  In many tissues, cell type varies over single-cell length-scales, creating
detailed spatial heterogeneities fundamental to physiological function. To gain
understanding of this relationship between tissue function and detailed
structure, and to one day engineer structurally and physiologically accurate
tissues, we need the ability to assemble 3D cellular structures having the
level of detail found in living tissue. Here we introduce a method of 3D cell
assembly that has a level of precision finer than the single-cell scale. With
this method we create numerous structures having well-defined spatial patterns,
demonstrating that cell type can be varied over the scale of individual cells
and showing function after their assembly. This technique provides innumerable
opportunities to study cellular behavior in defined contexts including complex
interactions operating during embryogenesis.
