Histological and immunohistochemical examination of triple-layered rabbit chondrocyte sheets. Staining for proteoglycan (A, C, E) and type II collagen (B, D, F) on cross-sections of cell sheets recovered after vitrification and rewarming. A, B: Non-vitrified control cell sheet exhibiting large amounts of proteoglycan and type II collagen in the extracellular matrix. C, D: Cell sheet vitrified with the coating method using VS containing COOH-PLL; the sheet exhibits a normal extracellular matrix. E, F: Cell sheets vitrified by the envelope method. The extracellular matrix exhibits no difference to samples from control and coating method groups. (Scale bar = 100 μm).