Fig. 4. Ultrastructure of vitreous collagen-hyaluronan (HA) interaction. The specimen was fixed in glutaraldehyde/paraformaldehyde and stained with ruthenium red. The collagen fibrils (C) are coated with an amorphous material (A) that is believed to be HA. The amorphous material may connect to the collagen fibril by another GAG, possibly chondroitin sulfate (see inset, lower right). Interconnecting filaments (IF) appear to bridge between collagen fibrils, inserting or attaching at sites of hyaluronan adhesion to the collagen fibrils. Bar = 0.1 μm. (From Asakura A. Histochemistry of hyaluronic acid of the bovine vitreous body as studied by electron microscopy. Acta Soc Ophthalmol Jpn 89:179, 1985, with permission)