Low-crystalline magnesium-doped carbonate apatite/β-tricalcium phosphate granules from sea urchin spine

Abstract

The development of synthetic granules with performances equivalent to those of autogenous bone grafts is critical for effective bone replacement. Herein, we report on the fabrication of low-crystalline Mg-doped biphasic carbonate apatite/β-tricalcium phosphate (Mg-CAp/β-TCP) granules, with cylindrical shapes, concave surfaces, and multiscale pores, from sea urchin spines. The β-TCP/CAp ratios and Mg contents in the Mg-CAp/β-TCP granules were controlled to remain within 0.46–0.87 and 6.03–9.32 mol%, respectively. The Mg-CAp/β-TCP granules preserved the multiscale pores and concave surfaces of the sea urchin spines. The Mg-CAp/β-TCP granules exhibited inner stereom micropores (3–25 µm), thickened stereom micropores (<14 µm), interseptal gaps (20–43 µm), and concavities (26–41 µm), along with micropores (<3 µm) and nanopores (<100 nm) corresponding to intercrystal spaces. The rounded and uniformly shaped Mg-CAp/β-TCP granules facilitated denser packing in a simulated defect mold. The Mg-CAp/β-TCP granules exhibited compressive and diametral tensile strengths of 1.12–1.51 and 0.17–0.21 MPa, respectively. The distinctive physicochemical and structural characteristics of the Mg-CAp/β-TCP granules can be anticipated to facilitate controlled resorption rates and promote osteogenesis and angiogenesis, facilitating rapid bone defect repair. Furthermore, the adequate mechanical features of the Mg-CAp/β-TCP granules enable ease of handling during bone defect filling and potential application in load-bearing sites.