Methylene Blue Doped Films of Wool Keratin with Antimicrobial Photodynamic Activity

In this work, keratin films doped with different amounts of methylene blue (MB) were
developed in order to prepare new biodegradable and biocompatible materials for tissue engineering
and wound healing, able to exert antimicrobial photodynamic activity upon irradiation with visible light.
Preliminary results indicated that the swelling ratio, as well as the MB release, increases by increasing
the pH. Moreover, the generation of reactive oxygen species (ROS) and singlet oxygen can be easily
triggered and controlled by a fine-tuning of the irradiation time and MB concentration in the films. As
concerns the photodynamic effects on keratin, the ROS attack does not induce any significant
photodegradation on the protein, even if a slight photo-oxidation of sulfonated amino acids occurs.
Finally, the film with the highest MB concentration (400 μg per gram of keratin) displays a significant
photobactericidal activity against Staphylococcus aureus with a bacterial reduction that increases by
increasing the irradiation time. In particular, the irradiation of KFMB400 film incubated with S. aureus at
a concentration of 108 cfu mL^−1 determined the 99.9% killing rate and the killing effect increased
proportionally with irradiation time.