Review of Gastrointestinal Capsule Robots: Materials, Actuation, Diagnostics, and Therapeutics

Gastrointestinal capsule robots are minimally invasive devices for diagnosis and therapy in the digestive tract. This review examines them from a systems engineering perspective, spanning the technological chain from materials and actuation to sensing, treatment, and clinical translation. Structurally, current designs employ rigid polymers and metals, flexible elastomers, and biodegradable or stimuli-responsive materials to balance mechanical stability, biocompatibility, and environmental adaptability. Locomotion strategies range from passive peristalsis-driven transit to magnetic, wireless-powered, multi-legged, and tethered actuation, paired with magnetic, radiofrequency, vision-based, MRI-based, X-ray-based, and hybrid localization. Diagnostic capabilities extend from ex situ tissue biopsy and fluid sampling to in situ multimodal sensing and optical imaging for physiological monitoring and biochemical analysis within the gut. Therapeutic developments include targeted drug delivery, microneedle injection, photodynamic therapy, thermal hemostasis, electrical stimulation, metabolic intervention, and mechanical clearance. Despite this progress, challenges persist in actuation capability, energy supply, precise navigation, and system-level integration. We conclude by highlighting current technological gaps and outlining future directions toward intelligent intraluminal platforms capable of autonomous navigation, multimodal diagnosis, and precision therapy. This work provides a comprehensive reference for advancing the science and application of gastrointestinal capsule robots across multiple fields.