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Design of an SMA Actuated Mechanotransductive Implant for Correcting Short Bowel Syndrome

[+] Author Affiliations
Brent Utter, Brian Barnes, Jonathan Luntz, Diann Brei, Daniel H. Teitelbaum, Manabu Okawada, Eiichi Miyasaka

University of Michigan, Ann Arbor, MI

Paper No. SMASIS2010-3895, pp. 875-892; 18 pages
doi:10.1115/SMASIS2010-3895
From:
  • ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
  • ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1
  • Philadelphia, Pennsylvania, USA, September 28–October 1, 2010
  • Conference Sponsors: Aerospace Division
  • ISBN: 978-0-7918-4415-1 | eISBN: 978-0-7918-3886-0
  • Copyright © 2010 by ASME

abstract

Short bowel syndrome is a serious medical condition afflicting an estimated 20,000 to 200,000 people in the United States with mortality rates as high as 40%, despite current treatments. Recent research on mechanotransduction, the process through which mechanical load induces tissue growth, has successfully demonstrated permanent growth of healthy, functional bowel in small animals. Unfortunately, the underlying technological approaches limit further research of growth under different load profiles and extension to safe clinical devices. This paper presents a fully implantable bowel extender which expands via a unique Shape Memory Alloy (SMA) driven ratcheting mechanism, measures the bowel tension and load, and enables studies of mechanotransductive bowel tissue growth where the displacement or load may be controlled wirelessly in real-time. The architecture and operation of the bowel extender is illustrated, focusing on the SMA driven ratcheting mechanism that incrementally expands the device. To help visualize the SMA wire and reset spring design, an alternative graphical method is outlined which transforms the SMA material curves into a Reset View based on predictions of the system forces. An analytical model predicts the ratchet mechanism force with tooth and pawl geometry selected based on packaging, load-bearing, and kinematic constraints. Force limits to maintain tissue health are established from ex vivo and in vivo porcine small bowel loading experiments. The Reset View methodology is applied to design a bowel extender prototype which is used to experimentally validate the ratchet force model. The functionality device is demonstrated, operating against loads much larger than specified, validating the device’s ability to enable new studies of mechanotransductive bowel growth in pigs.

Copyright © 2010 by ASME
Topics: Design

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