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Article

Multimodification of a 304 Stainless Steel Surface Based on DA/PEI/SiO2 for Improving Surface Antimicrobial Performance

by
Zhimin Cao
1,*,
Mingyi Zhu
2,
Xuxu Dong
2,
De Liu
2 and
Pan Cao
2,*
1
Institute of Intelligent Manufacturing and Smart Transportation, Suzhou City University, Suzhou 215104, China
2
School of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China
*
Authors to whom correspondence should be addressed.
Coatings 2023, 13(11), 1845; https://doi.org/10.3390/coatings13111845
Submission received: 7 October 2023 / Revised: 25 October 2023 / Accepted: 26 October 2023 / Published: 27 October 2023
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Abstract

:
An innovative antifouling composite coating comprising dopamine (DA), polyethyleneimine (PEI), and silica (SiO2) was developed through a straightforward and environmentally friendly approach. Initially, silica nanoparticles comodified with DA and PEI were meticulously deposited onto 304 stainless steel surfaces pretreated with dopamine to achieve a uniformly distributed nanocomposite surface. Comprehensive analytical techniques, including Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectrometry (XPS), field emission scanning electron microscopy (SEM), contact angle measurement (CA), and 3D optical profilometry, were employed to affirm the successful preparation of the silica nanocomposite coatings and the effective grafting of MAG II. The antibacterial and antibiofilm performance of the DA/PEI/SiO2-modified surface was rigorously assessed using Vibrio natriegens (V. natriegens), yielding compelling results indicating a substantial 51.4% reduction in biofilm formation on the SS-DA/PEI/SiO2 sample surfaces, coupled with an impressive 95.2% decrease in V. natriegens adhesion. This pioneering research introduces an innovative strategy for the development of antimicrobial surfaces with promising applications in medical devices, aquaculture, and related fields.

1. Introduction

The biofouling and contamination of metal surfaces caused by fouling organism adhesion are major problems in daily life and many industry fields [1,2]. For example, biological fouling on the hull surface can accelerate the deterioration of surface corrosion, leading to structural and functional defects, thereby increasing navigation resistance, and leading to higher fuel consumption and maintenance costs [3,4,5]. Nowadays, it is widely believed that fouling organisms use their cells to adhere to the substrate surface for survival, forming a multilevel phenomenon of biofilm and microbial communities. The biofilm of fouling organisms is considered a microbial population enclosed by biopolymer matrices that adhere to each other and/or a surface [6]. In the natural environment, bacterial survival can be classified into two states: planktonic (floating) and sessile (attached). Biofilms play a crucial role in enabling bacteria to thrive and withstand challenging environmental conditions. These biofilms readily form on both inert and biological surfaces in natural settings as well as in industrial installations, significantly impacting their performance [7].
Surface contamination can be mitigated through the utilization of well-suited materials or surface modifications [8]. Several researchers have demonstrated that developing novel techniques to alter the surface properties of existing materials is an effective and cost-efficient approach. In recent years, a multitude of methods for modifying the solid surfaces of antimicrobial peptides (AMPs) have been explored, encompassing monomer self-assembly (SAMs), chemical coupling, layer-by-layer assembly (LBL), and polymer brushing, among others. Despite the success achieved by these techniques in achieving their modification objectives, they may lack the broad-spectrum characteristics desired for the modified substrate [9]. Dopamine is prone to oxidative polymerization in oxygen-rich alkaline solutions, leading to the formation of polydopamine (PDA). PDA possesses exceptional adhesion properties and a profusion of functional groups, rendering it highly promising for surface modification applications. PDA has evolved into a widely employed precursor for surface-bound organic compounds, including antimicrobial peptides. During the oxidative polymerization of dopamine into PDA, numerous functional groups, such as catechins and amines, are generated [10]. At low concentrations of AMPs, surfaces modified with these peptides exhibit outstanding anti-adhesion and antibacterial activity against organisms like Pseudomonas aeruginosa [11]. Yu et al. introduced a straightforward, matrix-independent, antifouling surface by combining antimicrobial peptides with PDA, demonstrating remarkable effectiveness in deterring biofilm formation [12]. Xiao et al. used a combination of sum frequency generation (SFG) vibrational spectroscopy and ground microscopy to investigate the structure and activity of surface-immobilized AMPs. They observed that surface-immobilized peptides not only altered their orientation but also exhibited bactericidal properties [13]. In addition to AMPs, various substances like nanoparticles, polyethyleneimine (PEI), polyethylene glycol (PEG), and oligo (ethylene glycol) (OEG) have found application in antifouling through grafting onto substrates via PDA [14]. Nevertheless, the precise mechanism of dopamine polymerization and the interactions between AMPs and PDA remain subjects of ongoing research. Silicon dioxide nanoparticles, being among the most significant inorganic nonmetallic hydrophobic nanomaterials, are employed in the fabrication of antifouling coatings on surfaces [15]. Silicon dioxide is easy to self-aggregate in solution, reducing surface binding capacity and stability. Dopamine is widely used in material surface modification due to its excellent physical and adhesion properties. Previous studies have shown that adding PEI to a dopamine solution can promote the uniform polymerization of dopamine and the uniform codeposition of DA-PEI, thereby forming a smooth, positively charged coating [16,17,18]. By codepositing DA/PEI/silica nanoparticles to modify the metal surface, a uniformly distributed composite nano antifouling coating can be obtained.
304 stainless steel (SS) has good mechanical properties and corrosion resistance; therefore, it is used in multiple fields. In this investigation, uniformly distributed nanocoating was meticulously deposited onto the surface of dopamine-functionalized stainless steel through the codeposition of DA/PEI/silica nanoparticles. This process yielded a composite coating with exceptional antibacterial properties. The successful preparation and grafting of functionalized silica nanocomposites onto stainless steel substrates were unequivocally confirmed through the utilization of surface characterization techniques. To assess the antibiofilm and antibacterial attributes of these functionalized surfaces, they were subjected to testing with common Gram-negative bacteria, such as Vibrio natriegens. Additionally, the stability of the surface coating on the modified samples was thoroughly analyzed. Long-term experiments unequivocally demonstrated the exceptional antifouling stability of the modified surface. This research presents a pioneering strategy with the potential to revolutionize surface antifouling applications not only within the marine industry but also in various related fields.

2. Materials and Methods

2.1. Materials

304 annealed stainless steel (SS) samples were purchased from Jiangsu Congbang Special Steel Co., Ltd. (Suzhou, China). Silicon dioxide (SiO2, purity 99.5%, 30 nm) and polyethylenimine (PEI, 99%, molecular weight: 600) were purchased from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China). Dopamine hydrochloride (purity 98%), ethanol absolute (≥99.7%), tris (hydroxymethyl) aminomethane (TRIS ≥ 99.9%), acetic acid (33%), crystal violet (CV, 0.1%), propidium iodide (PI), and glutaraldehyde (purity 50%) were obtained from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). 2216E liquid medium and 2216E agar were purchased from Qingdao Hope Bio-Technology Co., Ltd. (Qingdao, China). Phosphate buffered saline (PBS, pH = 7.4) was supplied by Beijing Wokai Biotechnology Co., Ltd. (Beijing, China). Distilled water was obtained using a Milli-Q water purification system. All the reagents were of analytical grade.

2.2. Preparation of SS-DA/PEI/SiO2

304 SS surface was polished with sandpaper (400, 800, 1000, and 1200#) until it was smooth and clean. The polished samples were then immersed into acetone solution and ethanol solution in successive 10-minute intervals and cleaned with deionized water by ultrasound for 10 min. Subsequently, the treated and dried stainless steel sample was immersed in a 2 mg/mL dopamine (dissolved in Tris-HCl buffer, pH = 8.5) solution at 37 °C for 12 h to activate the sample’s surface. Silica dioxide (SiO2) particles weighing 1.0 g were immersed in a 50 mL Tris-HCl solution with a pH of 8.5. The suspension was then subjected to 10 min of sonication to achieve a uniform dispersion of the silica particles. Subsequently, a mixture of dopamine and polyethyleneimine (PEI) in a 1:1 mass ratio was introduced into the silica suspension, with a final concentration of 2 mg/mL. The mixed DA/PEI/SiO2 solution was obtained after the reaction under 25 °C for 12 h, and then the dopamine-treated surfaces (SS-DA) were immersed in DA/PEI/SiO2 solution under 25 °C for 24 h to prepare the surface modified with dopamine, PEI, and SiO2, which denoted as SS-DA/PEI/SiO2 (Figure 1). In order to compare the effect of dopamine addition sequence on the grafting amount of SS-DA/PEI/SiO2, a mixture solution of PEI/SiO2 was used to modify dopamine-treated SS directly, and the sample was named SS-DA-PEI/SiO2.

2.3. Surface Characterization

The ATR-FTIR spectrometer (NICOLET Is50, Thermo Fisher Scientific, Carlsbad, CA, USA) is used to collect surface functional groups, with a scanning range of 400–4000 cm−1 and a spectral resolution of 4 cm−1 for 128 scans. The sample surface’s water contact angle was evaluated by a contact angle measuring instrument (JC2000D, Shanghai, China); three points were taken for each sample surface measurement. X-ray photoelectron spectroscopy (XPS, ESCALAB250Xi, Thermo Fisher Scientific, Carlsbad, CA, USA) was used to analyze surface chemical compositions, and the surface profile measuring instrument (LI-3, Wuhan, China) was selected to characterize the roughness. The surface morphology of the samples and qualitative analysis of the antibacterial properties of the modified surfaces were characterized by scanning electron microscopy (SEM, GeminiSEM 300, Oberkochen, Germany) with an EDS (Energy Dispersive Spectrometer, Thermo Fisher Scientific, Carlsbad, CA, USA). UV-Vis spectrophotometer (L5S, Wuhan, China) was used to detect the optical density (OD) of sample surface eluate. The antibacterial performance of the surfaces was analyzed by the images of a confocal laser scanning microscope (CLSM, Leica TCS SP8 STED, Wetzlar, Germany).

2.4. Antimicrobial Testing

Vibrio natriegens is a common Gram-negative bacterium often used for evaluating surface antifouling performance due to its relatively strong adhesion and biofilm-forming capacity. In this study, V. natriegens was selected as the target fouling organism to analyze the surface antimicrobial performance.
Antibacterial testing: the 200 μL V. natriegens solution was tiled and cultured on the 2216E Agar culture plate for 24 h (30 °C), and then the monoclonal bacteria were picked to obtain the bacterial solution (30 °C, 130 rpm, 48 h). The bacterial solution was diluted into a concentration of 1 × 106 CFU/mL, and the 304 SS, SS-DA, and SS-DA/PEI/SiO2 were then cultured in the V. natriegens solution (30 °C, 48 h). The bacterial solution-treated samples were washed with sterile PBS solution to remove unattached or loosely attached bacteria; SS-DA/PEI/SiO2 was then immersed into 2.5% glutaraldehyde solution (4 °C, 12 h). Half of the glutaraldehyde-treated samples were sequentially dehydrated with ethanol at concentrations of 25% (5 min), 50% (5 min), 75% (5 min), 90% (5 min), and 100% (20 min), and dried in a vacuum drying oven for 24 h at 37 °C. The samples were used for SEM analysis. The other half of the glutaraldehyde-treated samples were stained with a sterile PBS solution containing PI at a concentration of 50 μg/mL for 30 min in the dark. The surface bacterial adhesion images were collected by CLSM after washing using a sterile PBS solution. The excitation wavelength of the microscopy is 535 nm and the emission wavelength is 615 nm. The attachment rate of bacteria was calculated by the formula: adhesion% = bacterial attachment area/total area of the field of view × 100%. The adhesion% is analyzed by ImageJ.
Antibiofilm testing: In the antibiofilm testing, Vibrio natriegens at a concentration of 1 × 106 CFU/mL was utilized to inoculate both SS and SS-DA/PEI/SiO2 samples, each placed in separate wells of a 24-well bacterial culture plate with 1 mL per well. Subsequently, the plate was sealed and incubation occurred on a shaker at 30 °C for 24 h. Following incubation, the samples were carefully removed and rinsed with sterile PBS buffer to eliminate loosely adhered bacteria. The surfaces were then stained using a 0.1% crystal violet solution for 15 min (500 μL per well). Subsequently, the stained surfaces underwent additional rinsing with a sterile PBS buffer until there was no noticeable residual color during the final rinse. The dried and stained surfaces were immersed in a 33% acetic acid solution for 15 min to collect the washing solution, which was later transferred to a colorimetric dish (3 mL per tube) for the determination of the optical density (OD) using a UV-Vis spectrophotometer.
Durability testing of the coating: To assess the durability of the coating, the samples were immersed in a sterile PBS solution for durations of 1, 3, and 7 days, respectively. Subsequent to each immersion period, the antibiofilm and antibacterial performance of the samples treated with sterile PBS solution was evaluated using the aforementioned antibiofilm and antibacterial testing methods.

3. Results and Discussion

The synthesis of SS-DA-PEI/SiO2 is illustrated in Figure 1. Dopamine is prone to self-aggregation and reaction under weakly alkaline and oxygen-rich conditions, thus adhering to almost all substrate surfaces [2,16]. A two-step modification method was used to obtain a uniformly distributed antibacterial layer on the surface. Compared with the previous preparation of antifouling coatings, this study first used dopamine as a coupling agent to enhance DA/PEI codeposited with silica nanoparticles onto the SS surface, which greatly improved the surface bonding performance and increased the binding amount. The dopamine was self-polymerized under enriched oxygen and weak alkali solution and adhered to silica particles’ surface. DA reacts with the -NH2 of polyethyleneimine via Michael addition or Schiff base reaction during the codeposition process to generate amino-rich silica nanocomposites. The DA-PEI/SiO2 then reacted with catechol groups of SS-DA of 304 SS to fabricate a uniformly distributed DA-PEI/SiO2 modified antimicrobial surface.
The successful fabrication of silica nanocomposite coatings was unequivocally established by assessing the surface functional groups of SS-DA/PEI/SiO2 and SS-DA-PEI/SiO2 samples through Fourier transform infrared spectrometry (FTIR). The FTIR analysis revealed distinctive peaks: the bands at 2970–3015 cm−1 were ascribed to the C–H stretching of CH3 and CH2, while the peak near 800 cm−1 was attributed to Si-OH stretching vibrations and the two peaks (blue circle) around 1100 cm−1 was contributed to Si-O-Si symmetric stretching vibrations, as depicted in Figure 2 [19]. Furthermore, the peak between 2300 cm−1 and 2400 cm−1 corresponded to O=C=O vibrations, and the peak at approximately 1660 cm−1 was associated with the C=N bond of polyethyleneimine (PEI) and dopamine (DA). Additional peaks near 1410 and 1566 cm−1 were attributed to C-N and N-H vibrations [20], whereas the broad peaks spanning from 3200 to 3500 cm−1 were attributed to -OH stretching vibrations [9]. The broader peaks ranging from 3500 to 3750 cm−1 were a consequence of -OH stretching vibrations arising from the oxidative polymerization of the nanosilica surface and dopamine, resulting in the formation of hydroxyl groups within polydopamine. The peak observed at 1750 cm−1 was a manifestation of the C=O stretching vibrations of polydopamine and its intermediate products [21]. Collectively, these analyses serve as conclusive evidence confirming the successful modification of SS with DA/PEI/SiO2. The presence of Si-containing functional groups on the surface of SS-DA/PEI/SiO2 and the significantly higher peaks of SS-DA/PEI/SiO2 compared to SS-DA-PEI/SiO2 indicated that dopamine modification followed by DA/PEI/SiO2 modification would lead to more silica binding to the surface.
For a comprehensive analysis of the elemental composition on the SS-DA/PEI/SiO2 surface, X-ray photoelectron spectroscopy (XPS) was employed to acquire XPS spectra and quantitative data (Figure 3 and Table 1). Figure 3D illustrates the C1s peaks of the surfaces. The C peaks at 284.8, 286.18, and 288.01 eV correspond to C-C/C-H, C-O/C-N, and C=N, respectively [20]. In Figure 3C, the N1s peaks are evident, with peaks at 399.93 and 402.23 eV corresponding to C-N and C=N, respectively [16]. The presence of C=N bonds is attributed to the reaction between polyethyleneimine (PEI) and dopamine [22,23]. Figure 3A displays the Si 2p peak at 103 eV, along with peaks at 102.06 and 103.85 eV, signifying the formation of Si-C and Si-O bonds [24]. Additionally, peaks at 154.8 and 198.9 eV are derived from Si2s and C-Cl, respectively, while peaks at 580.1 and 710.5 eV on the SS are attributed to Cr 2p3/2 and Fe 2p3/2 elements, respectively [25]. The elemental content of Fe in 304 SS was found to be 11.6%, while the surface contained only 1.9% N, with no detectable Si content. After dopamine treatment, the N and C content on the DA-SS surface significantly increased due to self-polymerization and the introduction of polydopamine under weak alkaline and oxygen-rich conditions. The N element content notably increased from 1.9% to 14.8% after modification, primarily as a result of the amine-related groups present in PEI, polydopamine, and intermediate products of polydopamine. Subsequently, changes in the C and O element content confirmed the presence of C, N, and O elements stemming from the introduction of DA/PEI/SiO2. The Si content increased to 2.0%, providing clear evidence of the successful deposition of DA/PEI/SiO2 onto the substrate.
Figure 4 demonstrates the SEM images of SS-DA/PEI/SiO2, from which the morphology of the DA/PEI/SiO2-treated surface can be found. A nanocoating was distributed uniformly on the SS surface after the DA/PEI/SiO2 treatment, and the enlarged SEM image illustrated that the DA/PEI/SiO2 intersect deposited on the 304 stainless steel surface. In order to measure the coating thickness, the sample was rotated 90 degrees to obtain a side view of the sample. From Figure S1, it can be seen that the surface thickness of the sample is between 700–750 nm. EDS can collect elemental information on the surface, and it can be seen that DA/PEI/SiO2 particles, especially SiO2, were uniformly distributed on the substance surface (Figure 5). In contrast, the peaks around 5.4, 5.8, and 6.4 KeV come from elements Cr, Mn, and Fe of the SS surface [26], which, because the sample surface has a porous structure, allows some of the substrate surface to be detected (Figure 4B). The measured amount of elements was different from the XPS results because the detected depth of EDS was usually up to 2 μm, while XPS only measures a few nanometers deep. Surface profile measuring instrument was used to analyze the surface parameters of the SS before and after DA/PEI/SiO2 modified. It is clear from Table 2 that after codeposition of DA/PEI/SiO2 onto 304 SS surface, the average surface roughness Ra of the surface decreased from 232.7 nm to 109.4 nm. The maximum profile peak height increased from 1.1 μm to 1.4 μm, the maximum profile valley depth value Rv increased from −2.8 μm to −2.2 μm, and the root mean square deviation of the profile Rq value changed from 316.7 nm to 180.2 nm, which may be due to that DA/PEI/silica filled the grooves of the SS surface. A layer of uniformly distributed composite coating was formed on the surface uniform composite coating so that the Rq value is reduced, which further confirmed that DA/PEI/SiO2 deposited onto the substrate surface.
Surface wettability is commonly assessed using contact angles, and the contact angle measurements for the sample surface before and after modification are presented in Figure 6. Following the dopamine modification, the contact angle decreased from 67.5° to 42.3°. Subsequently, with the codeposition of DA/PEI/silica, the contact angle on the SS-DA/PEI/SiO2 surface further decreased to 16.5°. This substantial reduction in contact angle reflects the outstanding hydrophilic properties of the modified sample surface. The remarkable hydrophilicity observed is attributed to several factors. Dopamine molecules are rich in hydrophilic functional groups, such as phenolic hydroxyl and amino groups. Additionally, polyethyleneimine (PEI) contains a significant number of amine groups, and silica nanoparticles possess hydrophilic groups, specifically hydroxyl groups. The surface of the silica nanocomposite, modified by dopamine and PEI, incorporates hydrophilic functional groups, including hydroxyl and amino groups, collectively contributing to the heightened hydrophilic nature of the modified sample surface [10,27].
Bacterial attachment and biofilm formation are the primary stages of surface fouling; therefore, the amount of bacterial attachment to the sample surface and the amount of biofilm formation are often used to quantify surface fouling. Figure 7 shows the morphology of bacteria in SS and SS-DA/PEI/SiO2 surfaces; the attached bacteria decreased by 78.3% after SS-DA/PEI/SiO2 treatment because DA and PEI possessed moderate antibacterial performance, and SiO2 nanoparticles have significant antibacterial adhesion properties. While the cell integrity of bacteria on the SS-DA/PEI/SiO2 surface has not been affected, the DA/PEI/SiO2 achieved a surface antifouling effect through antibacterial rather than killing bacteria [28].
Following the immersion of both SS and SS-DA/PEI/SiO2 samples in a bacterial solution, the surfaces were subsequently stained with crystal violet, and the optical density (OD) values of the acetic acid cleaning solution were recorded. It is important to note that higher OD values indicate a greater quantity of biofilm formation on the surfaces. Figure 8 illustrates the OD values at 590 nm for various surface eluents, with the data revealing that dopamine modification has a minimal impact on the formation of biofilms. The Figure illustrates that the eluate from the surface of the 304 stainless steel exhibited a higher optical density (OD) value. Subsequently, after the modification with DA/PEI/SiO2, the OD value decreased from 1.289 to 0.662. The untreated sample surface was prone to bacterial adhesion, resulting in a substantial biofilm formation. However, the application of DA/PEI/SiO2 nanoparticles led to a notable reduction in the quantity of biofilm on the surface. This reduction can be attributed to the synergistic antibacterial and adhesion-inhibiting effects imparted by the modification. The antibacterial robustness of the surface modified by DA/PEI/SiO2 was also explored by analyzing the biofilm amount on the surface for 7 days, and the results showed that the OD value of the sample surface slightly increased and stabilized after 3 and 7 days of immersion. After the treatment of nanoparticles, the adhesion ability of bacteria on the substrate surface was greatly reduced, and the number of bacteria attached to the substrate was significantly reduced, resulting in a decrease in their film-forming capacity on the surface and a reduction in the amount of biofilm generated on the surface [7,29].
SEM images have limitations in visualizing the extent of bacterial adhesion on the sample surface at a larger scale. To address this limitation, Confocal laser scanning microscopy (CLSM) was employed to provide a significantly broader field of view for the assessment of the sample surface’s antibacterial performance. CLSM images of the SS, SS-DA/PEI/SiO2 surface were acquired following a 24-hour coculture with a bacterial solution (Figure 9). The surface coverage for SS, SS-DA/PEI/SiO2, and SS-DA/PEI/SiO2 after 7 days of immersion was found to be 10.613%, 0.506%, and 2.711%, respectively. In the case of the original sample surface, a substantial amount of bacteria adhered to it. In contrast, after modification with DA/PEI/SiO2, the bacterial adhesion was significantly reduced. This reduction can be attributed to the synergistic antibacterial effect resulting from the interaction between dopamine (DA), polyethyleneimine (PEI), and SiO2. Moreover, quaternized PEI played a role in disrupting bacterial biofilms through electrostatic interactions with the biofilm [30,31,32]. The unbound nanoparticles detach from the surface and tend to stabilize as the soaking time increases, reducing the ability to inhibit bacteria and thus reducing the surface’s antibacterial ability.
The SS-DA-PEI/SiO2 surface preparation was compared with existing surface modification methods (Table S1). The surface was modified twice with dopamine, combining PEI and SiO2 onto the sample surface, giving it excellent antibacterial properties. Moreover, the modified material is inexpensive and easy to obtain, and the preparation process was also simple. It did not require the use of large instruments or high- or low-temperature conditions, making it easy to prepare in large quantities and apply to the field of antifouling on the surface of medical implants, food processing equipment, and marine facilities.

4. Conclusions

In summary, SS-DA/PEI/SiO2 nanocomposite-coated surfaces were prepared through DA, PEI, and SiO2 codeposition to modify the DA-treated 304 SS surface. The morphological structure, physicochemical properties, and antifouling ability of the surface before and after modification were tested and studied in detail. The following conclusions were obtained: (1) surface profile measuring instrument, contact angle measuring instrument, SEM, and EDS analysis showed that the surface roughness, wettability, and morphology of the modified sample changed. Compared to the 304 SS, a uniform nanocomposite coating was deposited on the surface of the SS-DA/PEI/SiO2 sample. Further XPS analysis revealed that the sample surface was successfully modified with nano-silica. (2) The antibiofilm and antibacterial properties of the SS-DA/PEI/SiO2 surface, both before and after modification, were assessed using Vibrio natriegens. The results demonstrated that the antibiofilm rates on the SS-DA/PEI/SiO2 sample surfaces reached 51.4%, and the antibacterial rates reached 95.2%. The collective action of DA, PEI, and SiO2 synergistically amplified the antimicrobial attributes of the stainless steel surface. Additionally, the modified surface exhibited good stability. This synthesis of a composite coating introduces a novel strategy for the application of antimicrobial coatings on various surfaces.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/coatings13111845/s1, Figure S1: Side view of SS-DA/PEI/SiO2 surface under scanning electron microscopy; Table S1: Surface modification techniques.

Author Contributions

Conceptualization, Z.C., D.L. and P.C.; methodology, Z.C. and D.L.; validation, Z.C. and M.Z.; formal analysis, Z.C.; investigation, Z.C. and X.D.; data curation, Z.C., X.D. and D.L.; writing—original draft preparation, Z.C. and P.C.; writing—review and editing, Z.C. and P.C.; supervision, P.C.; funding acquisition, Z.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Industry-University Cooperation Collaborative Education Project of the Ministry of Education (No. 22107131063105).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors gratefully acknowledge the financial support of the Industry-University Cooperation Collaborative Education Project of the Ministry of Education (No. 22107131063105).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic illustration of SS-DA/PEI/SiO2-treated surfaces and antimicrobial tests.
Figure 1. Schematic illustration of SS-DA/PEI/SiO2-treated surfaces and antimicrobial tests.
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Figure 2. FTIR spectra of SS, SS-DA-PEI/SiO2, and SS-DA/PEI/SiO2.
Figure 2. FTIR spectra of SS, SS-DA-PEI/SiO2, and SS-DA/PEI/SiO2.
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Figure 3. XPS spectra of the sample surface. (A): Full spectrum; (B): Si 2p; (C): N 1s; (D): C 1s.
Figure 3. XPS spectra of the sample surface. (A): Full spectrum; (B): Si 2p; (C): N 1s; (D): C 1s.
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Figure 4. SEM images of SS-DA/PEI/SiO2. (A): 10 KX; (B): 20 KX.
Figure 4. SEM images of SS-DA/PEI/SiO2. (A): 10 KX; (B): 20 KX.
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Figure 5. EDS elemental map of SS-DA/PEI/SiO2 surface (A) and individual elemental distribution maps (B).
Figure 5. EDS elemental map of SS-DA/PEI/SiO2 surface (A) and individual elemental distribution maps (B).
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Figure 6. The water contact angle of the SS-DA/PEI/SiO2 surface.
Figure 6. The water contact angle of the SS-DA/PEI/SiO2 surface.
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Figure 7. The SEM adhesion images of V. natriegens on surfaces of SS (A) and SS-DA/PEI/SiO2 (B).
Figure 7. The SEM adhesion images of V. natriegens on surfaces of SS (A) and SS-DA/PEI/SiO2 (B).
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Figure 8. The OD 590 nm values of different surface eluents. * p < 0.05, ** p < 0.01.
Figure 8. The OD 590 nm values of different surface eluents. * p < 0.05, ** p < 0.01.
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Figure 9. Confocal Laser Scanning Microscopy images depicting the attachment of Vibrio natriegens to the surfaces. (A): SS; (B): SS-DA/PEI/SiO2 (1 day); (C): SS-DA/PEI/SiO2 (7 days).
Figure 9. Confocal Laser Scanning Microscopy images depicting the attachment of Vibrio natriegens to the surfaces. (A): SS; (B): SS-DA/PEI/SiO2 (1 day); (C): SS-DA/PEI/SiO2 (7 days).
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Table 1. Quantitative analysis results obtained through XPS.
Table 1. Quantitative analysis results obtained through XPS.
SamplesC (at%)N (at%)O (at%)Si (at%)Ni (at%)Fe (at%)
SS30.31.949.506.611.6
SS-DA70.712.017.3000
SS-DA/PEI/SiO261.714.821.52.000
Table 2. Ra, Rv, and Rq values for different sample surfaces.
Table 2. Ra, Rv, and Rq values for different sample surfaces.
SamplesRa (nm)Rp (μm)Rv (μm)Rq (nm)
SS232.71.1−2.8316.7
SS-DA/PEI/SiO2109.41.4−2.2180.2
Notes: Ra denotes the arithmetical mean deviation of the profile. Rp denotes the maximum profile peak height. Rv denotes the maximum profile valley depth. Rq denotes the root mean square deviation of the profile.
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Cao, Z.; Zhu, M.; Dong, X.; Liu, D.; Cao, P. Multimodification of a 304 Stainless Steel Surface Based on DA/PEI/SiO2 for Improving Surface Antimicrobial Performance. Coatings 2023, 13, 1845. https://doi.org/10.3390/coatings13111845

AMA Style

Cao Z, Zhu M, Dong X, Liu D, Cao P. Multimodification of a 304 Stainless Steel Surface Based on DA/PEI/SiO2 for Improving Surface Antimicrobial Performance. Coatings. 2023; 13(11):1845. https://doi.org/10.3390/coatings13111845

Chicago/Turabian Style

Cao, Zhimin, Mingyi Zhu, Xuxu Dong, De Liu, and Pan Cao. 2023. "Multimodification of a 304 Stainless Steel Surface Based on DA/PEI/SiO2 for Improving Surface Antimicrobial Performance" Coatings 13, no. 11: 1845. https://doi.org/10.3390/coatings13111845

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