Fig. 1

Silk fibroin implants at the hind limb subcutaneous observed by 2D US at day 0, 4, 8, 12, 16, 18, and 20. The implants appeared low-level gray in the first few days and oval shape (a–d), then the shape of the implants were thinner and flatter from day 16 (e–f), and the silk hydrogel implants cannot be clearly recognized and the echogenicity equal to the surrounding’s at day 18 (g); arrows, outline of silk hydrogel implants