Influence of cationic substitution on antibacterial activity of nanosised calcium phosphate

Introduction
The structure of mammalian bones and teeth is often compared to the structure of apatites. The stoichiometric calcium hydroxyapatite (HAp), Ca10(PO4)6(OH)2 is considered as an idealised bone and dental inorganic composition model.
Recent trends in biomaterials are focused on overcoming the limitations on biological apatites. One of the research directions is the study of substituted calcium phosphates. To give calcium phosphate, several properties simultaneously, cation and anion substitution is performed. Single or multiple ion-doped or substituted calcium phosphates can be used as bone-forming agents, microbial agents, and drug delivery carriers. The present work describes the synthesis of silver Ag, copper Cu, zinc Zn and carbonate ions containing calcium
phosphates. Special attention is paid on the quantitative characterisation of synthesised calcium phosphate depending on the type of doped ion and the ion concentration and on the qualitative in vitro characterisation depending on the type of doped ion and the ion concentration.
Methods
Amorphous carbonated calcium phosphates (ACCP) exhibiting single and multiple cations at different concentrations were synthesised by the wet precipitation method. The powders were characterised by ED-XRF, FTIR and ICP-MS method to evaluate the structure and the effect of the different doping on the practical concentration in the ACCP structure. The dried powders were in vitro tested on gram-positive and gram-negative bacteria cultures to determine the presence of bacteria and the degree of colonisation depending on the type of doped ion and the ion concentration in samples.
Results and Discussion
To overcome the matrix effect, with ED-XRF method were tested not only doped calcium phosphates but also mechanical mixtures containing ACCP and corresponding metal compounds. Effectiveness of cationic substitution
and the influence of competitive cation was determined. Antibacterial properties of Zn, Cu, Ag and corresponding di-substituted HAP were evaluated.
The ion substituted calcium phosphates can have potential applications to their antibacterial activity and drug delivery carrier potential.
ACKNOWLEDGEMENTS. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 857287.