Histological analysis of ovine chondrocytes in three-dimensional scaffold-assisted cartilage grafts derived from 5thpassage chondrocytes. Propidiumiodide fluoresceindiacetate (PI/FDA) staining shows that the chondrocytes are evenly distributed within the PGA-fibrin scaffold and are vital after 1 (A), 2 (B) and 3 weeks (C) of in vitro cell culture. Alcian blue staining was negative after 1 (D) and 2 (E) weeks, while the scaffold fibers started to take on the dye after 2 weeks of cell culture (white arrowhead). After 3 weeks (F), alcian blue staining shows strong staining of the fragmented PGA fibers (white arrowhead) and vital chondrocytes adjacent to the fibers (black arrowhead). The extracellular matrix shows only marginal staining (black double arrowhead). Immune-staining of type II collagen – formed by chondrocytes expanded up to passage 3 (G) and up to passage 5 (H) – demonstrated the presence of this particular matrix molecule, typical for articular cartilage. Isotype controls (I) gave no signal and show specificity of the type II collagen immune-staining.