Fig. 4.

The internal structure of fibers is stabilized by repulsive electrostatic interactions. Fibers pulled out of a 0.4 mg/ml fibronectin solution in distilled H₂O (A,B,C,D) or 1 m NaCl (E) were chemically fixed with glutaraldehyde, ethanol dehydrated and embedded in Epon, ultrathin sectioned (50 nm) and observed by TEM (A, B, C, E) or high pressure frozen, freeze substituted and freeze dried and imaged in the SEM at −120 °C (D). For A, several images were required to capture the entire fiber cross section, and are shown stitched together. Scale bar: 500 nm for A, D and 200 nm for B, C, E.