Tough, Transparent, 3D printable and Self-healing Polyethylene Glycol-Gel (PEGgel).

Polymer gels, such as hydrogels, consisting of cross-linked polymer chains and small molecule solvents, have been widely used in biomedical applications, flexible electronics and soft machines due to the similarity of their mechanical properties to those of soft biological tissues. Polymer network design and its contribution to the properties of such materials has been extensively studied. In this study, we demonstrate the critical influence of the solvent nature on the mechanical properties and performance of soft polymer gels. Here, we report a polymer gel system (PEGgel) based on a poly(hydroxyethyl methacrylate-co-acrylic acid) copolymerized in the presence of poly(ethylene glycol) (PEG) used as the liquid phase of the PEGgel. Compared to the corresponding hydrogel or ethylene glycol based gel, the PEGgel demonstrates exceptional physical properties, such as high stretchability and toughness, rapid self-healing, and long-term stability under ambient conditions. Depending on the molecular weight and fraction of PEG, the tensile strength of PEGgels varied from 0.22 MPa to 41.3 MPa, fracture strain from 12% to 4336%, modulus from 0.08 MPa to 352 MPa, and toughness from 2.89 MJ m-3 to 56.23 MJ m-3 . The influence of PEG on the mechanical properties was evaluated using the coarse-grain molecular dynamics (CGMD) model and solid-state NMR, revealing abundant weak hydrogen bonding leading to the observed enhancement of mechanical properties. Finally, we demonstrated rapid self-healing of PEGgel materials and fabricated a self-healing pneumatic actuator by 3D printing of PEGgel structures. The enhanced mechanical properties of the PEGgel system could be extended to other polymer networks (both chemically and physically cross-linked). This study demonstrates the important influence of the liquid phase of polymer gels on their mechanical and other properties, and highlights the potential for finetuning different physical properties of gels through the use of PEG possessing weak but multiple hydrogen bond interactions with the polymer network. Such a simple 3D printable, self-healing and tough soft material holds promise for broad applications in wearable electronics, soft actuators and robotics. This article is protected by copyright. All rights reserved.