Reversible hydrogel-solution system of silk with high beta-sheet content.
Reversible hydrogel-solution system of silk with high beta-sheet content.
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可逆的水凝胶丝丝系统，具有高β片含量。
DOI：
10.1021/bm500662z
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发表时间：
2014-08-11
影响因子：
6.2
通讯作者：
Zhu, Hesun
中科院分区：
文献类型：
--
作者：
Bai, Shumeng;Zhang, Xiuli;Lu, Qiang;Sheng, Weiqin;Liu, Lijie;Dong, Boju;Kaplan, David L.;Zhu, Hesun
蚕丝因其优异的性能而被广泛用作纺织纤维、生物材料和光学功能材料。直径约为10-50 nm的富含β-片层的天然纤维素单元通常被认为是这些性质的起源，但仍不清楚丝是如何自组装成这些分级结构的。本文报道了一种由直径约10-20 nm的富含β-折叠的丝纳米纤维组成的新系统，其中这些纳米纤维在0.5-2%的溶液中形成“流动水凝胶”，并且可以在较低浓度下转化回溶液状态，即使具有高β-折叠含量。这与其他丝加工材料形成对比，其中显著的β-折叠含量否定了溶液和固体状态之间的可逆性。这些纤维是通过调节丝在水溶液中的自组装过程形成的，这改变了负电荷的分布，同时仍然支持结构中的β-折叠形成。从机械上讲，在我们目前的研究中，丝纳米纤维的外部似乎沿着向负电荷转移，导致比以前的丝材料更高的zeta电位（高于-50 mV），而以前的丝材料往往低于-30 mV。丝纳米纤维上较高的负电荷导致足够强的静电排斥以否定纳米纤维的进一步组装。改变丝浓度改变了富含β-片层的丝纳米纤维的疏水相互作用和静电排斥之间的平衡，导致可逆的水凝胶-溶液转变。此外，丝纳米纤维可以在从水凝胶转变为溶液之后在超声处理时分解成较短的纤维甚至纳米颗粒，这是由于疏水性较小颗粒的分散增加，而没有β-折叠含量的损失，并且在自组装期间通过回复到较长的纳米纤维而保留了在水凝胶和溶液状态之间转变的能力。这些可逆的溶液-水凝胶转变是可调的超声强度，时间，或温度。
Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The β-sheet-rich natural nanofiber units of about 10–50 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 β-sheet-rich silk nanofibers about 10–20 nm in diameter is reported here, where these nanofibers formed into “flowing hydrogels” at 0.5–2% solutions and could be transformed back into the solution state at lower concentrations, even with a high β-sheet content. This is in contrast with other silk processed materials, where significant β-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 β-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 −50 mV) than previous silk materials which tend to be below −30 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 β-sheet-rich silk nanofibers, resulting in reversible hydrogel–solution 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 β-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.
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