Surface Modification of Polyurethane Membrane with Various Hydrophilic Monomers and N-Halamine: Surface Characterization and Antimicrobial Properties Evaluation

Prevention of surface colonization and anti-biofilm effect of selected phytochemicals against Listeria innocua strain

This work aimed to determine the ability of Listeria innocua (L.i.) to colonize eight materials found in food-processing and packaging settings and to evaluate the viability of the sessile cells. We also selected four commonly used phytochemicals (trans-cinnamaldehyde, eugenol, citronellol, and terpineol) to examine and compare their efficacies against L.i. on each surface. Biofilms were also deciphered in chamber slides using confocal laser scanning microscopy to learn more about how phytochemicals affect L.i. The materials tested were silicone rubber (Si), polyurethane (PU), polypropylene (PP), polytetrafluoroethylene (PTFE), stainless steel 316 L (SS), copper (Cu), polyethylene terephthalate (PET), and borosilicate glass (GL). L.i. colonized Si and SS abundantly, followed by PU, PP, Cu, PET, GL, and PTFE surfaces. The live/dead status ranged from 65/35% for Si to 20/80% for Cu, and the estimates of cells unable to grow on Cu were the highest, reaching even 43%. Cu was also characterized by the highest degree of hydrophobicity (ΔG^TOT = -81.5 mJ/m²). Eventually, it was less prone to attachment, as we could not recover L.i. after treatments with control or phytochemical solutions. The PTFE surface demonstrated the least total cell densities and fewer live cells (31%) as compared to Si (65%) or SS (nearly 60%). It also scored high in hydrophobicity degree (ΔG^TOT = -68.9 mJ/m²) and efficacy of phytochemical treatments (on average, biofilms were reduced by 2.1 log₁₀ CFU/cm²). Thus, the hydrophobicity of surface materials plays a role in cell viability, biofilm formation, and then biofilm control and could be the prevailing parameter when designing preventive measures and interventions. As for phytochemical comparison, trans-cinnamaldehyde displayed greater efficacies, with the highest reductions seen on PET and Si (4.6 and 4.0 log₁₀ CFU/cm²). The biofilms in chamber slides exposed to trans-cinnamaldehyde revealed the disrupted organization to a greater extent than other molecules. This may help establish better interventions via proper phytochemical selection for incorporation in environment-friendly disinfection approaches.

Investigating migration potential of a new rechargeable antimicrobial coating for food processing equipment

Antimicrobial coatings are designed to inhibit the growth of pathogens and have been used to reduce foodborne illness bacteria on food processing equipment. Novel N-halamine based antimicrobial coatings are highly advantageous due to their unique properties and low cost, and are being investigated for applications in food safety, health care, water and air disinfection, etc. In this study, we evaluated the chemical safety of a novel N-halamine antimicrobial polymer coating (Halofilm) for use on food processing equipment. Migration tests were performed on stainless steel tiles prepared with four different treatment groups: negative control, positive control, Halofilm coating without chlorination, and Halofilm coating with chlorination. An LC-MS/MS method was developed and validated for four formulation components: polyethylenimine (PEI), Trizma^® base, hydantoin acrylamide (HA) and dopamine methacrylamide (DMA), followed by stability and recovery tests. Migration tests were conducted at 40 °C with three food simulants (10, 50 and 95% ethanol/water) to mimic various food properties, and aliquots of migration extracts were analyzed at 2, 8, 72, 240 and 720 h. In general, measured concentration levels were consistent among simulant types for the four tested chemicals. Chlorinated tiles had non-detects for three analytes (PEI, HA and DMA), and less than 0.05 mg/kg of HA migration over 30 days. A chlorination step could possibly change the measured mass (m/z) hence leading to non-detects in targeted LC-MS/MS. In non-chlorinated tiles, all four compounds were detected during the migration test. This suggests that addition of the chlorination step may have a stabilizing effect on the polymer. Additionally, full scan high resolution mass spectrometry (HRMS) analysis was employed to screen for migration of other extractable and leachable (E&L) chemicals, which led to the identification of eight common E&L chemicals. To our knowledge, this is the first report evaluating chemical migration from an N-halamine antimicrobial polymer coating product.

Polyvinylidene fluoride multi-scale nanofibrous membrane modified using N-halamine with high filtration efficiency and durable antibacterial properties for air filtration

HYPOTHESIS

Particulate matter (PM) pollution and the coronavirus (COVID-19) pandemic have increased demand for protective masks. However, typical protective masks only intercept particles and produce peculiar odors if worn for extended periods owing to bacterial growth. Therefore, new protective materials with good filtration and antibacterial capabilities are required.

EXPERIMENTS

In this study, we prepared multi-scale polyvinylidene fluoride (PVDF) nanofibrous membranes for efficient filtration and durable antibacterial properties via N-halamine modification.

FINDINGS

The N-halamine-modified nanofibrous membrane (PVDF-PAA-TMP-Cl) had sufficient active chlorine content (800 ppm), and the tensile stress and strain were improved compared with the original membrane, from 6.282 to 9.435 MPa and from 51.3 % to 56.4 %, respectively. To further improve the interception efficiency, ultrafine nanofibers (20-35 nm) were spun on PVDF-PAA-TMP-Cl nanofibrous membranes, and multi-scale PVDF-PAA-TMP-Cl nanofibrous membranes were prepared. These membranes exhibited good PM_0.3 interception (99.93 %), low air resistance (79 Pa), promising long-term PM_2.5 purification ability, and high bactericidal efficiency (>98 %). After ten chlorination cycles, the antibacterial efficiency against Escherichia coli and Staphylococcus aureus exceeded 90 %; hence, the material demonstrated highly efficient filtration and repeatable antibacterial properties. The results of this study have implications for the development of air and water filtration systems and multi-functional protective materials.