Optimization of hydrogel containing toluidine blue O for photodynamic therapy by response surface methodology

- The TBO hydrogel formulation was optimized by response surface methodology.
- Photodynamic therapy with optimal TBO hydrogel showed strong antimicrobial activity.
- The optimal TBO hydrogel was stable over time about appearance, pH and viscosity.

Photodynamic therapy with toluidine blue O (TBO) hydrogel exhibits antibacterial activity against Staphylococcus aureus and Escherichia coli in this paper. The response surface methodology is employed to optimize formulations for antibacterial activity. The optimal formulations are carbomer concentration of 3% (w/v), TBO concentration of 0.1 mg/mL and the quality ratio of NaOH and carbomer of 0.4 (w/w). Under the optimized formulations, the log-transformed of CFU mL− 1 on the Staphylococcus aureus and Escherichia coli are 0.84 and 1.26 (the log-transformed of CFU mL− 1 of negative control groups on the Staphylococcus aureus and Escherichia coli are 8.21 and 8.47), respectively. In comparison with photodynamic therapy with TBO aqueous solution, the proposed formulations provide a much stronger antibacterial activity against Staphylococcus aureus and Escherichia coli. TBO hydrogels are stable during 6 weeks at three different temperatures (4, 25 and 40 °C) with respect to no change of color, transparency, pH and viscosity. 50% and 68.26% of TBO are released from carbomer hydrogel after 4 h and 24 h, respectively. TBO hydrogel alone or light alone (630 nm) treatment is incapable of showing antibacterial activity against Staphylococcus aureus and Escherichia coli. Therefore, photodynamic therapy with the novel optimized TBO hydrogel formulations is a promising treatment strategy for periodontitis.

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