This study investigates the collective migration of an epithelial monolayer in response to a model wound, using an innovative microfabrication technique. The researchers used a soft elastic PDMS stencil to create a free surface for Madin–Darby canine kidney (MDCK) cells, which then migrated collectively. Key findings include: 1. **Collective Motility**: The release of the available surface triggers collective motility in the cells, independent of cell proliferation, which primarily occurs on the initially covered fraction of the surface. 2. **Duality of Motility**: The migration is characterized by both long-range coordinated movements within the monolayer and the presence of "leader cells" that precede a small cohort and destabilize the border through a fingering instability. 3. **Leader Cells**: Leader cells are active and lose their epithelial characteristics, developing a lamellipodium and maintaining cell-cell contacts with followers, forming fingers that reveal a pluricellular actin "belt." 4. **HGF Influence**: The presence of hepatocyte growth factor (HGF) accelerates healing but does not induce leader cells or fingers, suggesting a different mechanism from mechanical cues. 5. **Technical Advantages**: The microstencil-based assay offers advantages over classical scratch tests, including precise control over the initial conditions, parallel testing, and the ability to tune the chemical composition of the surface. These findings provide insights into the mechanical signaling between cells and suggest that collective migration can be triggered by the simple act of presenting a free surface to an epithelial monolayer.This study investigates the collective migration of an epithelial monolayer in response to a model wound, using an innovative microfabrication technique. The researchers used a soft elastic PDMS stencil to create a free surface for Madin–Darby canine kidney (MDCK) cells, which then migrated collectively. Key findings include: 1. **Collective Motility**: The release of the available surface triggers collective motility in the cells, independent of cell proliferation, which primarily occurs on the initially covered fraction of the surface. 2. **Duality of Motility**: The migration is characterized by both long-range coordinated movements within the monolayer and the presence of "leader cells" that precede a small cohort and destabilize the border through a fingering instability. 3. **Leader Cells**: Leader cells are active and lose their epithelial characteristics, developing a lamellipodium and maintaining cell-cell contacts with followers, forming fingers that reveal a pluricellular actin "belt." 4. **HGF Influence**: The presence of hepatocyte growth factor (HGF) accelerates healing but does not induce leader cells or fingers, suggesting a different mechanism from mechanical cues. 5. **Technical Advantages**: The microstencil-based assay offers advantages over classical scratch tests, including precise control over the initial conditions, parallel testing, and the ability to tune the chemical composition of the surface. These findings provide insights into the mechanical signaling between cells and suggest that collective migration can be triggered by the simple act of presenting a free surface to an epithelial monolayer.