β-Ca3(PO4)2- Ca9.95Li1.05(PO4)7 lamellar microstructure by chemical etching: Synthesis, characterization and in vitro bioactivity

In this study, new multilayer 3D porous scaffolds were designed with a core composed of Ca 3 O 5 Si (C 3 S) and external layers composed of Ca 5 Li 2 (PO 4 ) 4 . Scaffolds' surface topography was modified to reveal a lamellar microstructure by applying chemical etching. Scaffolds were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (FESEM/EDX), Fourier Transform Infrared Spectroscopy (FTIR) and Mercury Porosimetry. In vitro bioactivity was evaluated by immersing scaffolds in simulated body fluid (SBF) at 1, 3 and 7 days. Scaffolds presented calcium pyrophosphate, β-tricalcium phosphate (β-TCP), nonstoichiometric and stoichiometric calcium/lithium phosphate as the main phases. The calcium pyrophosphate and stoichiometric calcium/lithium phosphate in the external layer were eliminated by the chemical etching process, which revealed the lamellar microstructure. Lamellar width varied from 1.44 μm to 0.73 μm depending on the chemical etching time. The obtained mechanical strength results influenced samples’ macroporosity, which ranged from 50 % to 64 %. These samples also exhibited microporosity between 30.3 % and 49.0 %. During the bioactivity test, all the chemically etched samples showed a hydroxyapatite-like (HA-like) precipitate, except for the sample chemically etched for 30 s at day 1. At day 7, the lamellar microstructure in the samples chemically etched for 30 s and 45 s (C-30 s and C-45 s) was completely covered by the HA-like precipitate, whereas the lamellar microstructure in the sample chemically etched for 60 s (C-60 s) was only partially covered by the HA-like precipitate.