Megill William M, Gosline John M, Blake Robert W
Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
J Exp Biol. 2005 Oct;208(Pt 20):3819-34. doi: 10.1242/jeb.01765.
Hydromedusan jellyfish swim by rhythmic pulsation of their mesogleal bells. A single swimming muscle contracts to create thrust by ejecting water from the subumbrellar cavity. At the end of the contraction, energy stored in the deformation of the mesogleal bell powers the refilling stage, during which water is sucked back into the subumbrellar cavity. The mesoglea is a mucopolysaccharide gel reinforced with radially oriented fibres made primarily of a protein homologous to mammalian fibrillin. Most of the energy required to power the refill stroke is thought to be stored by stretching these fibres. The elastic modulus of similar fibrillin-rich fibres has been measured in other systems and found to be in the range of 0.2 to 1.1 MPa. In this paper, we measured the diameters of the fibres, their density throughout the bell, and the mechanical behaviour of the mesoglea, both in isolated samples and in an intact bell preparation. Using this information, we calculated the stiffness of the fibres of the hydromedusa Polyorchis penicillatus, which we found to be approximately 0.9 MPa, similar in magnitude to other species. This value is two orders of magnitude more compliant than the stiffness of the component fibrillin microfibrils previously reported. We show that the structure of the radial fibres can be modelled as a parallel fibre-reinforced composite and reconcile the stiffness difference by reinterpreting the previously reported data. We separate the contributions to the bell elasticity of the fibres and mesogleal matrix and calculate the energy storage capacity of the fibres using the calculated value of their stiffness and measured densities and diameters. We conclude that there is enough energy potential in the fibres alone to account for the energy required to refill the subumbrellar cavity.
水螅水母通过中胶层钟状体的有节奏脉动来游动。单一的游泳肌肉收缩，通过从伞下腔排出水来产生推力。在收缩结束时，中胶层钟状体变形所储存的能量为重新注水阶段提供动力，在此期间水被吸回伞下腔。中胶层是一种粘多糖凝胶，由主要与哺乳动物原纤蛋白同源的蛋白质构成的径向纤维加强。为重新注水冲程提供动力所需的大部分能量被认为是通过拉伸这些纤维来储存的。在其他系统中已测量过类似富含原纤蛋白的纤维的弹性模量，发现其在0.2至1.1兆帕的范围内。在本文中，我们测量了纤维的直径、它们在整个钟状体中的密度以及中胶层的力学行为，包括在分离的样本和完整的钟状体标本中。利用这些信息，我们计算了水螅水母多枝合胃水母纤维的刚度，发现其约为0.9兆帕，与其他物种的刚度大小相似。该值比先前报道的组成原纤蛋白微原纤维的刚度柔顺两个数量级。我们表明，径向纤维的结构可以建模为平行纤维增强复合材料，并通过重新解释先前报道的数据来调和刚度差异。我们分离了纤维和中胶层基质对钟状体弹性的贡献，并利用计算出的纤维刚度值以及测量的密度和直径来计算纤维的能量储存能力。我们得出结论，仅纤维中就有足够的能量潜力来解释重新填充伞下腔所需的能量。
