Hierarchical materials with interconnected pores from capillary suspensions for bone tissue engineering

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.