Design of the Bent On Site Steerable (BOSS) Clip Applier

Abstract

The shift from open surgery with one large incision to less invasive techniques with multiple small incisions brings benefits such as less trauma, less scar formation and a faster recovery for the patient. However, in minimally invasive surgery (MIS), surgeons struggle with basic tasks such as applying sutures and tying nots. Clip appliers have been developed to take away the need to apply sutures. From the literature research preceding this thesis and a state-of-the-art investigation, it turned out that current clip appliers do not combine simultaneous steerability and the ability to apply multiple clips. Reaching the surgical site can be difficult or impossible with conventional non-steerable clip appliers, and the reinsertion of a clip applier after every clip application is time consuming and can lead to damage to the instrumentation and patient. The goal of this thesis is to develop a reusable minimally invasive steerable clip applier that can bend clips at the surgical site to close ducts and cuts during laparoscopic procedures. Design requirements and obstacle points are determined for the laparoscopic instrument components by taking the SATA mechanism as a starting point in the design process. Possible solutions to the obstacle points are gathered in a morphological chart that is used to come up with six distinct concepts. A concept choice is made by experimentally finding the required torque to cut and bend a titanium clip and by verifying the ability of concepts to reach this torque by creating a simplified instrument tip on the same scale as the to be designed tip. The worst-case required torque to cut and bend a medium sized titanium clip of 0.5 by 0.8 mm turned out to be 0.6 Nm and 0.03 Nm respectively. During this experimentation it became clear that clips should be supported over the whole length and not just at the ends during the bending process to secure appropriate closing and compression. Several experiments are performed to find a cutting blade attachment that could transmit the worst-case cutting torque while remaining as bendable as possible.
The concept in which the clips are formed in the tip by cutting off a piece of titanium wire and then bent into a clip turned out to be the most promising because it has a theoretically unlimited number of clips at the implantation site without a cartridge, is sterilizable, relatively easy to fabricate due to its simplicity, and can be modified to produce clips with other dimensions. The concept is 3D printed on a 500% scale to verify functionality. This prototype showed that a revision of the actuation mechanism was required and that a few minor alterations could make the instrument easier to sterilize. 3D printing the new design on a 500% scale verified the functionality. The final functional prototype is also 3D printed at a 200% scale, which is the smallest scale that could be achieved with the available resources. The experiments showed that all the required actions could be performed and the prototypes showed that the mechanism functions as required. It is therefore achieved to design a Bend On Site Steerable (BOSS) clip applier that can make and bend clips in the tip from a continuous titanium wire. The instrument is easy to disassemble and sterilize due to the simple design and the small amount of parts. This simple design makes it also possible to make adjustments so that other sizes and shapes of clips can be made.