Titin molecules at different locations on the mica surface.

a. Place of sample application near the center of the mica surface. b. Edge of the sample application area. c. Surface near the edge of mica. Samples in Figs. a–c contained 1 M urea. d. Titin sample with no urea added. e. AFM image comparing the global structure of overstretched titin molecules in 0 mM (i) and 1 mM (ii) urea.