Multifunctionally Modified Superhydrophobic Aluminum and Fabric Surfaces with Reduced Gram-Negative and Gram-Positive Bacterial Attachment: A Possible Approach for Self-Cleaning Aircraft and Crew Cabin Surfaces

Abstract

Development of novel approaches for reducing the cost of routine cleaning of aircrafts and crew cabin surfaces is a challenge. In particular, the removal of bacterial pathogens engaged in biofilm formation and multi-drug resistance is of the utmost importance. “Self-cleaning” materials such as functionally modified superhydrophobic surfaces are of a greater use as they not only remove the bacteria by their antimicrobial component, but also do not allow the bacterial attachment to the superhydrophobic surfaces, thereby limiting the biofilm formation. In the present study, we tested three surface-modified fabrics and three aluminum sheet surfaces for their bacterial attachment properties using Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) bacteria. The surface-modified fabrics were coated Nomex fabric (1382 and 1386) and uncoated Nomex fabric (1384). The aluminum sheets were coated with fluorofunctionalized copper-doped magnesium oxide (Cu–MgO) (1381 and 1434) and fluorofunctionalized silver-doped magnesium oxide (Ag–MgO) (1437). A drop of 100 μl, containing 1 × 105 colony forming units (cfu/ml) of gram-negative/gram-positive bacteria, was placed on each material and the sample with bacteria was subsequently incubated for 1 h at 37°C. After incubation, the drop was removed and the surfaces were either washed three times with phosphate buffered saline (PBS) or left unwashed. Both the washed and unwashed surfaces were immersed in 1 ml of PBS and the solution was plated on plate count agar for bacterial enumeration. In case of unwashed #1382 fabric, very few bacteria were attached to the surface (60 ± 72 cfu for E. coli and 6 ± 11 cfu for Staphylococcus aureus) and after washing of the surface, there was no bacterial recovery. This indicates that the surface has less bacterial attachment, and if washed the attached bacteria can easily be removed. On the other hand, coated #1386 fabric did not show any bacterial attachment to the surface for both the pathogens compared to uncoated yellow fabric 1384 (9.3 × 103 cfu for E. coli and 4 × 102 cfu for Staphylococcus aureus). The droplet containing bacteria wetted the aluminum sheet surface of 1381 and 1434 samples, and the bacteria were recovered from both the surfaces even after washing three times. On the other hand, the drop of solution containing bacteria beaded up on the surface of aluminum sample 1437 exhibiting superhydrophobic property and showed no bacterial recovery for both the pathogens. Our results thus clearly indicate that surface-modified fabrics (1382 and 1386) and aluminum sheet (1437) do not allow bacterial attachment and therefore could be suitable for their application in developing self-cleaning aircraft and cabin crew surfaces materials.