Design and evaluation of a variable stiffness over tube based on low-melting-point-alloy for endoscopic surgery

Abstract

Flexible endoscopes have been widely used for diagnostic and therapeutic interventions in minimally invasive surgeries. The flexible property provides flexible endoscopes the unique ability to reach cavities and viscera. However, in natural orifice transluminal endoscopic surgery (NOTES), during ad vancing process, a flexible endoscope without shape control is unstable and could lead to cavity buckling. When the end of the endoscope reaches the target, the endoscope should be rigid enough to hold its shape against external forces for better surgery operations. To overcome this problem, a novel variable stiffness over tube based on low melting point alloy (LMPA) was proposed in this paper. It could provide a channel for endoscopic instruments to go through human cavity. The over tube exploits the phase transformation property of LMPA which enable the stiffness change of the over tube. Steel cables were used to control the shape of the over tube. A prototype was built and experiments were carried out to evaluate its shape control effectiveness, variable stiffness property and response characteristics. According to experimental results, it cost 14 s to make the over tube transform from rigid state to flexible state and 15 s to make the over tube transform from flexible state to rigid state. Experimental results also indicated that the over tube is very rigid in rigid state and flexible in compliant state.