Completed guidewire geometry. The guidewire transitions to this shape from being straight when exposed to body heat.
Description of the State of the Art for TAVI
Mechanism of action. The heart has body temperature water flowing through it.
Finite element model for estimating strains on guide wire during heart compression. This data was used to estimate fatigue life
A shape-trained nitinol guidewire to improve surgeon experience and patient outcomes during heart valve replacements
The Shape Memory Alloy Guidewire for Transcatheter Aortic Valve Implantation Surgery is a project with Dr. George Knopf of the Mechanical Engineering department of the University of Western Ontario and Dr. Bob Kiaii, the Ray and Margaret Elliott Chair in Surgical Innovation at the Schulich School of Medicine & Dentistry.
This project was initially envisioned by Dr. Knopf as the simple premise of using shape-memory alloys to create surgical guidewires that changed shape inside the body at the surgeon’s behest. However, the specific surgical application of this technology was unclear and unresearched. My team and I decided to tackle the problem of designing shape memory guidewires and determining how they could be best applied in a surgical environment.
The first step in the process was to go out, interview, and observe surgeons in order to determine what specific application to target. In speaking with surgeons we determined that one surgery where the guidewire technology was not yet performing to optimal levels was in the burgeoning Transcatheter Aortic Valve Implantation/Replacement (TAVI/TAVR) procedure. In TAVI, the surgeon threads a guidewire through the femoral artery into the heart and then uses that guidewire to deploy a bovine heart valve grown on a self-expanding nitinol stent over the existing diseased valve. Through research, observation, and ethnographic interviews, our team determined a number of ways that using a shape-memory guidewire could provide improvements to the procedure over the existing paradigm.
The subsequent phases of the design process included morphological analysis to break the guidewire down into it’s constituent subsystems, concept generation and selection, prototyping, and validation. Feedback from surgeons and health care practitioners was a key aspect of this process to ensure the design met the user needs. A series of quick prototypes with increasing fidelity and relevance to the final design helped generate quick wins that kept the project moving forward. Some of the technical aspects explored in this project were: biomedical design, tensile/compressive testing to generate hyperelastic material models, modeling of hyperelastic and shape memory materials, in-bloodstream forced convection transient heat transfer modelling.
The project concluded with a proof-of-concept nitinol guidewire that was shape-trained to achieve the intended distal geometry upon exposure to human body temperatures. This project was presented at the Western Mechanical Engineering Capstone Design Day.