Oriented bioactive glass (13-93) scaffolds with controllable pore size by unidirectional freezing of camphene-based suspensions: Microstructure and mechanical response.

Scaffolds of 13-93 bioactive glass (composition 6.0 Na₂O, 7.9 K₂O, 7.7 MgO, 22.1 CaO, 1.7 P₂O₅, 54.6 SiO₂ (mol.%)) containing oriented pores of controllable diameter were prepared by unidirectional freezing of camphene-based suspensions (10 vol.% particles) on a cold substrate (-196 °C or 3 °C). By varying the annealing time (0-72 h) to coarsen the camphene phase, constructs with the same porosity (86 ± 1%) but with controllable pore diameters (15-160 μm) were obtained after sublimation of the camphene. The pore diameters had a self-similar distribution that could be fitted by a diffusion-controlled coalescence model. Sintering (1 h at 690 °C) was accompanied by a decrease in porosity and pore diameter, the magnitude of which depended on the pore size of the green constructs, giving scaffolds with a porosity of 20-60% and average pore diameter of 6-120 μm. The compressive stress vs. deformation response of the sintered scaffolds in the orientation direction was linear, followed by failure. The compressive strength and elastic modulus in the orientation direction varied from 180 MPa and 25 GPa (porosity=20%) to 16 MPa and 4 GPa (porosity=60%), respectively, which were 2-3 times larger than the values in the direction perpendicular to the orientation. The potential use of these 13-93 bioactive glass scaffolds for the repair of large defects in load-bearing bones, such as segmental defects in long bones, is discussed.