Centre for Biomedical Engineering, Indian Institute of Technology Ropar, Punjab 140001, India.
Department of Mechanical Engineering, Indian Institute of Technology Ropar, Punjab 140001, India.
J Biomech Eng. 2020 Sep 1;142(9). doi: 10.1115/1.4046205.
The understanding of strain rate-dependent mechanical properties of the skin is important for accurate prediction of its biomechanics under different loading conditions. This study investigated the effect of strain rate, i.e., 0.025/s (low), 0.5/s (medium), and 1.25/s (high), ranging in the physiological loading rate of connective tissue, on the stress-relaxation response of the porcine dermis. Results show that in the initial phase of the relaxation, the value of stress relaxation (extent of relaxation) was found higher for high strain rate. However, the equilibrium stress was found strain rate independent. A Mooney-Rivlin-based five-term quasi-linear viscoelastic (QLV) model was proposed to determine the effect of strain rate on the stress-relaxation behavior of the porcine dermis. The value of relaxation modulus G1 and G2 were found higher for the high strain rate, whereas the reverse trend was observed for G3, G4, and G5. Moreover, the value of time constants τ1,τ2,τ3τ4, and τ5 were found higher for low strain rate. Statistical analysis shows no significant difference in the values of G5, τ4, and τ5 among the three strain rates. The proposed model was found capable to fit the stress-relaxation response of skin with great accuracy, e.g., root-mean-squared-error (RMSE) value equal to 0.015 ± 0.00012 MPa. Moreover, this hyper-viscoelastic model can be utilized: to quantify the effects of age and diseases on the skin; to simulate the stresses on sutures during large wound closure and impact loading.
对皮肤的应变速率相关力学性能的理解对于在不同加载条件下准确预测其生物力学行为非常重要。本研究探讨了应变速率（即 0.025/s（低）、0.5/s（中）和 1.25/s（高））对猪皮的应力松弛响应的影响，这些应变速率范围涵盖了结缔组织的生理加载率。结果表明，在松弛的初始阶段，高应变速率下的应力松弛值（松弛程度）较高。然而，平衡应力与应变速率无关。提出了一个基于 Mooney-Rivlin 的五参数准线性粘弹性（QLV）模型来确定应变速率对猪皮的应力松弛行为的影响。高应变速率下的松弛模量 G1 和 G2 值较高，而 G3、G4 和 G5 的趋势则相反。此外，低应变速率下的时间常数τ1、τ2、τ3、τ4 和τ5 值较高。统计分析表明，在这三个应变速率下，G5、τ4 和τ5 的值没有显著差异。所提出的模型被发现能够非常准确地拟合皮肤的应力松弛响应，例如，均方根误差（RMSE）值等于 0.015±0.00012 MPa。此外，这种超粘弹性模型可以用于：量化年龄和疾病对皮肤的影响；模拟大伤口闭合和冲击加载过程中缝线的应力。
