ABSTRACT

Background and Aim: Silver nanoparticles (AgNPs) have potential applications in bone regeneration; however, the concentration-dependent effects of their direct local administration at fracture sites remain insufficiently characterized. This study evaluated the effects of a single local application of AgNPs at different concentrations on fracture healing in a stabilized rat femoral osteotomy model and assessed associated changes in antioxidant enzyme activity.

Materials and Methods: Eighty healthy male albino rats, aged 5–6 months and weighing 300–350 g, were allocated equally to four groups (n = 20/group): control and AgNP treatments at 2.5, 5, and 10 μg/mL. Following standardized femoral osteotomy and intramedullary fixation, 1 mL of normal saline or the assigned AgNP suspension was administered once locally at the osteotomy site. Fracture healing was evaluated on postoperative days 7, 14, 21, and 30 using radiographic callus measurements, histological assessment, and histomorphometric quantification of osteoblasts, osteocytes, and osteoclasts. Catalase (CAT) and superoxide dismutase (SOD) activities were assessed on days 7 and 30.

Results: Local AgNP administration showed concentration- and time-dependent differences in fracture healing. On day 30, callus diameters were 5.28 ± 0.09, 6.20 ± 0.11, 7.01 ± 0.15, and 8.56 ± 0.05 mm in the control, 2.5, 5, and 10 μg/mL groups, respectively (p < 0.05). Histomorphometry demonstrated corresponding changes in bone-cell dynamics. On day 30, osteocyte counts were 3.60 ± 0.66, 8.53 ± 0.69, 10.14 ± 0.66, and 12.03 ± 1.39 cells/high-power field, respectively, whereas osteoblast counts were 5.53 ± 0.69, 7.87 ± 0.58, 10.73 ± 0.80, and 10.80 ± 0.84 cells/high-power field, respectively. CAT activity increased, whereas SOD activity generally decreased with increasing AgNP concentration.

Conclusion: A single local AgNP application was associated with concentration-dependent increases in radiographic callus formation and changes in histomorphometric indices of fracture repair, with the most pronounced responses generally observed at 10 μg/mL. AgNP exposure also altered antioxidant enzyme concentrations. However, these findings do not establish enhanced biomechanical strength or a specific mechanism of action. Further biomechanical, molecular, pharmacokinetic, and toxicological studies are required to establish functional efficacy and safety.

Keywords: antioxidant enzymes, bone regeneration, fracture healing, histomorphometry, local administration, rat femoral osteotomy, silver nanoparticles, tissue remodeling.