Sr-HA scaffolds fabricated by SPS technology promote the repair of segmental bone defects

Ideal bone defect repair scaffolds should be biodegradable, biocompatible, bioactive, porous, and provide adequate mechanical support. However, it is challenging to fabricate such an ideal bone repair scaffold. Previously, we showed that 5 wt.% strontium-doped hydroxyapatite (Sr-HA) scaffolds prepared by spark plasma sintering (SPS) technology exhibited good biocompatibility. Moreover, unlike pure hydroxyapatite (HA) scaffolds, HA scaffolds containing strontium (Sr) exhibited superior bioactivity, higher proliferation rate of BMSCs and MG-63 osteoblast cells, as well as enhanced BMSCs differentiation.

In this study, we prepared pure HA scaffolds and 5 wt.% strontium containing Sr-HA scaffolds by SPS technology without adhesive, ammonium bicarbonate as pore former. Subsequently, scanning electron microscope (SEM) and X-Ray diffraction (XRD) were used to characterize the properties of Sr-HA and HA scaffolds. The ability of the scaffolds to repair bone defects was evaluated using a critical-sized rabbit tibia-bone defect rabbit model. Thirty 3-month-old New Zealand white rabbits were randomly divided into three groups (blank control group, Sr-HA scaffolds implanted group and HA scaffolds implanted group) with 10 rabbits in each group. These rabbits are sacrificed after 8 weeks and 16 weeks of surgery, and the repair effects of each scaffold were evaluated with X-ray, micro-CT, and HE staining. The three-point bending test was employed to assess the mechanical property of repaired bones.

XRD pattern indicated that Sr-HA and HA scaffolds possess a similar crystal structure after sintering, and that incorporation of strontium did not form impure phase. SEM showed that the porosity of Sr-HA and HA scaffolds was about 40 %. Universal Testing Machine tests showed that Sr-HA scaffolds had better compressive strength than HA scaffolds. Bone defect was obvious, and the fibrous tissue was formed in the bone defects of rabbits in the blank control group after 8 weeks of surgery. Sr-HA and HA scaffolds enhanced osteointegration of the host bone, and extensive woven bone was formed on the surface of the Sr-HA scaffolds. After 16 weeks, the bone strump became blunt and a small amount of callus was formed in the blank control group. Comparatively, the scaffolds were substantially degraded in the Sr-HA scaffolds implanted group while scaffolds shadows still were observed in the HA implanted group. Bone remodeling and cavity recanalization were completely developed in the Sr-HA scaffolds group. The compressive strength of repaired bone in the Sr-HA scaffolds implantation group was higher than that of HA scaffolds implantation group after 8 weeks and 16 weeks of surgery.

Our results show that the Sr-HA composite scaffolds can effectively repair bone defects and have good biodegradable properties.