Reversible Hydrogel鈥揝olution System of Silk with High Beta-Sheet Content

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• 作者：Shumeng Bai ; Xiuli Zhang ; Qiang Lu ; Weiqin Sheng ; Lijie Liu ; Boju Dong ; David L. Kaplan ; Hesun Zhu
• 刊名：Biomacromolecules
• 出版年：2014
• 出版时间：August 11, 2014
• 年：2014
• 卷：15
• 期：8
• 页码：3044-3051
• 全文大小：512K
• ISSN：1526-4602

文摘

Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The 尾-sheet-rich natural nanofiber units of about 10鈥?0 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of 尾-sheet-rich silk nanofibers about 10鈥?0 nm in diameter is reported here, where these nanofibers formed into 鈥渇lowing hydrogels鈥?at 0.5鈥?% solutions and could be transformed back into the solution state at lower concentrations, even with a high 尾-sheet content. This is in contrast with other silk processed materials, where significant 尾-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting 尾-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above 鈭?0 mV) than previous silk materials which tend to be below 鈭?0 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of 尾-sheet-rich silk nanofibers, resulting in reversible hydrogel鈥搒olution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of 尾-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature.