Protein adsorption and in vitro behavior of additively manufactured 3D-silicon nitride scaffolds intended for bone tissue engineering.

Highly porous scaffolds of Si3N4 are fabricated by direct ink writing method (Robocasting) with a pattern of macroporous cavities of 650-700µm. Two different Si3N4 ink compositions regarding the oxide sintering aids (namely, Y2O3, Al2O3, and SiO2) are tried. Both inks reach solid volume fractions of ~0.40 with about 10-12wt% of polymeric additive content that imparts the necessary pseudoplastic characteristics. The printed structures are sintered under controlled N2 atmosphere either in a conventional graphite furnace or by the spark plasma sintering technique. Skeleton of the scaffolds reaches densities above 95% of the theoretical value with ≈18-24% of linear shrinkage. Analysis of the crystalline phases, microstructure and mechanical properties are comparatively done for both compositions. The bioactivity of these structures is addressed by evaluating the ion release rate in simulated body fluid. In parallel, atomic force microscopy is used to determine the effect of the filaments surface roughness on protein adsorption (Bovine Serum Albumin) for assessing the potential application of 3D-Si3N4 scaffolds in bone regeneration.