Embedded Files
UNIVERSITY OF CALIFORNIA, SAN DIEGO
SPONSORED BY DENISE KALMAZ, M.D.
Colonoscopy Air Retention Device
MAE 156B SPONSORED PROJECT, SPRING 2017
This technique of pressurizing the colon; however, is only successful if the patient’s sphincter can create a tight enough seal around the colonoscope. In cases where this seal is not sufficient, the air/water escapes from the colon and visibility is compromised. This issue can be resolved with an attachment that sits in the anal canal and helps retain the pressure while allowing the colonoscope to move freely in and out of the colon. The purpose of this project is to design a device that can reduce pressure leakage that leads to the loss of visibility during colonoscopy procedures.
A colonoscopy is a medical examination of the colon which requires inserting a colonoscope (a long medical device with a camera at the end of it) through the anal canal into the patient’s colon. The human colon naturally rests in a shriveled state with many folds that can conceal cancerous cells or other areas of concern. In order to have better visibility of the colonic walls, it is necessary to inflate the colon with either air or water to 0.425 psi or a max of 1.102 psi.
FINAL DESIGN
BACKGROUND
SOLUTION
Our solution is depicted in the figure below: an hourglass-shaped, hollow device that will be attached around the scope. The outer form of the device is designed such that the neck of the Air Retention Device (ARD) will sit against the sphincter muscles creating another seal between the device and the anal canal. The two conical flaps, which look like uplifted hands, flex forward for insertion and spring backward to hold the position of the device
throughout the rest of the procedure. These flaps are tapered in order to guide the scope into the anus and an inner seal at the neck of the device will ensure tight sealing against the scope throughout the entire procedure. The device also has a slit down the middle so that it can be opened and placed around the endoscope at any time during the procedure and the addition of a rigid clip holds the device together. The final design of the ARD is equipped with an inner seal, referred to as the “Ian seal” in the report, with a diameter of 0.47 inches. It has been tested and proved to withstand 1.3 psi of water pressure with less than 20 mL of leakage per minute in order to retain pressure between the endoscope and the device with less than 1 Newton of friction before lubrication. The results of these tests can be seen in the chart below:
With convenient access to high resolution 3D printers, the ARD was developed through seven iterations throughout a ten week period. Each iteration began with a consultation with a Subject Matter Expert, Dr. Kalmaz, Director of Small Bowel Endoscopy, then the design would be created and/or adjusted in Solidworks, printed using the Stratasys 3D printer, and finally brought back to the SME for qualitative feedback at which time the next iteration would begin. The table below is a checklist of how each iteration observably performed compared to initial requirements based on data observed.
CONCLUDING THOUGHTS
Due to medical board regulations the device could not be tested and verified on humans, however, it is scheduled for animal testing by the end of July. Nonetheless, this new medical device shows promising results based on both the friction and pressure tests as well as the feedback from Dr. Kalmaz. Upon further testing with human trials it is expected that the overall design will remain intact with only minor adjustments needing to be made based on sizes of different endoscopes and patients.
Acknowledgments
Firstly, the team would like to express our sincere gratitude to our sponsor Dr. Denise Kalmaz for the support throughout the project. Without her precious support it would not be possible to accomplish this project.
Besides our sponsor, the team would like to thank our instructor Mr. David Gillett and T.A. Young Woo Seo for their comments and encouragement. They are clearly the best instructor and T.A. at UC San Diego.
Our sincere thanks also goes to Dr. Monica Kim from UC Irvine and Caleb Christianson from Prof. Mike Tolley’s lab at UC San Diego. Their insightful comments on molding and silicone material lead the team to finally succeed on molding PDMS. Thanks to Alex Pham from the Center for Magnetic Recording Research for help with casting PDMS as well.
The team would also thank to Ian Richardson for the inspiration on inner seal and Chris Cassidy for the support on 3D printing material.
Because the material produced from the Stratasys 3D printer is not medically approved, the final device is made from polydimethylsiloxane (PDMS), a common silicone often used in prototyping medical devices, which is smooth and has an average durometer of 43 HA and tensile strength of 980 psi. A multi-piece mold was developed to cast the device in one part that was 3D printed as seen in the below figure. Similar to the ARD, the mold went through three design iterations which are discussed further in the report.
Page updated
Report abuse