Closed-loop SMA control for ingestible robotic capsules: a PID/FO-PID framework for accurate, low-power microbiota sampling

Ingestible robotic capsules must provide compact, accurate actuation to obtain microbiota samples from specific gastrointestinal locations. Although shape-memory-alloy (SMA) spring capsules have shown dependable duodenal and ileal sampling in vitro, the inherent limitations of SMA—slow thermal response, elevated current requirements, inconsistent output force, and lack of adaptive control—compromise in vivo reliability, energy efficiency, and sample integrity. This research presents a closed-loop actuation architecture that integrates classical PID with fractional-order PID (FO-PID) within the established 45 mm × 12 mm capsule dimensions. The controller, deployed on ultra-low-power microcontrollers (Nordic nRF52832, STM32L4, ATtiny3217), controls the shape memory alloy heating current in real time by utilising temperature and strain feedback to monitor force and position objectives while efficiently controlling power consumption. A cohesive software stack standardises high-frequency telemetry, on-device preprocessing, and metadata logging, producing labelled datasets and streamlined interfaces for further functionalities such as anomaly detection, adaptive sampling, and health-state inference. Simulation experiments demonstrate enhanced actuation precision, expedited settling times, and prolonged battery longevity, effectively addressing SMA constraints and facilitating dependable, untethered, site-specific sampling. The suggested platform promotes SDG 3 (Good Health and Well-Being) and SDG 9 (Industry, Innovation, and Infrastructure) by integrating energy-efficient control with a replicable data pipeline for next-generation ingestible diagnostics.