Colonoscopy provides a minimally invasive tool for examining and treating the colon without surgery, but current colonoscope designs still cause a degree of pain and mechanical trauma to the colon wall. The most common colonoscopes are long tubes inserted through the rectum with fiber optic lights, cameras, and biopsy tools on the distal end. The stiffness required to support these tools makes it difficult for the scopes to navigate the twisted path of the colon without causing mechanical trauma inside the colon wall or distorting its shape. The shaft of the colonoscope often causes looping (alpha, reverse alpha, or n), and it is very difficult to advance the distal tip of the colonoscope with looping. In order to avoid looping and minimize mechanical trauma, the author expanded on a design by Zehel et al., who proposed surrounding a flexible colonoscope with an external exoskeleton structure with controllable stiffness. The stiffenable exoskeleton device is comprised of rigid, articulating tubular units, which are stiffened or relaxed by four control cables. The stiffened or relaxed exoskeleton device guides navigation and provides stability for the colonoscope when it protrudes beyond the exoskeleton device for examination and procedures. This research determined the design requirements of such an exoskeleton device and tested requirements of such an exoskeleton device and tested its behavior in a colonoscopy training model. Moreover, the stiffenable exoskeleton device can be operated in purely a mechanical way, which is safe as a class II medical device, and no additional modification of the colonoscope is needed to use the stiffenable exoskeleton device. Colonoscopy training model is used to test the stiffenable exoskeleton device. First, the endoscopist inserted the colonoscope into the colonoscopy training model up to the end of the stiffenable exoskeleton device along the shaft of the colonoscope to the distal tip of the colonoscope, and then locked the stiffenable exoskeleton device and advanced the shaft of the colonoscope to examine the colon. When the distal tip reached the cecum, he or she unlocked the stiffenable exoskeleton device, retracted the shaft of the colonoscope and the stiffenable exoskeleton device, and checked for polyps or other colon disease. Also, the endoscopist can insert the stiffenable exoskeleton device and a colonoscope alternatively by stiffening and releasing the exoskeleton device. In that way, endoscopist can advance the colonoscope and the exoskeleton structure inch-by-inch without causing mechanical trauma in the rectum and the sigmoid colon. The endoscopist tested the stiffenable exoskeleton device using the colonoscopy training model and fulfilled its objectives. Several other diagnostic procedures involving the stomach, esophagus and the nose could also benefit due to the improvements provided by the stiffenable exoskeleton technology.