Accelerated In Vitro Degradation of Optically Clear Lowβ-Sheet Silk Films by Enzyme-Mediated Pretreatment

Abstract

To design patterned, transparent silk films with fast degradation rates for the purpose of tissue engineering corneal stroma. β-sheet (crystalline) content of silk films was decreased significantly by using a short water annealing time. Additionally, a protocol combining short water annealing time with enzymatic pretreatment of silk films with protease XIV was developed. Low β-sheet content (17%-18%) and enzymatic pretreatment provided film stability in aqueous environments and accelerated degradation of the silk films in the presence of human corneal fibroblasts in vitro. The results demonstrate a direct relationship between reduced β-sheet content and enzymatic pretreatment, and overall degradation rate of the protein films. The novel protocol developed here provides new approaches to modulate the regeneration rate of silk biomaterials for corneal tissue regeneration needs. Patterned silk protein films possess desirable characteristics for corneal tissue engineering, including optical transparency, biocompatibility, cell alignment, and tunable mechanical properties, but current fabrication protocols do not provide adequate degradation rates to match the regeneration properties of the human cornea. This novel processing protocol makes silk films more suitable for the construction of human corneal stroma tissue and a promising way to tune silk film degradation properties to match corneal tissue regeneration.