Fig. 5.

The swelling effect induced by ionic strength on the fiber structure is reversible. Fibers were pulled out of a 0.4 mg/ml fibronectin solution in PBS and remained in PBS (A) or incubated with H₂O (C) prior to fixation. Alternatively, fibers were pulled out of the H₂O solution and remained in H₂O (B) or incubated with PBS (D) prior to fixation. All samples were chemically fixed with glutaraldehyde, dehydrated in ethanol and embedded in Epon. 50 nm sections were observed by TEM. (E) Fibers were pulled out of a 0.4 mg/ml fibronectin solution in PBS onto microfabricated PDMS trenches. Using a MEMS sensor, force–extension curves were determined for the segments of the fibers freely suspended over the wells. Measurements were performed in PBS (black curves), after treating the fibers with H₂O (red curves) and after rehydrating them again with PBS (blue curves). Curves for an average of 12 fibers are shown. Scale bar: 200 nm.