Controlling the spatial assembly of multiple cell-types is one of the grand challenges in tissue engineering. Oour laboratories have discovered novel approaches to controlling the sequential assembly of different cell types using polyelectrolyte assembly, photocleavable cell-resistant polymers, and most recently using microarrays to amplify the natural directional persistence of cells. Like one-way signs, these microarrays impose directionality with overwhelming compliance and simultaneously guide the migration of arbitrary number of cells independently over arbitrary paths without chemoattractants, external fields, or mechanical manipulation.