Abstract: Antimicrobial resistance has become a significant global issue leading to health problems and reduced treatment effectiveness, which negatively impact life expectancy. In this context, Antimicrobial Photodynamic Therapy (aPDT) emerges as a potential alternative to circumvent resistance issues. The light-triggered activation of photosensitizers (PS) induces the generation of reactive oxygen species (ROS), effectively destabilizing cell walls and instigating cellular demise. Unlike conventional antibiotics, aPDT mechanisms have evaded observable resistance.

In our study, we center on the dose-response relationship, exploring the chemical aspects, including various methods for attaching PS to surfaces. We assess the efficacy of free versus bound PS in reducing bacterial counts, to gain insights into the chemical intricacies influencing the attachment strategies. The preliminary outcomes of investigation utilizing light with a wavelength of 660 nm, the PS methylene blue and Escherichia coli K12 bacteria reveal a reduction in bacterial count both for bound and unbound PS, depending on the concentrations and light intensity. Empirical investigation involves clinically relevant Gram-pos. and neg. bacteria. Additional parameters like PS surface loading, irradiation sequencing, potential tube material modifications, and aPDT robustness under storage, environmental, and sterilization conditions are examined. Our next step is to identify the specific ROS generated during aPDT on clinical polymer surfaces, specifically silicone and polyurethane, by combining expertise from (bio)material sciences, polymer and surface chemistry, microbiology, and optics/illumination technology. This effort aims to generate new insights into the nature and impact of ROS, establish dose-response relationships to delineate aPDT efficacy, and explore innovative strategies for covalent attachment of PS. The study will assess potential deleterious effects on surrounding tissues and critically evaluate the scalability of aPDT, contributing to a comprehensive understanding of its application in clinical settings for temporary implants like catheters, venous accesses, or dialysis shunts.