A shape-morphing bilayer hydrogel microrobot featuring prolonged retention for targeted cell delivery

Soft robots have attracted extensive attention in biomedical applications due to their adaptability, mechanical compliance, and conformability to biological tissues. The integration of soft materials such as hydrogels with functional components enables robots to respond to environmental stimuli and perform targeted tasks, including cargo transport and release. However, many soft systems lack effective retention mechanisms, limiting their efficiency in sustained delivery applications such as drug or cell therapy. In this study, we present a reversibly deformable microrobot for targeted delivery, fabricated from a bilayered hydrogel film of poly(N-isopropylacrylamide) (PNIPAm) and poly (ethylene glycol) diacrylate (PEGDA) embedded with magnetic nanoparticles. The microrobot can be magnetically actuated and undergoes reversible curling and unfolding near physiological temperature. We demonstrate its precise locomotion and shape morphing both in vitro and in vivo under endoscopic visualization. The microrobot also exhibits excellent structural integrity and stable magnetic actuation across a broad pH range (1.5-8.4) and maintains reversible shape morphing over repeated thermal cycles. Furthermore, the planar hydrogel surface allows high-density loading of stem cells, while its reversible transformation into a tubular configuration during transportation can protect the loaded cargo, and re-expansion at the target site enhances anchoring and retention. Quantitative evaluation confirms that the cell loading can achieve a density of approximately 944 cells per mm², with over 90% cell viability after release and a release efficiency of approximately 34%. This work provides a functionally adaptive microrobot platform that combines targeted navigation, cargo shielding, and sustained local delivery, offering a promising strategy for applications in regenerative medicine and long-term therapeutic interventions.