Biomedicine Cells Self-Assemble into Tissues Specially engineered cells arrange themselves into three-dimensional microtissues. by Jocelyn Rice March 11, 2009 Sponsored by All together now: A microstructure built from two different cell types (turquoise and blue). Complementary strands of DNA protruding from the cells’ membranes allow them to self-assemble into clusters like this one. Double trouble: Two clusters have joined together to form a larger, more structurally complex microtissue. By tweaking variables and adding cells in successive iterations, the researchers hope to generate increasingly sophisticated assemblies. Step by step: Multiple iterations could yield ever more complex structures. Once the initial clusters (red and green) are formed and unattached cells are washed away, a third cell type (gray) is added, with DNA decorations complementary to those on the red cells (inset). I will survive: The researchers tested to make sure that after self-assembly and purification, the cells comprising the microstructures remained viable. Clusters with green cells at the center–the majority–are alive and thriving, while clusters with red cells are dead. Form and function: Once they’d shown that it was possible to form microstructures, the researchers set out to build one that functioned like a real tissue. Genetically engineered Chinese hamster ovary cells (green) secrete a growth factor that hematopoietic progenitor cells (gray) require for survival. Here the two cell types–decorated with sticky matched strands of DNA–join in five different ratios (top to bottom) to form slightly varied glandlike microstructures. Because they’re linked up with a growth-factor supplier, the hematopoietic progenitor cells can proliferate, elaborating the microstructure over time (left to right).