High-Speed and High-Resolution 3D Printing of Self-Healing and Ion-Conductive Hydrogels via μCLIP

Conductiveand self-healing (SH) hydrogels have been receivingcontinuous attention, which could broaden the design of ionotronicdevices for health monitoring systems and soft robots with the abilityto repair damage autonomously. So far, three-dimensional (3D) fabricationof such SH hydrogels is mainly limited to traditional molding/castingor extrusion-based 3D printing methods, which limits the formationof sophisticated structures with high-resolution features. Furthermore,the need of external stimuli (e.g., water, heat, and pH change) toachieve SH behavior could restrict their wide application. Herein,we report an ion-conductive SH hydrogel suitable for a home-builthigh-resolution and high-speed 3D printing process, micro continuousliquid interface production (mu CLIP). This material system relieson interpenetrating polymer networks (IPN) hydrogel formed by physicallycross-linked poly-(vinyl alcohol) combined with chemically/ionicallycross-linked poly-(acrylic acid) and ferric chloride. By carefullyoptimizing the resin's composition, we can balance high-resolutionprintability and superb SH capability, at the same time manifestingsufficient ion conductivity. Specifically, complex 3D structures withmicroscale features (down to 100 mu m) can be printed at speedsup to 16.5 mu m s(-1). Upon damage occurs, hydrogenbonds within hydroxyl and carboxyl groups, as well as ionic bondsgenerated from ferric ions, contribute together to achieve fast andhigh efficiency SH, which can restore 90% (100%) of the original mechanicalstrength at room temperature within 4 h (8 h) without any externalstimulus. In addition, both the as-printed and self-healed hydrogelsmanifest superior ion conductivity and stretchability. Therefore,the SH hydrogels can be rapidly printed and tailored as customizedwearable sensors, and the sensing capabilities were quantitativelyinvestigated and compared. In terms of applications, SH hydrogel-basedknuckle sensors were prototyped to detect a finger's foldingand unfolding motions.