Yoshioka Taiyo, Hata Tamako, Kojima Katsura, Nakazawa Yasumoto, Kameda Tsunenori
Silk Materials Research Unit, National Agriculture and Food Research Organization (NARO), 1-2 Ohwashi, Tsukuba, Ibaraki 305-8634, Japan.
Division of Biotechnology and Life Science, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
ACS Biomater Sci Eng. 2017 Dec 11;3(12):3207-3214. doi: 10.1021/acsbiomaterials.7b00602. Epub 2017 Nov 30.
Films from silk fibroin protein are one of the most promising biomaterials because of their exquisite balance between mechanical properties and biocompatibility. Numerous schemes have been proposed for processing fibroin film, utilizing liquid silk fibroin (LSF) or regenerated silk fibroin (RSF). The films cast from LSF or RSF in the solution state are water-soluble, and therefore require postproduction treatment inducing β-sheet formation, to render them insoluble in water. Many kinds of postproduction treatments, using alcohol-water solution, water vapor, or controlled temperature, have been developed. However, the tuning and reproducibility of such treatments are quite sensitive and frequently render the fibroin films less flexible or even brittle because of the formation of an over content of β-sheet. To overcome this, we developed a novel scheme for fibroin processing using silk-gland fibroin (SGF). The essence of this scheme is to create a softly solidified fibroin-gel state of the silk glands with an imperfect β-sheet structure, by treating them with an ethanol/water mixture. Such a fibroin gel was found to dissolve in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The SGF film cast from the HFIP solution shows a flexible and water-insoluble nature with high reproducibility. In addition to this improvement, the SGF film produced by this method contains a significantly low level of residual HFIP molecules compared to the traditional RSF films prepared from an HFIP solution. The mechanism underlying these advantageous characteristics was investigated from the structural viewpoint, by using techniques such as C solid-state NMR, differential scanning calorimetry, and wide-angle X-ray diffraction.
丝素蛋白制成的薄膜是最具前景的生物材料之一，因为其在机械性能和生物相容性之间实现了精妙的平衡。人们已经提出了许多利用液态丝素蛋白（LSF）或再生丝素蛋白（RSF）来加工丝素蛋白薄膜的方案。由处于溶液状态的LSF或RSF浇铸而成的薄膜是水溶性的，因此需要进行后期处理以诱导β折叠的形成，使其不溶于水。人们已经开发出了多种后期处理方法，如使用酒精 - 水溶液、水蒸气或控制温度等。然而，这些处理方法的调节和可重复性非常敏感，并且由于β折叠含量过高，常常会使丝素蛋白薄膜变得不那么柔韧甚至易碎。为了克服这一问题，我们开发了一种使用丝腺丝素蛋白（SGF）加工丝素蛋白的新方案。该方案的核心是通过用乙醇/水混合物处理丝腺，使其形成具有不完全β折叠结构的柔软凝固的丝素蛋白凝胶状态。发现这种丝素蛋白凝胶可溶于1,1,1,3,3,3 - 六氟 - 2 - 丙醇（HFIP）。由HFIP溶液浇铸而成的SGF薄膜具有柔韧性、不溶于水且可重复性高的特点。除此之外，与由HFIP溶液制备的传统RSF薄膜相比，通过这种方法制备的SGF薄膜所含的残留HFIP分子水平显著较低。我们通过使用诸如碳固体核磁共振、差示扫描量热法和广角X射线衍射等技术，从结构角度研究了这些有利特性背后的机制。
