a, Bright-field (left) and fluorescent (right) images focused on the top face of an Au-coated membrane with entrapped fibroblast cells, stained with the LIVE/DEAD® assay immediately after tumbling showing 50–75 green fluorescent live cells; no dead red fluorescent cells were observed b, Bright-field (left) and fluorescent (right) images such as that in a, but following 48 h of incubation in cell culture media. The cells have multiplied and filled the membrane, even covering the tops and sides.