Design of an injection moldable steerable tip for a laparoscopic instrument

The field of minimally invasive surgery (MIS) is calling for steerable mechanisms to increase the functionality and versatility of the contemporary instruments. Since reusable steerable instruments cannot pass the sterilization regulations, disposable instruments could solve the cleaning problem. In order to be cost-competitive, a cheap production process like injection molding should be used to produce disposable tips. The goal of this study was to design a torsion stiff injection moldable disposable tip for laparoscopic instruments, which can steer 60° in all directions. Flexures were chosen to serve as joints for the new design, named MoldTip, because in this way the number of parts can be reduced, which is beneficial for the price of the tip. The flexures need also to guide the cables, therefore the tip is divided in two parts – the core and the sleeve, which could be injection molded. The parts could be injection molded by a mold with two moving inserts. A torsion stiff instrument was achieved by having a core made of polyetherimide (PEI) and a sleeve made of polycarbonate (PC). The torsion stiffness of the MoldTip (790 Nmm/rad) increased almost by a factor 8 with respect to a state-of-the-art disposable steerable instrument of CambridgeEndo (103 Nmm/rad). The cost of this improvement is that the bending stiffness increased by a factor 2, which means that more effort has to be made to steer the instrument. The MoldTip is torsion stiff, can be injection molded, and can steer 60° in all directions. With the MoldTip a promising direction in the development of steerable instruments is opened.
BMD
BioMechanical Engineering
Mechanical, Maritime and Materials Engineering