Simulation Called in for the Coronavirus
You’ve likely seen technical and news articles around the COVID-19 pandemic with pictures and videos comparing simulations of sneezes and coughs, or investigating how masks, face-shields and other protective equipment help people to resist infection.
It’s amazing to see these and realize how mainstream this type of analysis has become, and how the graphics and presentation of these results feels familiar, even to the general public. We also marvel at how quickly these types of analysis have been conducted and presented, and how widely democratized they’ve become, with new results and simulations being presented every day.
Sneeze simulation developed as part of Dassault Systèmes’ 3DEXPERIENCE Open COVID-19 community.
This is just one more sign that the use of analysis tools to predict product performance has gone from being a niche application only performed by expert users, to something that is routinely done as a standard part of the design process in all industries. The medical device industry is no different, but the design of medical devices does have several unique characteristics that sets it apart in its use of engineering analysis tools.
Analysis Elements Unique to Medical Devices
Complex Material Behavior
Whether you’re trying to model the response of human tissue to your models, or designing a shape-memory alloy for a vascular stent, the types of materials used for medical device design are often complex, and designed to perform very specific demanding tasks. The analysis techniques we use to analyze steel and aluminum structures just won’t cut it here.
Product Release is Glacially Slow
With the testing, clinical trials and documentation needed to release a medical product, it can take several years to get a product to market. Because of this, you can’t rush a minimum-viable product to market and then rapidly design a secondary iteration to optimize and improve it, like you can in other industries. Analysis helps in two ways: it allows you to fully test out a wide range of design ideas to get the released product as optimized as possible, and by spending up-front time in analysis, you can hopefully reduce the number of physical and clinical trial cycles as much as possible.
Failure is Not an Option
The medical device industry is notoriously risk-averse, for good reason. If your toaster breaks, you won’t be happy, but you can go buy a new one—but if your pacemaker quits unexpectedly, the consequences will be much more severe. The industry is well armed for this, with extensive computer analysis, physical testing and clinical trial protocols before any product release, but there are several applications that can’t easily be tested physically, where analysis is used as the sole validation tool.
Devices, particularly those involving electronics, are getting smaller and more powerful. Where electronics are involved, that means more heat, and with very strict reliability and touch-temperature requirements to meet, that heat has to be removed safely from the device. Best-guess techniques for thermal management just don’t cut it anymore, and a robust CFD analysis is needed to optimize heat dissipation from the PCB to the environment.
Keep the Noise Down
Electromagnetic noise, that is. Medical devices need to not only be compatible with the radio waves that are generated by other equipment and our cellphones, but also need to limit the amount of electromagnetic interference they emit. This EMI/EMC testing is expensive and complicated in real-life, so being able to predict a successful test is incredibly valuable.
Nonlinear Materials, Everywhere
If there’s one characteristic that rings true for almost any structural analysis of a medical device, it’s that the materials are nonlinear. Most materials in the human body are highly nonlinear in their structural behavior, and most devices that interact with the body are, too. From human tissue, nitinol stents, and elastomeric valves, nonlinear materials are everywhere.
To assess these properly, you’re going to want an analysis software with strong nonlinear capability. This means lots of material models, built-in tools for mapping real-life behavior to those material models, and a robust solver that is able to iterate through challenging problems. One example of a software package that meets all these requirements is SIMULIA Abaqus, which combines one of the most powerful nonlinear solvers in the industry with automated contact modeling and an incredible range of material models.
Test, Test, Then Test Again:
Because the clinical trial and product release process takes so long, medical device companies want to minimize the number of times a device goes through it. Because of this, the released product needs to be fully optimized – the opposite of other industries where an early product can be released to the market and then improved in later versions.
Because of this, you’re going to want to look for analysis solutions that let you fully explore the design space and provide tools for optimizing to an ideal solution.
This product exploration typically has three potential angles:
- Parametric iterations – where certain parameters within the design can be varied, and a large batch of analysis cases run with those variations. Key analysis numerical and graphical outputs can be reviewed for each design iteration to investigate the sensitivity of the device to changing parameters.
- Parametric optimization – similar to the above, but with the ability to home in on the ideal solution to meet a certain design set of design goals by varying those parameters. Tools like this allow an ideal solution to be developed by changing model parameters.
- Topological optimization – where the physical shape of the object is changed to provide the ideal shape to meet the design goal. This technology can be found in tools such as Tosca (and now available within the SOLIDWORKS 3D Creator cloud CAD package) and designers can apply these techniques for structural strength or fluid flow. Topological optimization methods were originally developed by mimicking how the human body grows bone, so applying them for medical devices feels appropriate!
Images before and after topology analysis performed with SIMULIA Tosca.
A good design exploration process often involves all three elements, so medical device designers are increasingly looking for a suite of tools that offer all these options.
The impact of a failed medical device can be catastrophic, so designers will do everything they can to minimize the risk of failure. This means that rigorous clinical testing will be employed over many years before a device is released; however, there are aspects of device performance, especially with how a device performs over a long period of time, that just can’t be feasibly tested in a clinical environment.
Expansion analysis of a vascular stent, performed in SIMULIA Abaqus.
Fatigue-life testing for evaluating the functional life of a vascular stent is one area where the use of analysis is becoming more critical. A stent is typically made up of a shape-memory metal alloy, which is compressed and inserted into a patient’s blood vessel, and then expands to its original shape, holding the blood vessel open and improving blood flow. It will remain in the patient forever and needs to continue to perform its function. Increasingly, regulatory bodies, such as the FDA, will accept finite-element stress results as a primary part of the product validation package for a product.
If you review the guidance published by bodies like the FDA, they stress the importance of capturing as many real-life elements as possible, including the temperature-dependent behavior of the material and accounting for the residual stresses created during the manufacturing process. When selecting an analysis package, you should make sure that it can capture all of these real-life aspects.
Keeping Your Cool
Devices are getting smaller and smarter every day, and that leads to big challenges when it comes to keeping electronics cool. All electronic devices give off heat, and the more powerful a device is, the more heat there is to give off. Removing heat is particularly important in the medical device realm, as increased operating temperature normally results in a reduction in reliability, which is unacceptable for most medical applications.
Traditionally, a fan or other forced cooling device was often included to keep things cool, but space, noise or aesthetic concerns increasingly rule this out as an option.
Today, a lot of the cooling strategy starts at the PCB board level, with thermal vias, in-plane heat spreaders or thermo-electric coolers, being employed to get the heat out of the system as efficiently as possible. Newer technologies, such as heat-pipes, are also being employed to aggressively move heat from one area in the system to a place where it can be safely dissipated.
CFD analysis of an electronic device, showing device temperatures and airflow paths.
These thermal problems are so intense that a best-guess approach to a solution is not good enough. Heat management strategies need to be carefully optimized, and a thermal analysis using a computational fluid dynamics (CFD) software package, such as SOLIDWORKS Flow Simulation, is a critical part of that process.
When selecting a software package, you’ll want to make sure that it can model all the heat management strategies you’ll need to employ – both now and in the future. The best of them have dedicated sub-models for things like heat-pipes and TECs, as well as the ability to approximate in-board cooling elements.
Electromagnetic Interference and Compatibility
Electromagnetic testing is one of the most important validation steps in the medical device design process and is often one of the most feared. Simple changes to a system can have major impacts on the electromagnetic interference it generates, as well its vulnerability to outside interference—and wireless transmission is critical to the function of many devices today. On top of that, the testing is expensive and logistically challenging. This combination of complexity and cost make electromagnetics a great candidate for investigation through electro-magnetic analysis.
Being able to test a device for EMI/EMC virtually means that design improvements can be rapidly cycled, giving confidence that a product will pass when subjected to validation testing. When selecting an EMI/EMC analysis package, it’s important to be able to consider all aspects of electromagnetics, so look for the different types of solvers and physics available. For example, CST Studio Suite offers finite element, finite integration and transmission line matrix solver techniques, covers low-frequency and high-frequency, and can optionally include thermal and particle calculations too.
Much has changed in the world of medical devices over the past 20 years, and the adoption of analysis technology has a big role to play in the advancement of that change. These tools allow products to be developed more quickly, safely and cost-effectively than ever before, and over the coming years we’ll see FEA, CFD and electromagnetic analysis tools becoming increasingly mainstream.