A Variable-Dimension Overtube for Natural Orifice Transluminal Endoscopic Surgery

In natural orifice transluminal endoscopic surgery, the insertion of surgical instruments can cause patient discomfort, even bleeding and perforation. This paper proposes a design of an overtube which can vary its radial dimension. It can be inserted through the natural orifice in a small diameter configuration and then enlarge its size and form a hollow and rigid channel to allow passing instruments, while to reduce the friction between the instruments and the surrounding tissue. A Bricard linkage is used as the basic unit of the overtube and a mechanism is designed to drive multiple Bricard units to fold or unfold. Optimization of the design parameters has been studied and comparison experiments have been completed to verify the feasibility of the design on reducing the shear forces and normal forces exerted during surgical instrument insertion. The ex vivo experiment is also completed to prove the protection of the overtube on the esophagus during the insertion.