Design and characterization of a deployable surgical overtube based on braided structure

The clinical use of natural orifice transluminal endoscopic surgery has increased markedly in recent years. However, the problems of the flexible instruments in insertion safety and operational precision continue to limit its wider adoption. In this paper, we propose a deployable surgical overtube with variable stiffness based on braided structure to guide and support the instrument. The structure is flexible and radially deployable, acquiring a variable diameter which enables the safe insertion of both the overtube and the subsequent instrument. The phase-change material mechanism, actuated by thermal stimulation, enables stiffness transition of the overtube, thereby enhancing operational stability and instrument controllability. Experimental results showed that the overtube’s outer diameter can expand from 15.1 to 24.5 mm using an inflatable airbag. By heating/cooling the TPU bonded at each fiber intersections, it can obtain a stiffness gain ratio of 9.4 times, which can also lock the deployed configuration of the overtube. Demonstration tests conducted on an in vitro body orifice model show the insertion force can be reduced from 1.41 to 0.09 N after using the overtube, validating its potential clinical value.