Preparation of multigradient hydroxyapatite scaffolds and evaluation of their osteoinduction properties

Abstract

Porous hydroxyapatite (HA) scaffolds are often used as bone repair materials, owing to their good biocompatibility, osteoconductivity and low cost. Vascularization and osteoinductivity of porous HA scaffolds were limited in clinical application, and these disadvantages were need to be improved urgently. We used water-in-oil gelation and pore former methods to prepare HA spheres and a porous cylindrical HA container, respectively. The prepared HA spheres were filled in container to assemble into composite scaffold. By adjusting the solid content of the slurry (solid mixture of chitin sol and HA powder) and the sintering temperature, the porosity and crystallinity of the HA spheres could be significantly improved; and mineralization of the HA spheres significantly improved the biological activity of the composite scaffold. The multigradient (porosity, crystallinity and mineralization) scaffold (HA-700) filled with the mineralized HA spheres exhibited a lower compressive strength; however, in vivo results showed that their vascularization ability were higher than those of other groups, and their osteogenic Gini index (Go: an index of bone mass, and inversely proportional to bone mass) showed a continuous decrease with the implantation time. This study provides a new method to improve porous HA scaffolds and meet the demands of bone tissue engineering applications.

Keywords: biocompatibility; bone tissue engineering; osteoinduction; porous hydroxyapatite; scaffold.

Graphical abstract

Figure 1.

Flow diagrams of experimental procedure

Figure 2.

SEM images of HA spheres: S30-1200 (A, A1, A2), S15-1200 (B, B1, B2), S15-700 (C, C1, C2) and S15-M (D, D1, D2)

Figure 3.

Cross-section SEM images of HA spheres: (A, A1) S30-1200, (B, B1) S15-1200 and (C, C1) S15-700

Figure 4.

(A) XRD patterns and (B) FTIR spectra of HAp, HA spheres and HA container; (C) drying and sintering shrinkages of HA spheres; (D) surface elemental analysis of S15-M. *P < 0.05 indicates statistically significant differences

Figure 5.

Optical and SEM images of (A, A1) sucrose spheres, (B) HA spheres, (C, E) HA container and (D) composite scaffold

Figure 6.

Masson’s trichrome and HE staining images of implant histological sections in abdominal cavity, showing scaffold changes and new bone formation at 4, 12 and 24 weeks post-operation; scale bars = 2 mm

Figure 7.

Masson’s trichrome and HE staining images of implant histological sections in dorsal muscle, showing scaffold changes and new bone formation at 4, 12 and 24 weeks post-operation; scale bars = 2 mm

Figure 8.

(A) HE staining images of blood vessels in scaffolds implanted in abdominal cavity at 4, 12 and 24 weeks (scale bars = 100 μm); (B) number of blood vessels; (C) diameter of blood vessels

Figure 9.

(A) HE staining images of blood vessels in scaffolds implanted in back muscles at 4, 12 and 24 weeks (scale bars = 100 μm); (B) number of blood vessels; (C) diameter of blood vessels. *P < 0.05 indicates statistically significant differences

Figure 10.

Bone regeneration activity of scaffolds at 4, 12 and 24 weeks after implantation in abdominal cavity. (A) HE staining and Masson’s trichrome images (scale bars = 1 mm), red arrow: new bone, M: materials; (B) osteogenesis area; (C) osteogenic Gini index. *P < 0.05 indicates statistically significant differences

Figure 11.

Bone regeneration activity of scaffolds at 4, 12 and 24 weeks after implantation in dorsal muscles. (A) HE staining and Masson’s trichrome images (scale bars = 1 mm), black arrow: Havers systems, red arrow: new bone, M: materials; (B) osteogenesis area; (C) osteogenic Gini index. *P < 0.05 indicates statistically significant differences