Two factors play the key role in application of hydrogels as biomedical implants (for example, for replacement of damaged intervertebral discs and repair of spinal cord injuries): their stiffness and strength (measured in tensile tests) and mechanical integrity (estimated under uniaxial compression). Observations show a pronounced difference between the responses of hydrogels under tension and compression (the Young's moduli can differ by two orders of magnitude), which is conventionally referred to as the tension–compression asymmetry (TCA). A constitutive model is developed for the mechanical behavior of hydrogels, where TCA is described within the viscoplasticity theory (plastic flow is treated as sliding of junctions between chains with respect to their reference positions). The governing equations involve five material constants with transparent physical meaning. These quantities are found by fitting stress–strain diagrams under tension and compression on a number of pristine and nanocomposite hydrogels with various kinds of chemical and physical bonds between chains. Good agreement is demonstrated between the experimental data and results of simulation. The influence of volume fraction of nanoparticles, concentration of cross-links, and topology of a polymer network on material parameters is analyzed numerically.

在将水凝胶用作生物医学植入物时（例如，用于替换受损的椎间盘并修复脊髓损伤），有两个因素起着关键作用：它们的刚度和强度（在拉伸试验中测量）和机械完整性（在单轴压缩下估算） 。观察结果表明，水凝胶在拉伸和压缩下的响应之间存在明显的差异（杨氏模量可以相差两个数量级），这通常被称为拉伸-压缩不对称（TCA）。针对水凝胶的机械行为开发了本构模型，其中在粘塑性理论中描述了三氯乙酸（可塑性流被视为链之间的连接相对于其参考位置的滑动）。控制方程涉及五个具有透明物理意义的材料常数。这些量是通过在许多原始的和纳米复合的水凝胶上，在链之间具有各种化学和物理键合的情况下，通过在拉伸和压缩条件下拟合应力-应变图而得出的。实验数据和模拟结果之间显示出良好的一致性。数值分析了纳米粒子的体积分数，交联浓度和聚合物网络拓扑对材料参数的影响。实验数据和模拟结果之间显示出良好的一致性。数值分析了纳米粒子的体积分数，交联浓度和聚合物网络拓扑对材料参数的影响。实验数据和模拟结果之间显示出良好的一致性。数值分析了纳米粒子的体积分数，交联浓度和聚合物网络拓扑对材料参数的影响。