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Esophageal stent placement has significantly improved the quality of life in patients with malignant as well as benign esophageal obstructing lesions. Despite its early success and rapid adoption, stent migration still occurs in as many as 30% of cases especially with fully covered stents. To date, few models of interaction between the stent and the esophageal wall have been published and these have only focused on the deployment of the stent or the static mechanical stress distribution of the stent material. To elucidate the mechanism behind esophageal stent migration we developed a simplified radially symmetric computational model of esophageal peristalsis and the stent. A thorough review of the literature on esophageal peristalsis was performed and pertinent data were implemented into the model. Similarly, mechanical properties of an existing esophageal stent were used for the stent model. A sensitivity analysis of the parameters of the model enabled identification of the key elements of stent design that influence the degree of stent migration including flares design, stent length as well as longitudinal and radial stiffness. A comparison of the model to the migration rate reported in clinical studies for various types of fully covered stents further verified our model, which can significantly contribute to the development of a more stable esophageal stent with lower rates of migration., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The behavior of the ASTM F1058 wrought cobalt-chromium-nickel-molybdenum-iron alloy (commonly referred to as Elgiloy or Phynox) is evaluated in terms of mechanical properties, magnetic resonance imaging, corrosion resistance, and biocompatibility. The data found in the literature, the experimental corrosion and biocompatibility results presented in this article, and its long track record as an implant material demonstrate that the cobalt superalloy is an appropriate material for permanent surgical implants that require high yield strength and fatigue resistance combined with high elastic modulus, and that it can be safely imaged with magnetic resonance.

Stents are tubular devices that are used in cylindrical passages of the body following trauma or disease in order to keep the cross section of these passages open. A mathematical model of a self-expanding metallic stent has been developed with the aim of predicting various geometrical and mechanical properties of the stent. The model was developed with the main assumptions that the stent acts as a combination of a number of independent open-coiled helical springs with ends fixed against rotation, and that the springs undergo elastic deformations only. A series of experiments has been carried out in order to assess the validity of the model. The experimental results show good agreement with theory for the tests involving stent diameter and longitudinal force as a function of stent length and fair agreement, limited by frictional effects, for the tests involving radial pressure as a function of stent diameter.