Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Department of Chemical & Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Int J Mol Sci. 2020 Aug 5;21(16):5593. doi: 10.3390/ijms21165593.
A male (, a frog) expands and contracts its gular skin to a great extent during mating calls, displaying its extraordinarily compliant organ. There are striking similarities between frog gular skin and the human bladder as both organs expand and contract significantly. While the high extensibility of the urinary bladder is attributed to the unique helical ultrastructure of collagen type III, the mechanism behind the gular skin of is unknown. We therefore aim to understand the structure-property relationship of gular skin tissues of . Our findings demonstrate that the male EC gular tissue can elongate up to 400%, with an ultimate tensile strength (UTS) of 1.7 MPa. Species without vocal sacs, () and (), elongate only up to 80% and 350% with UTS~6.3 MPa and ~4.5 MPa, respectively. Transmission electron microscopy (TEM) and histological staining further show that tissues' collagen fibers exhibit a layer-by-layer arrangement with an uninterrupted, knot-free, and continuous structure. The collagen bundles alternate between a circular and longitudinal shape, suggesting an out-of-plane zig-zag structure, which likely provides the tissue with greater extensibility. In contrast, control species contain a nearly linear collagen structure interrupted by thicker muscle bundles and mucous glands. Meanwhile, in the rat bladder, the collagen is arranged in a helical structure. The bladder-like high extensibility of gular skin tissue arises despite it having eight-fold lesser elastin and five times more collagen than the rat bladder. To our knowledge, this is the first study to report the structural and molecular mechanisms behind the high compliance of gular skin. We believe that these findings can lead us to develop more compliant biomaterials for applications in regenerative medicine.
一只雄性青蛙（雄性）在交配时会极大地扩张和收缩其颈皮，展示出其极其柔韧的器官。青蛙颈皮和人类膀胱之间存在惊人的相似之处，因为这两个器官都会显著地扩张和收缩。虽然膀胱的高拉伸性归因于 III 型胶原的独特螺旋超结构，但青蛙颈皮的扩张机制尚不清楚。因此，我们旨在了解雄性 EC 颈皮组织的结构-性能关系。我们的研究结果表明，雄性 EC 颈皮组织可以伸长至 400%，极限拉伸强度（UTS）为 1.7 MPa。没有声囊的物种，（）和（），伸长率仅为 80%和 350%，UTS 分别约为 6.3 MPa 和 4.5 MPa。透射电子显微镜（TEM）和组织学染色进一步表明，组织的胶原纤维呈层状排列，具有连续、无结、无间断的结构。胶原束交替呈现圆形和纵向形状，表明存在面外之字形结构，这可能为组织提供了更大的拉伸性。相比之下，对照物种的胶原结构几乎呈线性，其间被较厚的肌肉束和粘液腺打断。与此同时，在大鼠膀胱中，胶原呈螺旋结构排列。尽管青蛙颈皮组织的弹性蛋白含量比大鼠膀胱少八倍，胶原含量多五倍，但它仍具有类似膀胱的高拉伸性。据我们所知，这是首次报道青蛙颈皮高顺应性的结构和分子机制的研究。我们相信，这些发现可以帮助我们开发出更具顺应性的生物材料，用于再生医学应用。
