A braided overtube structure with variable diameter and stiffness towards natural orifice transluminal endoscopic surgery

Natural orifice transluminal endoscopic surgery has recently seen a surge in clinical use, but problems of the flexible instruments in insertion safety and operability remain a main barrier to its wider adoption. In this paper, based on a fibrous braided skeleton, an overtube structure with a variable diameter and stiffness is designed to path and support the instrument. The skeleton is flexible and radially deployable, enabling smooth insertions of both the overtube and the subsequent instrument. Encased in a thin film coating and actuated by negative pressure, the fibrous jamming mechanism enables a rapid stiffness transition, thereby enhancing the overtube stability and instrument operability. Experimental results demonstrate that the overtube’s outer diameter can expand from 13.7 to 20.5 mm using a removable airbag, while its stiffness can be increased by 4.4 times when negative pressure is applied. Demonstration tests conducted on an in vitro esophageal model further reveal that the insertion force is significantly reduced from 1.18 N to 0.08 N with the use of the overtube, validating its potential clinical value.