  In many natural multi-layered composites, such as in the dactyl club of
Stomatopods or the shell of bivalve mollusks, the defining functional and
structural properties are determined by locally varying orientations of
inorganic building blocks within each layer. One approach to artificially
produce textured microstructures inspired by such complex composites is
magnetically assisted slip-casting (MASC). MASC is a colloidal process in which
anisotropic particles are oriented at arbitrarily defined angles using a
magnetic field. The orientation of the particles is maintained during growth as
particles are collected from the wall of a porous mold. Whereas a number of
proof-of-concept studies have established the potential of the technique, the
full design space available for MASC-fabricated structures, and the limits of
the approach, have so far not been explored in a systematic manner. To fill
this gap, we have studied both theoretically and experimentally the various
torques that act on the particles at different stage of the assembly process.
We define the boundary conditions of the MASC process for magnetically
responsive alumina platelets suspended in a low-viscosity aqueous suspension,
considering the composition of the colloidal suspension and the dynamics of the
particle-alignment process under a rotating magnetic field. Taken together,
these findings define a design strategy for the fabrication of designed
multi-lamellar microstructures using MASC. Our guidelines are based on a
comprehensive understanding of the physical mechanisms governing the
orientation and assembly of anisotropic particles during MASC and indicate a
route to expanding this technique to building blocks of various chemistries,
and thus to broadening the range of bio-inspired composites with customized
multi-scale structures that can be produced for specific applications.
