Microstructure,phase compositions and in vitro evaluation of freeze casting hydroxyapatite-silica scaffolds

Hydroxyapatite-silica (HA-SiO₂) scaffolds with different SiO₂ content (0, 2, 5 and 10 wt% SiO₂) were fabricated by freeze casting. After sintering, the scaffolds maintained the interconnected unidirectional pore channels by removing the frozen ice crystals via sublimation. X-ray diffraction (XRD) analysis indicated that SiO₂ promoted the decomposition of HA to tricalcium phosphate (TCP), comprised of α-TCP and β-TCP, which became more apparent with the increase of SiO₂ content. The microstructure observation of scanning electron microscope (SEM) showed that the scaffolds surface feature had great changes in terms of grain size and grain boundary with the addition of SiO₂. Moreover, the addition of SiO₂ could increase the porosity and pore size of the scaffolds, even allowing it to reach a maximum as the SiO₂ content increased to 5 wt%. Compression tests investigated the variation in the compressive strength of the scaffolds with the increase in the SiO₂ content, which showed first decreasing and then increasing behavior. In vitro evaluation results in simulated body fluid (1.5×SBF) revealed that the introduction of SiO₂ enhanced the growth rate of bone-like layer, especially the scaffold with 5 wt% SiO₂, which exhibited faster growth rate of bone-like layer than the other scaffolds. The XRD and fourier transformed infrared spectroscopy (FT-IR) characterization confirmed that the bone-like layer formed on the scaffold surface was a carbonate-containing hydroxyapatite bone-like layer.