  The increasing demand for bone grafts due to the aging population has opened
new opportunities for the manufacture of porous ceramics to assist in bone
reconstruction. In our study, we investigate a new, promising method to
manufacture hierarchically porous structures in a straightforward, and tuneable
way. It consists of combining the novel technology of capillary suspensions,
formed by mixing solid particles and two immiscible liquids, one less than 5
vol%, with freeze casting. We have successfully achieved alumina and
$\beta$-TCP materials with both <2 $\mu$m and 20-50 $\mu$m as the smallest and
largest pore size, respectively. The microstructure exhibits fully open pores
and high levels of porosity (> 60%). The capillary suspensions' rheological
behaviour indicates that silica nano-suspensions as a secondary fluid creates a
stronger internal particle network than sucrose for the alumina system.
Conversely, the opposite was observed with the $\beta$-TCP system. These
differences were attributed to the change in affinity between the secondary
fluids and the solid loading. In our study, both systems have served to deepen
the knowledge about the new area of capillary suspensions and prove their use
in hierarchical porous scaffolds for bone tissue engineering.
