Abstract

Angioplasty, or the use of rapidly deploying stents, is a common treatment for reopening narrowed vasculature often caused by atherosclerotic plaque. However, in-stent restenosis (ISR) induced by intimal hyperplasia is a common challenge to angioplasty. High impact stresses from current stent deployment processes have been linked to intimal hyperplasia; thus a stent that is gradually deployed over a longer period of time holds potential to mitigate these stresses. This work hypothesizes that resorbable polymeric links can be used as a triggering mechanism to enable repeatably controlled deployment of a compliant nitinol stent design with the eventual goal of reducing intimal hyperplasia. The aims of this work include the structured design process and design validation of a stent intended to meet this challenge. A structured design process was used to develop a multi-stage, gradually deploying nitinol stent in which PDLG (DL-lactide/Glycolide copolymer) bioresorbable links constrained specific mechanical cells within the stent geometry, thus limiting initial deployment to an intermediate diameter and allowing for secondary gradual deployment as the PDLG degraded via a combination of bioresorption and creep. A finite element analysis was carried out to design the link geometry to hold the stent at an intermediate stage (90% of final diameter) upon initial deployment, and enable a gradual secondary deployment phase lasting several minutes. Prototypes were then manufactured and the design was validated in a flow chamber mimicking the conditions of human blood flow and temperature. Using a camera and image processing methods, the diameter increase of the stents was tracked over time to characterize the secondary gradual deployment process of the stents. Results showed the links constrained the stents to an initial ~90% diameter upon initial deployment, followed by a gradual, secondary deployment with an average 63.2% rise time of 16.2 minutes. Creep was observed to be the primary driver of the gradual deployment, followed by subsequent bioresorption of the material. All prototypes exhibited gradual secondary deployment without any visible delamination of the bioresorbable links from the stent struts. Based on these findings it can be concluded our hypothesis has been demonstrated, and that a feasible gradually deploying stent design has been mechanically validated, preparatory to pre-clinical studies of its efficacy. Prior to clinical application, future in vivo work is needed to compare actual ISR rates with this stent design to other commonly used stent designs in preclinical trials. In addition, further preclinical work is needed to compare ISR rates through several stent design parameters such as initial deployment diameter, gradual deployment rate, final deployment diameter, and stent sizes to give insights into the optimal stent design. We anticipate that this gradually expanding stent design could reduce in-stent restenosis and improve clinical outcomes.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

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