Figure 6.

Vertical section of strap. Two explants of human periodontal ligament fibroblasts were embedded in collagen gels, fixed after 1 (A and B) or 18 h (C and D), and sectioned vertically, parallel to the strap. The opposing explant is to the right, out of these views. (A) Cells are initially round. (B) Between the explants, at the interface of the upper and lower layers of collagen, no long fibers are seen. This indicates that fibers are projecting in and out of the plane of section, consistent with the view of a coarse isotropic mesh when seen from above (Fig. 1). (C) After 18 h, cells are elongated and collagen fibers radiate from cell processes extending into the developed strap. Dense collagen has accumulated near the cells, especially below the explant. (D) Within the strap, long straight aligned fibers are seen remaining in the plane of section for longer than 50 μm, although randomly oriented fibers persist.