Carbonate apatite granules with uniformly sized pores that arrange regularly and penetrate straight through granules in one direction for bone regeneration

Artificial bone substitutes that can solve the problems associated with autogenous bone grafts are essential. In this study, macroporous carbonate apatite (CO₃Ap) granules with the same composition as natural bone were implanted into distal epiphysis defects in rabbit femurs. Material resorption and bone regeneration were then evaluated. The macroporous granules were obtained by extruding honeycomb (HC) structure rods containing calcium hydroxide, pulverizing the rods to granules, carbonating them to calcite, and converting them from calcite to CO₃Ap. Notably, the HC-type macropores fully penetrated and spanned their diameters of the CO₃Ap granules in one direction, as well as being regularly arranged and uniformly sized (120 μm). They facilitated cell penetration into the granules and the induction of angiogenesis. As a result, bone remodeling occurred simultaneously within the granules and on the granule surfaces. Furthermore, the granules were gradually resorbed and replaced by bone. Thus, introducing HC-type macropores into granules is an effective approach for promoting bone regeneration.