Hydrothermal conversion of porous Ca carbonate

Hydrothermal conversion of porous Ca carbonate biominerals into antibiotic and antiosteoporotic Ca phosphate bone implant materials

Sethmann, Ingo

Millions of bone graft procedures are performed annually to repair bone defects caused by trauma or tumor resection. Synthetic calcium phosphate-based (CaP) porous materials (mostly ceramics) are commonly used as bone graft substitutes. Their chemical similarity to bone guarantees biocompatibility while macroporosity enables firm integration of CaP materials into the bone by ingrowth of natural bone tissue into the pores. Since the mechanical performance of the synthetic materials is generally inferior to natural bone, gradual resorption of synthetic CaP implants and simultaneous replacement by natural bone is often desirable. For optimum resorbability, many CaP implants represent biphasic calcium phosphates (BCP) as a composite of hydroxyapatite and the more soluble tricalcium phosphate (similar to the mineral whitlockite). The formation of whitlockite is favoured in the presence of Mg ions. After implantation, the material slowly degrades and Mg ions are released from whitlockite and stimulate the formation of natural bone. Furthermore, Sr ions are known to stimulate bone formation and retard bone resorption. Hence, these ions play an important role in the treatment of bone loss related to osteoporosis. The antibacterial effect of Ag ions can potentially be employed to avoid wound infection during and after surgical graft procedures.

This project aims at the development of novel BCP bone implant materials with antimicrobial and antiosteoporotic properties via a hydrothermal process, avoiding high-temperature sintering. By hydrothermal processing, macroporous calcium carbonate biominerals (coral skeletons and sea urchin spines) will be pseudomorphically replaced by BCP preserving the natural porosity. A method suitable for simultaneously incorporating functional ions (Mg, Sr and Ag) into the BCP scaffolds during the hydrothermal mineral replacement process will be developed. Dopant concentrations of the resulting materials will be optimized for stimulating bone formation and inhibiting bacterial growth. This research project is expected to provide an effective new method of producing BCP-based multifunctional bone replacement materials that may represent valuable alternatives to conventional CaP bone graft substitutes.