SURFACE FUNCTIONALIZATION OF MN-DOPED BIOACTIVE GLASSES BY GALLIC ACID FOR BONE TISSUE REGENERATION

Severe bone injuries often lead to elevated concentrations of reactive oxygen species (ROS), resulting in oxidative stress that can disrupt cellular repair mechanisms, induce cell death, or even trigger malignant transformations. Addressing oxidative stress in the defect microenvironment is thus pivotal for effective bone tissue regeneration. This study explores the multifunctional potential of bioactive glass co-releasing manganese ions and gallic acid (GA) as a strategy to mitigate oxidative damage. Two bioactive glasses, 58S and manganese-doped 58S-5Mn, were synthesized via the sol-gel method. Structural characterization revealed that 58S partially crystallized during calcination, forming apatite crystals within the glassy matrix. On the other hand, 58S-5Mn exhibited an amorphous structure, confirming successful manganese integration as a network modifier. Adsorption kinetics and isotherms demonstrated rapid GA uptake in both samples during the initial hours of contact. The kinetic profile fitting indicated that the pseudo-second-order model yielded the best fits, suggesting a retention process driven by the availability of active sites on the samples' surface. Besides, the adsorption isotherms revealed that the maximum loading capacity of the sorbents 58S and 58S-5Mn reached 45 mg/g and 40 mg/g, respectively. The functionalized samples were then denoted 58S-GA and 58S-5Mn-GA for the reference and manganese-doped, respectively. In vitro bioactivity tests in Simulated Body Fluid (SBF) showed that GA functionalization preserved the apatite-forming capability of the glasses. Within one day of immersion, 58S and 58S-GA induced apatite formation, likely due to their higher calcium content and pre-existing apatite crystals acting as nucleation sites. For Mn-doped samples, an amorphous calcium phosphate layer formed initially, with crystallization commencing after seven days, resulting in more apatite crystals in 58S-5Mn compared to 58S-5Mn-GA. Antioxidant assessments revealed significant ROS scavenging properties for the functionalized and manganese-doped samples. Manganese doping enabled 58S-5Mn and 58S-5Mn-GA to scavenge over 80% of hydrogen peroxide after 72 hours, while non-doped samples remained inactive. Similarly, DPPH radical scavenging assays highlighted the synergistic antioxidant effects of GA functionalization. Functionalized samples achieved DPPH scavenging rates of 80–90%, with 58S-5Mn-GA exhibiting an IC50 of 1 mg/ml, compared to 2 mg/ml for 58S-GA. These findings underscore the complementary roles of manganese doping and GA functionalization in enhancing the antioxidant properties of bioactive glasses, offering distinct mechanisms to stabilize various ROS and highlighting their potential for improving bone regeneration outcomes.