Homogeneous and Real Super Tough Multi-bond Network Hydrogels Created through a Controllable Metal Ion Permeation Strategy

Poly(acrylic acid) (PAA) hydrogels with multi-bond network (MBN) composed of sparse chemical crosslinks and carboxyl-Fe3+ coordination are prepared through a controllable permeation strategy utilizing ferric citrate (FeCA). The existing strategies that directly soak PAA hydrogels in Fe3+ solutions usually induce inhomogeneous network with densely crosslinked shells and uncertain water content of the hydrogels, which brings about ambiguity when investigating strengthening mechanisms because water content significantly affects the mechanical properties of hydrogels. Herein, the controllable permeation of Fe3+ into PAA networks based on the competition between citric acid (CA)-Fe3+ chelation and PAA-Fe3+ coordination guarantees sustained release of Fe3+, facilitating homogeneous distribution of ionic crosslinks and a certain water content. The obtained hydrogels exhibit excellent and balanced mechanical properties (high tensile strength of 3.28 MPa to 6.95 MPa with large elongation at break of 1400% to 780% ...