Centre National de la Recherche Scientifique, Laboratoire de Chimie de la Matière Condensée de Paris, LCMCP, Sorbonne Université, F-75005 Paris, France.
Harwell Science and Innovation Campus, Diamond Light Source, Didcot, Oxfordshire, OX11 0DE, UK.
Philos Trans A Math Phys Eng Sci. 2021 Sep 20;379(2206):20200343. doi: 10.1098/rsta.2020.0343. Epub 2021 Aug 2.
Nanofibres are an interesting phase into which amphiphilic molecules can self-assemble. Described for a large number of synthetic lipids, they were seldom reported for natural lipids like microbial amphiphiles, known as biosurfactants. In this work, we show that the palmitic acid congener of sophorolipids (SLC16:0), one of the most studied families of biosurfactants, spontaneously forms a self-assembled fibre network (SAFiN) at pH below 6 through a pH jump process. pH-resolved small-angle X-ray scattering (SAXS) shows a continuous micelle-to-fibre transition, characterized by an enhanced core-shell contrast between pH 9 and pH 7 and micellar fusion into a flat membrane between pH 7 and pH 6, approximately. Below pH 6, homogeneous, infinitely long nanofibres form by peeling off the membranes. Eventually, the nanofibre network spontaneously forms a thixotropic hydrogel with fast recovery rates after applying an oscillatory strain amplitude out of the linear viscoelastic regime: after being submitted to strain amplitudes during 5 min, the hydrogel recovers about 80% and 100% of its initial elastic modulus after, respectively, 20 s and 10 min. Finally, the strength of the hydrogel depends on the medium's final pH, with an elastic modulus fivefold higher at pH 3 than at pH 6. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.
纳米纤维是两亲性分子自组装的有趣相态。尽管有大量的合成脂质被描述为纳米纤维，但很少有关于微生物两亲分子（即生物表面活性剂）的报道。在这项工作中，我们表明，生物表面活性剂中研究最多的家族之一——槐糖脂的棕榈酸同系物（SLC16:0），通过 pH 跳跃过程，在 pH 值低于 6 时自发形成自组装纤维网络（SAFiN）。pH 分辨小角 X 射线散射（SAXS）显示出连续的胶束到纤维的转变，其特征是在 pH 9 和 pH 7 之间增强了核壳对比，并且在 pH 7 和 pH 6 之间胶束融合成扁平膜。在 pH 值低于 6 时，通过剥离膜形成均匀的、无限长的纳米纤维。最终，纳米纤维网络自发形成触变水凝胶，在施加超出线性粘弹区的振荡应变振幅后具有快速的恢复速率：在经受 5 分钟的应变振幅后，水凝胶在分别 20 秒和 10 分钟后恢复其初始弹性模量的约 80%和 100%。最后，水凝胶的强度取决于介质的最终 pH 值，在 pH 值为 3 时的弹性模量比 pH 值为 6 时高五倍。本文是主题为“新兴技术的生物衍生和仿生可持续先进材料（第 1 部分）”的一部分。
