Department of Biotechnology and Life Science, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan.
Silk Materials Research Unit, Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan.
Molecules. 2019 Oct 31;24(21):3945. doi: 10.3390/molecules24213945.
Silk fibroin (SF) produced by the domesticated wild silkworm, () is attracting increasing interest owing to its unique mechanical properties, biocompatibility, and abundance in nature. However, its utilization is limited, largely due to lack of appropriate processing strategies. Various strategies have been assessed to regenerate cocoon SF, as well as the use of aqueous liquid fibroin (LF) prepared by dissolution of silk dope obtained from the silk glands of mature silkworm larvae in water. However, films cast from these fibroin solutions in water or organic solvents are often water-soluble and require post-treatment to render them water-stable. Here, we present a strategy for fabrication of water-stable films from S silk gland fibroin (SGF) without post-treatment. Aqueous ethanol induced gelation of fibroin in the posterior silk glands (PSG), enabling its separation from the rest of the silk gland. When dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the SGF-gel gave a solution from which a transparent, flexible, and water-insoluble film (SGF) was cast. Detailed structural characterization of the SGF as-cast film was carried out and compared to a conventional, water-soluble film cast from LF. FTIR and C solid-state NMR analyses revealed both cast films to be -helix-rich. However, gelation of SGF induced by the 40%-EtOH-treatment resulted in an imperfect -sheet structure. As a result, the SGF-gel was soluble in HFIP, but some -sheet structural memory remains, and the SGF as-cast film obtained has some -sheet content which renders it water-resistant. These results reveal a structure water-solubility relationship in SF films that may offer useful insights towards tunable fabrication of novel biomaterials. A plausible model of the mechanism that leads to the difference in water resistance of the two kinds of -helix-rich films is proposed.
丝素蛋白（SF）由驯化的野蚕产生，由于其独特的机械性能、生物相容性和丰富的天然来源，越来越受到关注。然而，由于缺乏适当的加工策略，其应用受到限制。已经评估了各种策略来再生蚕茧 SF，以及使用通过将成熟蚕幼虫丝腺中的丝胶溶解在水中获得的丝胶溶液制备的水溶丝素（LF）。然而，从这些丝素溶液在水中或有机溶剂中浇铸的薄膜通常是水溶性的，需要后处理使其具有耐水性。在这里，我们提出了一种无需后处理即可从丝腺丝素（SGF）制备耐水薄膜的策略。丝素在后丝腺（PSG）中的乙醇诱导凝胶化，使其与丝腺的其余部分分离。当溶解在 1,1,1,3,3,3-六氟-2-丙醇（HFIP）中时，SGF-凝胶得到一种透明、柔韧且不溶于水的薄膜（SGF）。对 SGF 铸膜的详细结构进行了表征，并与从 LF 铸膜的常规水溶性薄膜进行了比较。FTIR 和 C 固态 NMR 分析表明两种铸膜均富含β-螺旋。然而，SGF 通过 40%-EtOH 处理凝胶化导致β-片层结构不完善。结果，SGF 凝胶在 HFIP 中可溶，但仍保留一些β-片层结构记忆，所获得的 SGF 铸膜具有一些β-片层含量，使其具有耐水性。这些结果揭示了 SF 薄膜的结构与水溶性之间的关系，这可能为可调节的新型生物材料的制造提供有用的见解。提出了一种合理的模型，该模型解释了两种富含β-螺旋的薄膜耐水性差异的机制。
