Shielding Surfaces from Viruses and Bacteria with a Multiscale Coating

Abstract

The spread of viral and bacterial pathogens mediated by contact with surfaces is a leading cause of infection worldwide. COVID-19 and the continuous rise of deaths associated with antibiotic-resistant bacteria highlight the need to impede surface-mediated transmission. A sprayable coating with an intrinsic ability to resist the uptake of bacteria and viruses from surfaces and droplets, such as those generated by sneezing or coughing, is reported. The coating also provides an effective microbicidal functionality against bacteria, providing a dual barrier against pathogen uptake and transmission. This antimicrobial functionality is fully preserved following scratching and other induced damage to its surface or 9 days of submersion in a highly concentrated suspension of bacteria. The coatings also register an 11-fold decrease in viral contamination compared to the noncoated surfaces.

Keywords: ZIF-8 metal-organic frameworks (MOFs); antibacterial; antiviral; infections; multiscale coatings.

Figure 1

Dual functional coating for shielding surfaces from bacteria and viruses. a) Schematic of the dual‐functional coating with the air layer or plastron preventing surface contamination by pathogens contained in a liquid environment. b) Schematic of the localized loss of superhydrophobicity of the dual‐functional coating and antimicrobial effect of ZIF‐8 nanoparticles.

Figure 2

Characterization of the water‐repellent coating. a) Illustration showing the fabrication of the coating. b) SEM images of spray‐coated IPN showing the microtextured morphology. c) SEM images of the IPN‐FS spray‐coated coating show the nanorough morphology of the water repellent coating. d) FTIR spectroscopy of IPN and its raw constituent chemicals. e) The plot shows the static water contact angle and rolling angle versus the number of abrasion cycles (n = 27).

Figure 3

Surface shielding mechanism. a,b) CLSM orthogonal projection of bacteria on steel and water repellent surfaces, respectively. On the water repellent coating, the plastron layer prevents bacteria from reaching and adhering to the surface. c–e) Snapshots from Movie S2 of the Supporting Information show the behavior of bacteria on the steel surface. Adhering bacteria are false colored to yellow and green represents moving bacteria at that particular time‐point. g–i) Snapshots from Movie S3 of the Supporting Information showing the behavior of bacteria on the water repellent coating. The substrate surface is colored purple for contrast. f) Plot showing the velocity profile of bacteria on the bare steel surface, n = 15 and j) plot showing the velocity profile of bacteria on water repellent surfaces, n = 15.

Figure 4

Surface shielding performance against bacteria. a–d) Axio‐observer images of the agar imprints of control‐steel and water repellent surfaces showing qualitatively the relative extent of adhesion under unwashed and washing conditions. e) Plot showing the serial dilution data. The water repellent surfaces resisted 99.99% of bacteria compared to the steel surface. (* represents p < 0.01 in a one‐way ANOVA test, n = 9.) Imaging experiments were repeated three times.

Figure 5

Bacterial adhesion on point defects. a) Orthogonal projection of the coating‐defect interface with bacteria on it. The two image planes are marked. The behavior of cells overtime on these planes is shown in Movies S4 and S5 of the Supporting Information. b,c) Screenshots of the coating‐defect interface captured from Movies S4 and S5 of the Supporting Information. A, B, and C represent three regions where the cell‐surface interactions are studied. d) Velocity profiles of bacteria on regions A, B, and C. e–g) SEM images of a defective coating after exposure to bacterial culture for 10 min. f) The defect is colonized by bacteria, whereas (g) the nondefective area has no bacteria attached to it.

Figure 6

Failure kinetic of water‐repellent shielding mechanism and performance of the secondary shielding mechanism. a–h) Axio‐observer images of the agar plate imprints corresponding to water repellent surfaces submerged in bacteria solutions for 1 h to 8 h. Up to <6 h immersion, a decrease in colonization concerning the bare steel coating is observed. i) Serial dilution data of the long immersion experiment, n = 9. j–m) Snapshots from Movie S5 of the Supporting Information show the plastron layer disruption over time.

Figure 7

Material characterizations of the dual‐functional coating. a) Contact angles of water repellent coating and the samples containing ZIF‐8 powders (5–20 wt%). b) XRD patterns, and c) FTIR spectra of the coatings (water repellent coating and the samples containing 5–15 wt% of ZIF‐8 powders) on stainless steel in comparison with ZIF‐8 powders. d–f) SEM images of the coating containing 15 wt% of ZIF‐8 powders at different magnifications, and g) EDX elemental mapping of the coating showing the distribution of oxygen, silicon, and zinc elements.

Figure 8

Antibacterial characterization of the dual‐functional coating. a) Plot showing the serial dilution data of the dual‐functional coatings containing ZIF‐8 nanograins after 1, 5, and 9 days continuous immersion in a highly concentrated bacteria solution (** represents p < 0.01 and *** represents p < 0.001 in a one‐way ANOVA test, n = 6). Results of the scratch‐experiment showing Axio‐observer images of the agar imprints of b) control‐steel, c) pristine water repellent coating, d) scratched water repellent coating, and e) scratched dual‐functional coating containing 15 wt% of ZIF‐8. All the imaging experiments were repeated three times.

Figure 9

Evaluation of viral pathogen shielding performance. a) Schematic of the experiment, where a metal rod is first dipped in a solution of an EGFP‐expressing lentiviral vector (1 × 107 TU mL⁻¹) and then through a series of wash solutions (fresh DMEM). The washes were then tested for virus by incubating with cells and detecting infection by fluorescence microscopy. b) Quantification of numbers of infected cells as counted by microscopy, representing levels of virus contamination. Each replicate is shown as a dot (n = 9), the bars and error are mean and SEM, respectively; * represents p < 0.01. c) Representative images of cells after incubation with the washes as labeled. Green indicates infection and blue is 4′,6‐diamidino‐2‐phenylindole (DAPI) stained nuclei, scale bar = 100 µm.