Exploration of new steerable mechanism for stiff handheld minimally invasive surgery instrument

Background: Minimally Invasive Surgery (MIS) gained increasing support in the surgical community over the last decades. Due to the rigid tip of current used rigid instruments the maneuverability is limited during a procedure. To increase maneuverability steerable instruments have been developed. However current handheld steerable instruments contain low bending stiffness, which is one of the reasons that these instruments are hardly used in clinical practice. This study aims to design and evaluate a new stiff steerable mechanism with 2 Degrees Of Freedom (DOF) for use in a handheld MIS instrument. Methods: Characteristics of the steering mechanisms were described and analyzed. The most suited approach for creating a stiff steerable mechanism was selected. Multiple 2 DOF stiff concepts were designed. Of these, three concept prototypes (scaled 10) were engineered and manufactured (3D printing). The ability to steer and the stiffness of the prototypes was evaluated. In addition, the most promising mechanism was redesigned to fit the required 5 dimensions. It’s robustness was verified using Finite Element Method (FEM) techniques. Results: Eight different mechanisms were described and analyzed. The most suited approach is a mechanism that consists of solid rods and universal joints to guide steering forces from handle to tip and external forces from tip to handle. Five concepts were designed that enable a parallel motion of which three were developed further in 10 scale prototypes. Preliminary results showed an increase in stiffness of a factor 2,7 compared to existing instruments. The real scale implementation study resulted in a 5 version of the mechanism that is capable of guiding the forces required to drive all the functionalities of a MIS instrument (steering, grasping). Conclusion: It can be concluded that a 5 steerable MIS instrument with a stiff tip is feasible. The mechanism contains a cardan mechanism and axially moving rods that slide over a special constructed surface. The scaled prototype provided at least 2,7 times higher stiffness compared to existing instruments.Mechanical, Maritime and Materials EngineeringBiomechanical Engineerin