Regrafting submillimeter-scale ferromagnetic soft continuums.

Submillimeter-scale ferromagnetic soft continuums (FSCs) own innate skills in performing desirable and delicate bending for confined space navigation, especially in biological lumens. However, such tiny structures are difficult to endow with complex designs, thereby challenging to realize more sophisticated functions for various purposes, especially in vivo therapies and manipulations. Inspired by grafting for muscles and plants, we propose submillimeter-scale FSCs that can actively divide into pieces at any region, and conversely, the pieces can actively graft to each other to form the original structure or novel shapes. We define these functions as regrafting, comprising self-division and self-mergence. Implementing regrafting implies actively switching between two opposing characteristics: sufficient continuum structural strength for steering loads and a low fracture strength for division and mergence. Therefore, we developed ferromagnetic thermoplastic soft materials to replace the widely applied thermoset materials for continuums and shed the commonly required coating layers. Being made of the ferromagnetic material family that can undergo reversible elastomer-fluid transitions, the proposed FSCs can perform arbitrary division-mergence and navigate confined spaces for multiple endoscopic tasks in one go. Endowed with enhanced flexibility and reconfigurability in situ by regrafting, the proposed FSCs may open a multifunctional path for operating a wider range of biomedical tasks.