Synthesis and characterization of 3D multilayer porous Si–Ca–P scaffolds doped with Sr ions to modulate in vitro bioactivity

In this study, multilayer ceramic scaffolds were prepared by sol-gel and polymeric replication methods. The objective was to fabricate scaffolds based on two different compositions: a core with composition SiO2-25P(2)O(5)-68CaO-6Li(2)O (mol%) to confer mechanical resistance and external layers with composition 29SiO(2)-3P(2)O(5)-(68-x)CaO-xSrO (mol%) (x = 0, 0.7, 2, 7, 17 and 34) to provide modulated bioactivity. The obtained scaffolds were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) and Mercury Porosimetry Techniques. In vitro bioactivity was evaluated by soaking samples in simulated body fluid (SBF). The results revealed that the core was not bioactive, but bioactivity could be modulated when the core was covered with external layers. The samples doped with 0.7 and 7 mol% SrO showed bioactivity after 3 days in SBF, while the sample doped with 2 mol% SrO displayed bioactivity after 14 days. The samples doped with 17 and 34 mol% SrO presented no bioactivity, rather precipitates on the surface after 14 days and 7 days, respectively, which could correspond to a modified apatite. Variation in bioactivity with increasing dopant concentrations is attributed to the fact that a certain amount of Ca2+ ions substituted for Sr2+ can distort the network at different levels. This makes the material more unstable, which favors the ion exchange needed for hydroxyapatite nucleation.