Artificial structures for human‐machine interfaces with closed‐loop interaction

Closed‐loop human‐machine interfaces (HMIs) establish bidirectional communication by pairing flexible sensors with wearable actuators. They allow users to command machines or virtual avatars and perceive contact, temperature, and kinaesthetic states in real time. Practical closed‐loop HMIs require stable, skin‐ or machine‐compatible devices that operate under large, multi‐axial deformation with low crosstalk and minimal perceptual artifacts. Here, we argue that artificial structures provide a unifying design paradigm beyond material selection. We summarize representative structural toolkits, including serpentine and island‐bridge layouts, kirigami/origami, auxetic and chiral metamaterials, cellular networks, and three‐dimensional architectures, and relate their mechanics to stretchability, conformability, stability, sensitivity, signal decoupling, and breathability. We then discuss their roles in five major sensing modalities (force, acoustic, temperature, bioelectrical, and multifunctional sensing) and four feedback modes (mechanical, electrical, thermal, and multimodal haptics), focusing on sensitivity amplification, deformation robustness, high‐density integration, crosstalk suppression, and receptor activation. Finally, we examine system‐level closed‐loop integration in distributed and integrated architectures for teleoperation, prosthetics, rehabilitation, and immersive virtual reality (VR) and augmented reality (AR), and outline challenges in scalable manufacturing, safety, and perception‐aware encoding. This review provides a structure‐centric framework for designing next‐generation closed‐loop HMIs that are compliant, reliable, and perceptually rich.