Ionic-doped β-Tricalcium Phosphate for Bone Tissue Engineering: Structural Analysis by Rietveld Refinement

Calcium phosphate (CaP) materials are the most appropriate bone substitutes owing to their chemical similarity to the mineral part of bone.¹ Ionic-doping extends their biological performance, playing vital roles in biomechanics and stimulating the stem cells niche towards osteogenesis and angiogenesis.² Among CaP, β-tricalcium phosphate (TCP) is greatly biocompatible and resorbable instigating the replacement of implants by the tissues, and is also an adequate ionic carrier. Doping TCP with Zn, Sr, and Mn have shown increased crystallinity, solubility, and mechanical strength of the materials, as well as enhanced cell proliferation/differentiation.² The present study investigated the influence of ionic dopants on the lattice structure by qualitative and quantitative analyses of the crystalline phases presented on the doped TCP performed by X-ray powder diffraction (XRD) using a high-resolution Bruker D8 Advance DaVinci diffractometer with Cu Kα radiation (l = 1.5406 Å). The phase composition of the TCP was calculated by means of Rietveld analysis with TOPAS 5.0 software using scale factor, sample displacement, background as Chebyshev polynomial of fifth order, crystallite size, and lattice parameters for refinement. Results showed the refined lattice data for pure β-TCP are a=b=10.439(8) Å, c = 37.395(0), α= β= 90º, and γ=120º in the hexagonal setting (space group R3c). Rietveld refinement of ionic-doped TCP revealed a clear decreasing of the lattice parameters a-axis and c-axis and consequently, of the cell volume, with addition of Zn and Mn, while adding Sr into the powders presented increased lattice parameters. This can be understood considering the ionic radii of the ions Zn (0.74 Å), Sr (1.12 Å), and Mn (0.83 Å) in comparison to Ca (0.99 Å).

References

1. S Pina, JM Oliveira, RL Reis, Advanced Materials 2015;27: 1143–1169.

2. S Pina, RF Canadas, G Jiménez, Cells Tissues Organs 2017;204:150.