Stretchable hydrogels with low hysteresis and anti-fatigue fracture based on polyprotein cross-linkers

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.

Anisotropically Fatigue‐Resistant Hydrogels

“…Scale bar: 5 mm. dry-annealed PVA, [12] biogels (i.e., biological tissue), [8] composite hydrogels, [27] mechanically trained PVA hydrogels, [15] polyprotein-based hydrogels, [28] single network i.e., and polyacrylamide hydrogel), [6,26] in terms of fatigue thresholds, without sacrificing their high water contents (Figure 3C). Moreover, as far as known to us, this is the first work which successfully fabricates hydrogel materials with record-high fatigue threshold (2,740 J m −2 ), and high anisotropic ratio (Γ 0⊥ /Γ 0|| ) over 40, at a high water content over 82 wt%.…”

Transparent, Conductive Hydrogels with High Mechanical Strength and Toughness

“…It can be seen from Figure 2 c that as the content of CaCl 2 increased, the fracture strain of the hydrogel gradually decreased from 935% to 319%, while the tensile strength increased from 0.70 MPa to 2.65 MPa, and then decreased to 1.61 MPa. This was because too much CaCl 2 cannot form stable metal coordination bonds with CMCS [ 26 , 27 ]. In addition, the toughness and elastic modulus of the hydrogel also increased first and then decreased ( Figure 2 d).…”

There Is Plenty of Room in The Folded Globular Proteins: Tandem Modular Elastomeric Proteins Offer New Opportunities in Engineering Protein‐Based Biomaterials

“…Many of these SAE protein hydrogels were constructed using the Ru 2+ ‐based photocrosslinking chemistry, due to its fast reaction kinetics and wide applicability to different proteins. [ 8,47 ] Other chemical crosslinking methods, such as spyTag‐spyCatcher chemistry [ 59,60 ] and click chemistry, [ 61 ] as well as noncovalent crosslinking based on mechanically stable ligand–receptor interactions, such Cohesin–Dockerin interaction, [ 57,62 ] were also used to construct protein hydrogels. Although mechanically labile ligand–receptor interactions can be used to engineer protein hydrogels, such hydrogels are often mechanically soft and weak, and prone to erosion.…”

“…[ 25 ] However, directly observing protein unfolding in hydrogel networks is challenging. [ 46,53,61 ] Theoretical/modeling work has started to offer some insights into the interplay between single‐molecule mechanics and macroscopic mechanical properties of hydrogel networks.…”