Problem description and significance:
Stents are widely used in the treatment on vascular disease and they represent one of the most valuable medical device markets. It has been observed that the mechanical characteristics of a stent influence clinical outcomes. For instance, foreshortening affects the deployment precision and compliance contribute to stent structural collapse, which results in migration.
Presence of a spatially repeating geometric pattern of a `unit’ or a cell is a striking feature of stents. Consequently, in the view of lattice mechanics, the mesh-like structure of the stent can be analyzed through the unit-cell m study. In one of the projects in our lab, we designed the expansion mechanisms of balloon expandable stents to study the effect of unit-cell geometry on the stent foreshortening. The unit-cell study can be also applied to self-expanding stents, which are preferred for occluded venous treatment. We employed unit-cell study to evaluate foreshortening, compliance, and collapse of venous stents and find the most suitable design for the treatment of each prevalent venous diseases such as Thrombosis and May-Thurner Syndrome.
In addition to the analytical study, we conduct In-vitro experiments using a custom-designed flow loop including pulsatile pump and silicone mock vessels. The silicone mock vessels can duplicate the mechanical properties of vein and pulsatile pumps simulate the blood flow characteristics such as heartbeat, flow rate, and Systole to Diastole rate ratio. Consequently, we can simulate appropriate flow profiles according to the hemodynamics of the vessel that is studied.
Selected publications:
- Douglas, G.R., Phani, A.S. and Gagnon, J., 2014. Analyses and design of expansion mechanisms of balloon expandable vascular stents. Journal of biomechanics, 47(6), pp.1438-1446.
- Tan, T.W., Douglas, G.R., Bond, T. and Phani, A.S., 2011. Compliance and longitudinal strain of cardiovascular stents: influence of cell geometry. Journal of Medical Devices, 5(4), p.041002.
- Hejazi, M., Phani, A.S., Gagnon, J., Hsiang, Y. and Sassani, F., 2018. Deformation Characteristics of Venous Stents: A Comparative Assessment. Journal of Vascular Surgery, 68(3), pp.e84-e85.
Funding:
The research on mechanics of stents is supported by the Department of Vascular Surgery at Vancouver General Hospital and also Canadian Institute of Health Research (CIHR).