Koeppel Andreas, Laity Peter R, Holland Chris
Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom.
Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom.
Acta Biomater. 2020 Nov;117:204-212. doi: 10.1016/j.actbio.2020.09.045. Epub 2020 Sep 29.
Whilst flow is the basis for silk fibre formation, subtle changes in a silk feedstocks' chemical environment may serve to increase both energetic efficiency and control hierarchical structure development during spinning. Despite the role of pH being largely understood, the influence of metal ions is not, only being inferred by correlative work and observations. Through a combination of rheology and microscopy, we provide a causative study of how the most abundant metal ions in the silk feedstock, Ca and K, affect its flow properties and structure. Our results show that Ca ions increase viscosity and prevent molecular alignment and aggregation, providing ideal storage conditions for unspun silk. In contrast, the addition of K ions promotes molecular alignment and aggregation and therefore seems to transfer the silk feedstock into a spinning state which confirms recent 'sticky reptation' modelling hypotheses. Additionally, we characterised the influence of the ubiquitous kosmotropic agent Li, used to prepare regenerated silk solutions, and find that it promotes molecular alignment and prevents aggregation which may permit a range of interesting artificial silk processing techniques to be developed. In summary, our results provide a clearer picture of how metal ions co-ordinate, control and thus contribute towards silk protein self-assembly which in turn can inspire structuring approaches in other biopolymer systems.
虽然流动是丝纤维形成的基础，但丝原料化学环境的细微变化可能有助于提高能量效率，并在纺丝过程中控制分级结构的发展。尽管pH值的作用已基本明确，但金属离子的影响却并非如此，仅通过相关工作和观察进行推断。通过流变学和显微镜的结合，我们对丝原料中最丰富的金属离子钙和钾如何影响其流动特性和结构进行了因果研究。我们的结果表明，钙离子会增加粘度并阻止分子排列和聚集，为未纺丝的丝提供了理想的储存条件。相比之下，钾离子的添加促进了分子排列和聚集，因此似乎将丝原料转变为纺丝状态，这证实了最近的“粘性蠕动”建模假设。此外，我们还表征了用于制备再生丝溶液的普遍存在的促溶剂锂的影响，发现它促进分子排列并防止聚集，这可能有助于开发一系列有趣的人造丝加工技术。总之，我们的结果更清楚地展示了金属离子如何协调、控制并进而促进丝蛋白的自组装，这反过来又可以启发其他生物聚合物系统的构建方法。
