Super-paramagnetic responsive nanofibrous scaffolds under static magnetic field enhance osteogenesis for bone repair in vivo

Abstract

A novel nanofibrous composite scaffold composed of super-paramagnetic γ-Fe2O3 nanoparticles (MNP), hydroxyapatite nanoparticles (nHA) and poly lactide acid (PLA) was prepared using electrospinning technique. The scaffold well responds extern static magnetic field with typical saturation magnetization value of 0.049 emu/g as well as possesses nanofibrous architecture. The scaffolds were implanted in white rabbit model of lumbar transverse defects. Permanent magnets are fixed in the rabbit cages to provide static magnetic field for the rabbits post surgery. Results show that MNP incorporated in the nanofibers endows the scaffolds super-paramagnetic responsive under the applied static magnetic field, which accelerates new bone tissue formation and remodeling in the rabbit defect. The scaffold also exhibits good compatibility of CK, Cr, ALT and ALP within normal limits in the serum within 110 days post implantation. In conclusion, the super-paramagnetic responding scaffold with applying of external magnetic field provides a novel strategy for scaffold-guided bone repair.

Figure 1. Characterization of the super-paramagnetic nanofibrous scaffolds.

(a): The scaffold pellet with diameter of ~ 5 mm. (b): Scheme image of the scaffold pellet being implanted in the defect of transverse process of L5 of rabbits. (c): SEM image of the scaffold showing randomly tangled nanofibers with diameter ranging from 300 nm to 1000 nm. (d): TEM image of fibers in the scaffold.

Figure 2. Representative histological images of the scaffolds implanted in the bone defect on day 10, 20, 30 post implantation.

Left column: Groups S; Right column: Group S + M. Macrophages were circled by green line and pointed by green arrow; Fibroblasts were pointed by yellow arrow; Vessels were pointed by blue arrow; Osteoblast cells were pointed by red arrow.

Figure 3. Osteocalcin (OC) expression induced by the scaffolds implanted in the bone defect on day 10, 20, and 30 post implantation.

Left column: Groups S; Right column: Group S + M. OC positive cells were circled by red line; the scaffolds were labeled by green rhombus.

Figure 4. Sirius red stain for the collagen deposition in the scaffolds implanted in the bone defect on day 10, 20, and 30 post implantation.

Figure 5. CT images of the bone defects for group S and Group S + M post 10, 50 and 90 days implantation.

The arrows pointed to the defects.

Figure 6. New bone formation analyzed by Micro-CT and histological observation on 110 day post implantation.

(a): The amount of the new bone formed in the defects obtained from Micro-CT. (b) and (c): Histological observation of the bone defects in group S and group S + M respectively. (d): Magnification of b, showing small amount of the scaffolds remaining unabsorbed after 110 days implantation. (e): Magnification of c, showing a homogenous and well organized bone formation in the defect.

Figure 7. Serum ALP (a), ALT (b), Cr (c) and CK (d) post 30 day implantation of scaffolds.