Hydroxyapatite Nanoparticles Facilitate Osteoblast Differentiation and Bone Formation Within Sagittal Suture During Expansion in Rats.

Background The potential of relapse of craniofacial disharmony after trans-sutural distraction osteogenesis is high due to the failure to produce a stable bone bridge in the suture gap. The aim of this study is to evaluate whether hydroxyapatite nanoparticles (nHAP) have the effect of promoting osteoblast differentiation of suture-derived stem cells (SuSCs) and bone formation in sagittal suture during expansion. Methods SuSCs were isolated from sagittal sutures and exposed to various concentrations of nHAP (0, 25, 50, and 100 μg mL-1) to determine the optimal concentration of nHAP in osteoblast differentiation via performing Western Blotting and RT-qPCR. Twenty 4-week-old male Sprague-Dawley rats were randomly assigned into 4 groups: SHAM (sham-surgery), distraction, ACS (absorbable collagen sponge) and ACS+nHAP groups. In the ACS and ACS+nHAP groups, saline solution and nHAP suspended in a saline solution were delivered by ACS placed across the sagittal suture, respectively. In the latter three groups, the suture was expanded for 14 days by 50 g of constant force via a W shape expansion device. Suture gap area, bone volume fraction (BV/TV) and bone mineral density (BMD) of sagittal sutures were assessed via micro-CT, while the mechanical properties of sagittal sutures were evaluated via nanoindentation test. The efficacy of nHAP on bone formation in sagittal suture was also evaluated via BMP-2 immunohistochemistry staining. Results The expression of osteoblast related genes and proteins induced by 25μg mL-1 nHAP were significantly higher than the other groups in vitro (p<0.05). Furthermore, treating with 25μg mL-1 nHAP in vivo, the suture gap area was significantly reduced when compared with the distraction group. Correspondingly, the BV/TV, BMD, hardness and modulus of sagittal sutures were significantly increased in the ACS+nHAP group (p<0.05). Conclusion The 25μg mL-1 dose of nHAP delivered by ACS can facilitate bone formation into the sagittal suture during expansion via inducing osteoblast differentiation of SuSCs.