Biological tissues, such as tendons or cartilage, have high strength and toughness and maintain minimal plastic deformation after undergoing deformation. In contrast, the commonly used strategies for enhanced and toughened hydrogels generally utilize a physical bond-based energy dissipation mechanism, which results in large plastic deformation, thus limiting their application as load-bearing components.
In view of this, Zhang Hang, a researcher at Aalto University in Finland, proposed a strategy to enhance toughened hydrogels using fibrillar connected double networks (fc-DN) containing fiber networks. They synthesized a hydrogel in which a polyacrylamide network and an acrylate-modified agarose fiber network are firmly bonded by chemical bonds. This design enables efficient stress transfer between the two networks, a highly oriented arrangement of the agarose fibers along the strain direction during deformation, and an enhanced pull-out effect of the agarose molecular chains, which together contribute to the high strength (8 MPa) and toughness (55 MJ m-3) of the hydrogel, while the chemical cross-linking ensures that the hydrogel maintains low plastic deformation after experiencing high strain. The research results were published in Advanced Materials under the title "Toughening hydrogels with fibrillar connected double networks". The corresponding author of this paper is researcher Zhang Hang of Aalto University, and the first author is Yu-Huang Fang, a doctoral student at Aalto University.
Key points of the article1. An interconnected double-network hydrogel (fc-DN) was synthesized using acrylate-modified agarose (AcAG) fibers as macromolecular cross-linkers and acrylamide as monomers. 2. The chemical bonding between AcAG fibers and polyacrylamide forms an interconnected double network, which achieves higher breaking strength and toughness than traditional small molecule cross-linked double network hydrogels. 3. In-situ SAXS demonstrated that the orientation of agarose fibers along the strain direction was higher than that of the traditional fiber double network (f-DN) during fc-DN deformation. The chemical bonding between the networks increases the interfacial strength and helps in stress transfer. 4. Compared with the interconnected dual network (c-DN), fc-DN has fiber orientation and agarose molecular chain extraction effect during the deformation process, so it has higher energy dissipation efficiency and higher mechanical strength. 5. When used as a load-bearing component, fc-DN hydrogel has better puncture and impact resistance.
Figure 1. Acrylate-modified agarose/polyacrylamide fc-DN hydrogel.
Figure 2. Cyclic tensile testing and in-situ SAXS characterization.
Fig. 3.FC-DN hydrogel performed better as a load-bearing component. Source: Frontiers of Polymer Science