Development of highly stretchable and sensitive soft strain sensors is of great importance for broad applications in artificial intelligence, wearable devices, and soft robotics, but it proved to be a profound challenge to integrate the two seemingly opposite properties of high stretchability and sensitivity into a single material. Herein, we designed and synthesized a new fully polymeric conductive hydrogel with an interpenetrating polymer network (IPN) structure made of conductive PEDOT:PSS polymers and zwitterionic poly(HEAA-co-SBAA) polymers to achieve a combination of high mechanical, biocompatible, and sensing properties. The presence of hydrogen bonding, electrostatic interactions, and IPN structures enabled poly(HEAA-co-SBAA)/PEDOT:PSS hydrogels to achieve an ultra-high stretchability of 4000–5000%, a tensile strength of ∼0.5 MPa, a rapid mechanical recovery of 70–80% within 5 min, fast self-healing in 3 min, and a strong surface adhesion of ∼1700 J m⁻² on different hard and soft substrates. Moreover, the integration of zwitterionic polySBAA and conductive PEDOT:PSS facilitated charge transfer via optimal conductive pathways. Due to the unique combination of superior stretchable, self-adhesive, and conductive properties, the hydrogels were further designed into strain sensors with high sensing stability and robustness for rapidly and accurately detecting subtle strain- and pressure-induced deformation and human motions. Moreover, an in-house mechanosensing platform provides a new tool to real-time explore the changes and relationship between network structures, tensile stress, and electronic resistance. This new fully polymeric hydrogel strain sensor, without any conductive fillers, holds great promise for broad human-machine interface applications.

Stimuli-responsive hydrogel strain sensors that synergize the advantages of both hydrogel and smart functional materials have attracted increasing interest from material design to emerging applications in health monitors and human–machine interfaces.

Zwitterionic materials as a new class of emerging materials have recently been developed and applied to a broad range of biomedical and engineering applications. Zwitterionic materials possess a unique molecular structure combining both cationic and anionic groups with overall charge neutrality and high hydrophilicity. In this review, we first provide the structure-property relationship of the zwitterionic materials at molecular level, from a molecular simulation viewpoint. Then, we discuss the recent experimental developments in the preparation, properties, and applications of zwitterionic materials, with a particular focus on their antifouling properties on coating surfaces and with additional functionality and applications. Finally, we offer our personal viewpoint of current challenges and future directions in this emerging area. Our goal is to introduce the current status of this type of new zwitterionic materials to researchers from different areas and motivate them to explore all the potentials.

Zwitterionic materials demonstrate the strong surface hydration to empower their antifouling property.