Recent successes in nanotechnology are reported about diversity of nanomaterials that can be successfully used in the various fields of biology and nanomedicine. Multifunctional nanomaterials may become especially desirable in tissue engineering field as factors leading to increased regeneration of fractured tissues, and as luminescent nanoprobes in bioimaging or bio-detection. One of the materials opening above possibilities are the basic elements of bone and dentin, the hydroxyapatites (Ca10(PO4)6(OH)2–HAp), characterized by exceptional biocompatibility, bioactivity, and mechanical properties.
The replacement of calcium ions in the crystal lattice of hydroxyapatite with lanthanide ions, e.g., terbium(III) ions that due to the small differences in ionic radius between Tb(III) (rion = 0.923 Å) and Ca(II) (rion = 1.10 Å) ions, can be successfully incorporated, results in enhanced luminescence properties in this material [1,2]. Rubidium(I) ions due to their large ionic radius (rion = 1.51 Å) in relation to Ca(II) ions, are also readily incorporated into the HAp matrix and show its enhanced bioactivity with maintaining full biocompatibility. In addition, rubidium(I) ions are like well-known lithium(I) ions influence on human bone development and cell proliferation which becomes promising for biomedical applications juxtaposed with the characteristics and functionalities of hydroxyapatite [3,4,5].
In our research, the basic structural, physical, and biological properties of hydrothermally synthesized hydroxyapatites co-doped with terbium(III) and rubidium(I) ions were thoroughly investigated. The X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) techniques were used in our study to determine the structural characteristics and morphology of the obtained nanocomposites. By measuring excitation spectra, emission spectra and fluorescence lifetime, luminescence in the green visible light range from terbium(III) ions was evaluated. The in vitro studies on selected cell lines (L929 mouse fibroblasts, 3T3 mouse fibroblasts, 7F2 mouse osteoblasts) confirmed the high biocompatibility of the resulting nanopowders and the positive effect on cell growth stimulation. In addition, investigations using the human monocyte THP-1 cell line showed that our compounds do not induce stimulatory immune response to the tested cells. In conclusion, obtained hydroxyapatite-based nanocomposites can be successfully used in biomedicine, both as a bio-labelling material and as a potential material for use in treatments involving regenerative medicine and tissue engineering.