Sucosky Philippe, Padala Muralidhar, Elhammali Adnan, Balachandran Kartik, Jo Hanjoong, Yoganathan Ajit P
Wallace H Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Parker H Petit Biotechnology Building, Atlanta, GA 30332-0363, USA.
J Biomech Eng. 2008 Jun;130(3):035001. doi: 10.1115/1.2907753.
Mechanical forces are known to affect the biomechanical properties of native and engineered cardiovascular tissue. In particular, shear stress that results from the relative motion of heart valve leaflets with respect to the blood flow is one important component of their mechanical environment in vivo. Although different types of bioreactors have been designed to subject cells to shear stress, devices to expose biological tissue are few. In an effort to address this issue, the aim of this study was to design an ex vivo tissue culture system to characterize the biological response of heart valve leaflets subjected to a well-defined steady or time-varying shear stress environment. The novel apparatus was designed based on a cone-and-plate viscometer. The device characteristics were defined to limit the secondary flow effects inherent to this particular geometry. The determination of the operating conditions producing the desired shear stress profile was streamlined using a computational fluid dynamic (CFD) model validated with laser Doppler velocimetry. The novel ex vivo tissue culture system was validated in terms of its capability to reproduce a desired cone rotation and to maintain sterile conditions. The CFD results demonstrated that a cone angle of 0.5 deg, a cone radius of 40 mm, and a gap of 0.2 mm between the cone apex and the plate could limit radial secondary flow effects. The novel cone-and-plate permits to expose nine tissue specimens to an identical shear stress waveform. The whole setup is capable of accommodating four cone-and-plate systems, thus concomitantly subjecting 36 tissue samples to desired shear stress condition. The innovative design enables the tissue specimens to be flush mounted in the plate in order to limit flow perturbations caused by the tissue thickness. The device is capable of producing shear stress rates of up to 650 dyn cm(-2) s(-1) (i.e., maximum shear stress rate experienced by the ventricular surface of an aortic valve leaflet) and was shown to maintain tissue under sterile conditions for 120 h. The novel ex vivo tissue culture system constitutes a valuable tool toward elucidating heart valve mechanobiology. Ultimately, this knowledge will permit the production of functional tissue engineered heart valves, and a better understanding of heart valve biology and disease progression.
已知机械力会影响天然和工程化心血管组织的生物力学特性。特别是，心脏瓣膜小叶相对于血流的相对运动所产生的剪切应力是其体内力学环境的一个重要组成部分。尽管已经设计了不同类型的生物反应器使细胞受到剪切应力作用，但用于使生物组织暴露于剪切应力的装置却很少。为了解决这个问题，本研究的目的是设计一种体外组织培养系统，以表征心脏瓣膜小叶在明确的稳定或随时间变化的剪切应力环境下的生物学反应。这种新型装置是基于锥板粘度计设计的。定义了该装置的特性以限制这种特定几何形状固有的二次流效应。使用经激光多普勒测速仪验证的计算流体动力学（CFD）模型简化了产生所需剪切应力分布的操作条件的确定过程。这种新型体外组织培养系统在再现所需锥旋转和维持无菌条件的能力方面得到了验证。CFD结果表明，0.5度的锥角、40毫米的锥半径以及锥顶与平板之间0.2毫米的间隙可以限制径向二次流效应。这种新型锥板允许将九个组织样本暴露于相同的剪切应力波形下。整个装置能够容纳四个锥板系统，从而可使36个组织样本同时处于所需的剪切应力条件下。这种创新设计使组织样本能够平齐安装在平板中，以限制由组织厚度引起的流动扰动。该装置能够产生高达650达因·厘米⁻²·秒⁻¹的剪切应力变化率（即主动脉瓣小叶心室表面所经历的最大剪切应力变化率），并已证明能够在无菌条件下将组织维持120小时。这种新型体外组织培养系统是阐明心脏瓣膜力学生物学的一个有价值的工具。最终，这些知识将有助于生产功能性组织工程心脏瓣膜，并更好地理解心脏瓣膜生物学和疾病进展情况。
