Fig. 2

Silk fibroin implants at the upper back subcutaneous observed by 2D US at day 0, 4, 8, 12, 16, 18, and 20 (a–g). The implants became thinner and flatter from day 4 (b–e), and cannot be recognized at day 18 and 20 (f–g); arrows, outline of silk hydrogel implants