Whitlockite (WH; Ca 18 Mg 2 (HPO4) 2 (PO4) 12 ) is a calcium phosphate based ceramic that contains magnesium ions. As the second most abundant mineral in living bone, WH occupies 25−35 wt % of the inorganic portion of human bone. Compared to hydroxyapatite (HAp, Ca 10 (PO 4 ) 6 (OH) 2 ), WH possesses better mechanical properties, faster resorbability, and promotion behavior on the osteogenesis. In this article, we introduced a fabrication method of interconnected porous WH granules through vacuum filtration, followed by sintering treatment based on the thermal stability of WH synthesized using the tri-solvent system. This study presents a histological, radiological, and immunohistochemical evaluation of the bone healing potential of these WH granules in a 5 mm diameter calvarial bone defect in rats. The histological evaluation shows no inflammation or foreign body reaction in the WH group. The WH group displays newly formed bone at the same thickness as the original bone. On the contrary, bone formation is not observed in the nontreated (NT) group. Besides, immunohistochemistry (IHC) confirmed that WH granules promoted bone regeneration with the significantly higher expression of bone morphogenetic proteins-2 (BMP-2), alkaline phosphatase (ALP), osteopontin (OPN), and osteocalcin (OCN) compared to the NT group without the addition of exogenous cells or growth factors. These results suggest that WH has excellent potential for application in bone tissue regeneration.

Background Whitlockite (WH; Ca18Mg2(HPO4)2(PO4)12) as the second most abundant ceramic of human bone after hydroxyapatite (HA; Ca10(PO4)6(OH)2), possessing high osteogenic activity, has been known that it can stimulate osteogenic differentiation as well as suppress osteoclastic activity, particularly, in the preparatory stage of bone regeneration. Methods In this work, we construct a unique ceramic structure by layering WH on the surface of HA granules (HAGs)s via dip-coating and sintering method. Results The cell proliferation of the WH-coated HAGs (WHHAGs) group in the cell counting kit (CCK-8) was about 1.15-fold higher than that of the NT group at 72 h after incubation. The western blot and qPCR results demonstrated that WHHAGs treatment readily stimulated the transcription of osteogenic genes by regulating the downstream signaling pathway of BMP and WNT receptors.This study presents a histological and radiological evaluation of the bone healing potential of the WHHAGs in a 7 mm diameter calvarial bone defect in rats, compared with/without the BMP and non-treated (NT) groups at the 8 weeks after surgery. The bone volume fraction (bone volume/tissue volume) of the WHHAGs group was about 7.32- and 3.56- fold higher than that of the NT group with/without the BMP, respectively. Besides, histological evaluation confirmed that the WHHAGs with BMP promoted bone regeneration. Conclusion These results suggest that the WHHAGs present the remarkable potential for application in dental and orthopedic bone regeneration.