Department of Mechanical Engineering, Boston University, Boston, MA 02215, United States.
Department of Mechanical Engineering, Boston University, Boston, MA 02215, United States; Department of Biomedical Engineering, Boston University, Boston, MA 02215, United States.
J Mech Behav Biomed Mater. 2018 Jan;77:634-641. doi: 10.1016/j.jmbbm.2017.10.023. Epub 2017 Oct 20.
Elastin is a critical extracellular matrix protein that provides many biological tissues with resilience. In elastic arteries such as aorta, elasticity is crucial for energy storage and transmission of the pulsatile blood flow. As one of the main mechanisms of aging, non-enzymatic glycation can greatly compromise the mechanical properties of the long-lived elastin. In this study, effect of glucose on the viscoelastic behavior of purified porcine aortic elastin was investigated through stress relaxation tests and the corresponding relaxation time distribution spectra. Elastin was incubated in 2M glucose solution at 37°C for 4, 7, 14, 21 or 28 days. Biaxial stress relaxation tests were performed to study the viscoelastic property of elastin. Elastin samples with glucose treatment show increased stress relaxation with incubation time. Continuous relaxation time distribution spectra were obtained from the stress relaxation data using Tikhonov regularization method. Generally the spectra of both untreated and treated elastin have a broad range of relaxation time constants and multiple peaks located between 0.1-10,000s. The intensity of the short-term peak (0.1-10s) increases after glucose exposure whereas the intensity of the long-term peak (> 100s) decreases. The dominant peaks, i.e., the long-term peak of untreated tissue and the short-term peak of glucose treated tissue, suggest different relaxation mechanisms. The initial stress level dependency of stress relaxation was studied and the results suggested that the intensity of all the peaks increases with higher initial stresses. A multi-exponential model was developed to describe the stress relaxation behavior with material parameters obtained directly from the continuous relaxation spectrum. To fully characterize the relaxation processes, a multi-exponential model with four exponential terms, located between 0.001-1s, 1-10s, 10-100s, and 100-10,000s and obtained directly from the corresponding relaxation spectrum, appears to best capture the stress relaxation behavior of elastin before and after glucose exposure.
弹性蛋白是一种关键的细胞外基质蛋白，为许多生物组织提供弹性。在主动脉等弹性动脉中，弹性对于储存能量和传递脉动血流至关重要。作为衰老的主要机制之一，非酶糖基化会极大地损害长寿弹性蛋白的机械性能。在这项研究中，通过应力松弛试验和相应的松弛时间分布谱研究了葡萄糖对纯化猪主动脉弹性蛋白的粘弹性行为的影响。弹性蛋白在 37°C 的 2M 葡萄糖溶液中孵育 4、7、14、21 或 28 天。进行双轴应力松弛试验以研究弹性蛋白的粘弹性特性。经葡萄糖处理的弹性蛋白样品随孵育时间的增加而表现出更大的应力松弛。使用 Tikhonov 正则化方法从应力松弛数据中获得连续的松弛时间分布谱。通常，未经处理和处理的弹性蛋白的谱都具有广泛的松弛时间常数和多个位于 0.1-10,000s 之间的峰。暴露于葡萄糖后，短期峰（0.1-10s）的强度增加，而长期峰（> 100s）的强度降低。主要峰，即未经处理组织的长期峰和葡萄糖处理组织的短期峰，表明不同的松弛机制。研究了初始应力水平对应力松弛的依赖性，结果表明所有峰的强度都随初始应力的增加而增加。开发了一个多指数模型来描述具有从连续松弛谱中直接获得的材料参数的应力松弛行为。为了充分描述松弛过程，一个具有四个指数项的多指数模型，位于 0.001-1s、1-10s、10-100s 和 100-10,000s 之间，直接从相应的松弛谱中获得，似乎最能捕捉到弹性蛋白在葡萄糖暴露前后的应力松弛行为。
