The project is a continuation from fall 2006 and is sponsored by Dr. Mathew and the Hershey Medical Center. Endoscopic suturing devices allow surgeries to be preformed inside the body without any external incisions. No incisions means less recovery time for the patient and no scars. The suturing instrument is designed to seal incisions made inside the body after an endoscopic surgery is performed. The flexible instrument is designed to move a needle through human tissue while sewing up incisions inside the body. It needs to open and close, and also move the needle from one side to another. Background research has proven that endoscopic suturing is a very new concept and only few designs have been created and tested. Our control device needs to be operable with one hand and lightweight.

The prototype was drawn up into two halves, one being the male side and the other being the female side. We decided to use a peg system to interlock the two halves, which allows us to take apart the prototype and change the internal mechanisms as we continue to alter the device rather than permanently securing the two sides together. The first mechanism, the toggle, will be attached to a wire that opens and closes the sheath that houses the suturing device. It will have a safety system that prevents the user from opening the sheath too far and it will lock in place in the open and closed positions to prevent the device from malfunctioning while entering or exiting a human body. The next mechanism was designed using an endocopic surgery book offered to us by Dr. Mathew. The text contained pictures of how the endoscope worked internally. The actual endoscope uses a gear and chain mechanism for moving the tool tip around in 3D space, similar to that of a bike. We decided to use that same design for locking and unlocking each side of the suturing device. The chain will have two ends attached to the wires used to move the locking mechanisms. The gear will only travel far enough to lock and unlock the suturing device. The third and final mechanism, the push button, is designed similar to that of a pen. It will be spring loaded, engaging and remaining engaged upon one push followed by a permanent disengagement upon a second push. The button is attached to a rod that will enter and exit two holes in the gear. The first hole will represent the locked position of one side of the suturing tip and the unlocked position of the other side. The second hole will represent exactly the opposite. This design feature prevents the user from prematurely opening or closing either side of the tool tip in order to prevent losing the needle inside the patient.

We have decided that the best material to build our prototype out of will be ABS plastic because of its light weight and we have prototyped this from the FDM machine. Many of our structural tests revolved around the strength of this material. Several of the components for the design are aluminum, so testing this material proved to be irrelevant since the device will be used to perform very delicate procedures. The wires used are .042 inches in diameter and are actually made for electric guitars. They are wound with nickel plated steel and are built to handle about 14.8 lbs of tension (which translates into 10.70 ksi) when in normal use in a guitar and are built to withstand drastic changes (musicians bend strings) in tension and length (www.daddario.com). They are heavy enough to achieve the push and pull we need.

There were several ways to go about testing the prototype to ensure that it was built to withstand an actual endoscopic surgery. First off, we wanted to choose a wire that is appropriate to the surgical procedure and can withstand the amount of tension needed to open and close the suturing device. The amount of tension needed to open and close the suturing device was measured using a force meter. This helped us determine a maximum value for the necessary tensile of strength of the wires. A similar procedure was completed for the chain to ensure that it does not break under real time pressures. These parameters narrowed down our selection, and a tensile test was performed on all of the selected materials in order to prove their predicted tensile strength.

The suturing device is controlled by a mechanism that needs to withstand the bending stresses imposed by the surgeon. For our prototype, the chain needs to stay stiff to prevent sag. The channels holding the chain and wires together in linear unison need to be strong enough to withstand the device’s desire to sag during operation. On the other end, the actual suture itself needs to be able to create enough pressure to pierce the flesh inside the human body. We could not determine what this number will be, but the device can be tested on ballistics gel, and an estimated amount of pressure can be measured using a force sensor. Ballistics gel is the best known imitation of human skin, so being able to cut through this material should prove the device strong enough for any surgery, excluding cutting through bone. The sheath that protects the suture was the toughest part to move. By measuring the force it takes to combat the friction, we were able to have a good idea of the maximum parameters for the project. In summary, both the suture, the hand controlled mechanism, and the wires all have to be in tune to one another and strong enough to collectively withstand the demands of endoscopic surgery.

In addition to the devices under bending and tensile stresses, part of our concept has a feature that is under a certain amount of torque. This part rotates the suturing device 180° to complete the suture. Similar to those devices that move laterally, these rotating devices need to be measured in accordance to their ability to withstand the conditions they are routinely put through. Similar to what was mentioned above, the necessary parameters were established based on the required strength of a particular rotating part and the maximum torques were measured using a torque meter.

One other important detail includes using the right materials for any gears that are being used. Past experiences have proved that plastic gears wear down way to easily, but at the same time metal gears need to be accurate and require a decent amount of lubrication. We have decided to go with nylon gears, for they are the lightest of the materials we could choose from without compromising a lot of strength.