The trick will be to reassemble the slices into a 4D object :-)
Just looking at these cross sections could be interesting. Also printing the same object at different resolutions along the fourth dimension could be insightful.
In this case, as the PR specifically says, the fourth dimension is time: they are encoding a temporal path within the object.
"""...has evolved their microscale 3D printing technology to the fourth dimension, time."""
I suppose the next step would be desinging a structure that responds independently to two or more types of stimuli at the same time.
For example, a leaf-like object that bends in the Y direction in response to humidity and in the Z direction in response to light.
Unless I'm missing something, this describes all behavior above the subatomic level, plant or otherwise.
By aligning cellulose fibrils during printing, the hydrogel composite ink is encoded with anisotropic swelling and stiffness, which can be patterned to produce intricate shape changes. The anisotropic nature of the cellulose fibrils gives rise to varied directional properties that can be predicted and controlled.