Scaffold-free tissue sheets harvested after 12 days culture in KDM were fixed and imaged by TEM as described in Methods. (a) Lower and (b) higher magnification images of the top view of scaffold-free tissue sheets shows that the constructs contain long, parallel organized collagen fibrils. (c) Lower and (d) higher magnification images of engineered corneal stroma tissues in cross section show collagen fibrils are approximately uniform in diameter. (e) Size distribution of collagen fibril diameters as measured from TEM images of cross section of engineered tissues show that collagen fibril diameter are similar to the collagen fibril diameter seen in native, human corneal stromal tissue. Scale bars: (a) = 2 μm, (b) = 500 nm, (c) 2 μm, and (d) = 100 nm