Hematoxylin-eosin staining of matrices explanted after two (A, B, E, F) and four (C, D, G, H) weeks. After two weeks vascular density was low in group A (without growth factors) (A, E) and considerably increased in group B (treated with growth factors) (B, F). After four weeks construct size was decreased in both groups (compare A, B with C, D). Compared to group A (C, G), however, the number of India ink-positive vessels was higher in the growth factor group B (D, H). Arrows indicate India Ink-perfused, patent parts of the AVL. Scale bars A-D = 1 mm, scale bars E-H = 50 µm.