Fig. (1) (A) Collagen hydrogel. (B) Sponge form of collagen. (C) Collagen hydrogel scaffold. (D) Thin-sliced sections of collagen hydrogel scaffold. Penetration of hydrogel (light-stained area) was observed in the sponge form of collagen. Staining: hematoxylin and eosin. (Scale bars represent 5 mm (B, C) and 100 µm (D)).