Movie S1.

Time-lapse movie of the sandwiched ECM during the immersion process. A time-lapse movie of the sandwiched ECM was used to analyze in detail the mechanical process during immersion. It shows that the entire immersion process was mainly divided into three steps: First, the sandwiched ECM extruded toward the center of the ECM channel (in the first frame) by osmotic pressure; then, the volume of Matrigel began increasing by ion or liquid exchange during the immersion process (from the second to the seventh frame); finally, the volume change of Matrigel tended to be stabilized (from the seventh frame to the last frame).