Variable stiffness outer sheath with "Dragon skin" structure and negative pneumatic shape-locking mechanism.

Background/purpose:    Natural orifice transluminal endoscopic surgery (NOTES) offers the possibility of surgery without visible scars. To overcome the limitations of NOTES, we developed a novel surgical device called the rigid and flexible outer sheath with multi-piercing surgery (MPS).

Methods:    This sheath can switch between flexible and rigid modes using a novel "Dragon skin" structure and a negative pneumatic shape-locking mechanism. In addition, it has an integrated bending structure that enables it to flex in four directions at the distal end. The insertion part of the prototype is 575 mm long with a 20 mm outer diameter. The rigid and flexible shaft is separated into two parts. The primary and secondary shape-locking shafts are 300 and 200 mm long, respectively. The two parts of shape-locking shaft can be locked independently, including both being locked simultaneously. In addition, the model was equipped with one 7- and 1.7-mm-diameter, and three 3-mm-diameter working channels. When the sheath approaches the target, the surgeon locks the shape and then easily inserts flexible instruments through the path created by the sheath. In this study, we evaluated the stiffness of the prototype. Furthermore, an in vivo partial gastrectomy experiment was also performed.

Results:    The experimental results regarding the shape property suggest that the rigidity of the shaft was considerably increased using this mechanism. An in vivo partial gastrectomy experiment performed using a swine was successfully performed using the outer sheath for assistance. The outer sheath was inserted through a percutaneous route during the in vivo experiment.

Conclusions:    The evaluation results show that the advanced outer sheath system has great promise for solving access and stability problems with NOTES.