  Composites are often made heterogeneous in nature to fulfill the functional
demands imposed by the environment, but remain difficult to fabricate
synthetically due to the lack of adequate and easily accessible processing
tools. We report on an additive manufacturing platform to fabricate
complex-shaped parts exhibiting bio-inspired heterogeneous microstructures with
locally tunable texture, composition and properties and unprecedentedly high
volume fractions of inorganic phase (up to 100%). The technology combines an
aqueous-based slip casting process with magnetically-directed particle assembly
to create programmed microstructural designs using anisotropic stiff platelets
in a ceramic, metal or polymer functional matrix. Using quantitative tools to
control the casting kinetics and the temporal pattern of the applied magnetic
fields, we demonstrate that this robust approach can be exploited to design and
fabricate heterogeneous composites with thus far inaccessible microstructures.
Proof-of-concept examples include bulk composites with periodic patterns of
micro-reinforcement orientation and tooth-like bilayer parts with intricate
shapes displaying site-specific composition and texture.
