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. 2024 Jul 9;16(29):38631–38644. doi: 10.1021/acsami.4c02371

Long-Term Prevention of Biofilm Formation by Polycatechol-Based Supramolecular Assemblies with Low Molecular Weight Polymers on Surfaces

Hossein Yazdani-Ahmadabadi †,‡, Kai Yu †,§, Kevin Gonzalez †,§, Haiming D Luo †,‡, Dirk Lange ∥,⊥, Jayachandran N Kizhakkedathu †,‡,§,#,*
PMCID: PMC11285367  PMID: 38980701

Abstract

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Achievement of a stable surface coating with long-term resistance to biofilm formation remains a challenge. Catechol-based polymerization chemistry and surface deposition are used as tools for surface modification of diverse materials. However, the control of surface deposition of the coating, surface coverage, coating properties, and long-term protection against biofilm formation remain to be solved. We report a new approach based on supramolecular assembly to generate long-acting antibiofilm coating. Here, we utilized catechol chemistry in combination with low molecular weight amphiphilic polymers for the generation of such coatings. Screening studies with diverse low molecular weight (LMW) polymers and different catechols are utilized to identify lead compositions, which resulted in a thick coating with high surface coverage, smoothness, and antibiofilm activity. We have identified that small supramolecular assemblies (∼10 nm) formed from a combination of polydopamine and LMW poly(N-vinyl caprolactam) (PVCL) resulted in relatively thick coating (∼300 nm) with excellent surface coverage in comparison to other polymers and catechol combinations. The coating properties, such as thickness (10–300 nm) and surface hydrophilicity (with water contact angle: 20–60°), are readily controlled. The optimal coating composition showed excellent antibiofilm properties with long-term (>28 days) antibiofilm activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. We further utilized the combination of optimal binary coating with silver to generate a coating with sustained release of silver ions, resulting in killing both adhered and planktonic bacteria and preventing long-term surface bacterial colonization. The new coating method utilizing LMW polymers opens a new avenue for the development of a novel class of thick, long-acting antibiofilm coatings.

Keywords: supramolecular assemblies, low molecular weight amphiphilic polymers, thick polydopamine coatings, antibiofilm coatings, long-term activity, antifouling coatings, broad spectrum antibacterial coating

1. Introduction

The risk of the incidence of infection remains high during implantation/insertion of medical devices.1−4 One of the strategies to overcome this challenge is to coat devices with antimicrobial and antibiofilm coatings. Catechol chemistry has been intensively used for the development of antibacterial coatings in recent years.5−8 The most well-known catechol-containing molecule is dopamine, which is used in coating preparations. Polydopamine (PDA) can be readily formed through the polymerization of dopamine under weakly basic conditions at room temperature. It was demonstrated that the PDA coating can be readily adapted to coat diverse materials irrespective of their surface chemistry and geometry.9−12 While the PDA coating is easily formed, its efficiency against bacterial adhesion and antibacterial activity is not very compelling, mainly due to low coating thickness (∼30 nm), poor/partial surface coverage, high surface heterogeneity, and diverse surface functional (hydrophobic/hydrophilic) groups, resulting in a lack of long-term antibiofilm activity.13−18

To improve antibiofilm activity of catechol-based coatings, the following passive (preventing bacterial adhesion) and active (killing of bacteria) approaches have been utilized: (1) changing the physicochemical properties of PDA coatings (topology, wettability, thickness, etc.),19−21 (2) anchoring antifouling, antibacterial, or dual-functional polymers onto the surface via codeposition or surface grafting,22−28 and (3) incorporating antimicrobial agents (metallic nanoparticles, antimicrobial peptides, antibiotics, nitric oxide, etc.) into coatings.15−18

PDA coatings have shown antibacterial and antibiofilm activity through photoinitiation capacity to generate reactive oxygen species (ROS) and contact-active killing effects.15−18 The antibacterial activity of PDA coatings could be enhanced by optimizing the polymerization conditions, which change the presentation of chemical groups on the surface and surface morphology under aqueous conditions. Modified PDA coatings showed enhanced photoinitiation activity—synergistic effects due to surface modification and ROS generation—resulting in increased antibacterial effects.19−21 However, the antibacterial capacity of bare PDA coatings is relatively moderate. The aromatic groups in PDA coatings could also enhance bacterial adhesion due to hydrophobic interactions, which further compromise the antibiofilm activity over time.

The structural complexity in the polycatechol coating offers an opportunity for introducing nonfouling polymers,22−25 antimicrobial polymers, or dual-functional polymers26−28 by codeposition through covalent and noncovalent interactions. The codeposition of nonfouling polymers provides a hydration layer on the surface that prevents the interaction of bacteria with hydrophobic patches on polycatechol coating and the underlying substrate. However, the polymers used so far in the codeposition process were shown to interfere with and inhibit the polymerization of catechol or deposition of polycatechol on the surface, resulting in a thinner coating, which leads to poor surface coverage in some cases and limiting the antibiofilm activity of the coated surfaces.29−33 We have previously utilized the codeposition of PDA and ultrahigh molecular weight (uhmw) hydrophilic polymers to generate an antibiofilm coating.34 Silicon wafer coupons coated with a binary solution containing dopamine and uhmw poly(N,N-dimethylacrylamide) (PDMA) (300–1000 kDa) effectively suppressed biofilm formation over 3–4 weeks irrespective of the bacterial strains tested. It was demonstrated that the introduction of uhmw hydrophilic polymers into the dopamine solution significantly impacted PDA nanoparticle formation and self-assembly,30 resulting in a decreased coating thickness. Limitations of such thinner coatings include a significant risk of exposure of the underlying surface with deterioration of the coating material and inadequate capacity of loading antimicrobial reagents into the coating.

Antimicrobial polymers can also be incorporated into PDA and render the final coating antibacterial, as the charged groups in the polymers can disrupt the integrity of bacteria.26−28 However, the charged groups on antimicrobial polymers could promote protein adsorption as well as the adhesion of dead bacteria or bacterial debris onto the coated surface, leading to the loss of bactericidal activity.35,36

Another strategy to prevent biofilm formation on polycatechol-based surfaces is to generate a relatively thick coating loaded with antimicrobial agents.6 PDA is rich in catechol, amine, imine, quinone, and other active groups, which can be combined with many other antibacterial substances such as silver nanoparticles (AgNPs), quaternary ammonium salt, nitrous oxide (NO) precursors, antibiotics, and antimicrobial peptides.15−18,37−40 The benefit of these types of coatings is that the increased thickness of the coating keeps the substrate and bacteria farther apart while providing a greater volume to load higher amounts of antimicrobial agents that can be released on demand. The route is very promising as it can utilize both chemical conjugation and noncovalent interaction to achieve better synergistic antibacterial ability.

Despite these developments, medical device infection, long-term antibiofilm activity, controlled release of bactericidal agents, and stability of infection-resistant devices still pose significant challenges.15−18,36 A novel coating approach is desirable to create thick, nonfouling coatings with high capacity for film formation with modular properties. Moreover, this method should also facilitate the incorporation of antibacterial substances into the coating, thereby amplifying the bacterial killing activity and enhancing protection against biofilm formation.

Here, we present a novel supramolecular approach for the creation of thick antifouling polycatechol-based coatings with exceptional antibiofilm properties. Our study delves into the coassembly of various catechols with a range of low molecular weight hydrophilic/amphiphilic polymers to arrive at coating compositions that yield supramolecular assemblies. These assemblies generate thick coatings upon surface deposition, exhibiting outstanding surface coverage and long-term sustained antibiofilm efficacy, unlike previous studies. We closely examined the coassembly behavior of low molecular weight polymers with polycatechols, contrasting their effects with those of high molecular weight polymers in coating deposition and film formation. Our findings revealed distinct impacts of low molecular weight polymers on the polymerization kinetics of catechols, the interaction of polymers with polycatechols, the aggregation of polycatechol nanoparticles, self-assembly of nanoparticles, and ultimately forming a thick coating upon surface deposition. Furthermore, we enhanced the antibiofilm activity of the supramolecular coating by incorporating silver nanoparticles, which are formed in situ.

2. Materials and Methods

2.1. Materials

Dopamine (DA) hydrochloride, serotonin (Ser) hydrochloride, pyrogallol (PG), pyrocatechol (PC), resorcinol (Res), and silver nitrate were purchased from Sigma-Aldrich and used without any further purification. Low molecular weight (lmw) polymers, including polyethylenimine (PEI, 700 Da), poly(N-vinyl amine) (PVAM, 6 kDa), and poly(ethylene glycol) (PEG, 700 Da), were purchased from Sigma-Aldrich. Poly(vinylpyrrolidone) (PVP, 1 kDa), poly(N-vinyl caprolactam) (PVCL, 1.3 kDa, 36 kDa and 356 kDa), poly(N,N-dimethylacrylamide) (PDMA, 5 kDa), poly(2-ethyl oxazoline) (PEOX, 5 kDa), and polyacrylamide (PAM, 1 kDa) were purchased from the Polymer Source. Polypropylene (PP) and polyurethane (PU) sheets or coupons were acquired from Professional Plastics. All cell culture-related media and supplements (TriplE, Dulbecco’s phosphate-buffered saline (DPBS), fetal bovine serum (FBS), and penicillin/streptomycin) were received from Life Technologies Inc. T24 bladder carcinoma cells were supplied by the American Type Culture Collection (ATCC CRL-2922 Manassas, VA). Modified Eagle’s medium (MEM) was purchased from Gibco.

2.2. Coating Preparation

2.2.1. PDA-Alone Coating Preparation

The silicon wafer (5 × 5 mm2) was treated by the previously reported oxygen plasma method.30 The plasma-treated silicon wafer was placed in a well (of 48-well plate) containing dopamine solution (350 μL, 2 mg/mL in tris buffer (pH = 8.5)). Dopamine solution was prepared by dissolving 4 mg of dopamine in tris buffer (2 mL, pH 8.5) followed by vortexing for ∼30 s. After 48 h, the substrate was taken out and rinsed gently with water, followed by drying in air.

2.2.2. PVCL-Alone Coating Preparation

The substrate (plasma-treated silicon wafer, 5 × 5 mm2) was placed in a well of 48-well plate containing 350 μL of low molecular weight PVCL (1.3 kDa) solution (3 mg/mL, tris buffer, pH = 8.5). After 48 h, the substrate was removed, washed, and dried in air.

2.2.3. PDA/PVCL Coating Preparation

A stock solution of PVCL was prepared by dissolving 100 mg of PVCL (1.3, 36, and 356 kDa) in 0.9 mL of water. To prepare the dopamine/PVCL solution, PVCL solution (20, 60, and 100 μL) was initially added to tris buffer (2 mL, pH = 8.5). Afterward, dopamine (4 mg) was dissolved in the resulting PVCL solution. The dopamine/PVCL solution was vortexed for ∼30 s. The plasma-treated silicon wafer (5 × 5 mm2) was placed in a well of a 48-well plate containing dopamine/PVCL solution (350 μL). After 48 h, the substrate was removed and gently washed with water, followed by placing it on a benchtop for air-drying.

2.2.4. Catechol/Polymer Coating Preparation

Diverse binary dopamine/polymer and catechol/PVCL compositions were tested for screening studies. To prepare the dopamine/polymer coating solution, instead of using PVCL in the above-mentioned procedure, the polymer of interest (PVP, PDMA, PEOX, PEG, HPG, PVAM, and PAM) was utilized. The coating parameters (solution volume, time, temperature, etc.) were kept similar. To prepare the catechol/PVCL coating solution, the catechol of interest (norepinephrine, resorcinol, pyrogallol, serotonin, and pyrocatechol) was used instead of dopamine. The coating parameters (solution volume, time, temperature, etc.) were kept similar.

2.2.5. PDA/PVCL/Ag Coating Preparation

To prepare the dopamine/PVCL/Ag coating solution, silver nitrate (10 μL, 100 mg/mL) was added to the dopamine/PVCL solution (2 mL) prepared according to the procedure mentioned previously. The resulting solution was vortexed for ∼30 s. The plasma-treated silicon wafer (5 × 5 mm2) was placed in a well (of a 48-well plate) containing the dopamine/PVCL/Ag solution (500 μL). After 24 h, the substrate was removed and gently washed with water for 10 s, followed by placing it on a benchtop for air-drying.

2.3. Scanning Electron Microscopy (SEM) Measurements

An FEI-Helios SEM (acceleration voltage of 1 kV) was employed. To prepare samples, a piece of the substrate (coated/uncoated) was cut and adhered onto the aluminum SEM stub using conductive carbon double-sided tape. The SEM stub with the sample was loaded on a Leica sputter coater (working distance: 3 cm and current: 80 mA) for coating the sample with a 20 nm iridium (Ir) layer. To measure the thickness of the coating with a deposition time of 48 h, the sample was etched with a focused ion beam. The etched area was scanned to capture the image of the coating-substrate cross-section (working distance: 4 mm, accelerating voltage: 2 kV; current density: 50 pA).

2.4. Transmission Electron Microscopy (TEM) Measurements

An FEI-TEM was used to measure the size of supramolecular assemblies synthesized in solution. To prepare the sample, a droplet of the solution was put on a copper TEM grid coated with an ultrathin carbon film. The acceleration voltage used for the TEM analysis was adjusted to 100 kV.

2.5. Water Contact Angle (WCA) Measurements

WCA of samples was measured using a homemade goniometer (camera: Retiga 1300, Q-imaging Co.). A water droplet (4 μL) was placed manually using a 20-μL pipet. The raw image was analyzed by using Northern Eclipse software.

2.6. Ellipsometry Analysis

A variable angle spectroscopic ellipsometer (VASE) (J.A. Woollam, Lincoln, NE) was employed to determine a coating thickness of less than 200 nm. The light source of the VASE used was an M-2000 50W quartz-tungsten halogen lamp. Different VASE spectra were recorded at different angles, including 55, 65, and 75° in the range of 480–700 nm. The data analysis was carried out by using WVASE32 software.

2.7. UV–Vis Spectroscopy Analysis

A microplate reader (Molecular Devices SpectraMax Gemini EM) was used to probe the light behavior of the solutions in the range of 250–500 nm with a wavelength step of 5 nm. The volume of the solution loaded into the well (96-well plate used) was 200 μL (dilution factor: 50).

2.8. Dynamic Light Scattering (DLS) and Surface ζ-Potential (SZP) Measurements

A Malvern Zetasizer was used to measure the hydrodynamic size and ζ-potential of assemblies in solution. The Zetasizer was also equipped with a surface ζ-potential accessory to measure the surface charge of the coating. To prepare a sample for hydrodynamic size/ζ-potential measurement, 10 μL of the working solution was added to 1 mL of water in a polystyrene cuvette or folded capillary Zeta cell cuvette and loaded onto the Zetasizer. To measure the SZP, the coated silicon wafer was mounted on the SZP probe and fitted into a cuvette containing 1 mL of ζ-potential transfer standard suspension (DTS1235).

2.9. X-ray Photoelectron Spectroscopy (XPS) Analysis

An XPS instrument equipped with an EA125 energy analyzer and DAR400 Dual X-ray performed with a Mg Ka source was used to assess the chemical composition surfaces. We utilized both survey and high-resolution XPS scans for the analyses.

2.10. Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) Analysis

To prepare samples for ICP-OES measurements, PDA/PVCL/Ag-coated silicon wafers (5 × 5 mm2) were incubated with water on a shaker at 75 rpm. The supernatants were collected at different time points. Fresh water was used to replace the solution at each time point. The supernatants were diluted with 2 wt % nitric acid at the ratio supernatant to acid of 1:2. The nitric acid diluted supernatant was analyzed using a Varian 725ES Optical Emission Spectrometer.

2.11. Fourier Transform Infrared (FTIR) Analysis

A Bruker 670 TensoII FTIR instrument with an MCT/A liquid nitrogen cooled detector, a KBr beam splitter, and a VariGATR Grazing Angle accessory were used in combination for collecting FTIR or attenuated total reflectance-FTIR (ATR-FTIR) spectra. The scan resolution and number of scans were 2 cm–1 and 128, respectively. To isolate assemblies/nanoparticles, the PDA solution was centrifuged at 20,000g for 10 min, followed by washing with water. The washed assemblies/nanoparticles were air-dried overnight and vacuum-dried for FTIR measurements.

2.12. Bacterial Culture Assay

The bacterial adhesion and killing activity of coated silicon wafer pieces (5 × 5 mm2) were assessed. The bacteria were cultured overnight and diluted to 1 × 106 CFU/mL in LB. The samples were placed in the wells (48-well plate), followed by covering with 500 μL of the freshly prepared bacterial suspension (1 × 106 CFU/mL). The samples were incubated at 37 °C on a shaker at 100 rpm. At different time points, a portion of the bacterial suspension (∼50 μL) was aliquoted for counting planktonic bacteria by using the agar plating method. At different time points, samples were removed and washed with sterile PBS 3 times and used for surface-attached bacteria counts. To count the bacterial colonies, the washed samples were sonicated in 1 mL of sterile PBS for 10 min in a sonication bath. The supernatant was serially diluted and analyzed by utilizing the agar plating method. Every 48 h, half of the bacterial solution (250 μL) was replenished with fresh LB to supply the nutrients needed for bacterial growth. To visualize the surface of samples upon exposure to bacterial suspension, the samples were taken out at specified time points and washed with sterile PBS 3 times. Then, the samples were stained using a fluorescent stain kit containing SYTO-9 (3 μL/mL) and propidium iodide (PI) (3 μL/mL) for 15 min. The stained samples were washed with 1 mL of sterile water 3 times and dried in air. Finally, washed samples were illuminated under a fluorescence microscope (Zeiss Axioskop 2 plus, Carl Zeiss Microimaging) to visualize bacterial attachment. The fluorescence intensity of the images was determined by converting them to grayscale. The mean value derived from the histogram was then extracted as the representative fluorescence intensity.

2.13. Stability Measurements

To assess the stability of the PDA/PVCL/Ag coating, the samples (PDA/PVCL/Ag-coated silicon wafers) were challenged under different conditions. Some samples were placed in 1.5 mL microtubes containing 1 mL of water, followed by placing then in the sonication bath for 10 min. Afterward, the samples were removed and air-dried. Some samples were soaked in ethanol for 24 h, followed by air-drying. Some samples were loaded into an autoclave (121 °C and 15 psi) for 1 h. Afterward, the samples were removed and kept on the benchtop overnight. Then, all collected samples were incubated with bacterial suspension (1 × 106 CFU/mL, LB) for 24 h to assess antiadhesive activity utilizing the bacterial adhesion assay described above.

2.14. Protein Adsorption Studies

The fluorescein isothiocyanate-tagged bovine serum albumin (FITC-BSA) solution (1 mg/mL) was prepared in PBS. The PDA-alone and PDA/PVCL-coated silicon wafers were immersed in the FITC-BSA solution for 1 h at 37 °C. Afterward, the samples were taken out and washed with PBS 5 times, followed by imaging under the fluorescence microscope (Zeiss Axioskop 2 Plus).

2.15. Cell Adhesion Assay

The number of cells used for cell adhesion experiments was 5–10. The T24 cells (bladder cells) were cultured in RPMI 1640 medium supplemented with FBS (10%) and penicillin–streptomycin (1%) in the incubator (37 °C and 5% CO2). The 70% confluent cells were trypsinized for 3 min at 37 °C, followed by addition to the supplemented media. The detached cells were centrifuged at 300g for 5 min, followed by seeding at 30,000 cells per well in the coated 8-well glass slides. After 24 h, the cells were washed with cold 1× DPBS, followed by marking using a nuclear stain (Hoechst 33342, 1:10,000 dilution; Thermo Fisher Scientific). The samples were fixed with Fluoromount-G mounting medium (SouthernBiotech Birmingham, AL) and illuminated under a Zeiss Axioskop 2 Plus fluorescent microscope for cell adhesion assessment.

2.16. Statistical Analysis

All of the data values are presented as the mean ± standard derivation (SD). Statistical significance was determined using Student’s t-test, and p < 0.05 was considered statistically significant.

3. Results and Discussion

We aimed to develop binary catechol-polymer assemblies that can form thick antibiofilm coatings in a one-step process. We hypothesized that codeposition of polycatechols with a low molecular weight (LMW) polymer (<10 kDa) could induce self-assembly of polymer-polycatechol nanoparticles, and the interaction of polycatechol nanoparticles with the LMW polymer can be altered by changing polymer chemistry. The supramolecular assemblies of polymer/catechol nanoparticles and their deposition on the surface could improve the coating formation, resulting in a thicker coating with excellent antibiofilm properties. Thus, to identify the optimal polymer candidate and the polycatechol that can generate a thick antibiofilm coating, we have screened a diverse range of LMW hydrophilic/amphiphilic polymers with different chemistries along with different catechols.

3.1. Polymer Selection toward the Generation of Thicker Polycatechol/Polymer Coatings

We began with the screening of diverse LMW hydrophilic/amphiphilic polymers, including poly(N-vinylpyrrolidone) (PVP), poly(N-vinyl caprolactam) (PVCL), poly(ethylene glycol) (PEG), poly(N,N-dimethylacrylamide) (PDMA), poly(2-ethyl-2-oxazoline) (PEOX), polyethylenimine (PEI), poly(N-vinyl amine) (PVAM), and polyacrylamide (PAAM) (see Table S1 for details of the polymers), in combination with dopamine as a catechol in tris buffer solution (pH 8.5). To generate a coating, the substrate of interest (e.g., silicon wafer for initial studies) was dipped in the coating solution consisting of dopamine and polymer in Tris buffer and incubated for 48 h at room temperature (Figure 1a). We initially evaluated the surface morphology and antibiofilm activity of the formed coatings.

Figure 1.

Figure 1

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Identification of PDA/polymer binary coating composition. (a) A schematic for coating preparation protocol. (b) SEM images of (i) uncoated silicon wafer, (ii) silicon wafer coated with PDA-alone, silicon wafer treated with coating solutions containing (iii) PVCL (the inset is high magnification image), (iv) PEI, (v) PAM, (vi) PDMA, (vii)PEG, (viii) PEOX, (ix) PVP, and (x) PVAM. The yellow and white scale bars are 1 and 10 μm, respectively. The red arrows point out the aggregates deposited on the surface. (c) Fluorescence microscopy images of bacterial attachment to the surface of (i) uncoated silicon wafer, (ii) PDA-alone coated silicon wafer and surface of coatings formed based on (iii) PVCL, (iv) PEI, (v) PAM, (vi) PDMA, (vii) PEG, (viii) PEOX, (ix) PVP, and (x) PVAM after 24 h incubation with Escherichia coli (1 × 106 CFU/mL, LB). The scale bar is 100 μm. (d) The fluorescence intensity of the surface showing bacterial attachment onto different surfaces. PDA was used as the control (e) ATR-FTIR spectra of PU sheets treated with coating solutions containing different polymers. (f) ATR-FTIR spectra of coating on the PU substrate at 1730 cm–1 (normalized with respect to peak at 2920 cm–1, C–C bond) for coatings formed based on different polymers.

We utilized scanning electron microscopy (SEM) to investigate the influence of different polymers on the surface morphologies of different coatings (Figure 1b). PDA, without the added polymers, formed a nonuniform coating with a deposition of aggregates on the surface. The addition of PEI resulted in a porous coating with noticeable defects (i.e., cracks; Figure 1b; (iv)). Among the diverse polymers tested, PVCL was the only polymer that gave a thick coating with excellent surface coverage in combination with dopamine (Figure 1b; (iii)). Despite the similarity of the chemical structure of PVP and PVCL polymers (except the length of the hydrophobic side chain), PVP did not produce a uniform coating in comparison to PVCL (Figure 1b; (iii and ix)). This could be attributed to the difference in the size of the hydrophobic segments of these polymers (PVP with three methylene groups vs PVCL with five methylene groups); the larger hydrophobic segment of PVCL (compared to PVP) might be increasing the hydrophobic interactions with PDA segments forming a more stable and thick coating. Stronger hydrogen-bonding interactions of PVP with PDA32 provided increased stabilization of the nanoparticles, resulting in a thinner coating.

Early-stage biofilm formation was assessed over 24 h using E. coli to identify the LMW polymer candidate that yields a thick coating with potent antibiofilm activity (Figure 1c,d). Significant bacterial colonization was observed for all control surfaces: uncoated silicon wafers and those with PDA-alone (Figure 1c; (i and ii)), as shown by the green fluorescence stain from the bacteria. Dopamine/PEI combination showed the highest amount of bacterial biomass on the surface, which is attributed to the increased attractive interactions between negatively charged bacteria and the positively charged PEI.41 The dopamine/PVCL-treated silicon wafer was found to effectively suppress bacterial attachment and biofilm formation by up to 95% compared to the PDA surface control (Figure 1d). The other coating compositions with LMW polymers and dopamine showed weaker antibiofilm inhibition activity. The surface coverage of the coating was determined using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, which was used as another parameter to differentiate coating compositions.42 Polyurethane sheets coated with different PDA/polymer compositions were used in this study. The ATR-FTIR absorbance peak at 1730 cm–1, which corresponds to the carbonyl group of polyurethane, was utilized as a measure of the surface coverage of the coating (Figure 1e,f). The disappearance of this peak indicated that the coating was thick enough (the penetration depth of ATR is about 1 μm)42 to mask the underlying substrate. In comparison to the other coating compositions, the diminished peak intensity at 1730 cm–1 for the PDA/PVCL coating suggests that this combination resulted in a thick coating with good surface coverage. The coatings formed based on PEI and PVAM partially covered the substrate. The substrates treated with solutions containing other LMW polymers, such as PVP and PDMA, were not masking the peak at 1730 cm–1, suggesting a thinner coating or poorer surface coverage. These results are consistent with the SEM data and analyses discussed above. Among the different binary solutions tested, the dopamine/PVCL was found to be the optimal combination for the generation of a coating with high surface coverage, thickness, and antibiofilm activity.

3.2. Influence of Different Polycatechols, Molecular Weight of PVCL, and Composition on Antibiofilm Activity and Surface Coverage

Next, we evaluated the effect of different experimental parameters, including catechol chemistry in combination with PVCL, catechol:PVCL ratio, molecular weight of PVCL, and coating time, on the surface wettability and thickness of the resulting coating. The catechols used include dopamine, serotonin, norepinephrine, pyrocatechol, resorcinol, and pyrogallol (Figure S1). Among the six different catechols tested in combination with PVCL, the highest thickness (∼500 nm) and the lowest water contact angle (∼20°) were observed for the dopamine/PVCL or norepinephrine/PVCL combinations (Figures 2a,b, and S2a). The use of other catechols, including resorcinol, pyrocatechol, pyrogallol, and serotonin, with PVCL failed to generate a thick coating.

Figure 2.

Figure 2

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Thickness and surface wettability of different coatings. (a) Water contact angle and (b) thickness of coatings formed based on PVCL in combination with different catecholamines. (c) Water contact angle and (d) thickness of coatings formed based on different DA:PVCL ratios. (e) Water contact angle and (f) thickness of coatings formed based on different molecular weights of PVCL. (g) Water contact angle and (h) thickness of coatings formed based on PDA:PVCL (1.3 kDa) 2:3 on the surface of a silicon wafer at different coating times.

Overall, the results showed that the presence of both catechol and amine on the same molecule, as in dopamine, in combination with PVCL, is needed for the generation of a coating with good thickness and hydrophilicity. This is due to the enhanced hydrogen bonding, hydrophobic interactions (see Section 3.2 for detailed discussion), and covalent bond formation between amines and quinones via Michael addition reactions.11 The data is consistent with the report that the presence of amine groups along with catechol is important to produce material-independent surface functionalization.11 Amine-free catechol analogues often fail to show this versatility in the generation of surface coatings. The coating could also be applied to diverse materials mainly due to the use of dopamine, which is a known adhesive to any surface irrespective of its chemistry and dimensions, as reported previously.6,11,30,34,39,40

Among the different dopamine:PVCL ratios tested, the optimal dopamine:PVCL ratio, which resulted in the highest thickness (∼500 nm) and high wettability (water contact angle ∼20°), was 2:3 wt/wt (Figures 2c,d and S3a,b). The use of either low or high PVCL concentration in combination with dopamine yielded a PDA/PVCL coating with a thickness of 100–150 nm and a water contact angle of 30–40°. The surface of the coating based on dopamine/PVCL = 2:3 (w/w) was nonporous and mostly defect-free. In contrast, the coating based on DA:PVCL = 2:1 (w/w) showed superficial defects (i.e., holes and cracks) (Figure S3c).

The thickness and surface wettability of the PDA/PVCL coating are also dependent on the molecular weight of PVCL. The thickness of the PDA/PVCL coating decreased with the molecular weight of PVCL reaching 500, 60, and 10 nm for 1.3, 36, and 356 kDa, respectively (Figure 2f). The surface of the silicon wafer treated with dopamine solutions containing high molecular weight PVCL (36 and 365 kDa) remained nearly as smooth as the untreated silicon wafer (Figure S4b). The lowest water contact angle (∼20°) was observed for the PDA/PVCL coating formed based on the PVCL with the lowest molecular weight (1.3 kDa) (Figures 2e and S4a). We also characterized the surface of the silicon wafer treated with the optimized coating solution (DA/PVCL = 2:3, 1.3 kDa) for different periods. The data showed that the water contact angle of PDA/PVCL coating gradually decreased with coating time (Figures 2g and S4a,b). Figure 2h shows that the thickness of the PDA/PVCL coating increased with coating time. The thickness of the coating reached ∼500 nm after 48 h, confirmed by SEM and the cross-sectional analysis (Figure S5). The difference in the surface morphology of PDA/PVCL coatings formed at different time points was insignificant (Figure S4c).

3.3. Surface Characterization of Optimal PDA/PVCL Coating

We further characterized the surface of the PDA/PVCL coating by utilizing XPS, FTIR, and surface ζ-potential measurements. The survey XPS spectrum of the PDA/PVCL coating was found to be similar to that of the PVCL-alone coating (Figure 3a). The XPS spectrum of the PDA/PVCL coating did not show any distinguishable peaks around 100 eV, which corresponds to Si (2p), demonstrating the excellent surface coverage by the PDA/PVCL coating. The high-resolution XPS data showed that the carbon and nitrogen spectra of the PDA/PVCL coating are nearly identical to that of the PVCL-alone coating, suggesting that the PDA/PVCL coating is mainly composed of PVCL (Figure 3b,c). The oxygen spectrum of the PDA/PVCL coating can be decomposed with one peak (∼531 eV) and a shoulder (∼533 eV). The O 1s peak (∼531 eV) was observed for the PVCL-alone spectrum, which corresponds to the oxygen atoms of carbonyl groups of PVCL (Figure 3d). The O 1s peak at 533 eV was observed for the PDA-alone coating, which was attributed to the oxygen atoms in the hydroxyl groups of PDA. The presence of both peaks (∼531 and ∼533 eV) in the spectrum of PDA/PVCL coating demonstrated the presence of PDA within the PDA/PVCL coating.

Figure 3.

Figure 3

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Surface characterization of PDA/PVCL coating. (a) XPS Survey scan spectra of PDA-alone coating and PDA/PVCL coating. (b) Carbon, (c) nitrogen, and (d) oxygen XPS high-resolution spectra of PDA-alone and PDA/PVCL coating. (e) ATR-FTIR spectra of coatings and (f) expanded the region from 1800 to 1400 cm–1. (g) Schematic representation of the most probable intermolecular interactions between PVCL and PDA within the PDA/PVCL coating, including hydrogen bonding and dipole–dipole interactions. (h) Surface ζ-potential of PDA-alone and PDA/PVCL coatings.

We further analyzed the chemical composition of the PDA/PVCL coating utilizing ATR-FTIR spectroscopy (Figure 3e,f). The spectrum of the PDA-alone coating showed two distinct peaks at 1600 and 3400 cm–1, which were attributed to quinone and hydroxyl groups, respectively. The peak at 1730 cm–1, which is due to the underlying PU substrate, observed for the PDA coating revealed incomplete surface coverage. The PVCL-alone control showed a characteristic peak at 1634 cm–1, which was attributed to the stretching vibration of the carbonyl group. The 23 cm–1 blue shift of the carbonyl peak of PVCL was observed in the presence of PDA (Figure 3f), which can be attributed to the intermolecular hydrogen bonding between the hydrogen donors (hydroxyls and amines) of PDA and the carbonyl group of PVCL.43 The similarity between the spectra of PVCL-alone and the PDA/PVCL coating and the presence of a strong carbonyl peak indicates that the PDA/PVCL coating was rich in PVCL, which agrees with the XPS data. The peak at 1458 cm–1 (C=C bonds of the phenyl group) was observed in the spectrum of the PDA/PVCL coating, demonstrating the presence of PDA within the coating. The characteristic peaks from the spectra of PDA/PVCL and the PVCL-alone coating are summarized in Table 1.

Table 1. Characteristic Peaks of ATR-FTIR Spectra of PVCL-Alone and PDA/PVCL Coatings.

PVCL-alone peak (cm–1) PDA/PVCL peak (cm–1) peak shift (cm–1) assignment
1082 1085 +3 C–N–C bending
1148 1154 +6 C–N–C bending
1195 1198 +3 C–N stretching
1262 1263 +1  
1423 1423 0 CH2
1444 1444 0 CH2
  1458   C=C
1475 1482 +7 C–N stretching
1634 1611 –23 C=O (lactam) stretching
2855 2855 0 C–H stretching
2926 2926 0 C–H stretching
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The peaks at 1082, 1148, 1195, and 1475 cm–1 are attributed to the C–N bond of PVCL. The 7 cm–1 shift of the C–N stretching was observed following codeposition with PDA, demonstrating the inclusion of lactam nitrogen of PVCL in intermolecular interactions with PDA. Taken together, these data confirm that both carbonyl groups and lactam nitrogen atoms of PVCL are interacting with PDA within the PDA/PVCL coating (Figure 3g), generating a stable supramolecular assembly.

The coating assembly was also examined by surface ζ-potential (SZP) measurements. The SZP values of the PDA-alone and PDA/PVCL coatings were found to be ∼−30 and −10 mV, respectively (Figures 3h and S6). The decrease in the surface charge of the PDA/PVCL coating compared to the PDA-alone coating could be due to the high enrichment of neutral PVCL on the surface of the PDA/PVCL coating at the aqueous interface.

3.4. Characterization of PDA/PVCL Assemblies Formed in Solution

We further measured the size of the solution-borne PDA/PVCL assemblies by utilizing transmission electron microscopy (TEM) and dynamic light scattering (DLS). The size of dehydrated PDA/PVCL assemblies was ∼5 nm based on TEM micrographs (Figure 4a). The hydrodynamic size of the PDA/PVCL assemblies was ∼30 nm (Figure 4b). The ζ-potential of PDA-alone and PDA/PVCL assemblies were found to be ∼−40 and −10 mV, respectively (Figure S7). The higher ζ-potential of PDA/PVCL assemblies compared to that of PDA-alone nanoparticles also supports the presence of PVCL in the PDA/PVCL assemblies. The PDA-alone nanoparticles were reported to have hydrodynamic sizes over 4000 nm.30 The much smaller size (20–30 nm) of PVCL/PDA nanoassemblies at 4 h and 24 h indicated that PVCL controlled the PDA particle aggregation and the self-assembly process.

Figure 4.

Figure 4

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Particle characterization of PDA/PVCL assemblies. (a) The TEM image of PDA/PVCL assemblies. The scale bar is 20 nm. (b) The hydrodynamic size of PDA/PVCL assemblies at two different time points. (c) UV–vis spectra of PDA and PDA/PVCL solutions after 24 h. (d) FTIR of PDA-alone nanoparticles and solution-borne PDA/PVCL assemblies and (e) expanded region from 1400 to 1800 cm–1. (f) Chemical structures of DA and PVCL along with intermolecular hydrogen bonding. PVCL interacts with DA through hydrogen bonding between lactam carbonyls and hydroxyls and amines of DA, inhibiting DA polymerization in solution.

We also utilized ultraviolet–visible (UV–vis) spectroscopy to assess the stability of different PDA/polymer assemblies (Figure 4c). After 24 h, the PDA-alone solution showed negligible absorbance in the range of 310–500 nm, suggesting a low concentration of PDA in the solution, which could be due to uncontrolled sedimentation of PDA particles over time. Digital images (Figure S8) of the PDA-alone solution showed uncontrolled precipitation at the bottom of the vial, supporting the UV–vis data. The absorbance of the PDA/PVCL solution was higher than PDA-alone, which indicated that PVCL interacted with dopamine nanoaggregates (with sizes between 20 and 30 nm, Figure 4b) and prevented the aggregation.

We also acquired the FTIR spectra of PDA nanoparticles and PDA/PVCL assemblies to further explore the mechanism of coating formation (Figure 4d). A broad peak span from 3000 to 3600 cm–1 (N–H stretching and OH stretching) was observed for both PDA and PDA/PVCL nanoparticles, which indicated the successful incorporation of the PDA component in the PDA/PVCL assemblies. The PDA/PVCL showed a peak at 1634 cm–1 with a shoulder (1623 cm–1, shift of 15 cm–1) compared to the single peak (1638 cm–1) for the PVCL-alone. Together with the spectra collected from the PDA/PVCL surface coating, the blue shift of the carbonyl group in the PVCL/PDA coating or nanoparticles in the solution suggests that hydrogen bonding may be the main interaction between PDA and PVCL. Dipole–dipole interactions and attractive hydrophobic forces could also be involved in preventing the immediate destabilization of PDA nanoparticles.44,45

3.5. Antibiofilm Activity of PDA/PVCL Coating

Next, we assessed the long-term antibiofilm activity of the PDA/PVCL coating against both Gram-positive and Gram-negative bacterial species. The level of accumulated bacterial biomass (based on the fluorescence intensity) on the surfaces of PDA-alone and PVCL-alone coatings increased over time. In contrast, the PDA/PVCL coating effectively suppressed biofilm formation by E. coli over 28 days (Figure 5a–d) with less than 7 and 8% adhered bacteria, live and dead, respectively, compared to the PDA control (Figure 5e). SEM analysis (Figure 5f) showed that the PDA-alone coating was covered with a relatively thick layer of bacterial biomass. In contrast, only a few bacterial cells were adhered to the surface coated with PDA/PVCL. In addition, the surface morphology of the PDA/PVCL coating did not significantly change following incubation with bacteria over the long term (28 days) (Figure 5f). We also evaluated the resistance of the coating to colonization and biofilm formation against Gram-positive bacterial species S. aureus. The data showed that a few randomly distributed individual bacterial cells deposited on the surface of PDA/PVCL coating following 28 days of incubation with S. aureus solution compared to the PDA-alone control on which significant accumulation of live and dead bacteria was observed (Figure 5g). The reduction in the biomass accumulation brought by the PDA/PVCL coating for the live and dead bacteria was 92.3 and 96%, respectively, on day 28 (Figure 5h).

Figure 5.

Figure 5

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Antibiofilm activity of PDA/PVCL coating. Fluorescence microscopy images of biofilm formation on the surface of PDA-alone, PVCL-alone, and PDA/PVCL coatings after (a) 1 day, (b) 7 days, (c) 14 days, and (d) 28 days of incubation with E. coli (1 × 106 CFU/mL, LB). The scale bar is 100 μm. (e) Reduction in live and dead bacteria deposition brought by different coatings over 28 days (PDA coating at day 28 was used as the 100% control). (f) SEM images of biofilm formation on the surface of PDA-alone and PDA/PVCL coatings after 7 and 28 days of incubation with E. coli (1 × 106 CFU/mL, LB). The scale bar is 4 μm. The red arrows point out individual bacteria attached. (f) Fluorescence microscopy images of biofilm formation on the surface of PDA-alone and PDA/PVCL coatings after 28 days of incubation with S. aureus (1 × 106 CFU/mL, LB). The scale bar is 100 μm. Green represents live bacteria, and red represents dead bacteria. Statistical analysis between PDA and PDA/PVCL pair, *** indicates p < 0.001. (h) Reduction in biomass accumulation (live and dead bacteria) brought by different coatings on day 28 (PDA coating on day 28 was used as the 100% control). Statistics analysis between PDA and PDA/PVCL, *** indicates p < 0.001.

The incorporation of PVCL serves to mitigate the interaction between the coating or underlying substrate and the bacteria through several mechanisms: (1) enhancement of coating hydrophilicity, thereby reducing hydrophobic–hydrophobic interactions between the coating and bacteria (Figure 2g); (2) minimization of underlying substrate exposure due to the excellent surface coverage provided by the coating, thus limiting the bacterial adhesion (Figure 1b); and (3) promotion of coating smoothness, resulting in a reduction in the apparent specific surface area and subsequent reduction in surface–bacteria interactions (Figure 1b).

3.6. Antifouling Properties of PDA/PVCL Coating

Given that the fouling of materials in various biofluids, especially blood and urine, results in the failure of novel antimicrobial technologies, we assessed the ability of the PDA/PVCL coating to resist protein deposition and cell adhesion. Fluorescently labeled bovine serum albumin (FITC-BSA) was used as a model protein for these adsorption studies. Significant adsorption of FITC-BSA was observed on the surface of the silicon wafer coated with the PDA-alone control (Figure 6a), while the PDA/PVCL coating showed excellent resistance with over 98% reduction to the deposition of FITC-BSA (Figure 6b). Water contact angle images of the PDA-alone and PDA/PVCL coatings following FITC-BSA incubation were compared to those of the as-made coatings and showed that the water contact angle of the PDA/PVCL coating remained unchanged at ∼25° while that of the surface coated with PDA-alone increased to ∼65° (Figure 6c). These observations further supported the ability of the PDA/PVCL coating to resist protein deposition and fouling of the surface.

Figure 6.

Figure 6

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Antiadhesive performance of the PDA/PVCL coating. Fluorescence images of deposition of FITC-BSA on the surface of the (a) PDA-alone coating and (b) PDA/PVCL coating. (c) Water contact angle images of PDA-alone (i) and PDA/PVCL coatings (ii) after 1 h immersion in PBS and FITC-BSA solution at 37 °C. Fluorescence images of cell adhesion (T24 cells, 24 h, 37 °C) to the surface of (d) PDA-alone and (e) PDA/PVCL coatings. The scale bars are 100 μm.

We further investigated the effect of PDA-alone and PDA/PVCL surface treatments on cell adhesion. T24 bladder cells were used to assess cell adhesion following a 24 h period. Adhered cells were stained and assessed. The results showed that the number of cells attached to samples coated with PDA-alone was noticeably higher than that of the cells attached to the surface of the PDA/PVCL coating (Figure 6d,e). The excellent antiadhesive (resistance to bacterial, protein, and cellular deposition) and antibiofilm performance of the PDA/PVCL coating is likely attributed to the synergy between excellent surface coverage and low roughness along with the presence of nonadhesive PVCL stabilized with PDA within the coating. Collectively, these data illustrate the significant antifouling properties of the PDA/PVCL coating, making it a good candidate coating for biomedical device materials exposed to complex environments such as blood or urine.

3.7. Silver Incorporated PDA/PVCL Coating

The binary PDA/PVCL coating generated long-term antibiofilm activity without the incorporation of antimicrobial agents in a passive manner. While this type of repellent coating is effective at preventing fouling by bacteria, some bacterial species may adapt over time by changing their surface characteristics, resulting in adhesion and biofilm formation. Furthermore, some applications may require direct killing of planktonic bacteria repelled into the surrounding environment. To enhance the direct antimicrobial activity of the repellent coating and increase the versatility of this coating, we incorporated silver with a one-step coating process. While bacteria-killing approaches hold considerable promise, they also raise concerns regarding antimicrobial resistance. Thus, we have selected silver, known for its potent bactericidal properties and reduced susceptibility to microbial resistance compared to other antimicrobial agents like antibiotics.39,40 Silver nitrate was added to a solution of dopamine and PVCL (three-component system) and deposited on the substrate for 24 h. The silver nitrate is anticipated to get reduced and form silver nanoparticles or nanoclusters within the coating.42−44 As shown in Figure 7, silver incorporation changed the surface morphology and thickness of the coating, giving it a rough structure with increased porosity (Figure 7a). The addition of silver considerably increased the thickness of the PDA/PVCL coating (Figure 7b) from ∼500 nm in the absence of silver to ∼5 μm in the presence of silver. ICP-OES confirmed that the silver release from the PDA/PVCL/Ag coating was slow, with ∼3000 ppb silver ions released over 28 days (Figure 7c). We also investigated the size of PDA/PVCL/Ag assemblies using TEM and DLS. The TEM image demonstrated the formation of larger assemblies (∼100 nm) embedded with small silver nanoparticles (<30 nm) (Figure 7d). The hydrodynamic size of PDA/PVCL/Ag composite assemblies was ∼125 nm, which is much higher than that of the PDA/PVCL assemblies described earlier (Figure 7e). Subsequent antibacterial assays using E. coli (1 × 106 CFU/mL, LB, 24 h) showed the complete killing of planktonic bacteria and the prevention of bacterial adhesion/colonization over the 24 h period compared to the PDA and PDA/PVCL coatings (Figure 7f).

Figure 7.

Figure 7

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Characterization of PDA/PVCL/Ag coating. (a) The SEM image of the top surface and (b) FIB-created cross-section of the PDA/PVCL/Ag coating. The white and yellow scale bars are 5 and 2 μm, respectively. (c) The silver release profile of the PDA/PVCL/Ag coating. (d) The TEM image of a PDA/PVCL/Ag assembly. The black scale bar is 50 nm. (e) Hydrodynamic size of PDA/PVCL and PDA/PVCL/Ag assemblies. (f) The concentration of planktonic present in the bacterial solution E. coli (1 × 106 CFU/mL, LB, 7 days) incubated with different coatings. The black point-down arrow was used to highlight zero planktonic CFU count obtained by the PDA/PVCL/Ag coating. (g) The percentage of bacterial adhesion reduction of PDA/PVCL/Ag coating exposed to different conditions after 24 h incubation with E. coli (1 × 106 CFU/mL, LB). Fluorescence images of biofilm formation on the surface of the PDA-alone and PDA/PVCL/Ag coatings after (i) 1 day, (j) 7 days, (k) 14 days, and (l) 28 days incubation with E. coli (1 × 106 CFU/mL, LB). The scale bar is 100 μm. (h) Reduction in biomass (live and dead bacteria) deposition brought by the different coatings over 28 days (PDA coating at day 28 was used as the 100% control). Statistics analysis between PDA and PDA/PVCL, *** indicates p < 0.001.

We further evaluated the stability of the PDA/PVCL/Ag coating under different conditions, including sonication for 10 min, immersion in ethanol for 24 h, and autoclaving (1 h, 121 °C, and 15 psi). Subsequent antibacterial assays with E. coli (1 × 106 CFU/mL, LB) showed no loss in killing activity of the PDA/PVCL/Ag coating following exposure to any of the conditions (Figure 7g). These data demonstrate significant stability of our PDA/PVCL/Ag coating despite being exposed to very harsh conditions.

Considering that medical device coatings need to resist biofilm formation for extended periods of time, we assessed the long-term activity of PDA/PVCL/Ag to resist biofilm formation by E. coli within a 28-day period. Overall, no bacteria were observed on surfaces coated with PDA/PVCL/Ag within the 28-day incubation period (Figure 7i–l), demonstrating extended antibacterial activity that, in combination with the nonadhesive performance of the PVCL incorporated into the coating, prevented biofilm formation (Figure 7h) compared to the PDA control.

3.8. Mechanism of PDA/PVCL and Silver-Embedded PDA/PVCL Coating Formation

PVCL can generate strong interactions, including hydrogen bonding and hydrophobic interactions with PDA, as evident from the ATR-FTIR studies (Figures 3 and 4). The use of low molecular PVCL allows effective interactions with PDA while not generating highly stabilized PDA/PVCL assemblies/nanoparticles due to the limited/short-range steric/osmotic stabilization of low molecular weight PVCL chains (Figure 8a). PDA and low molecular weight PVCL combination results in PDA/PVCL nanoparticles that can self-assemble and deposit on the surface with time, interfuse, and generate an integrated thick coating with high surface coverage. The inclusion of high molecular weight PVCL polymers offers increased steric stabilization of PDA particles that prevent their aggregation and deposition on the surface, resulting in a very thin layer (Figure 8b). In the presence of silver ions (Figure 8c), the PDA/PVCL/Ag solution resulted in larger assemblies embedded with small silver nanoparticles. The deposition of the large nanoparticles created a void and formed a porous/rough coating.

Figure 8.

Figure 8

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Proposed mechanism of the formation of (a) PDA/lmwPVCL coating, (b) PDA/hmwPVCL coating, and (c) PDA/lmwPVCL/Ag coating. PDA, polydopamine; lmwPVCL, low molecular weight PVCL; and hmwPVCL, high molecular weight PVCL.

4. Conclusions

We developed a new coating method utilizing polycatecholamine and low molecular weight polymers that interact strongly to endow surfaces with significant antifouling and antibiofilm activity. Our screening studies identified a binary composition containing dopamine and PVCL (low molecular weight) that generates ultrasmall supramolecular assemblies, which can be deposited/self-assembled in a controlled manner and form an integrated thick coating on a surface. The optimal coating showed excellent surface coverage and inhibited biofilm formation for up to 28 days (maximum tested time) against both Gram-positive and Gram-negative bacterial species. The coating thickness, wettability, and surface roughness of the coating can be readily adjusted by changing the ratio of dopamine to PVCL ratio and coating time. We showed that the interaction between polydopamine and LMW PVCL in solution impacts dopamine polymerization and particle aggregation, while surface-adsorbed DA/PDA/PVCL assemblies can be polymerized to form a stable film. Hydrogen bonding and the hydrophobic interaction between polydopamine and PVCL are key factors in determining the formation of the thick coating. Antibiofilm activity and stability of the coating were enhanced via the incorporation of silver nanoparticles, which release silver ions in a controlled manner, making this coating highly attractive for use on biomedical device materials to prevent associated infections.

Acknowledgments

The authors acknowledge funding by the Canadian Institutes of Health Research (CIHR) Natural Sciences, Engineering Council of Canada (NSERC), and the Michael Smith Foundation for Health Research (MSFHR). HYA and HDL acknowledge the NSERC NanoMat CREATE funding. HDL acknowledges the NSERC CGS-D scholarship. JNK held a Career Investigator Scholar award from the MSFHR. JNK is a Tier 1 Canada Research Chair in Immunomodulating Materials and Immunotherapy. The authors also acknowledge the Bioimaging facility and Center for High-Throughput Phenogenomics (CHTP) at the University of British Columbia.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.4c02371.

  • Chemical structures of dopamine, serotonin, norepinephrine, pyrocatechol, resorcinol, and pyrogallol; water contact angle images of the silicon wafer treated with different catecholamine/PVCL solutions; water contact angle images of PDA/PVCL coatings formed at different DA/PVCLratios; SEM image of cross-section of the coating formed based on PDA:PVCL (1.3 kDa) 2:3 on the surface of the silicon wafer; raw surface ζ-potential data of PDA-alone coating and optimalPDA/PVCL coating; ζ-potential of PDA-alone nanoparticles and PDA/PVCL assemblies; digital images of vials containing different PDA/polymer solutions; and characteristics of different polymers used in this study (PDF)

The authors declare no competing financial interest.

Supplementary Material

am4c02371_si_001.pdf (4.8MB, pdf)

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