Comparing stiffness of solid and scaffold nano-TiO2 structures produced by material extrusion method

This study corresponds to the first stage of a project that focuses on optimizing the mechanical properties of titanium dioxide (TiO2) for use in bone implants. The goal of the study is to characterize and compare the stiffness of solid and scaffold TiO2 samples fabricated via three-dimensional material extrusion method.
The sample specimens were sintered in a furnace at three different temperatures, namely-1200 °C, 1250 and 1300 °C- for 4 h. The sintering procedure caused shrinkage in all dimensions and the maximum shrinkage (57.5%) was observed in the direction perpendicular to the work plate. The morphology of the sintered samples was analyzed via scanning electron microscopy. This revealed that increasing the sintering temperature increased the grain size and decreased porosity. For example, the porosity of the samples sintered at 1300 °C was 20% less than that of samples sintered at 1200 °C. Uniaxial compression tests showed that scaffold structures had a lower stiffness than their solid counterparts, and the decrease in stiffness was comparable to the reduction in cross-sectional area. The elastic modulus of TiO2 produced here by material extrusion was between 2.08–5.90 GPa, which is close to the elastic modulus of high density cancellous bone at 0.8–1.5 GPa. This is an important advantage as minimizing the mismatch in stiffness between bone and implant is critical to avoid problems such as stress shielding and bone resorption.