Goniopora was hydrothermally converted to coralline hydroxyapatite (CHA) and incorporated with Sr (Sr-CHA). The pore size of Goniopora was in the range of 40–300？μm with a porosity of about 68%. Surface morphologies of the coral were modified to flake-like hydroxyapatite structures on CHA and the addition of Sr detected on Sr-CHA as confirmed by SEM and EDX. As the first report of incorporating Sr into coral, about 6%–14% Sr was detected on Sr-CHA. The compressive strengths of CHA and Sr-CHA were not compromised due to the hydrothermal treatments. Sr-CHA was studied in vitro using MC3T3-E1 cells and in vivo with an ovariectomized rat model. The proliferation of MC3T3-E1 cells was significantly promoted by Sr-CHA as compared to CHA. Moreover, higher scaffold volume retention (+40%) was reported on the micro-CT analysis of the Sr-CHA scaffold. The results suggest that the incorporation of Sr in CHA can further enhance the osteoconductivity and osteoinductivity of corals. Strontium has been suggested to stimulate bone growth and inhibit bone resorption. In this study, we have successfully incorporated Sr into CHA with the natural porous structure remained and explored the idea of Sr-CHA as a potential scaffolding material for bone regeneration. 1. Introduction Reconstruction of massive bone defects caused by severe traumas and tumors remains a great challenge in orthopaedics. The preferred treatment is autologous bone graft, but the supply is usually limited due to the mobility and pain caused to the patient [1, 2]. Immunological response of our body and possibility of contamination have limited the use of allograft. Emergence of tissue engineering has been growing promisingly in orthopaedics as an alternative approach for bone regeneration. Before supplementing scaffolds with marrow stromal cells and growth factors to further enhance bone regeneration, the choices of scaffold with osteoconductivity or even osteoinductivity are important to start with. Coral, which usually refers to the exoskeleton of natural coral, has been a material of interest in orthopaedic biomaterial due to its chemical composition and structural and mechanical properties. Other materials have to be further modified to meet the essential structural, physical, or mechanical requirements of ideal bone substitutes; however, natural coral, primarily reef-building coral, has certain degrees of similarity to human bone without the need of modification [3]. Major component of coral is calcium carbonate (97–99%), in aragonite form, with 1–1.5% of organic substances and little trace elements
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