Superhydrophobic Surfaces as a Source of Airborne Singlet Oxygen through Free Space for Photodynamic Therapy

Effect of treatment frequency on the efficacy of superhydrophobic antimicrobial photodynamic therapy of periodontitis in a wistar rat model

Superhydrophobic antimicrobial photodynamic therapy (SH-aPDT) is advantageous wherein airborne singlet oxygen (1O2) is delivered from a device tip to kill a biofilm with no photosensitizer exposure and no bacterial selectivity (Gram + or Gram -). For effective treatment of periodontitis, the frequency of treatment as well as the optical light fluence required is not known. Thus, we sought to determine whether single or repeated SH-aPDT treatments would work best in vivo using two fluence values: 60 and 125 J/cm2. We assessed the efficacy of three protocols: single treatment; interval treatments (days 0, 2, and 7); and consecutive treatments (days 0, 1, and 2). After 30 days of evaluation, we found that, SH-aPDT in 3 consecutive treatments significantly decreased Porphyromonas gingivalis levels compared to single and interval SH-aPDT treatments, as well as SRP-chlorhexidine (CHX) controls (p < 0.05). Notably, clinical parameters also improved (p < 0.05), and histological and stereometric analyses revealed that consecutive SH-aPDT treatments were the most effective for promoting healing and reducing inflammation. Our study shows what works best for SH-aPDT, while also demonstrating SH-aPDT advantages to treatment of periodontitis including no bacterial selectivity (Gram + or Gram -) and preventing the development of bacterial resistance.

Singlet oxygen generation on a superhydrophobic surface: Effect of photosensitizer coating and incident wavelength on 1O2 yields

Photochemical generation of singlet oxygen (1O2) often relies on homogenous systems; however, a dissolved photosensitizer (PS) may be unsuitable for some applications because it is difficult to recover, expensive to replenish, and hazardous to the environment. Isolation of the PS onto a solid support can overcome these limitations, but implementation faces other challenges, including agglomeration of the solid PS, physical quenching of 1O2 by the support, photooxidation of the PS, and hypoxic environments. Here, we explore a superhydrophobic polydimethylsiloxane (SH-PDMS) support coated with the photosensitizer 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin (TFPP). This approach seeks to address the challenges of a heterogeneous system by using a support that exhibits low 1O2 physical quenching rates, a fluorinated PS that is chemically resistant to photooxidation, and a superhydrophobic surface that entraps a layer of air, thus preventing hypoxia. Absorbance and fluorescence spectroscopy reveal the monomeric arrangement of TFPP on SH-PDMS surfaces, a surprising but favorable characteristic for a solid-phase PS on 1O2 yields. We also investigated the effect of incident wavelength on 1O2 yields for TFPP in aqueous solution and immobilized on SH-PDMS and found overall yields to be dependent on the absorption coefficient, while the yield per absorbed photon exhibited wavelength independence, in accordance with Kasha-Vavilov's rule.

Superhydrophobic Dressing for Singlet Oxygen Delivery in Antimicrobial Photodynamic Therapy against Multidrug-Resistant Bacterial Biofilms

The rise of antimicrobial resistance poses a critical public health threat worldwide. While antimicrobial photodynamic therapy (aPDT) has demonstrated efficacy against multidrug-resistant (MDR) bacteria, its effectiveness can be limited by several factors, including the delivery of the photosensitizer (PS) to the site of interest and the development of bacterial resistance to PS uptake. There is a need for alternative methods, one of which is superhydrophobic antimicrobial photodynamic therapy (SH-aPDT), which we report here. SH-aPDT is a technique that isolates the PS on a superhydrophobic (SH) membrane, generating airborne singlet oxygen (1O2) that can diffuse up to 1 mm away from the membrane. In this study, we developed a SH polydimethylsiloxane dressing coated with PS verteporfin. These dressings contain air channels called a plastron for supplying oxygen for aPDT and are designed so that there is no direct contact of the PS with the tissue. Our investigation focuses on the efficacy of SH-aPDT on biofilms formed by drug-sensitive and MDR strains of Gram-positive (Staphylococcus aureus and S. aureus methicillin-resistant) and Gram-negative bacteria (Pseudomonas aeruginosa and P. aeruginosa carbapenem-resistant). SH-aPDT reduces bacterial biofilms by approximately 3 log with a concomitant decrease in their metabolism as measured by MTT. Additionally, the treatment disrupted extracellular polymeric substances, leading to a decrease in biomass and biofilm thickness. This innovative SH-aPDT approach holds great potential for combating antimicrobial resistance, offering an effective strategy to address the challenges posed by drug-resistant wound infections.

Self-Sterilizing 3D-Printed Polylactic Acid Surfaces Coated with a BODIPY Photosensitizer

Herein, we report the use of polylactic acid coated with a halogenated BODIPY photosensitizer (PS) as a novel self-sterilizing, low-cost, and eco-friendly material activated with visible light. In this article, polymeric surfaces were 3D-printed and treated with the PS using three simple methodologies: spin coating, aerosolization, and brush dispersion. Our studies showed that the polymeric matrix remains unaffected upon addition of the PS, as observed by dynamic mechanical analysis, Fourier transform infrared, scanning electron microscopy (SEM), and fluorescence microscopy. Furthermore, the photophysical and photodynamic properties of the dye remained intact after being adsorbed on the polymer. This photoactive material can be reused and was successfully inactivating methicillin-resistant Staphylococcus aureus and Escherichia coli in planktonic media for at least three inactivation cycles after short-time light exposure. A real-time experiment using a fluorescence microscope showed how bacteria anchored to the antimicrobial surface were inactivated within 30 min using visible light and low energy. Moreover, the material effectively eradicated these two bacterial strains on the first stage of biofilm formation, as elucidated by SEM. Unlike other antimicrobial approaches that implement a dissolved PS or non-sustainable materials, we offer an accessible green and economic alternative to acquire self-sterilizing surfaces with any desired shape.

Interparticle Delivery and Detection of Volatile Singlet Oxygen at Air/Solid Interfaces

An interparticle system has been devised, allowing airborne singlet oxygen to transfer between particle surfaces. Singlet oxygen is photogenerated on a sensitizer particle, where it then travels through air to a second particle bearing an oxidizable compound-a particulate-based approach with some similarities to reactive oxygen quenching in the atmosphere. In atmospheric photochemistry, singlet oxygen is generated by natural particulate matter, but its formation and quenching between particles has until now not been determined. Determining how singlet oxygen reacts on a second surface is useful and was developed by a three-phase system (particle-air-particle) interparticulate photoreaction with tunable quenching properties. We identify singlet oxygen quenching directly by near-IR phosphorescence in the airborne state and at the air/particle interface for total quenching rate constants (k_T) of adsorbed anthracene trapping agents. The air/solid interface k_T of singlet oxygen by anthracene-coated particles was (2.8 ± 0.8) × 10⁷ g mol^-1 s^-1 for 9,10-dimethylanthracene and (2.1 ± 0.9) × 10⁷ g mol^-1 s^-1 for 9,10-anthracene dipropionate dianion, and the lifetime of airborne singlet oxygen was measured to be 550 μs. These real-time interactions and particle-induced quenching steps open up new opportunities for singlet oxygen research of atmospheric and particulate processes.