Photodynamic Coatings on Polymer Microfibers for Pathogen Inactivation: Effects of Application Method and Composition

Abstract

A substantial increase in the risk of hospital-acquired infections (HAIs) has greatly impacted the global healthcare industry. Harmful pathogens adhere to a variety of surfaces and infect personnel on contact, thereby promoting transmission to new hosts. This is particularly worrisome in the case of antibiotic-resistant pathogens, which constitute a growing threat to human health worldwide and require new preventative routes of disinfection. In this study, we have incorporated different loading levels of a porphyrin photosensitizer capable of generating reactive singlet oxygen in the presence of O2 and visible light in a water-soluble, photo-cross-linkable polymer coating, which was subsequently deposited on polymer microfibers. Two different application methods are considered, and the morphological and chemical characteristics of these coated fibers are analyzed to detect the presence of the coating and photosensitizer. To discern the efficacy of the fibers against pathogenic bacteria, photodynamic inactivation has been performed on two different bacterial strains, Staphylococcus aureus and antibiotic-resistant Escherichia coli, with population reductions of >99.9999 and 99.6%, respectively, after exposure to visible light for 1 h. In response to the current COVID-19 pandemic, we also confirm that these coated fibers can inactivate a human common cold coronavirus serving as a surrogate for the SARS-CoV-2 virus.

Toward Universal Photodynamic Coatings for Infection Control

“…While the resultant coating thicknesses varied two-fold across the different materials [PRU (~1.8 μm) > Wolin (~1.4 μm) > Deans (~0.91 μm) > Capri (~0.76 μm)], the thickness of the coating applied to the Husk specimen could not be determined due to the lack of identifiable individual fibers at the highest magnification employed. Compared to our earlier study employing SbQ-PVA/ZnTMPyP 4+ that yielded a coating thickness of ~150-200 nm ( 30 ), here we see a 5-10-fold increase in coating thickness. We attribute the increase here to two factors: (i) a larger quantity of initial SbQ-PVA/ZnTMPyP 4+ solution was used to saturate the thicker Vescom materials compared with the spunbond nylon mats previously employed, resulting in a thicker photoactive base layer; and (ii) the use of two “sealant” coats (achieved by sequential spray and dip coating) on top of the base layer as opposed to a single “sealant” coat (dip only) performed in our previous study.…”

“…Unless otherwise noted, all in vitro aPDI assays were performed under fixed illumination conditions (60 min, 400-700 nm, 65 ± 5 mW/cm 2 ). These illumination conditions were chosen on the basis of our prior works, and we note that we have previously reported that illumination alone (e.g., light-only control) at the aforementioned intensity and duration is not sufficient to inactivate pathogens without the presence of a PS ( 30 , 43 , 44 ); this was again confirmed here as light-only controls did not show any statistically significant pathogen inactivation ( Supplementary Figure 2 ). As displayed in Figure 6A , neither the SbQ-PVA-only coated materials (PS-free) nor the non-illuminated SbQ-PVA/ZnTMPyP 4+ coated samples (dark controls) exhibited any statistically significant antibacterial activity against methicillin-susceptible S. aureus ATCC-29213, thereby confirming the requirement for both light and addition of PS for photodynamic inactivation of this pathogen (in an oxygen-containing environment).…”

“…In our previous study ( 30 ), SbQ-PVA/ZnTMPyP 4+ was successfully applied by both spray- and dip-coating methods to relatively uniform nylon-PA6 spunbond fibers. To determine if SbQ-PVA/PS coatings could be applied to a broader range of materials commonly utilized in areas such as hospital waiting rooms and patient rooms, a variety of commercially-available materials (from Vescom America) having applications from curtains to upholsteries and wallpaper were examined.…”

“…To determine if SbQ-PVA/PS coatings could be applied to a broader range of materials commonly utilized in areas such as hospital waiting rooms and patient rooms, a variety of commercially-available materials (from Vescom America) having applications from curtains to upholsteries and wallpaper were examined. Here, we primarily employed ZnTMPyP 4+ for characterization and antimicrobial evaluation for comparative purposes to our previous studies employing this and related tetrapyrrole photosensitizers ( 30 , 33 , 34 , 37 – 40 , 43 , 44 ). Other photosensitizers, e.g., MB and RB, were also evaluated for antimicrobial efficacy and will be discussed further below.…”

“…The coating protocol was performed as previously described ( 30 ) with minor modifications. The SbQ-PVA was dissolved in deionized (DI) water at a fixed concentration of 10% w/v SbQ-PVA/water and stirred until fully dissolved according to the unaided eye.…”