Tough Semi-interpenetrating Polyvinylpyrrolidone/Polyacrylamide Hydrogels Enabled by Bioinspired Hydrogen-bonding Induced Phase Separation

Semi-interpenetrating(semi-IPN)hydrogels formed by the continuous interpenetration of cross-linked polymer network and linear non-crosslinked polymer with multifunctionality are widely used in biomedical and other fields.However,the negative impact of linear polymer on the homogeneity of the cross-linked network often leads to a decrease in the mechanical properties of semi-IPN hydrogels and severely limits their applications.Herein,a bioinspired hydrogen-bonding induced phase separation strategy is presented to construct the tough semi-IPN polyvinylpyrrolidone/polyacrylamide hydrogels(named PVP/PAM hydrogels),including the linear polymer polyvinylpyrrolidone(PVP)and cross-linked polyacrylamide(PAM)network.The resultant PVPx/PAM hydrogels exhibit unique phase separation induced by the hydrogen bonding between PVP and PAM and affected by the amount of substance of PVP.Meanwhile,the phase separation of PVPx/PAM hydrogels results in excellent mechanical properties with a strain of 2590%,tensile strength of 0.28 MPa and toughness of 2.17 MJ/m^(3).More importantly,the hydrogen bonding between PVP and PAM firstly disrupts to dissipate energy under external forces,so the PVPx/PAM hydrogels exhibit good self-recovery properties and outperform chemically cross-linked PAM hydrogels in impact resistance and damping applications.It is believed that the PVPx/PAM hydrogels with hydrogen-bonding induced phase separation possess more potential application prospects.

Ultra-robust Metallosupramolecular Hydrogels with Unprecedented Self-recoverability using Asymmetrically Distributed Carboxyl-Fe3+Coordination Interactions

Recently,numerous mechanically robust synthetic hydrogels have been created.However,unlike natural loading-bearing materials such as cartilages and muscles,most hydrogels have inherently contradictory requirements,obstructing the design of hydrogels with characteristics of robustness and rapid self-recoverability.Herein,we present a facile strategy for constructing mechanically robust and rapidly self-recoverable hydrogels.The linear poly(acrylamide-co-itaconic acid)chains crosslink via coordination bonds and minimal chemical crosslinkers to form the hydrogel network.Such design endows the coordination interactions to be asymmetrically distributed.Under deformation,the coordination interactions exhibit a reversible dissociation-and-reorganization property,demonstrating a new mechanism for energy dissipation and stress redistribution.Thus,the hydrogels possess tensile strength up to 12.5 MPa and toughness up to 28.2 MJ/m3.Moreover,the inherent dynamic nature of the coordination bonds imparts these hydrogels with stretch rate-and temperature-dependent mechanical behavior as well as excellent self-recovery performance.The method employed in this study is universal and is applicable to other polymers with load-bearing yet rapid recovery conditions.This study will facilitate diverse applications of most metallosupramolecular hydrogels.