Schematic process flow for drawing fabrication of arrays of PDMS posts with variable height and constant top surface topology.
Scanning electron microscopy (SEM) image of double height holes in silicon substrate after fabrication of the step height and before removing of the oxide. The thickness of the deposited oxide is . The deposition thickness is chosen such that the resulting film protects the holes from further fabrication process.
SEM image of double height holes in silicon substrate. The diameter of the holes is and the pitch size is . The height of the deeper hole is and the height of the shallower hole is .
Scanning electron micrograph of double height PDMS posts. The diameter of posts is constant but the height is different such that the top contact area of the posts lies in one plane. This will generate controlled step increase in substrate stiffness. The diameter of the posts is and the pitch is . The shorter posts are about 13 times stiffer than the taller posts.
Time-lapse optical micrograph of migration of 3T3 cells on a double rigidity substrate. The stiff part (left side) is about five times stiffer than the soft part. The cell on the boundary migrates toward the rigid part (time interval of between frames).
SEM image of an immortalized mesenchymal stem cell attached to a hexagonal array of posts with a constant diameter of , pitch of , and two different heights of 6.6 and , which causes a change in rigidity of the substrate. The cell is more spread on the rigid part (right part) than the softer part (left part). Also, on the softer area, the posts are bent to a greater extent compared to the rigid posts. The arrows indicate the direction of pillar deflection.
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