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Simulation Spurs Stent Innovation

Medicine comprises multiple challenges due to the ongoing development of science and daily discoveries regarding the treatment of diseases. As human life expectancy increases, medical devices, such as a stents and many others, must also continue to evolve to offer more effective and accessible technology for patients of all ages. There are still many countries, however, in which there is no access to appropriate healthcare due to poverty, corruption or appropriation of the resources.

Bioana is a Mexican company dedicated to the design and development of accessible medical technology. Its innovations begin with the recognition of real medical needs and are realized with the use of simulation software to create medical devices used in cardiology, diagnostics and orthopedics.

Finding the Functional Design

For a medical device to be sold commercially, manufacturers must first and foremost demonstrate its functional safety to ensure there is no risk to patients. Before we identify the best performing device, we cycle through multiple design iterations and use ANSYS simulation software for geometry testing and design enhancement. According to the World Health Organization (WHO), cardiovascular disease is the leading cause of death around the globe. To address this, we design our vascular implants with the aim to increase the accessibility of this hard-to-afford technology. In cardiovascular disease, fatty deposits build up within the inner walls of the blood vessels. Once the deposits grow, they can produce blood flow blockage that can cause heart attacks or strokes. Vascular stents open the vessels and help restore the blood flow.

Of all the design requirements for these vascular devices, the most important is the devices’ ability to withstand the permanent loading applied due to the pulsatile blood flow.

How Stents Work

A stent is a small tubular mesh — usually metal — that is inserted into the vessel to keep the wall from collapsing. It is implanted through a surgical procedure known as angioplasty into the femoral vein (in most cases) and guided to the site of the blockage using a balloon catheter. The balloon is radially expanded to open the blockage, then deflated, leaving the stent in place. The stent must be able to withstand the loads produced by the pulsatile blood flow and remain fixed to the blood vessel walls.

Design iterations for vascular stents.Design iterations for vascular stents, each with different expansion capabilities.

Typically, doctors use an imaging technique that consists of injecting a radio-opaque contrast agent into the arteries to illuminate the blood flow and the size of the vessel opening. Using a fluoroscope, doctors can also observe the effect on the flow once they stent is implanted.

We also saw it was possible to use ANSYS simulation software to analyze the blood flow behavior resulting from a specific stent design at the implantation Site. Most frequently Stenosis (or narrowing) occurs most commonly at the bifurcation where the left main coronary artery (LMCA) divides into the left anterior descending artery (LAD) and the left circumflex artery (LCX). We created a 3D model of this bifurcation and the implanted stent. According to the literature, the blood velocity of healthy arteries oscillates at approximately 64 ± 26 cm/s, while the velocity for arteries with fatty deposits is significantly lower (41 ± 26 cm/s). As expected, our results show a higher flow velocity toward the center of the vessel. And although the velocity is reduced on the stented side, it is still higher — an improvement of 15 cm/s — than it would it would be in a fatty artery.

Velocity vectors show reduced velocity in the stented branch of a coronary artery.

Another important hemodynamic factor requiring analysis is the shear stress on the vessel wall (i.e., the tangential force produced by the blood flow on the endothelial surface). High shear stress values are desirable as they promote flow alignment and secretion of anticoagulants. Low values, conversely, promote apoptosis (cell death).

High wall shear stress values indicate proper stent placement.High wall shear stress values indicate proper stent placement.

According to the literature, regular shear stress values on the LMCA anatomy range from 1 to 2.25 Pa and from 1.41 to 4.65 Pa on the LCX with increased values around the struts and apex of the stent. Our analysis shows a high shear stress value of 4.55 Pa around the stent structure and validates the device’s performance for significantly lowering the possibility of restenosis.

Meeting the Goals

Using ANSYS software, obtained through the ANSYS Startup Program, we have reduced our time and cost for testing protocols and increased our productivity and revenues through expanded development efforts. We can now enter new biomedical fields and continue to innovate — to create high-impact, accessible medical technologies in Mexico.