Safety and sustainability assessment of non-metal-based antiviral and antibacterial coatings applied on porous and non-porous surfaces

Antimicrobial coatings have become a pivotal technology for tackling pathogen spreading, particularly in healthcare settings. Novel coatings are designed to prevent microbial survival and biofilm formation on various surfaces, thereby reducing the risk of infections from person to person by inhibiting the growth and spread of pathogens. The mechanisms of action include the release of antimicrobial agents (biocidal), the retention of agents on the surface (contact-killing), and anti-adhesion properties (anti-fouling). Frequently applied antimicrobial coatings often contain silver or other metals which are suspected to cause skin sensitization or allergies, and the metal ion release may pose an environment treat. The need for novel metal-free antimicrobials is therefore evident. New coatings based on quaternary ammonium, antimicrobial polysaccharides or peptides, oxidizing agents releasing radical oxygen species (ROS) to name only a few are at the research forefront. Despite recent progress, several challenges remain, including human safety assessment, long-term functionality, broad-spectrum antimicrobial activity and the potential environmental impact of these materials. History thought us that the human biocompatibility aspects were not given much attention during the development of novel antibiotics. Therefore, the safety aspects of the newest generation of antimicrobial coatings according to “safe by design” (SbD) principles, directly from the start of their development should be assessed. Two case studies were defined, including highly infectious nosocomial hospital settings and highly dense public transportation systems such as trains and airplanes. In-vitro models were adapted and improved to assess the potential adverse effects of tailored coatings, directly on the most likely exposure ways of skin and lungs identified. At the beginning of the COVID-19 pandemic, the safety assessment of newly emerging mask textiles had the highest priority due to the proximity of textiles to our airways as well as their prolonged wearing time. Here, acute lung toxicity evaluation of fiber and particle debris release from diverse types of textiles were investigated. No acute in-vitro cytotoxicity was observed in the human alveolar basal epithelial lung cell model for any facemask textiles investigated. After investigation of the lung toxicity of textile debris from mask textiles, the skin irritation and sensitization capacity of a novel metal-free coating based on quaternary ammonium compounds developed by BASF was assessed. This technology allows rapid functionalization by an easy-to-apply coating for textiles that provide antiviral and antibacterial properties. The functionalized hospital curtains demonstrated an excellent antibacterial and antiviral activity against pathogens like Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii, with a 98% to 100% reduction and murine hepatitis virus (MHV) with a >99% reduction. A conducted KeratinoSens® skin sensitization & irritation assay, according to OECD guidelines No. 442D, showed no acute in-vitro skin toxicity or sensitization in the functional applied coating concentration. For the transportation case study, the incineration toxicity of light-activated antimicrobial coatings, intended for high-traffic enclosed spaces such as airplanes, was investigated with an improved co-culture lung model. This new class of antimicrobial coatings includes hydrophobic carbon quantum dots (hCQDs) and silicate-based upconverters (UPC) which release ROS or UV-light when irradiated with blue light. An in-depth hazardous fume assessment was conducted using a cone calorimeter incineration platform also considering the potential hazards during accidents, such as the formation of harmful polycyclic aromatic hydrocarbons (PAHs). Finally, the airborne soot particles were assessed for their acute in-vitro cytotoxicity on the co-culture lung model and their potential to cause a pro-inflammatory cytokine response. No changes in burning and smoke toxicity behavior and no severe acute toxicity response on the studies lung model of the coated substrates was observed in contrast to the controls. This thesis highlights the potential of novel non-metal based antimicrobial coatings since their antimicrobial efficacy is similar, and their human safety aspects are superior to the previous applied metal-based antimicrobial coatings. These promising results may lead the way for a substitution of harmful antimicrobials with more safe and environmentally friendly alternative coatings. However, continued research and development is needed to overcome existing challenges, enhance the effectiveness and durability of these coatings, and ensure their safe application in diverse use-case scenarios. The integration of these advanced coating materials will likely contribute to improved public health care systems by reducing infection rates in the future.