How the SIMULIA Portfolio Powers Design Innovation
Cardiovascular disease is the leading cause of death worldwide and is projected to remain so for decades, according to the World Health Organization. Surgical intervention, including the use of balloon angioplasty and stent insertion, continues to be a lifesaver for many patients.
If you are a designer and/or manufacturer of medical stents—cardiovascular or otherwise—your team is continually searching for the most efficient way to produce your product to the highest standards of quality demanded by the life sciences industry and the Food and Drug Administration. You may be asking, “Is our current stent design the most optimal?” “How can we pinpoint what makes a better design?” And, “As we create that ‘better’ design, how can we accurately assess its fatigue life?”
You may already be using computer-aided engineering to help answer some of these questions. But you may only be scratching the surface with your inquiries so far. Simply delivering a few stress and deformations plots, and letting someone else extrapolate about durability and lifespan, is no longer sufficient.
Simulation as a Key Driver for Design Innovation
Your company’s senior management has become keenly aware of how advanced simulation can drive innovation—and they are demanding more complete, actionable solutions to the design challenges their teams face. They are demanding innovation, not simply simulation, requiring a powerful set of tools that will help deepen your knowledge base about the geometry and physics of stents, expand your skillset and boost your ability to achieve optimum, verifiable results.
This technical demonstration will show you how a suite of tools composed of FEA, process integration, design optimization and fatigue analysis can be equipped to focus on, and drill down into, the many and varied challenges of stent design to foster innovation and promote product quality.
The example provided here is of a generic coronary stent design, not a specific product. We will follow a workflow that starts with SolidWorks CAD modeling, through Abaqus FEA, to parametric optimization with Isight and finally non-parametric shape optimization with Tosca. You will also see how fatigue life assessment with fe-safe can be used as an adjunct to the workflow whenever the analyst desires additional insight into the results of design decisions.
Automating Structural Analysis
First a 2D CAD model of a proposed stent design is created in SOLIDWORKS. Using Python scripting, the model is imported into the Abaqus/CAE environment for 2D meshing, then extruded to obtain a 3D mesh and wrapped (cylindrically) to obtain the final stent mesh.
With the stent model in hand, the next task is to construct the other components of the simulation required for full finite element analysis in Abaqus. These include the blood vessel in which the stent is being balloon-deployed, the devices that expand and then crimp the stent before it’s placed inside the vessel, and finally the cyclic pressure load on the interior surface of the vessel caused by blood flow (Figure 1).
A Parametric Way of Optimizing the Design
So far we have demonstrated the kind of stepwise processes that you would carry out manually using SIMULIA’s Abaqus and fe-safe toolkits. You’ve arrived at a new stent design idea that meets your minimum reliability criteria. Now it’s time to apply the powerful process automation and optimization capabilities of Isight that will provide you with even deeper insights by tweaking the relevant parameters in order to determine whether yours is truly the best design possible.
Begin by identifying the parameters in your model that you would like to query, such as length, radius or thickness of a stent segment. You can then set up a Design of Experiments (DOE) sequence in Isight that will automatically modify each parameter, produce a new CAD output file for each modification, convert each one into an Abaqus analysis and provide feedback about peak stresses in the form of a response surface that maps the results of the parameter modifications (Figure 2).
The example shows the Isight workflow (Figure 2) used to set up the DOE runs. At right are two views of response surfaces from a stent-crimping simulation, with the “design sweet spot” (blue portion) identified.
Now let’s compare the original stent design against the DOE-optimized one:
The figure at far right in this image shows the overlap of the baseline and optimized models. The thickness of the optimized stent design has been slightly reduced; the extrusion thickness has increased while the radius has decreased.
A Non-parametric Way of Optimizing the Design
Now you have a stent model that has been optimized using the parametric approach in Isight. Yet you can gain even deeper, richer insight into your design by next using Tosca for non-parametric, shape optimization (Figure 3). Tosca works by querying the sets of nodes where peak stresses are occurring and searching for the configuration that has the least amount of peak stress. A control algorithm within Tosca homogenizes the
stress distribution inside each stent strut, while adhering to defined constraints within the intrinsically, cyclically symmetric model. Tosca modifies the design shape until, in six iterations in this case, it reaches an optimum decrease in Mises stress values of 13%—significantly more than the 5% reduction that was achieved with the non-parametric DOE-based approach in Isight alone (Figure 4).
Why Parametric and Non-parametric Approaches?
From the example presented here, you can see the significant value of using Isight and Tosca together to optimize stent designs. It may seem that parametric and shape optimization are two different, even mutually exclusive approaches, but by using them both you end up with a richer, deeper analysis that ensures that you have arrived at your best possible design.
Although the two tools can be set up in whatever sequence is preferred, in the case of stents, where the analyst tends to start from an existing design, it’s ideal to begin with a parametric (Isight) approach and then take the results into Tosca for shape optimization. And fe-safe can be used at a number of points alongside the workflow to prove out how such sequential optimization results in measurably increased fatigue life.
Access SIMULIA’s Portfolio for Stent Design on a Single Token
The full extent of SIMULIA’s portfolio for stent design can be explored with the Extended Token program, which allows you access to all solutions—Abaqus, Isight, Tosca and fe-safe—on a single token. The advantages of working with this complete toolset are many:
- Deeper understanding of loading conditions, durability and reliability.
- Powerful capabilities for design exploration of materials and geometries, parametric and shape optimization and manufacturing tolerances.
- Insights into fatigue and failure through evaluation of stress concentration and cyclic loading.
- Support of future patient-specific modeling with customized geometries and loading conditions.
Want to Learn More?
Watch our webinar, “Using Simulation to Power Innovation in Life Sciences,” to learn how realistic simulation can help improve device behavior for better patient outcome.
