Exoskeleton robotics: from rigid structures to bio-integrated systems

Exoskeleton robots have become a representative class of wearable robotic systems for rehabilitation, mobility assistance, occupational support, and human performance augmentation. As the field moves from laboratory prototypes toward clinical, industrial, and daily life deployment, research priorities are shifting from device-centered performance improvement to human-centered integration. This mini review provides a structured and critically oriented synthesis of exoskeleton technologies from four interconnected perspectives: technical architecture, technological paradigm evolution, deployment barriers, and future research directions. To improve transparency and reproducibility, we adopted a narrative review strategy with explicit literature selection criteria. Publications were identified from major scientific databases using combinations of keywords related to exoskeleton robotics, actuation, control, human-robot interaction, soft robotics, neural interfaces, rehabilitation, and wearable assistance. Representative studies were selected according to relevance, technical influence, clinical or engineering significance, and coverage of major technological paradigms. The review first analyzes three core technical dimensions-actuation systems, control strategies, and human-robot interaction which jointly determine the performance, adaptability, and usability of exoskeleton systems. Rather than only summarizing these technologies, we compare their trade-offs in terms of power density, control precision, compliance, energy efficiency, personalization, safety, and deployment readiness. The review then examines the evolution from rigid exoskeletons, which provide high structural support and precise force transmission, to soft exoskeletons, which improve compliance and comfort, and further to bio-integrated systems that combine neural interfaces, functional electrical stimulation, multimodal sensing, and mechanical assistance. Based on this synthesis, we organize the review using a Human-Exoskeleton Integration Maturity Framework spanning mechanical coupling, physical compliance, functional adaptation, and cognitive/bio-integrated coupling. Persistent barriers, including energy supply, personalization, safety assurance, cost, regulatory translation, and ethical governance, are critically discussed. Finally, future directions are outlined, including neural-interface-driven control, multimodal perception, human-in-the-loop optimization, hybrid rigid-soft architectures, and socially responsible design. Overall, this review argues that the next stage of exoskeleton development will depend not merely on stronger actuators or more intelligent algorithms, but on integrated systems that are adaptive, trustworthy, affordable, and seamlessly embedded in human movement and function.