Anti-fatigue-fracture hydrogels | 2/11/2019 | Staff
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Hydrogels are polymer networks infiltrated with water, widely used for tissue engineering vehicles of drug delivery and novel platforms for biomedical engineering. Emerging applications for new hydrogel materials call for robustness under cyclic mechanical loads. Materials scientists have developed tough hydrogels that resist fracture under a single cycle of mechanical load, yet these toughened gels still suffer from fatigue fracture under multiple cycles of loads. The present fatigue threshold for synthetic hydrogels is reported in the order of 1 to 100 J/m2.

In a recent study, Shaoting Lin and a team of materials scientists at the Massachusetts Institute of Technology (MIT) proposed the design of an anti-fatigue-fracture hydrogel. To develop the proposed hydrogel, the scientists needed the materials to have energies per unit area at a much higher value than that required to fracture a single layer of polymer chains. To accomplish this, they controlled the introduction of crystallinity in to hydrogels to substantially enhance their anti-fatigue-fracture properties. In this work, Lin et al. disclosed the fatigue threshold of polyvinyl alcohol (PVA) with a crystallinity of 18.9 weight percent (18.9 wt%) in the swollen state to exceed 1000 J/m2. The results are now published in Science Advances.

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The pioneering work of Gong et al has inspired materials scientists to engineer hydrogels that are increasingly tough to resist crack propagation in a single cycle of mechanical load for industrial and biomedical applications. Hydrogels are toughened via mechanisms to dissipate mechanical energy, such as the fracture of short polymer chains and reversible crosslinks into stretchy polymer networks. Yet, the existing tough hydrogels suffer from fatigue fracture under multiple cycles of mechanical loads. The highest fatigue threshold on record so far is 418 J/m2 for a double network hydrogel, poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS)-PAAm. The outcome is credited to the high intrinsic fracture energy of the...
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