Ag-, Zn-doped calcium phosphate bone cements for tissue engineering

Calcium phosphate cements (CPC) are biocompatible materials, nowadays widely used for non-load bearing small bone fractures, maxillo- and craniofacial defects. Being compositionally affinitive to the mineral part of the bone tissue, these biomaterials are non-cytotoxic and able to promote a suitable host bone/material interface. When proposing a new synthetic calcium phosphate material, it should be considered that natural bone tissue is composed of the substituted hydroxyapatite, containing a number of cations and anions, each one of them playing a particular role in the new tissue formation and growth chemistry. Therefore, trying to improve the properties of CPC, one might introduce into their composition ionic additives naturally occurring in the human body with the scope to improve or to induce a certain property. Ag+ and Zn2+ are known to possess antibacterial properties, moreover, the latter has also osteogenetic and angiogenetic ones, enhancing the proliferation of osteoblastic cells and activating the large group of enzymes, such as MatrixMetalloProteinases, involved in the process of construction of new blood vessels. The aim of this work was to perform an X-Ray diffraction insight into the hardening process of three cement compositions: TCP (tricalcium phosphate), Ag- and Zn-containing TCP (both in 0.6 wt% and 1 wt%). The Energy Dispersive X-Ray Diffraction (EDXRD) technique was proved to be a suitable tool for in situ real-time monitoring of the hardening process of CP bone cements. By means of this technique it is possible to obtain information about phase transformations (new phases and intermediate products) and amorphous-into-crystalline conversion (primary and secondary crystallization processes). Moreover, characteristic setting and hardening times and grain size evolution can be followed. Different reagents-to-products rate of conversion, hardening times and crystallinity were registered for doped and non-doped cement samples, and a number of intermediate phases, evidencing the complex hardening mechanism were observed for the Zn-TCP cement. The role of doping elements is discussed