Soft Materials Laboratory, Institute of Materials, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, 1015, Switzerland.
Engineering Mechanics of Soft Interfaces Laboratory, Institute of Mechanical, Engineering, École Polytechnique Fédérale de Lausanne, (EPFL), Lausanne, 1015, Switzerland.
Macromol Rapid Commun. 2023 Aug;44(16):e2200864. doi: 10.1002/marc.202200864. Epub 2023 Mar 10.
The stiffness and toughness of conventional hydrogels decrease with increasing degree of swelling. This behavior makes the stiffness-toughness compromise inherent to hydrogels even more limiting for fully swollen ones, especially for load-bearing applications. The stiffness-toughness compromise of hydrogels can be addressed by reinforcing them with hydrogel microparticles, microgels, which introduce the double network (DN) toughening effect into hydrogels. However, to what extent this toughening effect is maintained in fully swollen microgel-reinforced hydrogels (MRHs) is unknown. Herein, it is demonstrated that the initial volume fraction of microgels contained in MRHs determines their connectivity, which is closely yet nonlinearly related to the stiffness of fully swollen MRHs. Remarkably, if MRHs are reinforced with a high volume fraction of microgels, they stiffen upon swelling. By contrast, the fracture toughness linearly increases with the effective volume fraction of microgels present in the MRHs regardless of their degree of swelling. These findings provide a universal design rule for the fabrication of tough granular hydrogels that stiffen upon swelling and hence, open up new fields of use of these hydrogels.
传统水凝胶的硬度和韧性随着溶胀度的增加而降低。这种行为使得水凝胶的硬度-韧性折衷对于完全溶胀的水凝胶更加局限，特别是对于承重应用。通过用水凝胶微球、微凝胶增强水凝胶可以解决水凝胶的硬度-韧性折衷问题，从而引入双网络（DN）增韧效应。然而，在完全溶胀的微凝胶增强水凝胶（MRHs）中，这种增韧效应在多大程度上得以保持尚不清楚。本文证明了 MRHs 中所含微凝胶的初始体积分数决定了它们的连通性，而连通性与完全溶胀的 MRHs 的硬度密切相关，但呈非线性关系。值得注意的是，如果用高体积分数的微凝胶增强 MRHs，它们在溶胀时会变硬。相比之下，断裂韧性与 MRHs 中存在的微凝胶的有效体积分数呈线性关系，而与它们的溶胀程度无关。这些发现为制造在溶胀时变硬的坚韧颗粒水凝胶提供了一个通用的设计规则，从而为这些水凝胶开辟了新的应用领域。
