The in vitro response to silk fibroin was similar to the response to collagen and tissue culture plastic (TCP) controls. In vivo, silk showed a lower inflammatory response when compared to collagen and PLA15. The inflammatory potential has also been assessed in vitro with macrophages where silk was shown to exhibit a similar tumor necrosis factor-alpha (TNF-α), a cytokine indicative of an inflammatory response, levels to that of tissue culture plastic16. In addition, silk fibroin has been used in several in vivo studies for brain17, soft tissue18, subcutaneous19, and bone20 applications.