The defense mechanism of hagfish slime is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a concentrated material into a comparably “infinite” sea of water to form a dilute, sticky, cohesive elastic gel. This raises questions about the robustness of gel formation and rheological properties across a range of concentrations, which we study here for the first time. Across a nearly 100-fold change in concentration, we discover that the gel has similar viscoelastic time-dependent properties with constant power-law exponent ($\alpha =0.18\pm 0.01$), constant relative damping $\tan \delta =G^{″}/G^{\prime }\approx 0.2-0.3$, and varying overall stiffness that scales linearly with the concentration ($\sim c^{0.99\pm 0.05}$). The power-law viscoelasticity (fit by a fractional Kelvin-Voigt model) is persistent at all concentrations with nearly constant fractal dimension. This is unlike other materials and suggests that the underlying material structure of slime remains self-similar irrespective of concentration. This interpretation is consistent with our microscopy studies of the fiber network. We derive a structure-rheology model to test the hypothesis that the origins of ultra-soft elasticity are based on bending of the fibers. The model predictions show an excellent agreement with the experiments. Our findings illustrate the unusual and robust properties of slime which may be vital in its physiological use and provide inspiration for the design of new engineered materials.

Statement of Significance

Hagfish produce a unique gel-like material to defend themselves against predator attacks. The successful use of the defense gel is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a small quantity of biomaterial which then expands by a factor of 10,000 (by volume) into an ”infinite” sea of water. This raises questions about the robustness of gel formation and properties across a range of concentrations. This study provides the first ever understanding of the mechanics of hagfish slime over a very wide range of concentration. We discover that some viscoelastic properties of slime are remarkably constant regardless of its concentration. Such a characteristic is uncommon in most known materials.

中文翻译：

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g鱼泥的浓度无关力学和结构

考虑到ha鱼不能直接控制所得凝胶的浓度，of鱼粘液的防御机制非常显着。他们只是将浓缩的物质散布到相对“无限”的海水中，形成稀薄，粘稠，凝聚的弹性凝胶。这就提出了关于在一定浓度范围内凝胶形成的稳健性和流变特性的疑问，这是我们首次在这里进行研究。在几乎100倍的浓度变化中，我们发现该凝胶具有类似的粘弹性时间依赖性，并且具有恒定的幂律指数（$\alpha =0.18\pm 0.01$），恒定相对阻尼 $\mathrm{棕褐色}\delta =G^{\text{'}\text{'}}/G^{\prime }\approx 0.2--0.3$，以及随着浓度变化呈线性比例变化的整体刚度（$〜C^{0.99\pm 0.05}$）。幂律粘弹性（通过分数Kelvin-Voigt模型拟合）在所有浓度下都具有近似恒定的分形维数。这与其他材料不同，这表明粘液的基本材料结构保持自相似，而与浓度无关。这种解释与我们对光纤网络的显微镜研究一致。我们导出了一种结构流变模型，以测试超软弹性起源是基于纤维弯曲的假设。模型预测表明与实验非常吻合。我们的发现说明了粘液的异常和坚固特性，这在其生理用途中可能至关重要，并为新型工程材料的设计提供灵感。

重要声明

g鱼会产生独特的凝胶状物质，以抵御捕食者的袭击。考虑到ha鱼不能直接控制所得凝胶的浓度，因此成功使用防御凝胶非常引人注目。他们只是散发少量的生物材料，然后以10,000（体积）的倍数膨胀成“无限”的海水。这就提出了关于一定浓度范围内凝胶形成的稳健性和性能的问题。这项研究提供了在很宽的浓度范围内对ha鱼泥的机理的首次了解。我们发现，粘液的某些粘弹特性无论其浓度如何都非常恒定。这种特性在大多数已知材料中并不常见。