dimensions. The nominal composition of the Al 2024 alloy, as provided by the supplier, is detailed in Table S1 (see Electronic supplementary information ESI). Chitosan powder sourced from squid pens was obtained from Mahtani Chitosan Pvt. Ltd. (Veraval, Gujarat, India). The degree of deacetylation (DDA) was determined to be 98 %, with a molecular weight of 500,000 g.mol⁻¹

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** Experimental setup for applying chitosan coatings on silanized and non-silanized aluminium surfaces. a) Samples and corresponding techniques used in chitosan coating evaluation for (bio)corrosion prevention. a) Fluorescence microscopy was used only for the samples incubated for 48 h. b) XPS was used exclusively for the samples prior to and subsequent to five weeks of incubation with *N. vulgaris*; b) Schematic of dip-coating process, with the substrate immersion into the chitosan solution at 0.1 mm s⁻¹, followed by the substrate-solution system stabilization, and the subsequent substrate removal at 0.01 mm s⁻¹ with the coating formation.</figcaption></figure>
measured using combining viscosimetry with ¹H NMR spectroscopy in D₂O containing 1 % of D₃COOD.

Glacial acetic acid (≥ 99 %) and triethoxysilylpropyl succinic anhydride (TESPSA, 95 %) were purchased from VWR Chemicals (Fontenay-sous-Bois, France) and Gelest Ltd. (Maidstone, England), respectively. For aluminium surface finishing, diamond suspension (MetaDi Supreme, 3 µm) and polishing cloth (MicroFloc) were acquired from Buehler (Leinfelden-Echterdingen, Germany).

## 2.2. Preparation of chitosan coating on the Al alloy surface

The Al 2024 alloy sheets were cut into coupons of three different dimensions for the various investigations of this study (Fig. 1a): i) rectangles measuring 60 mm x 25 mm x 1.6 mm, used for adhesion tests, contact angle measurements, and infrared (IR) spectroscopy analyses; ii) rectangles measuring 20 mm x 10 mm x 1.6 mm, used in biocorrosion assays and for all subsequent analyses (profilometry, weight loss analysis, fluorescence microscopy, X-ray photoelectron spectroscopy, XPS); and iii) disks of 8 mm diameter, specifically for electrochemical tests.

All aluminium alloy pieces underwent polishing with two ultra-fine grit sandpapers (P600, P1200), followed by a finish using 3 µm diamond suspension to achieve mirror-polished surfaces. Subsequently, the substrates were cleaned in acetone, ethanol, and ultrapure water using ultrasound for 15 min each. The ultrapure water used in this research was generated by an ultrapure water system (MilliQ Millipore, Merck, France). These samples, referred to as "non-silanized aluminium" underwent a silanization process to enhance chitosan-substrate adhesion, following a protocol established by D'Almeida et al. [39]. The substrates were immersed in a TESPSA solution dissolved in pentane (0.1 % v/v) for one hour, then dried, and heated at 150 °C for 12 h. The resulting samples are referred to as "silanized aluminium" and were cleaned in pentane, tetrahydrofuran, and dichloromethane via ultrasound for 15 min each.

Chitosan coatings were deposited onto both silanized and non-silanized aluminium surfaces via dip-coating using an ACEdip 2.0 dip-coater model (SolGelWay, Paris, France). The process involved immersing the substrate in a precursor solution at a 0.1 mm s⁻¹ velocity for 60 s, its stabilization, and then withdrawing the substrate at a rate of 0.01 mm s⁻¹ (Fig. 1b). The coated substrates were heated at 80 °C for 24 h to ensure complete solvent evaporation. Coating thickness was adjusted by varying the chitosan concentration in the precursor solution. For each concentration (1 %, 2 %, and 3 % w/v), the chitosan powder was dissolved overnight at room temperature in a 3 % v/v aqueous solution of acetic acid using a magnetic stirrer to achieve homogenous solutions.

All rectangular substrates were immersed in the solution up to half their depth to maintain an un-coated control area on the same side. Disk-shaped substrates intended for electrochemical tests were secured to a glass slide with double-sided tape to allow for complete immersion and coating.

## 2.3. Bacterial strain and culture medium

Microbiological tests were conducted using the model strain N. vulgaris Hildenborough [40]. The strain DSM644 was acquired from the German collection of microorganisms and cell cultures (DSMZ, Braunschweig, Germany) and cultivated according to their recommendations (Medium 63), without FeSO₄·7 H₂O, maintaining a pH of 7.3 at 37 °C.

## 2.4. Characterization methods

### 2.4.1. Chitosan solution viscosity

The shear viscosity of chitosan solutions was evaluated with an Anton Paar MCR 302 rotational rheometer (Les Ulis, France). Measurements were conducted using concentric cylinder geometry suitable

for fluids analysis, with a cup radius of 15 mm and a rotor radius of 14 mm. The shear rate was varied from 0.01 to 100 s⁻¹, with five data points collected per log cycle. All experiments were performed with freshly prepared chitosan solutions at varying concentrations (1 %, 2 %, or 3 % w/v) at a temperature of 30 °C.

### 2.4.2. Fourier transform infrared (FTIR) spectroscopy

FTIR spectroscopy was conducted on chitosan coatings deposited on both non-silanized and silanized aluminium surfaces coated with chitosan solutions of various concentrations (1 %, 2 %, or 3 % w/v). FTIR spectra were recorded from three distinct locations on each sample using a Perkin-Elmer Spectrum One FTIR Spectrometer (Waltham, Massachusetts, USA) in the attenuated total reflection (ATR) mode, covering a range of 650–4000 cm⁻¹, with a resolution of 4 cm⁻¹ after 128 scan accumulations.

### 2.4.3. Adhesion tests

The adhesion of chitosan coatings on the Al alloy was evaluated using an Elcometer 1542 Cross Hatch Adhesion Tester Basic Kit. This method assesses coating adhesion by applying and then removing a pressure-sensitive tape over cuts made in the coating using a standard cutter. Coatings applied at different chitosan concentrations on both non-silanized and silanized aluminium were tested. Due to the transparency and thinness of the chitosan coatings, all samples were observed using optical microscopy at 5x magnification, and the results were analyzed according to the ASTM D 3359-B standard [41].

### 2.4.4. Contact angle measurements

The wetting properties of the samples were assessed using the static contact angle method with a custom-made optical tensiometer. For each sample, ten water droplets (8–9 µL) were placed consecutively on the surface and allowed to settle for one minute before capturing images. In addition, the evolution of contact angles for each chitosan coating was monitored over a five-minute period using a video-capturing system set at 2 frames per second, starting from droplet deposition at time zero. All contact angles and their evolution were analyzed with a custom software, while the contact line and droplet cross-sectional area were examined using the ImageJ software. Measurements were conducted at room temperature (21 °C).

### 2.4.5. Electrochemical corrosion tests

Electrochemical analyses were performed to evaluate the corrosion resistance of the substrate coated with chitosan. The measurements were made in 3.5 % NaCl solution at room temperature using the three-electrode system with coated aluminium sample as working electrode, Ag/AgCl, saturated KCl as a reference electrode, and Pt gauze as counter electrode, directly immersed into the electrolyte. Potentiodynamic polarization curves were obtained from -1.6 V to + 0.4 V against an open circuit potential (OCP) at a sweep rate of 5 mV s⁻¹, with the working electrode rotating at 1000 rpm. The acquired polarization curves were analyzed using the Nova 2.1.6 software.

### 2.4.6. Bio-corrosion assay

Uninoculated medium was used for abiotic assays. For biotic assays, the medium was inoculated to achieve 10 % inoculation, corresponding to an optical density of 0.012 at 600 nm (Spectronic Instruments; Spectronic 401), equating to a concentration of 3.1 10⁷ cells mL⁻¹. All assays were conducted in sterile conditions inside 40 mL glass vials. Silanized or non-silanized aluminium coupons were placed flat at the bottom of these vials. The vials were sealed with septa and aluminum caps, and the gas phase was replaced by filter-sterilized nitrogen (PES 33 mm membrane, 0.22 µm, Millex Merck Millipore). Five milliliters of either uninoculated or inoculated medium were injected into each vial, depending on the conditions being tested, without stirring. Each trial consisted in using either non-silanized or silanized aluminium surfaces coated with chitosan at various concentrations (1 %, 2 %, and 3 % w/v).
Each sample was coated on one half to maintain an uncoated control area. In parallel, a culture without any metal coupon was incubated in a glass tube (Bellco) to monitor bacterial growth spectrophotometrically. After 48 h, the maximum optical density recorded was 0.124 at 600 nm (3.3 10⁸ cells mL⁻¹). For each of the three conditions tested, two trials were ended after 48 h (one coupon for epifluorescence microscopy and one for surface analysis). One trial was stopped after two weeks and another after five weeks. As a negative control, non-silanized aluminium was incubated in a bacteria-free medium, monitored throughout the incubation period, and removed after five weeks.

After incubation periods of 48 h, 2 weeks, and 5 weeks at 37 °C without agitation, samples were removed from the glass flasks. Bacteria were detached from the surfaces by shaking in ultrapure water with 0.01 % v/v Tween 20 surfactant [42]. The samples were then washed three times with fresh ultrapure water and dried with nitrogen. All samples used in the biocorrosion assays, except those for microscopy, were weighed before and after incubation using a high-precision balance (± 0.1 mg).

### 2.4.7. Epifluorescence microscopy

Coupons incubated for 48 h were analyzed with epifluorescence microscopy to visualize bacteria on the surfaces. Coupons were carefully removed from the flasks and treated with a drop of 10 µL of SYTO9 dye (1 µL; Invitrogen, S34854) diluted with sterile distilled water. The mixture was incubated at room temperature in the dark for 15 minutes, followed by three rinses in sterile ultrapure water to remove excess dye and bacteria brought to the surface by sedimentation. The preparation was then observed by microscopy. Samples were placed on a coverslip and examined with an Axio Observer Z1 inverted fluorescence microscope (Zeiss, Jena, Germany). This microscope is equipped with a 63x oil immersion objective (NA 1.4). We used a BP 470/40 excitation filter, a FT 495 beam splitter, and a BP 525/50 emission filter to visualize the cells. Images were acquired using a Zeiss Axiocam 506 mono camera and were monitored with Zeiss Zen 2012 software.

### 2.4.8. Confocal profilometry

Coating thickness and surface roughness were measured with a MICROMESURE STIL system using a non-contact chromatic sensor, following the ISO 25178 standard. The optical pen had a measurement range of 80 µm. For each coated sample, five 4 mm profiles were taken at the edges of the coatings to measure thickness, with intervals of 0.3 µm between measured points. Surface roughness was assessed using 1 mm profiles scanned along the coating deposition direction at five different spots for each sample, with a step size of 0.1 µm. These profiles were filtered using a Gaussian filter with a cut-off of 250 µm to smooth out waviness before calculating the root mean square (RMS) roughness. The acquisition software SurfaceMap® was used to control the measuring station, and MountainsMap® software facilitated the analysis of profiles and the calculation roughness parameters.

### 2.4.9. X-ray photoelectron spectroscopy (XPS)

XPS analysis of the surface chemical composition was conducted using a Thermo K-alpha spectrometer. This device utilized a hemispherical analyzer and a micro focused (400 µm diameter microspot) monochromatic radiation (Al Kα, 1486.6 eV) operating at 72 W under a residual pressure of 1 10⁻⁹ mbar. Pass energy was adjusted to 20 eV. To balance the charge effects, setting during the analysis, a dual beam charge neutralization system (low energy electrons and Ar⁺ ions) was used with the unique ability to provide consistent charge compensation. All spectral quantification was based on the relative sensitive factors (R. S.F.) from the Scofield cross sections database. The calibration of all spectra was based on the binding energy at 285.0 eV of aliphatic carbon present on all sample surfaces. Data fitting was performed with the Casa XPS software using a least-squares algorithm and a non-linear baseline (Shirley). The experimental curve peaks were fitted using a combination of Gaussian (70 %) and Lorentzian (30 %) distributions.

### 2.4.10. Statistical analysis

We applied a one-tailed t-test to assess if the RMS roughness at subsequent time points was greater than a specified value.

## 3. Results and discussion

We first show the results related to the processing and characterization of chitosan coatings processed on the Al 2024 alloy surface. The preparative silanization step involved treating mirror-polished aluminium surfaces with TESPSA as a coupling agent. This treatment enhances chitosan adhesion by creating a chemical bond between the carboxyl groups of TESPSA and the amino groups of chitosan (Fig. 2). We measured the viscosity of chitosan solutions at different concentrations, finding that the zero-shear viscosity was 4.1 × 10⁻³, 7.9 × 10⁴, and 3.9 × 10⁵ mPa s for concentrations of 1 %, 2 %, and 3 % w/v, respectively (ESI, Figure S1).

Following the protocols described in the "Experimental section", aluminium substrates were dip-coated with chitosan at a withdrawal speed of 0.01 mm s⁻¹ to ensure deposition in the "capillary regime". As highlighted by Grosso [43], this regime, characterized by the inverse relationship between withdrawal speed and coating thickness, is ideal for achieving smooth, non-porous, and ultra-thick coatings from low-volatile solvents. Conditions of 10 % relative humidity and a temperature of 40 °C were chosen to expedite the evaporation process.

## 4. Chemical characterization of chitosan coatings

We utilized FTIR spectroscopy in the ATR mode to chemically characterize the chitosan coatings, measuring at three different locations on each sample. The representative FTIR spectra of chitosan coatings deposited on both non-silanized and silanized aluminium are presented in ESI (Figure S2a and S2b, respectively). The spectra for 2 % and 3 % w/v chitosan coatings on non-silanized aluminium display characteristic absorption bands of chitosan, whereas the 1 % w/v coating lacks discernable signals (Figure S2a). Notably, a broad band at 3450 cm⁻¹ indicates the axial stretching of the O-H and N-H bonds, whereas a band at 2860 cm⁻¹ corresponds to C-H stretching. The bands at 1650 and 1590 cm⁻¹ are associated with amide I (C=O stretching mode) and amide II (N-H bending and C-N stretching modes) vibrations, respectively [44–46]. The weak intensity of the band at 1650 cm⁻¹ suggests a high degree of deacetylation of the chitosan used [46]. Other bands at 1420 and 1380 cm⁻¹ correspond to C-N axial stretching and N-H angular deformation, whereas bands between 1150 and 897 cm⁻¹ relate to the polysaccharide backbone, including glycosidic bonds, C-O and C-O-C stretching [44]. All absorption bands are listed in ESI (Table S2).

The spectra of 2 % and 3 % w/v chitosan coatings on silanized aluminium were similar to those on non-silanized aluminium, though of reduced intensity. They display the characteristic absorption bands of chitosan from the amino groups and from the polysaccharide backbone. In contrast, the spectrum of the 1 % w/v chitosan coating exhibited a prominent peak at 1710 cm⁻¹, indicative of the asymmetric stretching vibrations of the hydrolyzed anhydride group of the TESPSA [47,48]. Additional peaks at 1082 cm⁻¹, 1250 cm⁻¹, and 800 cm⁻¹ correspond to Si-O-Si stretching vibrations [48,49]. This suggests that the FTIR spectrum for the 1 % w/v coating on silanized aluminium is dominated by TESPSA signals, which are masked by chitosan at higher chitosan concentrations.

## 5. Wettability of chitosan coatings

Water contact angles, as shown in Table 1, were measured on both uncoated aluminium substrates and chitosan-coated samples (1 %, 2 %, and 3 % w/v) after 60 s of deposition to ensure consistency. The polishing step significantly improved the wettability of the aluminium substrate, with the contact angle decreasing from (79 ± 2)° for the as-
<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Schematic representation of the covalent grafting of chitosan on poli-mirror aluminium surface by the TESPSA coupling agent method. Step 1: Silane functionalization of aluminium substrates was achieved by immersion in a TESPSA/Toluene 0.1 % v/v solution for one hour, followed by drying and cleansing to remove physisorbed compounds. Step 2: Chitosan was covalently grafted onto silanized aluminium surfaces by peptide bonds using dip-coating.</figcaption></figure>

**Table 1**

Characteristics of the elaborated chitosan coatings of various concentrations. Water contact angle values are presented as the mean of ten droplets ± standard deviation, coating thickness values are presented as the mean of five measured profiles ± standard deviation.

<table><thead><tr><th rowspan="2"></th><th colspan="2">Non-silanized substrate</th><th colspan="2">Silanized substrate</th></tr><tr><th>Water contact angle</th><th>Coating thickness, µm</th><th>Water contact angle</th><th>Coating thickness, µm</th></tr></thead><tbody><tr><td>Uncoated Al</td><td>(18 ± 2)°</td><td>No coating</td><td>(54 ± 2)°</td><td>No coating</td></tr><tr><td>1 % w/v</td><td>(59 ± 4)°</td><td>(0.5 ± 0.3)</td><td>(59 ± 3)°</td><td>Undiscernible</td></tr><tr><td>2 % w/v</td><td>(57 ± 3)°</td><td>(1.1 ± 0.4)</td><td>(59 ± 3)°</td><td>(0.9 ± 0.3)</td></tr><tr><td>3 % w/v</td><td>(80 ± 4)°</td><td>(2.0 ± 0.4)</td><td>(64 ± 2)°</td><td>(2.2 ± 0.4)</td></tr></tbody></table>

supplied bare aluminium to (18 ± 2)° for the polished aluminium. Silanization further increased the contact angle from (18 ± 2)° to (54 ± 2)°, though the surface remained quite hydrophilic. For 1 % and 2 % w/v chitosan coatings on both non-silanized and silanized aluminium, the contact angles were approximately 57–59°. In contrast, 3 % w/v chitosan coating resulted in a contact angle of 80° on non-silanized aluminium and 64° on silanized aluminium.

Farris et al. [50] noted that the concept of water contact angle equilibrium is not applicable to most biopolymers. Once a water droplet is placed on a chitosan-coated surface, its profile continuously changes, preventing true equilibrium from being reached. Our analysis revealed that the contact angle decreased by approximately 10° for all chitosan coatings over a 5-minute observation period (ESI, Figure S3 and Table S3). This decrease in droplet volume reflects absorption by the biopolymer, while the increased droplet contact area reflects spreading. We assume that the polymer chains are randomly (and therefore isotropically) dispersed on the substrate, allowing the droplet shape to be approximated by a perfectly spherical dome. In this case, the absorption can be characterized by changes in droplet volume relative to the initial volume, while spreading is reflected in the variation in the contact area with chitosan ΔA (ESI, Figure S4). The decrease in droplet volume for each chitosan coating ranged from 10 % to 20 %, indicating water absorption by the biopolymer matrix. The increase in the droplet contact area, which reflects droplet spreading, was less pronounced (1 % to 9 %), but still noticeable (ESI, Figure S4 and Table S3). These findings are in line with those of Farris et al. [50], who indicated that absorption and spreading are key factors driving the surface wetting mechanism of approximately 1.3 µm thick chitosan coatings.

**6. Coating thickness evaluation**

We measured the thickness of the chitosan coatings using confocal profilometry, the results of which are listed in Table 1. Coating thickness

increased with chitosan solution concentrations, ranging from 0.5 to 2.2 µm.

**7. Adhesion assessment of chitosan coatings**

To determine the suitability of chitosan coatings for practical applications, adequate adhesion to the desired substrates is essential. We applied a standard procedure to evaluate adhesion by applying and subsequently removing pressure-sensitive tapes over cuts made in the coating. All chitosan coatings (1 %, 2 %, and 3 % w/v) on both non-silanized and silanized aluminium were classified as grade 1, the highest ranking, with less than 5 % detachment. Six grades exist ranging from 0 (no detachment) to 5 (completely detached) [41]. The results of this adhesion assessment, captured through optical microscopy, are presented in ESI (see Figure S6).

**8. Electrochemical corrosion tests**

To evaluate the corrosion behavior of the aluminium alloy with chitosan coatings at different concentrations (0 %, 1 %, 2 %, and 3 % w/v), we conducted conventional electrochemical corrosion tests. This technique involves applying a potential between the working and reference electrodes and recording the resulting current *I* of oxidation or reduction processes. The corrosion potential *E*<sub>corr</sub> and corrosion current density *j*<sub>corr</sub> (Table 2), were determined from Tafel curves analyses, log*I* vs. potential *E* (ESI, Figure S6).

The corrosion potential and current density of polished non-silanized aluminium alloy were –0.56 V and 31.18 µA cm<sup>-2</sup>, respectively, findings consistent with those of anodized aluminium as reported by Cojo-caru et al. [51]. They used an identical three-electrode system and found the *E*<sub>corr</sub> of –0.563 V for anodized aluminium, compared to –0.944 V for the untreated pure aluminium. As shown in Table 2, chitosan-coated non-silanized aluminium exhibited corrosion potentials ranging from –0.67 V and –0.58 V, indicating increased susceptibility to corrosion compared to uncoated aluminium. However, the chitosan coating

**Table 2**

Corrosion potential and current density of both non-silanized and silanized aluminium coated with chitosan of various concentrations (0 %, 1 %, 2 %, and 3 % w/v).

<table><thead><tr><th>Sample</th><th></th><th><i>E</i><sub>corr</sub>, V</th><th><i>j</i><sub>corr</sub>, µA cm<sup>-2</sup></th></tr></thead><tbody><tr><td>Un-coated Non-silanized Al</td><td></td><td>-0.56</td><td>31.18</td></tr><tr><td rowspan="3">Chitosan coatings on Non-silanized Al</td><td>1 % w/v</td><td>-0.67</td><td>6.01</td></tr><tr><td>2 % w/v</td><td>-0.58</td><td>9.24</td></tr><tr><td>3 % w/v</td><td>-0.61</td><td>22.02</td></tr><tr><td>Un-coated Silanized Al</td><td></td><td>-0.66</td><td>2.27</td></tr><tr><td rowspan="3">Chitosan coatings on Silanized Al</td><td>1 % w/v</td><td>-0.65</td><td>3.70</td></tr><tr><td>2 % w/v</td><td>-0.65</td><td>2.31</td></tr><tr><td>3 % w/v</td><td>-0.66</td><td>0.58</td></tr></tbody></table>
appeared to reduce the corrosion current density, a measure of the metal dissolution rate. Interestingly, non-silanized aluminium with 3 % w/v chitosan coating exhibited a corrosion current density of 22.02 µA cm⁻², closely approaching that of uncoated non-silanized aluminium (31.18 µA cm⁻²). This similarity suggests that the coating may partially detach during the measurement. As discussed further, 3 % w/v chitosan coatings on non-silanized aluminium show systematic detachment when exposed to liquid environments, highlighting poor interfacial adhesion.

Silanization of aluminium led to a slight shift in the corrosion potential to –0.66 V and a significant reduction in the current density to 2.27 µA cm⁻² compared to non-silanized aluminium (31.18 µA cm⁻²). When coated with chitosan, the silanized aluminium maintained a low corrosion current density, with a minimum 0.58 µA cm⁻² for the 3 % w/v coating. This indicates that chitosan coatings on non-silanized aluminium performed poorly due to weak adhesion, silanization effectively stabilizes the coatings. Thus, the combination of silanization and chitosan coating may significantly reduce the corrosion rate, despite a slight increase in corrosion susceptibility.

## 9. Bacterial activity of *N. vulgaris*

The model strain used in this study, *N. vulgaris*, is a sulfate-reducing bacterium. Sulfate-reducers are considered as a major contributor to microbially influenced corrosion (MIC). These anaerobic microorganisms indirectly participate in aluminum corrosion through metabolic byproducts such as sulfides and organic acids and lowering of pH [1].

Initially, we visually examined the quality of the samples subjected to *N. vulgaris* activity during incubation. Fig. 3a are representative images of the samples at three different incubation time points. Notably, there were no fractures, detachments, shrinkage, or swelling observed, except for the non-silanized aluminium coated with 3 % w/v chitosan, which consistently detached from the substrate regardless of the incubation time, likely due to swelling. When dried after removal from suspension, the 3 % w/v chitosan coating appeared completely wrinkled (Fig. 3a, highlighted by a red frame). Uncoated aluminium parts of the samples appeared matte, likely due to oxidation, after the first 48 h of biological exposure. Interestingly, non-silanized aluminium, used as a negative control, remained unaffected by incubation in the bacteria-free medium; even after five weeks, the coupon maintained its pristine appearance (ESI, Figure S7). This suggests that any degradation

<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Chitosan film adhesion and stability on Silanized vs. Non-silanized aluminium substrates. a) Chitosan coatings at different concentrations (1 %, 2 %, and 3 % w/v) are shown on (left) non-silanized and (right) silanized aluminium pictured at three time points: before incubation, after 48 h, and five weeks. Samples are positioned so that the coating is on the bottom half. b) Weight of chitosan coatings at various concentrations (1 %, 2 %, and 3 % w/v) on (orange bars) non-silanized and (red bars) silanized aluminium before and after (a) 48 h, (b) 2 weeks, and (c) 5 weeks of incubation. Error bars indicate the uncertainty limits of the high-precision balance.</figcaption></figure>
observed is likely caused by *N. vulgaris* activity.

The weights of the chitosan coatings were assessed before and after incubation, as illustrated in Fig. 3b. For the 1 % w/v chitosan coatings, the weight changes fell within the uncertainty limit of the high-precision balance (0.1 mg), making accurate weight loss analysis challenging. Conversely, the 2 % w/v chitosan coatings showed no significant variations over time regardless of substrate treatment. In contrast, the weights of the 3 % w/v chitosan coatings exhibited noticeable decrease post-incubation. On silanized aluminium, weight loss ranged from 0.3 mg to 0.6 mg (10–25 % of the initial weight), whereas on non-silanized aluminium, weight loss ranged from 1 mg to 1.5 mg (20–30 %). This indicates that silanization markedly enhances the adhesion and stability of chitosan coatings. Additionally, 2 % w/v chitosan coatings demonstrated greater stability in the bacterial suspension compared to the 3 % w/v chitosan coatings, which likely experienced degradation or detachment.

Confocal profilometry measurements of chitosan coating thickness (ESI, Table S4) showed independence from incubation time, potentially due to inter-sample thickness variations overshadowing bacterial agitation effects. The 1 % w/v chitosan coating thickness was below 0.5 µm, whereas the 2 % and 3 % coatings ranged from 1 to 2 µm and from 2 to 3 µm, respectively, independent of incubation duration.

## 10. Surface roughness measurement

Table 3 presents the root mean square (RMS) roughness values for aluminium surfaces, both uncoated and coated with chitosan at various concentrations, measured during incubation via confocal profilometry. The letters (a) and (b) denote pairs of consecutive in time values with statistically significant differences identified by the one-tailed *t*-test. Notably, silanization of the polished aluminium substrate more than doubled its RMS roughness.

Following incubation in the bacterial suspension, both non-silanized and silanized aluminium substates showed a marked increase in RMS roughness during the first 48 h, rising from (57 ± 5) to (131 ± 36) nm and from (136 ± 12) to (174 ± 13) nm, respectively. The standard

deviation from five profiles per sample also increased, indicating greater surface inhomogeneity. The RMS roughness of the control non-silanized Al incubated in the bacteria-free medium for 5 weeks showed no change. The RMS roughness significantly increased for all chitosan coatings on non-silanized aluminium, regardless of concentration, and for the 3 % w/v chitosan coatings on silanized aluminium. Conversely, the 1 % and 2 % w/v chitosan coatings on silanized aluminium exhibited no change in roughness.

As shown in the fluorescence micrographs (Fig. 4a-f), bacteria affinity varied between uncoated and chitosan-coated regions on individual silanized aluminium coupon. Quantitative analysis (Fig. 4g) reveals that chitosan-coated surfaces generally exhibited lower bacterial coverage compared to uncoated ones after 48 h of incubation. Statistical analysis using the Student's *t*-test (*p* < 0.05) confirmed a significant decrease in bacterial growth on chitosan-coated surfaces, with the exception of the thinnest 1 % w/v coating, whether deposited on non-silanized or silanized aluminium.

Table 4 summarizes the elemental surface composition as assessed by XPS at various stages of coating preparation, including non-silanized aluminium, silanized aluminium, and silanized aluminium coated with 2 % w/v chitosan, prior to and after five weeks of incubation. The corresponding XPS survey spectra are available in ESI, Figure S8a-f. Deconvolution analyses of high-resolution XPS spectra are provided in ESI, Table S5 to S10 and showed that 27.7 % C content on non-silanized aluminium likely resulted from surface contamination during finishing and cleaning processes, such as diamond suspension used for finishing and the solvents used in the cleaning step, indicating a high level of surface reactivity. The grafting of TESPSA onto the substrate is confirmed by the presence of 19.1 % Si content. Moreover, the vanishing of the aluminium peak in silanized aluminium suggests complete surface masking achieved through the silanization process. After chitosan deposition on silanized aluminium, there was a significant increase in both C and N content, attributed to the chitosan, with the absence of detectable Al and Si peaks indicating full coverage by the chitosan layer. These observations are in line with previous studies [39,52].

An important increase in N, Ca, Mg, P, S (labeled as “Others” in Table 4) on non-silanized aluminium after five weeks of incubation, coupled with a decrease in aluminium content, suggests partial surface coverage by molecules adsorbed from the liquid environment, forming a conditioning film [53]. The elevated nutrient content on the surface can promote microbial growth, potentially leading to biofouling and corrosion. The increase in N and P content may indicate the presence of extracellular polymeric substances (EPS), characterized by polysaccharides, proteins, and DNA secreted by bacteria during biofilm formation [54]. Deconvolution of the S2p XPS spectrum (ESI, Table S6) confirms the presence of sulfides at binding energies of 162.4 eV and 163.8 eV, as well as sulfates at 169.1 eV and 170.3 eV on non-silanized aluminium at 1:8 ratio. *N. vulgaris* uses sulfate ions (SO₄²⁻) as electron acceptors and reduces them to sulfides (HS⁻, S²⁻, and H₂S), contributing to the initial stages of the corrosion process [55]. Moreover, the whole content of Al goes down to 13.5 %, which suggests the *N. vulgaris* contributed to the formation of some corrosion products, i.e. phosphates like products, on the non-silanized Al.

In comparison to silanized aluminium prior to incubation (ESI, Table S7), silanized aluminium after five weeks showed a lower C/Al ratio (103.4 after incubation versus 149 before). There was also an appearance of N, Ca, Mg, P (ESI, Table S8) on the silanized substrates. Bacterial activity resulted in a significant decrease in Si content, likely due to the formation of biofilm and molecules adsorbed from the medium damaging the silanized TESPSA layer. For silanized aluminium coated with 2 % w/v chitosan, bacterial activity had a minimal impact, as indicated by a relative consistent C/N ratio before and after five weeks of biological exposure (ESI, Table S9&$S10$; C/N = 7.4 +/- 0.2).

### Table 3

RMS roughness evolution of the aluminium surfaces both un-coated and coated with chitosan of various concentrations during the incubation in the *N. vulgaris* suspension. Values correspond to the (mean RMS roughness ± standard deviation) from fives measured height profiles for each sample. <sup>a</sup>One-tailed *t*-test between a pair of data at two consecutive points of time (*p* < 0.001) showed a significant difference. <sup>b</sup>One-tailed *t*-test with the p-value lower than 0.05 showed a significant difference.

<table><caption>RMS roughness, nm</caption><thead><tr><th>Incubation time</th><th></th><th>t<sub>0</sub></th><th>48 h</th><th>2 weeks</th><th>5 weeks</th></tr></thead><tbody><tr><td>Un-coated Non-silanized Al</td><td></td><td>57<br/>± 5<sup>a</sup></td><td>131<br/>± 36<sup>a</sup></td><td>297<br/>± 187</td><td>286<br/>± 134</td></tr><tr><td>Chitosan coatings on Non-silanized Al</td><td>1 %<br/>w/v</td><td>75<br/>± 11<sup>a</sup></td><td>149<br/>± 15<sup>a</sup></td><td>133<br/>± 33</td><td>137<br/>± 33</td></tr><tr><td></td><td>2 %<br/>w/v</td><td>110<br/>± 11<sup>b</sup></td><td>152<br/>± 29<sup>b</sup></td><td>139<br/>± 12<sup>a</sup></td><td>170 ± 9<sup>a</sup></td></tr><tr><td></td><td>3 %<br/>w/v</td><td>127<br/>± 53<sup>b</sup></td><td>—</td><td>—</td><td>251<br/>± 62<sup>b</sup></td></tr><tr><td>Un-coated Silanized Al</td><td></td><td>136<br/>± 12<sup>a</sup></td><td>174<br/>± 13<sup>a</sup></td><td>261<br/>± 79</td><td>210<br/>± 104</td></tr><tr><td>Chitosan coatings on Silanized Al</td><td>1 %<br/>w/v</td><td>160<br/>± 14</td><td>156 ± 1</td><td>169<br/>± 11</td><td>149<br/>± 17</td></tr><tr><td></td><td>2 %<br/>w/v</td><td>204<br/>± 29</td><td>161<br/>± 17</td><td>172<br/>± 17</td><td>174<br/>± 21</td></tr><tr><td></td><td>3 %<br/>w/v</td><td>111<br/>± 32<sup>a</sup></td><td>209<br/>± 39<sup>ab</sup></td><td>292<br/>± 44<sup>b</sup></td><td>252<br/>± 34</td></tr><tr><td></td><td></td><td>57 ± 5</td><td>—</td><td>—</td><td>60 ± 12</td></tr></tbody></table>

<footnote>* Sample used as a negative control</footnote>
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Bacterial coverage on chitosan-coated vs. Uncoated aluminium substrates. a-f) Representative epifluorescence microscopy images (scale bar: 50 µm) show *N. vulgaris* growth on (a, b, c) uncoated silanized aluminium and (d, e, f) chitosan-coated silanized aluminium at concentrations of (d) 1 % w/v, (e) 2 % w/v, and (f) 3 % w/v, after 48 h of incubation. g) The percentage area covered by *N. vulgaris* on both non-silanized and silanized aluminium (hatched bars) and on chitosan coatings (solid bars) at various concentrations (1 %, 2 %, and 3 % w/v) following 48 h of incubation. Each data point represents the average from 5 images taken at different locations on a sample. An asterisk (*) indicates a 95 % significance level between samples. Error bars show standard deviations.</figcaption></figure>

<table><caption>**Table 4**

Elemental surface composition (%) of the surfaces at various stages of coating preparation prior to and subsequent to 5 weeks of incubation.</caption><thead><tr><th>Sample</th><th></th><th>C 1 s (%)</th><th>N 1 s (%)</th><th>O 1 s (%)</th><th>Al 2p (%)</th><th>Si 2p (%)</th><th>Others (%)</th></tr></thead><tbody><tr><td rowspan="3">Pristine</td><td>Non-silanized Al (un-coated)</td><td>27.7</td><td>-</td><td>47.8</td><td>24.4</td><td>-</td><td>0.1</td></tr><tr><td>Silanized Al (un-coated)</td><td>44.7</td><td>-</td><td>35.9</td><td>-</td><td>19.1</td><td>-</td></tr><tr><td>Silanized Al coated with 2 % w/v chitosan</td><td>61.3</td><td>8.5</td><td>30.2</td><td>-</td><td>-</td><td>-</td></tr><tr><td rowspan="3">5 weeks of incubation</td><td>Non-silanized Al (un-coated)</td><td>19.9</td><td>1.3</td><td>52.5</td><td>13.5</td><td>-</td><td>12.8</td></tr><tr><td>Silanized Al (un-coated)</td><td>51.7</td><td>5.2</td><td>30.2</td><td>0.6</td><td>4.9</td><td>7.4</td></tr><tr><td>Silanized Al coated with 2 % w/v chitosan</td><td>64.1</td><td>8.4</td><td>26.7</td><td>-</td><td>0.6</td><td>0.2</td></tr></tbody></table>

## 11. Conclusion

This study investigates the use of chitosan coatings on aluminium alloy surfaces, specifically focusing on their adhesion, biocorrosion resistance, and protective properties against corrosive and microbial environments. Given the conflicting conclusions in the literature on the influence of surface roughness on coating adhesion [56,57], we ruled out roughness as a factor affecting coating adhesion. This research is pioneering in its application of chitosan coatings to poly-mirror metal surfaces and the exploration of their biocorrosion resistance on aluminium alloy. Our electrochemical and biocorrosion assays demonstrate that chitosan coatings, particularly when functionalized with TESPSA, offer promising protective properties. The covalent grafting of TESPSA enhances the coatings' adhesion to aluminium alloys, with higher chitosan concentrations (2 % and 3 % w/v) effectively reducing bacterial growth and showing lower bacterial coverage on coated surfaces. Notably, the 2 % w/v chitosan coating exhibited exceptional adhesion stability even after five weeks of incubation with *N. vulgaris*, suggesting its potential for use in anoxic microbial environments. These findings underscore the potential of chitosan as an effective protective coating material, particularly when combined with surface treatments like silanization to combat corrosion and microbial effects on aluminium alloys.

### CRediT authorship contribution statement

**Cyril Cugnet:** Writing – review & editing, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Susana Fernandes:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Methodology,

Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.
**Jean-Charles Dupin:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.
**Marion Guignard:** Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Viktoriaia Drebezghova:** Writing – original draft, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Anthony Ranchou-Peyruse:** Writing – review & editing, Visualization, Validation, Supervision, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.
**Magali Ranchou-Peyruse:** Writing – review & editing, Visualization, Validation, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Corinne Nardin:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Funding acquisition, Formal analysis, Data curation, Conceptualization.

### Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Corinne Nardin reports financial support was provided by Carnot Institutes Network. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgement

The program Carnot Isifor (grant numbers P450801ISI and
P451214ISI) and the IPREM institute are greatly acknowledged for financial support.

## Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.colsurfb.2025.114751.

## Data availability

Data will be made available on request.

## References

[1] H.A. Videla, L.K. Herrera, Microbiologically influenced corrosion: looking to the future, Int. Microbiol. Off. J. Span. Soc. Microbiol. 8 (2005) 169–180. PMID: 16200495.

[2] H. Liu, C. Fu, T. Gu, G. Zhang, Y. Lv, H. Wang, H. Liu, Corrosion behavior of carbon steel in the presence of sulfate reducing bacteria and iron oxidizing bacteria cultured in oilfield produced water, Corros. Sci. 100 (2015) 484–495, https://doi.org/10.1016/j.corsci.2015.08.023.

[3] Z. Zhang, C. Liu, Z. Lin, L. Guo, Y. Shuai, Y.F. Cheng, Effect of nutrient concentration on corrosion mechanism of X80 pipeline steel caused by sulfate-reducing bacteria, J. Electroanal. Chem. 956 (2024) 118096, https://doi.org/10.1016/j.jelechem.2024.118096.

[4] J. Knisz, R. Eckert, L.M. Gieg, A. Koerdt, J.S. Lee, E.R. Silva, T.L. Skovhus, B.A. An Stepec, S.A. Wade, Microbiologically influenced corrosion - more than just microorganisms, FEMS Microbiol. Rev. 47 (2023) fuad041, https://doi.org/10.1093/femsre/fiad041.

[5] M. Olivia, N. Moheimani, R. Javaherdashti, H. Nikraz, M. Borowitzka, On the impact of algae on accelerating the biodeterioration/biocorrosion of reinforced concrete: a mechanistic review, Eur. J. Sci. Res. 36 (2009) 394–406, https://doi.org/10.4028/www.scientific.net/AMR.626.861.

[6] E. Imo, R.A. Nwokorie, A review of fungal influenced corrosion of metals, Zast. Mater. 62 (2021) 333–339, https://doi.org/10.5937/zasmat.

[7] L.L. Barton, G.D. Fauque, Biocorrosion, in: L.L. Barton, G.D. Fauque (Eds.), in: *Sulfate-Reducing Bacteria and Archaea*, Springer International Publishing, Cham, 2022, pp. 427–462, https://doi.org/10.1007/978-3-030-96703-1_8.

[8] D. Enning, J. Garrelfs, Corrosion of Iron by Sulfate-Reducing Bacteria: New Views of an Old Problem, Appl. Environ. Microbiol. 80 (4) (2013) 1226–1236, https://doi.org/10.1128/aem.02848-13.

[9] I.B. Beech, Doctoral dissertation, City of London Polytechnic, Council for National Academic Awards, UK, Biofilm Form. Met. Surf. (1990).

[10] T. Ueki, D.R. Lovley, *Desulfovibrio vulgaris* as a model microbe for the study of corrosion under sulfate-reducing conditions, *mLife* 1 (2022) 13–20, https://doi.org/10.1002/mlf2.12018.

[11] L. Fan, Y. Sun, D. Wang, Y. Zhang, M. Zhang, E. Zhou, D. Xu, F. Wang, Microbiologically influenced corrosion of a novel pipeline steel containing Cu and Cr elements in the presence of *Desulfovibrio vulgaris* Hildenborough, Corros. Sci. 223 (2023) 111421, https://doi.org/10.1016/j.corsci.2023.111421.

[12] D. Wang, C. Yang, B. Zheng, M. Yang, Y. Gao, Y. Jin, Y. Dong, P. Liu, M. Zhang, E. Zhou, T. Gu, D. Xu, F. Wang, Microbiologically influenced corrosion of CoCrFeMnNi high entropy alloy by sulfate-reducing bacterium *Desulfovibrio vulgaris*, Corros. Sci. 223 (2023) 111429, https://doi.org/10.1016/j.corsci.2023.111429.

[13] A. Jayaraman, D. Ornek, D.A. Duarte, C.C. Lee, F.B. Mansfeld, T.K. Wood, Axenic aerobic biofilms inhibit corrosion of copper and aluminum, Appl. Microbiol. Biotechnol. 52 (1999) 787–790, https://doi.org/10.1007/s002530051592.

[14] S. Lu, H. Zhu, J. Sun, T. Gu, N. Xue, S. Chen, W. Dou, Eutrophication of seawater intensified biocorrosion of copper caused by *Desulfovibrio vulgaris* biofilm, J. Mater. Sci. Technol. 194 (2024) 110–123, https://doi.org/10.1016/j.jmst.2024.01.031.

[15] Y. Pu, S. Chen, Y. Hou, S. Hou, F. Feng, Z. Guo, Y.F. Cheng, Unlocking the effect of interfacial microstructure and *Desulfovibrio vulgaris* corrosion characteristics in copper-nickel alloy welded joint, Corros. Sci. 230 (2024) 111947, https://doi.org/10.1016/j.corsci.2024.111947.

[16] F. Guan, X. Zhai, J. Duan, J. Zhang, K. Li, B. Hou, Influence of sulfate-reducing bacteria on the corrosion behavior of 5052 aluminum alloy, Surf. Coat. Technol. 316 (2017) 171–179, https://doi.org/10.1016/j.surfcoat.2017.02.057.

[17] J.S. de Andrade, M.R.S. Vieira, S.H. Oliveira, S.K. de Melo Santos, S.L.URTIGA FILHO, Study of microbiologically induced corrosion of 5052 aluminum alloy by sulfate-reducing bacteria in seawater, Mater. Chem. Phys. 241 (2019) 122296, https://doi.org/10.1016/j.matchemphys.2019.122296.

[18] E.J.C. Goldstein, D.M. Citron, V.A. Peraino, S.A. Cross, *Desulfovibrio desulfuricans* bacteremia and review of human *Desulfovibrio* infections, J. Clin. Microbiol. 41 (2003) 2752, https://doi.org/10.1128/JCM.41.6.2752-2754.2003.

[19] C.C. Johnson, S.M. Finegold, Uncommonly encountered, motile, anaerobic gram-negative bacilli associated with infection, Rev. Infect. Dis. 9 (6) (1987) 1150–1162, https://doi.org/10.1093/clinids/9.6.1150.

[20] R. Akshatha, R. Biswas, G.M. Sasidharan, S. Das, Uncommon isolation of *Desulfovibrio vulgaris* from a depressed fracture wound on the forehead, Anaerobe 65 (2020) 102264, https://doi.org/10.1016/j.anaerobe.2020.102264.

[21] B. Gutarsowska, R. Kotynia, D. Bielinski, R. Anyszka, J. Wrczycki, M. Piotrowska, A. Koziróg, J. Berlowska, P. DziuganNew sulfur organic polymer-concrete composites containing waste materials: Mechanical characteristics and resistance to biocorrosion, Materials 12 (2019) 2602. https://doi.org/10.3390/ma12162602.

[22] J. Guo, S. Yuan, W. Jiang, L. Lv, B. Liang, S.O. Pehkonen, Polymers for combating biocorrosion, Front. Mater. 5 (2018).

[23] K. Chen, X. Yang, Q. Qu, T. Wu, S. Chen, L. LiInhibition of microbiologically influenced corrosion and biofouling of X70 carbon steels by near-superhydrophobic D-cysteine/Ag@ZIF-8 coatings, Corros. Sci. 208 (2022) 110682. https://doi.org/10.1016/j.corsci.2022.110682.

[24] S.M. Chhipa, S. Sharma, A. Kumar Bagha, Recent development in polymer coating to prevent corrosion in metals: a review, Mater. Today Proc. (2024), https://doi.org/10.1016/j.matpr.2024.09.001.

[25] Ö.V. Rúnarsson, J. Holappa, C. Malainer, H. Steinsson, M. Hjálmarsdóttir, T. Nevalainen, M. Mässon, Antibacterial activity of N-quaternary chitosan derivatives: Synthesis, characterization and structure activity relationship (SAR) investigations, Eur. Polym. J. 46 (2010) 1251–1267, https://doi.org/10.1016/j.eurpolymj.2010.03.001.

[26] M. Fathy, A. Badawi, A.M. Mazrouaa, N.A. Mansour, E.A. Ghazy, M.Z. Elsabee, Styrene N-vinylpyrrolidone metal-nanocomposites as antibacterial coatings against sulfate reducing bacteria, Mater. Sci. Eng. C. Mater. Biol. Appl. 33 (2013) 4063–4070, https://doi.org/10.1016/j.msec.2013.05.048.

[27] S.T. Kalajahi, A. Misra, A. Koerdt, Nanotechnology to mitigate microbiologically influenced corrosion (MIC), Front. Nanotechnol. 6 (2024), https://doi.org/10.3389/fnano.2024.1340352.

[28] E.A. González, N. Leiva, N. Vejar, M. Sancy, M. Gulppi, M.I. Azócar, G. Gomez, L. Tamayo, X. Zhou, G.E. Thompson, M.A. Páez, Sol-gel coatings doped with encapsulated silver nanoparticles: inhibition of biocorrosion on 2024-T3 aluminum alloy promoted by *Pseudomonas aeruginosa*, J. Mater. Res. Technol. 8 (2019) 1809–1818, https://doi.org/10.1016/j.jmrt.2018.12.011.

[29] A.I. Suvorova, I.S. Tyukova, Biodegradable systems: Thermodynamics, rheological properties, and biocorrosion, Polym. Sci. Ser. A 50 (2008) 743–750, https://doi.org/10.1134/S0965545X08070031.

[30] P. Jain, B. Patidar, J. Bhawsar, Potential of nanoparticles as a corrosion inhibitor: a review, J. Bio-Tribo-Corros. 6 (2020) 43, https://doi.org/10.1007/s40735-020-00335-0.

[31] P.A. Rasheed, K.A. Jabbar, H.R. Mackey, K.A. Mahmoud, Recent advancements of nanomaterials as coatings and biocides for the inhibition of sulfate reducing bacteria induced corrosion, Curr. Opin. Chem. Eng. 25 (2019) 35–42, https://doi.org/10.1016/j.coche.2019.06.003.

[32] S.S. Sudha, K. Rajamanickam, J. Rengaramanujam, Microalgae mediated synthesis of silver nanoparticles and their antibacterial activity against pathogenic bacteria, *Indian J. Exp. Biol.* 51 (2013) 393–399.

[33] J. Carneiro, J. Tedim, S.C.M. Fernandes, C.S.R. Freire, A.J.D. Silvestre, A. Gandini, M.G.S. Ferreira, M.L. Zheludkevich, Chitosan-based self-healing protective coatings doped with cerium nitrate for corrosion protection of aluminum alloy 2024, Prog. Org. Coat. 75 (2012) 8–13, https://doi.org/10.1016/j.porgcoat.2012.02.012.

[34] J. Carneiro, J. Tedim, S.C.M. Fernandes, C. Freire, A. Gandini, M. Ferreira, M. L. Zheludkevich, Chitosan as a smart coating for controlled release of corrosion inhibitor 2-mercaptobenzothiazole, ECS Electrochem. Lett. 2 (2013) C19–C22, https://doi.org/10.1149/2.002306ee1.

[35] J. Carneiro, J. Tedim, S.C.M. Fernandes, C.S.R. Freire, A. Gandini, M.G.S. Ferreira, M.L. Zheludkevich, Functionalized chitosan-based coatings for active corrosion protection, Surf. Coat. Technol. 226 (2013) 51–59, https://doi.org/10.1016/j.surfcoat.2013.03.035.

[36] S.C.M. Fernandes, C.S.R. Freire, A.J.D. Silvestre, C.P. Neto, A. Gandini, J. Desbrières, S. Blanc, R.A.S. Ferreira, L.D. Carlos, A study of the distribution of chitosan onto and within a paper sheet using a fluorescent chitosan derivative, Carbohydr. Polym. 78 (2009) 760–766, https://doi.org/10.1016/j.carbpol.2009.06.012.

[37] X.N. Gu, Y.F. Zheng, Q.X. Lan, Y. Cheng, Z.X. Zhang, T.F. Xi, D.Y. Zhang, Surface modification of an Mg-1Ca alloy to slow down its biocorrosion by chitosan, Biomed. Mater. 4 (2009) 044109, https://doi.org/10.1088/1748-6041/4/4/044109.

[38] V.V. Nelson, O.T. Maria, S.V. Mamiè, P.C. Maritza, Microbiologically influenced corrosion in aluminium alloys 7075 and 2024. Aluminium Alloys - Recent Trends in Processing, Characterization, Mechanical Behavior and Applications, IntechOpen, 2017 in:10.5772/intechopen.70375.

[39] M. D'Almeida, N. Attik, J. Amalric, C. Brunon, F. Renaud, H. Abouelleil, B. Toury, B. Grosgeoseat, Chitosan coating as an antibacterial surface for biomedical applications, PLoS ONE 12 (2017) e0189537, https://doi.org/10.1371/journal.pone.0189537.

[40] J.R. Postgate, L.L. Campbell, Classification of *Desulfovibrio* species, the nonsporulating sulfate-reducing bacteria, Bacteriol. Rev. 30 (1966) 732, https://doi.org/10.1128/br.30.4.732-738.1966.

[41] 2017, ASTM D335909e2, Standard Test Methods for Rating Adhesion by Tape Test10.1520/D3359-09E02.

[42] V. Drebezhova, F. Hakil, R. Grimaud, H. Gojzewski, J.G. Vancso, C. Nardin, Initial bacterial retention on polydimethylsiloxane of various stiffnesses: the relevance of modulus (mis)match, Colloids Surf. B Biointerfaces 217 (2022) 112709, https://doi.org/10.1016/j.colsurb.2022.112709.

[43] D. Grosso, How to exploit the full potential of the dip-coating process to better control film formation, J. Mater. Chem. 21 (2011) 17033–17038, https://doi.org/10.1039/C1JM12837J.
[44] S.C.M. Fernandes, Doctoral dissertation, Universidade de Aveiro, Nov. Mater. Based Chitosan, Deriv. Cellul. Fibres (2010).

[45] X. Wang, Z. Xi, Z. Liu, L. Yang, Y. Cao, The fabrication and property of hydrophilic and hydrophobic double functional bionic chitosan film, J. Nanosci. Nanotechnol. 11 (2011) 9737-9740, https://doi.org/10.1166/jnn.2011.5327.

[46] M. Gatto, D. Ochi, C.M.P. Yoshida, C.F. da Silva, Study of chitosan with different degrees of acetylation as cardboard paper coating, Carbohydr. Polym. 210 (2019) 56-63, https://doi.org/10.1016/j.carbpol.2019.01.053.

[47] A.I. Barabanova, T.A. Pryakhina, E.S. Afanas'ev, B.G. Zavin, Ya.S. Vygodskii, A. Askadskii, O.E. Philippova, A.R. Khokhlov, Anhydride modified silica nanoparticles: preparation and characterization, Appl. Surf. Sci. 258 (2012) 3168-3172, https://doi.org/10.1016/j.apsusc.2011.11.057.

[48] R. Chen, H. Qu, S. Guo, P. Ducheyne, The design and synthesis of a soluble composite silica xerogel and the short-time release of proteins, J. Mater. Chem. B 3 (2015) 3141-3149, https://doi.org/10.1039/C4TB01622J.

[49] S. Falaize, S. Radin, P. Ducheyne, *In vitro* behavior of silica-based xerogels intended as controlled release carriers, J. Am. Ceram. Soc. 82 (1999) 969-976, https://doi.org/10.1111/j.1151-2916.1999.tb01861.x.

[50] S. Farris, L. Introzzi, P. Biagioni, T. Holz, A. Schiraldi, L. Piergiovanni, Wetting of biopolymer coatings: Contact angle kinetics and image analysis investigation, Langmuir 27 (2011) 7563-7574, https://doi.org/10.1021/la2017006.

[51] A. Cojocaru, I. Maior, I.A. Ciobotaru, D.-I. Văireanu, The influence of chitosan biopolymer on aluminum corrosion resistance in chloride ions environment,

Macromol. Symp. 396 (2021) 2000317, https://doi.org/10.1002/masy.202000317.

[52] D.M. Campos, B. Toury, M. D'Almeida, G.N. Attik, A. Ferrand, P. Renoud, B. Grosgogeat, Acidic pH resistance of grafted chitosan on dental implant, Odontology 103 (2015) 210-217, https://doi.org/10.1007/s10266-014-0162-5.

[53] F. Song, H. Koo, D. Ren, Effects of material properties on bacterial adhesion and biofilm formation, J. Dent. Res. 94 (2015) 1027-1034, https://doi.org/10.1177/0022034515587690.

[54] Y. Wang, Z. Bian, Y. Wang, Biofilm formation and inhibition mediated by bacterial quorum sensing, Appl. Microbiol. Biotechnol. 106 (2022) 6365-6381, https://doi.org/10.1007/s00253-022-12150-3.

[55] H. Li, D. Xu, Y. Li, H. Feng, Z. Liu, X. Li, T. Gu, K. Yang, Extracellular electron transfer is a bottleneck in the microbiologically influenced corrosion of C1018 carbon steel by the biofilm of sulfate-reducing bacterium *Desulfovibrio vulgaris*, PLoS ONE 10 (2015) e0136183, https://doi.org/10.1371/journal.pone.0136183.

[56] J.P. Fernández-Hernán, A.J. López, B. Torres, J. Rams, Influence of roughness and grinding direction on the thickness and adhesion of sol-gel coatings deposited by dip-coating on AZ31 magnesium substrates. A Landau-Levich equation revision, Surf. Coat. Technol. 408 (2021) 126798, https://doi.org/10.1016/j.surfcoat.2020.126798.

[57] H. Zhao, M. Yu, J. Liu, S. Li, B. Xue, M. Liang, Effect of surface roughness on corrosion resistance of sol-gel coatings on AA2024-T3 alloy, J. Electrochem. Soc. 162 (2015) C718, https://doi.org/10.1149/2.0271514jes.