Mechanical properties of hydrogels are of considerable interest for applications including tissue engineering and drug delivery. However, mechanical characterization of hydrogels is inherently challenging due to their multiphasic construction. Under mechanical loading, internal fluid redistribution affects the gel response, leading to a time- and length-scale-dependent material behavior, known as poroelasticity. Traditional mechanical tests are effective for determining instantaneous flow-independent gel response, and they are limited in characterizing poroelastic behavior as a function of loading time- and length-scales. Here, micro- and nanoindentation experiments are combined to characterize the full range of poroelastic behavior of a hydrogel. A master curve is presented to demonstrate that the relative competition of poroelastic relaxation time with ramp loading time determines gel response across different time- and length-scales. The master curve provides a novel mechanism to establish the instantaneous and equilibrium limits on the elastic modulus for a material, useful for designing hydrogel biomaterials.

水凝胶的机械性质对于包括组织工程和药物递送在内的应用具有相当大的兴趣。然而，由于水凝胶的多相结构，其机械表征固有地具有挑战性。在机械载荷下，内部流体的重新分布会影响凝胶响应，从而导致时间和长度依赖于材料的行为，即多孔弹性。传统的机械测试可有效地确定与流量无关的瞬时凝胶响应，并且它们在表征多孔弹性行为（取决于加载时间和长度尺度）方面受到限制。在这里，微观和纳米压痕实验相结合，以表征水凝胶的多孔弹性行为的整个范围。提出了一条主曲线来证明多孔弹性弛豫时间与斜坡加载时间的相对竞争决定了不同时间和长度范围内的凝胶响应。主曲线提供了一种新颖的机制来建立材料弹性模量的瞬时和平衡极限，可用于设计水凝胶生物材料。