Abstract
Hydrogel-based devices are widely used as flexible electronics, biosensors, soft robots, and intelligent human-machine interfaces. In these applications, high stretchability, low hysteresis, and anti-fatigue fracture are essential but can be rarely met in the same hydrogels simultaneously. Here, we demonstrate a hydrogel design using tandem-repeat proteins as the cross-linkers and random coiled polymers as the percolating network. Such a design allows the polyprotein cross-linkers only to experience considerable forces at the fracture zone and unfold to prevent crack propagation. Thus, we are able to decouple the hysteresis-toughness correlation and create hydrogels of high stretchability (~1100%), low hysteresis (< 5%), and high fracture toughness (~900 J m−2). Moreover, the hydrogels show a high fatigue threshold of ~126 J m−2 and can undergo 5000 load-unload cycles up to 500% strain without noticeable mechanical changes. Our study provides a general route to decouple network elasticity and local mechanical response in synthetic hydrogels.
Highlights
Hydrogel-based devices are widely used as flexible electronics, biosensors, soft robots, and intelligent human-machine interfaces
We flanked both ends of the G8 with SNAP protein (SNAP-G8-SNAP) and allowed it to react with O6-benzylguanine styrene (BS) to covalently link a vinyl group to each end of the polyprotein (Fig. 1a)
The hydrogels were prepared by a one-pot free radical polymerization of acrylamide and BS-linked SNAP-G8-SNAP in the phosphate buffer saline (PBS) buffer for 30 min using lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as the photo initiator (Fig. 1a)
Summary
Hydrogel-based devices are widely used as flexible electronics, biosensors, soft robots, and intelligent human-machine interfaces. We propose a network structure that is made of the unstructured polymers as the percolating phase and the polyproteins as the cross-linker to achieve combined low hysteresis and anti-fatigue fracture properties. The fracture zone (gradual rupture region, Fig. 2e, k) existed in all PAA-G8 hydrogels, which further suggested that GB1 domains only unfolded locally at the crack sites.
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