Air Retention Device

This research was supported in part with funds from the John Woollam Foundation for the 2018-2019 academic year.

Paper and Presentation (DMD Conference 2020)

Link to paper:

Link to presentation:


This study is carried out to redesign an air retention device (ARD) for use in colonoscopy[1] to enable scaled-up manufacturing.

Colonoscopy is a common procedure in which a long colonoscope is inserted via the anus to diagnose or treat problems in the large intestine. During this procedure, gas is pumped into the large intestine to improve visualization, reduce friction, and reduce the risk of the colonoscope becoming “looped” or snagged within the large intestine. However, due to insufficient sphincter tone at the anus, some patients experience gas leaking; as a result, the gas must be replenished during the procedure, which increases risk due to time under anesthesia.


The ARD consists of a main tube through which the colonoscope will be inserted, a seal to prevent gas leaking between the colonoscope and the main tube, and rings which hold the device in position by mounting on either side of the anal sphincter. The prototype was made using commercially available Ecoflex™ 00-35 (Smooth-On). This material ensures that the overall manufacturing time is short, and the product is made into the size as intended.

A validation experiment was performed for the ARD designed. The validation was conducted at the time when the colonoscope device is inserted in the ARD to check for leaks and other indications of manufacturing process issues. In this test, the ARD was connected to one end of a PVC tube, and a balloon was attached at another end of the tube; then air was pumped through a small hole drilled in the PVC. Air leakage can be seen by observing the size change (and rate of change) of the balloon.

Hand drawn manufacturing process

Actual mold for manufacturing

Hand drawn testing setup

Actual test setup

Prototype in SolidWorks

Actual Manufactured Prototype


In the final iteration of this device, the main tube, rings, and seal were fabricated in one piece. This shortens the overall manufacturing time as there is no additional step required.

For the final prototype, proper sealing between the colonoscope and ARD up to a certain pressure was visually observed. Under that threshold pressure, no significant escape of air was observed (in other words, the balloon was observed to retain its inflated size). As water-based lubricant will be used during the surgery, hand soap was used in the validation test to facilitate colonoscope motion, by reducing the friction between the colonoscope device and ARD.


A simple, inexpensive prototype ARD for facilitating colonoscopy procedures was fabricated and tested based on a previous design presented in [2]. A mold-based method for quick and accurate production was developed, which helps keep the device production cost low, improving the potential for market acceptance.

The device was demonstrated to fulfill the primary functional requirements of allowing easy colonoscope motion and retaining some degree of gas inflation. The authors believe this can significantly improve diagnostic visibility and increase efficiency in colonoscopy procedures.


  1. McEniry MR, Nelson CA, Oborny RD, Glett LC, Wolfe J. Air Retention Device for Colonoscopy Procedures. ASME. J. Med. Devices. 2014;8(3):030923-030923-2. doi:10.1115/1.4027044.

  2. Nelson CA, Sayago Capielo MF, McEniry MR. Experimental Validation of an Air Retention Device for Colonoscopy. ASME. J. Med. Devices. 2015;9(3):030927-030927-2. doi:10.1115/1.4030560.

  3. Kozarek RA, Earnest DL, Silverstein ME, et al. Air-pressure-induced colon injury during diagnostic colonoscopy. Gastroenterology 1980;78:7-14.