Sericultural and Apicultural Materials Division, National Institute of Agricultural Sciences, RDA, Wanju-gun 55365, Korea.
Biomolecules. 2021 Jan 7;11(1):70. doi: 10.3390/biom11010070.
Silk fibroin (SF)-based materials are exposed to both natural and artificial ultraviolet (UV) light during preparation or administration. However, the effects of UV irradiation on SF films prepared under different conditions have not yet been described in detail. In this study, four SF films with different molecular weight (MW) distribution were fabricated using SF solutions, which were prepared by dissolving degummed SF for 0.5-24 h. We observed UV (365 nm) irradiation on SF films induced the increase of yellowness and absorbance at 310 nm of SF films, indicating the formation of new photo-products and di-tyrosine bonds by photo-oxidation. Due to di-tyrosine cross-links between SF chains, UV-irradiated SF films were not fully dissociated in urea solution. In addition to formation of new products, UV reduced the crystallinity of SF films by breaking hydrogen bonds of β-sheet conformation. Unlike the UV-induced decomposition of physical interactions, UV did not affect the covalent bonds (i.e., peptide bonds). Through these experiments, we could expect that SF with higher MW was more susceptible and SF with lower MW was more resistant to UV-induced photo-oxidation and photo-degradation. These results provide useful information about UV-induced aging of SF-based materials under natural sunlight and UV irradiating conditions.
丝素（SF）基材料在制备或给药过程中会受到自然和人工紫外线（UV）的照射。然而，尚未详细描述在不同条件下制备的 SF 薄膜受到 UV 照射的影响。在这项研究中，使用 SF 溶液制备了四种具有不同分子量（MW）分布的 SF 薄膜，SF 溶液是通过将脱胶 SF 溶解 0.5-24 小时制备的。我们观察到 SF 薄膜在 365nm 的 UV 照射下，SF 薄膜的黄度和 310nm 处的吸光度增加，表明通过光氧化形成了新的光产物和二酪氨酸键。由于 SF 链之间的二酪氨酸交联，UV 辐照的 SF 薄膜在尿素溶液中未完全解离。除了形成新产物外，UV 通过破坏β-折叠构象的氢键降低了 SF 薄膜的结晶度。与物理相互作用的 UV 诱导分解不同，UV 不会影响共价键（即肽键）。通过这些实验，我们可以预期 MW 较高的 SF 更容易受到影响，MW 较低的 SF 对 UV 诱导的光氧化和光降解更具抵抗力。这些结果为 SF 基材料在自然阳光和 UV 照射条件下的 UV 诱导老化提供了有用的信息。
