Understanding the difference between ex vivo and in vivo measurements is critical to interpret the load carrying mechanisms of living biological systems. For the past four decades, the ex vivo stiffness of thin biological membranes has been characterized using uniaxial and biaxial tests with remarkably consistent stiffness parameters, even across different species. Recently, the in vivo stiffness was characterized using combined imaging techniques and inverse finite element analyses. Surprisingly, ex vivo and in vivo stiffness values differed by up to three orders of magnitude. Here, for the first time, we explain this tremendous discrepancy using the concept of prestrain. We illustrate the mathematical modeling of prestrain in nonlinear continuum mechanics through the multiplicative decomposition of the total elastic deformation into prestrain-induced and load-induced parts. Using in vivo measured membrane kinematics and associated pressure recordings, we perform an inverse finite element analysis for different prestrain levels and show that the resulting membrane stiffness may indeed differ by four orders of magnitude depending on the prestrain level. Our study motivates the hypothesis that prestrain is important to position thin biological membranes in vivo into their optimal operating range, right at the transition point of the stiffening regime. Understanding the effect of prestrain has direct clinical implications in regenerative medicine, medical device design, and tissue engineering of replacement constructs for thin biological membranes.

了解离体和体内测量之间的差异对于解释活生物系统的承载机制至关重要。在过去的四年中，薄生物膜的离体刚度已经使用单轴和双轴测试进行了表征，刚度参数非常一致，即使在不同物种之间也是如此。最近，使用组合成像技术和逆有限元分析表征了体内刚度。令人惊讶的是，离体和体内刚度值相差多达三个数量级。在这里，我们第一次使用预应变的概念来解释这种巨大的差异。我们通过将总弹性变形乘法分解为预应变引起的和载荷引起的部分来说明非线性连续介质力学中预应变的数学建模。使用体内测量的膜运动学和相关的压力记录，我们对不同的预应变水平进行了逆有限元分析，并表明所得的膜刚度可能确实存在四个数量级的差异，具体取决于预应变水平。我们的研究激发了这样一个假设，即预应变对于将 体内 薄生物膜定位到其最佳操作范围很重要，就在硬化制度的过渡点。了解预应变的作用对再生医学、医疗器械设计、