A rapidly magnetically assembled stem cell microtissue with "hamburger" architecture and enhanced vascularization capacity.

With the development of magnetic manipulation technology based on magnetic nanoparticles (MNPs), scaffold-free microtissues can be constructed utilizing the magnetic attraction of MNP-labeled cells. The rapid construction and vascularization of microtissues with complex hierarchical architectures are of great importance to the viability and function of stem cell microtissues. Endothelial cells are indispensable for the formation of blood vessels and can be used in the prevascularization of engineered tissue constructs. Herein, safe and rapid magnetic labeling of cells was achieved by incubation with MNPs for 1 h, and ultrathick scaffold-free microtissues with different sophisticated architectures were rapidly assembled, layer by layer, in 5 min intervals. The transplantation results showed that in a stem cell microtissue with trisection architecture, the two separated human umbilical vein endothelial cell (HUVEC) layers would spontaneously extend to the stem cell layers and connect with each other to form a spatial network of functional blood vessels, which anastomosed with the host vasculature. The "hamburger" architecture of stem cell microtissues with separated HUVEC layers could promote vascularization and stem cell survival. This study will contribute to the construction and application of structural and functional tissues or organs in the future.