Photophysics and drug delivery behavior of methylene blue into Arabic-gum based hydrogel matrices

Abstract Methylene blue (MB) is an efficient photosensitizer for Photodynamic Therapy treatment. The photodynamic action is based on the interaction between light with a specific wavelength, a photosensitizer, and oxygen. Reactive oxygen species (ROS), including singlet oxygen (1O2), are created and support the photodynamic action. We verified that the MB presents a high 1O2 quantum yield in distilled water and simulated fluids (simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 6.8)). Hydrogels are investigated for MB delivery to overcome undesirable effects and avoid the formation of non-effective leuco-methylene blue. The glycidyl methacrylate (GMA) was used to modify the Arabic gum structure. pH-responsive hydrogels composed of Arabic gum with different methacrylation degrees (82 and 94% - MAG82 and MAG94, respectively) are created from the free-radical polymerization mechanism. The low methacrylation degree promotes high MB internalization in the hydrogel. The hydrogels' swelling degree depends on the MB incorporation, methacrylation degree, and pH of the simulated fluid. The MB release in the simulated fluids shows an unusual behavior due to the hydrogel erosion/degradation, attributed to the acid hydrolysis. The amount of released MB in SGF and SIF is similar for the hydrogel containing the high methacrylation degree. On the other hand, the MAG82 hydrogel releases more MB (twice) in SGF than in SIF. The erosion/degradation is more pronounced in the MAGH82 incorporated with the MB (hydrogel MAG82 + MB). Hydrogels matrices containing MB (which acts as photosensitizer) has showed great potential for the treatment of gastrointestinal cancer via Photodynamic Therapy.