Mechanically Strong and Highly Tough Prolamin Protein Hydrogels Designed from Double-Cross-Linked Assembled Networks

This study introduced uniquely constructed double-cross-linked hordein/zein protein hydrogels with outstanding mechanical properties. Notably, the optimized hydrogels demonstrated a compressive stress of 1.90 MPa at a strain of 70%, excellent self-recovery after 40 cycles of loading-unloading treatments, and superior foldable properties. Further study of the hydrogel nanostructures and properties has revealed that the hordein highly participated in the formation of chemically cross-linked networks which maintained the elasticity of the hydrogels; whereas physical cross-linked domains that consisted of beadlike particles (diameter similar to 80 nm) by hordein/zein assembly were evenly integrated inside the large chemical cross-linked framework and acted as "load carriers" to effectually absorb energy. Consequently, the intertwined spatial network structures and beadlike particles collectively and efficiently dispersed and absorbed energy to withstand large deformations throughout the chemically and physically cross-linked networks. Such a prolamin protein-based hydrogel has potential to be used in biobased load-bearing soft devices, which will diversify the use of zein and hordein as the byproducts of maize and barley. In addition, the generated knowledge may offer new opportunities to design and construct strong hydrogels from many other plant protein resources to unlock their potential as biopolymer and biocompatible materials.