A method of 4D printing a hydrogel composite structure comprises depositing a first layer of
filaments on a substrate in a first predetermined arrangement, where each filament
comprises a hydrogel matrix and a plurality of anisotropic filler particles embedded therein.
A second layer of the filaments is deposited in a second predetermined arrangement on the
first layer. The filaments from the second layer contact the filaments from the first layer at a
number of contact regions. The first layer and the second layer are hydrated, and the …