Cell-enriched granular bioinks enable vascular integration and endometrial repair

3D bioprinting is essential for constructing functional tissue mimics but remains challenging due to the difficulty of simultaneously achieving adequate cell-cell interactions and appropriate biomaterial support. Here, we introduce a cell-driven clustering strategy that assembles hydrogel microparticles into cell-rich aggregates, in which cells occupy the interstitial spaces and establish pre-organized cellular interactions prior to printing. The cell volume fraction and aggregate size are tunable by microparticle properties and cell type. When applied to digital light processing 3D bioprinting, the cell-clustered granular bioink exhibits high printability while maintaining high cell density and viability. Importantly, preserving pre-established cellular organization translates into enhanced function, including improved stemness maintenance and a more regenerative paracrine profile characterized by increased angiogenic factor secretion and reduced inflammatory signaling. In vivo, implanted constructs show improved cell retention, successful vascular integration with host circulation, and significantly enhanced endometrial repair with reduced fibrosis. These results establish cell-clustered granular bioinks as a generalizable biofabrication strategy for engineering transplantable artificial tissues.