Xue Ye, Wang Fang, Torculas Maria, Lofland Samuel, Hu Xiao
Center of Analysis and Testing, Nanjing Normal University, Nanjing 210023, China.
ACS Biomater Sci Eng. 2019 Dec 9;5(12):6361-6373. doi: 10.1021/acsbiomaterials.9b00577. Epub 2019 Nov 7.
Flexible and water-insoluble regenerated silk materials have caught considerable interest due to their mechanical properties and numerous potential applications in medical fields. In this study, regenerated Mori (China), Thai, Eri, Muga, and Tussah silk films were prepared by a formic acid-calcium chloride (FA) method, and their structures, morphologies, and other physical properties were comparatively studied through Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). FTIR results demonstrated that the secondary structures of those five types of silk films are different from those of their respective natural silk fibers, whose structures are dominated by stacked rigid intermolecular β-sheet crystals. Instead, intramolecular β-sheet structures were found to dominate these silk films made by FA method, as confirmed by WAXS. We propose that silk I-like structures with intramolecular β-sheets lead to water insolubility and mechanical flexibility. This comparative study offers a new pathway to understanding the tunable properties of silk-based biomaterials.
柔性且水不溶性的再生丝材料因其机械性能以及在医学领域的众多潜在应用而备受关注。在本研究中，采用甲酸 - 氯化钙（FA）法制备了再生的桑蚕丝（中国）、泰丝、蓖麻蚕丝、柞蚕丝和野蚕丝薄膜，并通过傅里叶变换红外光谱（FTIR）、广角X射线散射（WAXS）、扫描电子显微镜（SEM）、差示扫描量热法（DSC）、动态力学分析（DMA）和热重分析（TGA）对其结构、形态及其他物理性能进行了比较研究。FTIR结果表明，这五种丝薄膜的二级结构与其各自的天然丝纤维不同，天然丝纤维的结构以堆叠的刚性分子间β - 片层晶体为主。相反，如WAXS所证实的，FA法制备的这些丝薄膜中分子内β - 片层结构占主导。我们认为具有分子内β - 片层的类丝I结构导致了水不溶性和机械柔韧性。这项比较研究为理解丝基生物材料的可调谐性能提供了一条新途径。
