Tough, Transparent, 3D‐Printable, and Self‐Healing Poly(ethylene glycol)‐Gel (PEGgel)

Abstract

These gels represent a class of soft materials with unique properties resembling soft biological tissues, such as tendons, ligaments, cartilage, muscles, and skin. [6] Hydrogels, obtained by cross-linking hydrophilic polymer chains in aqueous solutions, [7] possess the intrinsic lowmodulus nature and tissue-like properties, which make them applicable to tissue engineering, [8] optical devices, [9] biomedicine [10] and actuators. [11] In the pursuit of high performance, most research in the field of polymer gels has been focused on the chemical nature and polymer network architectures and their interactions, [12] such as ideal polymer networks, [13] interpenetrating polymer networks, [14] nano/micro composite polymer networks, [10,15] and hierarchically structured polymer networks. [16] The small molecule solvent is the second component of gels and is often considered to be a nonfunctional liquid that impregnates and expands a functional polymer network. Recently, ionic liquids have been used to replace water in hydrogels, [17] resulting in soft materials with long-term stability. [18] Multicomponent solvent systems, in which water is mixed with organic solvents (such as glycerol, [19] ethylene glycol [20] and sorbitol [21] ), were introduced into gel networks to maintain the performance of materials in harsh environments. However, because of the low molecular weight of solvents used and weak interactions with polymer networks, the reported Polymer gels, such as hydrogels, have been widely used in biomedical applications, flexible electronics, and soft machines. Polymer network design and its contribution to the performance of gels has been extensively studied. In this study, the critical influence of the solvent nature on the mechanical properties and performance of soft polymer gels is demonstrated. A polymer gel platform based on poly(ethylene glycol) (PEG) as solvent is reported (PEGgel). Compared to the corresponding hydrogel or ethylene glycol gel, the PEGgel with physically cross-linked poly(hydroxyethyl methacrylate-co-acrylic acid) demonstrates high stretchability and toughness, rapid self-healing, and long-term stability. Depending on the molecular weight and fraction of PEG, the tensile strength of the PEGgels varies from 0.22 to 41.3 MPa, fracture strain from 12% to 4336%, modulus from 0.08 to 352 MPa, and toughness from 2.89 to 56.23 MJ m -3 . Finally, rapid self-healing of the PEGgel is demonstrated and a self-healing pneumatic actuator is fabricated by 3D-printing. The enhanced mechanical properties of the PEGgel system may be extended to other polymer networks (both chemically and physically cross-linked). Such a simple 3D-printable, self-healing, and tough soft material holds promise for broad applications in wearable electronics, soft actuators and robotics.

An Extensively Adhesive Patch with Multiple Physical Interactions and Chemical Crosslinking as a Wound Dressing and Strain Sensor

“…After the five cycles of cut-off and contact, the resistance can return to the original state rapidly. After the sample is destroyed, the “viscous” groups at the interface become the key to trigger self-healing (Figure g) . The H-bond and Ag coordination bond form a new weak interface through non-covalent interactions, and the disulfide bond forms a strong interface through dynamic covalent exchange.…”

Digital light processing 3D printing of hydrogels: a minireview

“…Moreover, Wang et al developed a special polymer gel (PEGgel) system by polymerizing hydroxyethyl methacrylate and acrylic acid in poly(ethylene glycol) (PEG) medium. 89 A pneumatic soft actuator with an asymmetric hollow structure was printed by DLP 3D printing with the PEG gel precursor (Fig. 4c).…”

Three-Dimensional Printable, Highly Conductive Ionic Elastomers for High-Sensitivity Iontronics

“…Recently, several solvent-free ionic conductive elastomers (ICEs) have been investigated as alternatives to hydrogels and ionic gels. − Ding et al . proposed introducing a salt into a polymer to prepare solvent-free ICEs, which simultaneously displayed high flexibility, thermal stability, and transparency.…”