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Design and Simulation of a Magnesium Based Biodegradable Stent for Hemodialysis Application

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2015, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
Stents are widely used as blood vessel scaffolding in medical applications, e.g., coronary stents. Stents can provide early stage scaffolding, increase blood flow, and optimize hemodynamics. Stainless steel is the most popular material for conventional stents and it has excellent mechanical behavior. High yield stress and high ductility allow stainless steel stents to expand safely. On the down side, stainless steel stents remain in the body permanently and may cause complications or lead to occlusion of the vessel. Biodegradable stents that eventually dissolve and disappear from the body are being developed to overcome these shortcomings. However, biodegradable materials, such as a magnesium alloy, also have limitations. Magnesium based materials have lower mechanical strength and stiffness than stainless steel, and biodegradable stents lose strength as they dissolve. Thus the design of magnesium biodegradable stents is complicated and computational validation is needed to optimize their design. Computational analysis is a time-saving and low-cost approach to evaluate biodegradable stent designs before expensive manufacturing of the stent and experimental tests are performed. Computational analysis is able to examine the mechanical performance, predict potential problems, and guide stent optimization. In this thesis, two designs (Design #1 and #2) of magnesium stents were evaluated. A computational analysis using Abaqus software simulated the expansion and recoiling process for both designs. Stent design #1 expanded from 6.0 mm to 10.0 mm in the radial direction with a strut perimeter to lumen diameter ratio of 4.68. Stent Design #2 has a strut perimeter to lumen diameter ratio of 6.15. Stent Design #2 expanded to 76% of the expansion of Design #1 stent. The peak strain and stress values safely stayed under the upper limit of the stent material. Stent Design #1 was selected as a better structural design because of its larger expansion ratio and greater coverage of the struts in the stent which inhibits restenosis (tissue ingrowth). A number of stents were fabricated for in-vivo testing in a pig. A new application for stents proposed by medical collaborators is considered in this thesis. The application is biodegradable stenting for hemodialysis access. Our medical collaborators implanted stents into pigs for in-vivo verification of the design. The right and left symmetrical femoral blood vessels were used to evaluate the stents. One side was a control vessel with no stent, and the other side was a vessel that was stented. Computer tomography and ultrasound were used to record changes of the vessels and blood flow during weeks to months of testing. On average, the biodegradable stents increased the blood flow and retained a larger lumen diameter as compared to the non-stented vessels. Also, the majority of the stent dissolved within 1-2 months. In summary, in this study a biodegradable magnesium stent was designed, analyzed using computational simulation, and evaluated in a pig model. It is demonstrated that the stent Design #1 is a proper design for the hemodialysis access application. The stent meets the mechanical requirement, provides adequate medical function, and degrades at a proper rate.
Mark Schulz, Ph.D. (Committee Chair)
Woo Kyun Kim, Ph.D. (Committee Member)
Zhangzhang Yin, Ph.D. (Committee Member)
107 p.

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Citations

  • Xu, C. (2015). Design and Simulation of a Magnesium Based Biodegradable Stent for Hemodialysis Application [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1445342007

    APA Style (7th edition)

  • Xu, Chenhao. Design and Simulation of a Magnesium Based Biodegradable Stent for Hemodialysis Application. 2015. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1445342007.

    MLA Style (8th edition)

  • Xu, Chenhao. "Design and Simulation of a Magnesium Based Biodegradable Stent for Hemodialysis Application." Master's thesis, University of Cincinnati, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1445342007

    Chicago Manual of Style (17th edition)