Tough, self-healing and weldable hydrogel via thermal engineering optimized multi-scale structures

Abstract

Synthetic hydrogels are generally mechanically weak due to their single-component composition and simple polymeric networks, limiting their practical applications. Bioinspired strategies to engineer molecular- and microscale-level hierarchical structures have shown promise in the development of tough hydrogels but often involve complex, time- and energy-intensive processes. Here, we present a simple yet effective thermal engineering approach to optimize the multiscale structure of physically cross-linked polyacrylamide (PAM) hydrogels. Thermal engineering enhances polymer chain packing at the molecular level and refines the porous structure at the microlevel, leading to synergistic mechanical improvements. Compared to as-prepared PAM hydrogels, the thermally engineered PAMs demonstrate an 11-fold increase in tensile strength and a 60-fold increase in toughness. Furthermore, the disentangling and re-packing of polymer chains at the molecular level during thermal engineering endows the hydrogel with self-healing capabilities and weldability to polymers. By integrating the PAM hydrogel with shape memory polyurethane, this approach facilitates precise hydrogel assembly, creating a versatile platform for applications in soft robotics, smart biomedical devices, and advanced electronics by leveraging desired polymer functionalities into hydrogel-based systems. Synthetic hydrogels often suffer from mechanical weakness due to their simple polymeric networks, limiting their utility in advanced applications. Here, a thermal engineering approach is used to enhance the multiscale structure of polyacrylamide hydrogels, achieving improvements in strength, toughness, and functionality.