Doped, mechanically reinforced calcium phosphate cements for bone tissue engineering applications

Calcium phosphate based cement (CPC) materials are currently among the most favoured synthetic bone tissue substitutes, used to repair and reconstruct small bone and teeth defects and non-load bearing fractures. Due to their chemical similarity to the mineral phase of natural tissue, they are suitable candidates for this purpose. However, bulk calcium phosphate materials are known to be brittle, and the proposed up to now new cement formulations lack for the required mechanical properties, which ideally should be similar to those of the host bone. Among the key mechanical properties, their compressive strength must be significantly improved. A cement system usually is composed of one/several components powder and a hardening liquid. After mixing of these components, their interaction takes place, followed by the hardening process. Our previous investigations demonstrated that the CPC hardening mechanism is much more complex than expected, since an anomalous micro- and macroscopic behaviour of a CPC was registered by means of an Energy Dispersive X-Ray Diffraction (EDXRD) technique, supplemented by the standard compressive strength measurements [1-3]. The EDXRD method is most suitable for real-time monitoring of the CPC hardening process in situ, allowing to follow such processes as: amorphousinto- crystalline conversion (i.e. the primary and secondary crystallization); chemical reaction and phase transformations (new phases and intermediate products). Furthermore, a diffraction 3D map can be obtained: a sequence of diffraction patterns, collected as a function of the scattering parameter and of time. Our goal was to develop CPCs for implant use in bone tissue engineering, being the purpose twofold: (1) to provide the antibacterial properties to a CPC based on ?-tricalcium phosphate by introducing Ag+ and Zn2+ ions, and (2) to enhance the mechanical characteristics of the cements. For this latter task, SWCNT and MWCNT additions are under investigation, since a very recent literature [4] reports the results indicating much increased compressive strength of CPC-MWCNT systems, being able to promote the osteogenic differentiation of osteoblasts, and to serve as promising bone repairing graft material. Furthermore, during the in situ time-resolved high-energy diffraction monitoring of the hardening process of a number of CPC based bone cement compositions it is expected to deepen the knowledge on their hardening mechanism. The obtained results will be used to develop the materials science paradigm «composition-structure-property», which in our case can be detailed as chemical and phase composition of the initial systems - macro/micro/nanostructure of material - functional properties to maintain and promote osteogenesis. The actuality of the project is based on the modern medical requirements in novel materials for traumatology and orthopaedics and on the necessity to decrease the rehabilitation time and to increase the life quality of post-operation patients. The expected results will contribute to the development of new biomedical technologies devoted to the replacement and reconstruction of the damaged human bone tissue.