Development of Phosphatized Calcium Carbonate Biominerals as Bioactive Bone Graft Substitute Materials, Part I: Incorporation of Magnesium and Strontium Ions

Abstract

Synthetic materials based on calcium phosphate (CaP) are frequently used as bone graft substitutes when natural bone grafts are not available or not suitable. Chemical similarity to bone guarantees the biocompatibility of synthetic CaP materials, whereas macroporosity enables their integration into the natural bone tissue. To restore optimum mechanical performance after the grafting procedure, gradual resorption of CaP implants and simultaneous replacement by natural bone is desirable. Mg and Sr ions released from implants support osteointegration by stimulating bone formation. Furthermore, Sr ions counteract osteoporotic bone loss and reduce the probability of related fractures. The present study aimed at developing porous Ca carbonate biominerals into novel CaP-based, bioactive bone implant materials. Macroporous Ca carbonate biominerals, specifically skeletons of corals (aragonite) and sea urchins (Mg-substituted calcite), were hydrothermally converted into pseudomorphic CaP materials with their natural porosity preserved. Sr ions were introduced to the mineral replacement reactions by temporarily stabilizing them in the hydrothermal phosphate solutions as Sr-EDTA complexes. In this reaction system, Na, Mg, and Sr ions favored the formation of correspondingly substituted β-tricalcium phosphate over hydroxyapatite. Upon dissolution, the incorporated functional ions became released, endowing these CaP materials with bioactive and potentially osteoporotic properties.

MgCl2 promotes mouse mesenchymal stem cell osteogenic differentiation by activating the p38/Osx/Runx2 signaling pathway

“…in our previous study, mouse mesenchymal stem cells (MMScs) were cultured in Mg-containing hydroxyapatite (Mg-Ha) solution for 72 h. The reverse transcription-quantitative Pcr (rT-qPcr) results demonstrated that the mrna expression levels of alP, osx and runx2 in the Mg-Ha group were significantly higher compared with MMSCs cultured without Mg-Ha, suggesting that Mg-Ha promoted MMSc osteogenic differentiation (5). To meet clinical requirements, several bone-related ions were added to synthetic Ha to improve its effects, which indicated that Mg-Ha was suitable for clinical application (6). Magnesium and hydroxyapatite composites can overcome the shortcomings of traditional bioceramics, including lack of bone formation inducing ability (7).…”

Phase-specific bioactivity and altered Ostwald ripening pathways of calcium carbonate polymorphs in simulated body fluid

“…15,16 This triggered a smaller series of detailed investigation on the formation mechanisms and on the exploitation of coralline calcium carbonate for biomedical applications. [17][18][19][20][21][22][23] These contributions evidenced that coralline calcium carbonate is a potential bone lling material with good osteoconductivity. 20,[24][25][26][27] However, the use of biogenic and thus pre-formed porous ceramic matrices comes at a price which made this general approach less attractive: they typically pose problems due to their meager mechanical integrity and loadbearing capabilities which arise due to their ungovernable porosity.…”

Conversion of sub-µm calcium carbonate (calcite) particles to hollow hydroxyapatite agglomerates in K2HPO4 solutions

“…Natural CaCO 3 of a porous framework from coral can also be a source of apatite. For example, Sethmann et al [9] prepared macroporous apatite ceramics via a hydrothermal treatment of aragonite coral skeletons. Fujita et al investigated the factors influencing the conversion of lithium calcium borate glass to HAp in dilute K 2 HPO 4 solutions [10].…”