(A-7) Nanoparticle-derived superamphiphobic coating-material combination for potential antimicrobial applications

Introduction: Healthcare-associated infections (HAIs) affect 1 in 31 patients every day, costing US hospitals an additional $28.4 billion each year [1]. Invasive procedures involving blood-contacting medical devices such as catheters, cannulas, and implants increase the risk of contracting HAIs and often introduce thrombotic morbidity [1]. Bacterial biofilms and thrombosis may develop even in short-term applications, but slippery hydrophobic surfaces have shown potential in reducing bacteria and fibrinogen adhesion [2,3]. These surfaces have been paired with nitric oxide (NO) donors to increase antifouling and bactericidal capabilities, though surfaces of a superamphiphobic nature have yet to be ventured, due to their non-biocompatibility and instability on polymer surfaces. Thus, we propose a widely applicable, antifouling, biocompatible, superamphiphobic coating for use in a dual-action antibacterial material-coating combo for blood-contacting devices. Selected for its cytocompatibility and previous use in various medical devices [4,5,6], a poly(dimethylsiloxane) (PDMS) film is swelled with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor chosen for its broad-spectrum bactericidal properties and ability to disperse and prevent biofilms [7,8,9]. The superamphiphobic coating is composed of silane-modified ZnO and SiO₂ nanoparticles and microparticles that form an antifouling, hierarchical nano-microstructure when dip-coated [10]. Catalyzed by light, heat, and metal ions, the inclusion of Zn catalyzes SNAP, complimentarily increasing NO flux [11]. The facile application process, combined with slippery surface properties independent of the base material, suggests potential as a multi-material surface modifier. Together, this pairing of successful antifouling and antithrombotic material modifications may prove to be integral to the reduction of HAIs and associated thrombotic morbidities.

Materials and Methods: ZnO + SiO₂ nanoparticles were modified with 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTCS), then mixed with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTS) to form the coating. To determine the superamphiphobicity of the ZnO + SiO₂ coating, static contact angle was measured with ImageJ immediately after dropping 5 μL of deionized (DI) water or n-hexadecane. Roll-off angle was determined with angled slides. Coating stability was evaluated in 1 mL solutions of DI water, 10 mM phosphate-buffered saline (PBS) with 100 μM ethylenediaminetetraacetic acid (EDTA), 1 mM dimethyldioctadecylammonium bromide (DDAB), and 1 mM sodium dodecyl sulfate (SDS). Thin films samples (8 mm diameter) were incubated at 37 °C for 1 and 3 d, then removed from solution and allowed to dry for 1 h before being tested for both water contact angle (WCA) and oil (n-hexadecane) contact angle (OCA). Similar wettability characterization was conducted for sand abrasion cycles (5 mL of sand from a height of 20 cm) and UV light degradation at 365 nm for 1 and 3 d. The amount of loaded SNAP was calculated by incubating SNAP-swelled samples in tetrahydrofuran (THF) for 24 h then quantified with UV-vis spectroscopy and compared to a calibration curve. To determine the percentage of SNAP leached, samples were incubated at 37 °C in 10 mM PBS with 100 μM EDTA. Leachate was quantified with UV-vis spectroscopy at 340 nm then summed and similarly evaluated with a calibration curve. NO flux for SNAP-swelled samples was quantified with a chemiluminescence nitric oxide analyzer up to 3 d.

Results, Conclusions, and Discussions:

Superamphiphobicity of ZnO + SiO₂ coated PDMS was measured against PDMS, PVDF-PDMS, SNAP swelled-PDMS, and ZnO + SiO₂ SNAP-PDMS. ZnO + SiO₂ PDMS and SNAP-PDMS coated samples showed no significant difference in WCA. Coated PDMS displayed a significantly higher WCA and OCA than the PVDF-PDMS control. All solutions maintained superhydrophobicity for 24 h, with DDAB losing superhydrophobicity at 72 h. All other solutions maintained pseudo-superoleophobicity after 24 h. ZnO + SiO₂ PDMS retained superhydrophobicity after 3 cycles of sand abrasion. The coating of UV sterilized samples sustained superhydrophobic contact angles for 3 d and superoleophobic contact angles for 1 d. SNAP-swelled samples were loaded with an average of 2.09 ± 0.09 mg/cm² of SNAP. Over 3 d, ZnO + SiO₂ coated samples leached significantly less SNAP than uncoated samples, likely due to their superhydrophobicity. Average NO flux for coated samples was 7.94, 1.93, and 0.98 × 10^-10 mol min^-1 cm^-2 for day 0, 1, and 3, exhibiting a significantly higher flux than SNAP-PDMS on day 0. 

In this work we exhibit the superamphiphobic properties of a ZnO + SiO₂ nano/microstructure coating. Under physiological conditions we report promising coating stability in salt solutions, positive surfactants, and negative surfactants, suggesting an ability to repel both bacterial and blood droplets. Abrasion testing indicates low adhesion strength while maintaining superhydrophobicity. Preservation of superamphiphobicity after UV light treatment infers the possibility of UV sterilization, as 30 min is often the suggested duration [12]. A consistent and heightened NO flux profile with low SNAP leaching proposes an antifouling, antimicrobial coating capable of drug diffusion. 

The ZnO + SiO₂ SNAP-PDMS material-coating combo proposes a compelling methodology to reduce HAIs and thrombosis in blood-contacting medical devices, though notably, the ZnO + SiO₂ coating individually exhibits stability in a variety of scenarios. Its superamphiphobic property is independent of the associated SNAP-PDMS base material. The coating stability demonstrated with PDMS, which is often challenging to coat, may hint at a wider, more stable applicability to other materials such as steel or wood. We later hope to run biological studies to characterize the antibacterial and antithrombotic effects of the material-coating combo.

Acknowledgements:

This material is based upon work supported by a National Science Foundation Research Experience for Undergraduates (REU) site program under grant No. 1950581

References:

[1] Office of Policy, Performance, and Evaluation. (2021, June 21). Health Topics - Healthcare-Associated Infections (HAI). Centers for Disease Control and Prevention. Retrieved June 26, 2023, from https://www.cdc.gov/policy/polaris/healthtopics/hai/index.html#

[2] Merritt, J. H., Kadouri, D. E., & O'Toole, G. A. (2005). Growing and analyzing static biofilms. Current protocols in microbiology, Chapter 1, Unit–1B.1. https://doi.org/10.1002/9780471729259.mc01b01s00

[3] Baskin, J. L., Pui, C. H., Reiss, U., Wilimas, J. A., Metzger, M. L., Ribeiro, R. C., & Howard, S. C. (2009). Management of occlusion and thrombosis associated with long-term indwelling central venous catheters. Lancet (London, England), 374(9684), 159–169.

[4] Miranda, I., Souza, A., Sousa, P., Ribeiro, J., Castanheira, E. M. S., Lima, R., & Minas, G. (2021). Properties and Applications of PDMS for Biomedical Engineering: A Review. Journal of functional biomaterials, 13(1), 2. https://doi.org/10.3390/jfb13010002

[5] Burgener, K., & Bhamla, M. S.. (2021). A polymer-based technique to remove pollutants from soft contact lenses. Contact Lens and Anterior Eye, 44(3), 101335. https://doi.org/10.1016/j.clae.2020.05.004

[6] Yoo, B. Y., Kim, B. H., Lee, J. S., Shin, B. H., Kwon, H., Koh, W. G., & Heo, C. Y. (2018). Dual surface modification of PDMS-based silicone implants to suppress capsular contracture. Acta biomaterialia, 76, 56–70. https://doi.org/10.1016/j.actbio.2018.06.022

[7] R. Raulli, G. McElhaney-Feser, J. Hrabie and R. Cihlar, Recent Res. Dev. Microbiol., 2002, 6, 177–183

[8] Allan RN, Morgan S, Brito-Mutunayagam S, Skipp P, Feelisch M, Hayes SM, et al. Low concentrations of nitric oxide modulate Streptococcus pneumoniae biofilm metabolism and antibiotic tolerance. Antimicrob Agents Chemother 2016;60:2456e66.

[9] Ren H, Wu J, Colletta A, Meyerhoff ME, Xi C. Efficient eradication of mature Pseudomonas aeruginosa biofilm via controlled delivery of nitric oxide combined with antimicrobial peptide and antibiotics. Front Microbiol 2016;7:1e8. https://doi.org/10.1016/S0140-6736(09)60220-8

[10] Dou, X.-Q., Zhang, D., Feng, C., & Jiang, L.. (2015). Bioinspired Hierarchical Surface Structures with Tunable Wettability for Regulating Bacteria Adhesion. ACS Nano, 9(11), 10664–10672. https://doi.org/10.1021/acsnano.5b04231

[11] Askew, S. C., Butler, A. R., Flitney, F. W., Kemp, G. D., & Megson, I. L. (1995). Chemical mechanisms underlying the vasodilator and platelet anti-aggregating properties of S-nitroso-N-acetyl-DL-penicillamine and S-nitrosoglutathione. Bioorganic & medicinal chemistry, 3(1), 1–9. https://doi.org/10.1016/0968-0896(94)00139-t

[12] Is UV Sterilization Effective For Viruses and Bacteria? (n.d.). Advanced Biotechnologies. Retrieved July 21, 2023, from https://abionline.com/is-uv-sterilization-effective-for-viruses-and-bacteria/