Magnesium, manganese and cobalt substituted nanocrystalline apatites obtained by hydrothermal transformation of biogenic calcium carbonate

Fishery industry waste seashells represent an important environmental issue and imply the loss of potentially useful biomaterials [1]. They are composite materials made of CaCO3 and an organic matrix (1-5 wt.%) formed mainly of proteins and polysaccharides. Fabrication of functional calcium phosphates (eg. doped nanoapatites) using this type of biogenic CaCO3 as a calcium source may partially alleviate the ecological problem and be an alternative source of biocompatible materials intended for biomedical uses. In this work, the one-pot hydrothermal method [2] has been used in the preparation of biocompatible Mg2+, Mn2+, and Co2+-doped apatites. These divalent transition metal ions fulfill different roles in skeletal metabolism and may stimulate bone tissue regeneration [3-5]. The experiments were performed in a hydrothermal multitube set-up as well as in an autoclave, using oyster shell calcium carbonate particles from the species Crassostrea gigas, the KH2PO4 as a P reagent (P/CaCO3 0,6), and temperatures from 25ºC to 200ºC. Full transformation of CaCO3 was obtained at 160 ºC, yielding platy-shaped apatite nanoparticles doped with either 0.22 mol% Mg2+, 0.012 mol%Mn2+, or 0.16 mol% Co2+, and sizes within the range 75-90 nm. All samples showed a high cytocompatibility/biocompatibility when incubated with human mesenchymal stem cells for 1 and 3 days, and a small decrease in cell viability after 7 days of incubation in a dose-dependent concentration. Overall, the method was demonstrated to be promising in the preparation of doped biocompatible apatite nanocrystals with osteogenic features, and the biogenic CaCO3 a huge and unexplored calcium source for the preparation of apatite-based biomaterials. Acknowledgements: Grant ref. PCI2020-112108 is funded by MCIN/AEI/10.13039/501100011033 (Spain) and the European Union "NextGenerationEU"/PRTR". PCI2020-112108 is part of the project CASEAWA of ERA-NET Cofund BlueBio H2020.