Figure 4.

TEM thin sections of drawn atelo-fibers showing their typical shell, transition, and core structure. (A) Longitudinal section of the fiber depicts the peripheral shell of highly organized fibrils and the poorly organized core of the fiber. (B) Striking alignment of fibrils in the shell, in the direction of the applied strain, was highly mimetic of native tendon morphology. (C) High magnification of the rectangular region (outlined in image B) shows the discrete, uniform diameter, consistent spacing, and continuous nature of the fibrils in the shell where the extensional strain was highest. (D) Transition from high density, continuous fibrils to randomly arranged, sparse, shorter fibrils was sometimes abrupt (typically in thinner regions of the fiber). (E) In sections of fibers with a larger diameter (>20 μm), a transitional region was present, comprising short and wavy fibrils that were oriented in the general direction of the extensional strain. (F) Core of the fibril comprised discrete, isotropic fibrils with low spatial density.