Additive manufacturing technologies such as 3D printing of bone substitute materials attracts more and more attention as it makes porous bodies with adjustable geometries and controlled material properties readily available.
We successfully transferred the recently presented processing route for manufacturing highly open porous, hierarchically structured ceramics via direct ink writing (DIW) of Al2O3  to β-tricalcium phosphate (TCP) for bone substitute materials. This manufacturing concept is based on the capillary suspensions concept , i.e. the ink consists of particles, a bulk fluid, and a small fraction of an immiscible secondary fluid. The secondary fluid induces the formation of a sample spanning network serving as pre-cursor for the porous sintered body and also provides the characteristic shear thinning and yield stress necessary for the DIW process. Here, the composition of the ink, the debinding and sintering process had to be adjusted according to the distinct wetting and surface properties of the used TCP particles.
We manufactured honeycomb samples and log-pile structures to be used as porous bone scaffolds and characterized them with respect to their pore structure (porosity, pore size) using SEM and mechanical strength employing compression tests, respectively. The printed specimen consisted of fully open-porous struts with porosities between 45 and 60% and strut pore sizes x50,3 = 6 µm, the total porosity of the cellular structure reached up to 88%. The log-pile samples had printed pore sizes between 50 and 500 µm and strut width with a minimum of 150 µm. The samples showed a max. compressive strength of 20 MPa.
 Maurath, J., and N. Willenbacher, “3D printing of open-porous cellular ceramics with high specific strength,” J. Eur. Ceram. Soc. 37, 4833–4842 (2017).
 Dittmann, J., E. Koos, and N. Willenbacher, “Ceramic capillary suspensions: Novel processing route for macroporous ceramic materials,” J. Am. Ceram. Soc.96, 391–397 (2013).