Figure 4. High-power examination of tissue-engineered cranial suture and controls. (A) The tissue-engineered cranial suture consisted of collagen-fiber-like structures (c), fibroblast-like cells (Fb), osteoblast-like cells (Ob), and osteocyte-like cells (Oy) in apparently mineralized bone. Osteoblast-like cells formed an approximate layer on the surface of an apparent bone formation front. (B) The adjacent natural sagittal suture showed fibroblast-like cells in suture mesenchyme, osteoblasts lining the sutural bone formation front, and osteocytes (Oy) in the mineralized bone. (C) Complete bony fusion occurred in the surgically created calvarial defect filled with tissue grafts consisting of two rhBMP-loaded collagen sponges, but without the intervening fibroblast-seeded gelatin scaffold. (D) Histomorphometric analysis and statistical comparison of the widths of the fibrous tissue interface between two mineralized bone formation fronts. The average width of tissue-engineered sutures consisting of autologous fibroblast-populated gelatin scaffold sandwiched between two rhBMP2-loaded microporous collagen sponges was 1.13 ± 0.39 mm (SD), significantly greater than the average widths of either tissue grafts without intervening autologous fibroblast-gelatin scaffolds (0.006 ± 0.004 mm) or an intervening fibroblast-free gelatin scaffold (0 ± 0 mm; N = 3) **P < 0.01.