Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, PA, USA.
Department of Pharmacology & Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA.
Biomech Model Mechanobiol. 2018 Apr;17(2):403-417. doi: 10.1007/s10237-017-0968-5. Epub 2017 Oct 16.
In this work, we re-evaluated long-standing conjectures as to the source of the exceptionally large compliance of the bladder wall. Whereas these conjectures were based on indirect measures of loading mechanisms, in this work we take advantage of advances in bioimaging to directly assess collagen fibers and wall architecture during biaxial loading. A custom biaxial mechanical testing system compatible with multiphoton microscopy was used to directly measure the layer-dependent collagen fiber recruitment in bladder tissue from 9 male Fischer rats (4 adult and 5 aged). As for other soft tissues, the bladder loading curve was exponential in shape and could be divided into toe, transition and high stress regimes. The relationship between collagen recruitment and loading curves was evaluated in the context of the inner (lamina propria) and outer (detrusor smooth muscle) layers. The large extensibility of the bladder was found to be possible due to folds in the wall (rugae) that provide a mechanism for low resistance flattening without any discernible recruitment of collagen fibers throughout the toe regime. For more extensible bladders, as the loading extended into the transition regime, a gradual coordinated recruitment of collagen fibers between the lamina propria layer and detrusor smooth muscle layer was found. A second important finding was that wall extensibility could be lost by premature recruitment of collagen in the outer wall that cut short the toe region. This change was correlated with age. This work provides, for the first time, a mechanistic understanding of the role of collagen recruitment in determining bladder extensibility and capacitance.
在这项工作中，我们重新评估了关于膀胱壁异常大顺应性的来源的长期推测。虽然这些推测是基于加载机制的间接测量，但在这项工作中，我们利用生物成像的进展来直接评估在双轴加载过程中胶原纤维和壁结构。使用与多光子显微镜兼容的定制双轴机械测试系统，直接测量了来自 9 只雄性 Fischer 大鼠（4 只成年和 5 只老年）的膀胱组织中的层依赖性胶原纤维募集。与其他软组织一样，膀胱加载曲线呈指数形状，可以分为脚趾、过渡和高应力区。在内在（固有层）和外在（逼尿肌平滑肌）层的背景下评估了胶原募集与加载曲线之间的关系。发现膀胱的大伸缩性是由于壁的折叠（皱襞）造成的，这些皱襞提供了一种低阻力扁平化的机制，而在整个脚趾区没有明显的胶原纤维募集。对于更具伸缩性的膀胱，随着加载进入过渡区，固有层和逼尿肌平滑肌层之间的胶原纤维逐渐协调募集。第二个重要发现是，通过过早募集外壁中的胶原纤维，可以缩短脚趾区，从而导致壁的伸缩性丧失。这种变化与年龄有关。这项工作首次提供了一种关于胶原募集在确定膀胱伸缩性和电容中的作用的机制理解。
