Enhanced regeneration of large cortical bone defects with electrospun nanofibrous membranes and low-intensity pulsed ultrasound

Poly-L-lactic acid (PLLA) nanofibrous membranes are widely utilized for tissue regeneration. Low intensity pulsed ultrasound (LIPUS) has been considered as a feasible modality for bone union. The aim of the present study was to investigate the potential synergistic effect of LIPUS and PLLA electrospun nanofibrous membranes on large cortical bone defects in rabbits in vivo. The bilateral rabbit tibia defect model was constructed using 18 adult NZ rabbits and the defect sites were treated with the nanofibrous membranes combined with LIPUS or nanofibrous membranes alone. A total of 3 to 6 weeks after surgery, bone defect healing was evaluated radiologically and histologically. Radiographs demonstrated that nascent bone formation in the central part of the defect regions was only observed in the nanofibrous membrane plus LIPUS group, whereas the bone defects were not fully healed in the group treated with nanofibrous membrane alone. Histology analysis of the LIPUS-treated group indicated that bone formation was thicker and more mature in the center of the defect site of the nanofibrous membrane plus LIPUS group. However, no differences were detected in the spatial and temporal pattern of the newly formed bone. Furthermore, the bone scores in the nanofibrous membrane plus LIPUS group were significantly greater than the scores exhibited in the nanofibrous membrane group at 3 and 6 weeks after surgery, respectively (P<0.01). In conclusion, the PLLA electrospun nanofibrous membrane combined with LIPUS indicated the capacity to improve the formation of nascent bone in rabbits with tibia defects. Further studies are required to fully elucidate the cell ingrowth depths inside nanofibrous membranes with scanning electron microscopy and the molecular effects of LIPUS on integrin and fibronectin.