Stokes Grace Y, DiCicco Evangelea N, Moore Trevor J, Cheng Vivian C, Wheeler Kira Y, Soghigian John, Barber Richard P, Edgerly Janice S
Department of Chemistry & Biochemistry, Santa Clara University, 500 El Camino Real, Santa Clara, CA 95053, USA.
Department of Physics and Center for Nanostructures, Santa Clara University, 500 El Camino Real, Santa Clara, CA 95053, USA.
R Soc Open Sci. 2018 Sep 12;5(9):180893. doi: 10.1098/rsos.180893. eCollection 2018 Sep.
Insects from the order Embioptera (webspinners) spin silk fibres which are less than 200 nm in diameter. In this work, we characterized and compared the diameters of single silk fibres from nine species-, , , , , , , and . Silk from seven of these species have not been previously quantified. Our studies cover five of the 10 named taxonomic families and represent about one third of the known taxonomic family-level diversity in the order Embioptera. Naturally spun silk varied in diameter from 43.6 ± 1.7 nm for to 122.4 ± 3.2 nm for Mean fibre diameter did not correlate with adult female body length. Fibre diameter is more similar in closely related species than in more distantly related species. Field observations indicated that silk appears shiny and smooth when exposed to rainwater. We therefore measured contact angles to learn more about interactions between silk and water. Higher contact angles were measured for silks with wider fibre diameter and higher quantity of hydrophobic amino acids. High static contact angles (ranging up to 122° ± 3° for ) indicated that silken sheets spun by four arboreal, webspinner species were hydrophobic. A second contact angle measurement made on a previously wetted patch of silk resulted in a lower contact angle (average difference was greater than 27°) for all four species. Our studies suggest that silk fibres which had been previously exposed to water exhibited irreversible changes in hydrophobicity and water adhesion properties. Our results are in alignment with the 'super-pinning' site hypothesis by Yarger and co-workers to describe the hydrophobic, yet water adhesive, properties exhibited by webspinner silk fibres. The physical and chemical insights gained here may inform the synthesis and development of smaller diameter silk fibres with unique water adhesion properties.
纺足目（足丝蚁）昆虫吐出的丝纤维直径小于200纳米。在这项研究中，我们对9个物种（分别为……）的单根丝纤维直径进行了表征和比较。其中7个物种的丝此前尚未进行过定量分析。我们的研究涵盖了10个已命名分类科中的5个，约占纺足目已知分类科级多样性的三分之一。自然纺出的丝直径各不相同，[物种1]的丝直径为43.6±1.7纳米，[物种2]的丝直径为122.4±3.2纳米。平均纤维直径与成年雌虫体长无关。亲缘关系较近的物种之间的纤维直径比亲缘关系较远的物种更相似。野外观察表明，丝在接触雨水时显得有光泽且光滑。因此，我们测量了接触角，以更多地了解丝与水之间的相互作用。对于纤维直径较宽且疏水氨基酸含量较高的丝，测量到的接触角更高。高静态接触角（[物种3]的接触角高达122°±3°）表明，由4种树栖足丝蚁物种纺出的丝片是疏水的。对先前已湿润的丝片进行的第二次接触角测量结果显示，所有4个物种的接触角都较低（平均差异大于27°）。我们的研究表明，先前接触过水的丝纤维在疏水性和水粘附特性方面表现出不可逆的变化。我们的结果与亚格尔及其同事提出的“超级钉扎”位点假说是一致的，该假说描述了足丝蚁丝纤维所具有的疏水但又能粘附水的特性。此处获得的物理和化学见解可能为合成和开发具有独特水粘附特性的更细直径丝纤维提供参考。
