Evaluation of Open Hollow Hydroxyapatite Microsphere on Bone Regeneration in Rat Calvarial Defects

Hollow hydroxyapatite (HA) microspheres showed the ability to facilitate bone regeneration in rats with non-healing calvarial defects. However, new bone formation in the rat calvarial defect implanted with the closed HA microspheres was limited. The objective of this work is to evaluate size-, time, and structure-dependent bone regeneration between open and closed HA microspheres in an osseous model. Open HA microspheres were obtained by sectioning closed HA microspheres. The open HA microsphere had dense convex surface and rough and porous concave surface. For both size ranges ({phi}106-150 m vs. {phi}212-250 m), the open HA microsphere were more effective in facilitating bone regeneration than the closed HA microspheres in rat calvarial defects. Bone regeneration in the open HA microspheres (49 {+/-} 7% for {phi}106-150 m; 40 {+/-} 8% for {phi}212-250 m) were higher than the closed HA microsphere (26 {+/-} 8% for {phi}106-150 m; 30 {+/-} 9% for {phi}212-250 m) at 12 weeks. Furthermore, the open HA microspheres of smaller size showed a significant increase in bone regeneration than the open HA microspheres of larger size at both 6 weeks and 12 weeks. The difference in bone regeneration between these microspheres could be due to their differences in microstructures, namely curvature, concavity, porosity, surface roughness, and total surface area available for cells to attached to.