Unravelling the precipitation pathway of biorelevant minerals: from fundamental studies to biomedical applications

The formation pathway of biominerals archetypes, namely calcium carbonate (CaC) and calcium phosphates (CaPs), was investigated using a multidisciplinary approach. The time-resolved analytical data were collected using a controlled-composition method and interpreted using a computational tool. Some basic-science questions were identified arising from long-lasting debates on the details about the solid formation mechanism. Some of these questions are here addressed by the accurate experimental data collection, the application of new cutting-edge techniques, and the development of a rigorous thermodynamic-kinetic model for the entire solid formation process from solution. The time-resolved data were collected analysing the aqueous species in-situ. In parallel, the amount of chemicals added into the reactor, to maintain iso-pH conditions, was mathematically correlated to the bonded carbonate or phosphate ions, allowing the collection of two independent series of data and the assessment of both the cation and the anion during the solid formation process. This analytical approach went beyond the state-of-the-art. The complex mechanism was partitioned into its sub-processes, and a new strategy was identified to indirectly disclose the nature of the building units involved in the solid growth. Some assumptions embedded in the derivation of the nucleation theory did not compromise the theoretical validity of the framework, and the thermodynamic quantities expressed in the formulation have to be properly related to the nucleating phase and not extended as intensive properties of the solid. As main scientific results, for both CaC and CaPs systems, the experimental data are consistent with a classical nucleation and crystallisation mechanism, where primary, secondary, and diffusion limited growth are taken into account. The associated thermodynamic and kinetic quantities, such as the surface energy for primary and secondary nucleation as well as the nucleation and growth rate are reported and critically discussed in this dissertation. The models allowed detailed investigations in the pre-nucleation zone with the aim of evaluating the presence of clusters at controlled T, pH, ionic strength, and cation/anion ratio against saturation level. An experimental setup was developed to study clusters in-situ: a reactive horizontal micrometric pulsation-free liquid jet was investigated with a focused synchrotron X-ray beam, and the small angle scattering signals were collected for both CaC and CaPs systems. Preliminary results confirm the presence of clusters and attempts to identify their size distribution are ongoing. The agreement between experimental data, standard and cutting-edge analytical investigations, and modelling results allowed the definition of a plausible solid formation pathway, for both the investigated systems, based on the nucleation theory framework, in which the plausible influence of clusters was assessed. Beside the basic-science activities, some applications in the biomedical field were also evaluated. Among them, the controlled growth of CaPs phase on pre-treated Ti implants, e.g., dental implants, was achieved. This application opened exciting perspectives toward the production and the commercialisation of implants characterised by a faster healing time and improved stability. The scientific results were published in peer-reviewed papers and an international patent application; two additional papers are under finalisation.