Methylene blue is a dye currently used in dentistry for antimicrobial neutral photodynamic therapy apdt (ph 7.0). however, we change its ph to acid (ph 1.0). Thus, the current tests we have performed have shown that this biocompatibility test substance showed better behavior than methylene blue in ph7. Below is a summary of the work done with the product which we are applying for patent registration； Objective: The aim of this study was to investigate the biocompatibility of methylene blue at different ph levels through the method of implantation of tubes in subcutaneous tissue. Materials and methods: Eighty-four sterile polyethylene tubes were allocated to subcutaneous tissue of 28 rats, each receiving 4 tubes that were divided into 4 groups: tube group (g-t) - empty tube； fibrin group (g-f) - fibrin sponge filled tube； methylene blue group ph 7 (g-am / ph7) - tube filled with fibrin sponge soaked in methylene blue (100 µg / ml) with ph 7.0； methylene blue group ph 1 (g-am / ph1) - tube filled with fibrin sponge soaked in methylene blue (100 µg / ml) with ph 1,0. After 7, 15 and 30 days, 7 animals from each group were euthanized and the tubes surrounded by surrounding tissue were removed and fixed with 4% buffered formaldehyde solution. The collected pieces were processed and the histological sections (4 µm) were stained with hematoxylin and eosin and analyzed by light microscopy. scores were attributed to the analysis of histopathological parameters. the results were statistically analyzed by the kruskal wallis test (p = 0.05). Results: At 7 and 30 days, the g-am / ph1 group showed no significant difference compared to the g-t control group, while g-am / ph7 showed a significant increase in tissue reaction, also when compared to g-t. At 15 days there was no statistical difference between the groups. Conclusion: Within the limits of this study, it was concluded that methylene blue at ph 1.0 provided better biocompatibility than at ph 7.0.o azul de metileno é um cor
