April 2013 Design for Medical Devices Conference, Minneapolis, MN
by: Dr. Robert Tryon – VEXTEC CTO
Traditionally the design and development of medical device products has been largely based on extensive physical testing. Over the last few years advancements in computing power (cloud computing) and software capabilities such as FEA (finite element analysis) and ICME (Integrated Computational Material Engineering), have provided an avenue for the computational simulation of medical device performance. These computational tools can simulate the performance of a medical device under realistic conditions, thereby providing OEMs greater insight into potential product performance issues, and the opportunities to develop higher reliability products more quickly than traditional physical testing dependent methods.
Today these computational tools are in the early adoption stage within the medical device community, typically replacing some of the traditional test based design and analysis methods, thereby accelerating development and reducing costs. VEXTEC has been working with Boston Scientific Corporation to implement software that integrates computational structural engineering with computational material science to simulate the variations that can exist in a medical device and how these variations can influence product reliability and life. It’s called Virtual Life Management® (VLM).
Medical device manufacturers, working with government regulatory agencies have developed methods to assure the design of safe implantable medical devices. One test method cyclically loads the devices to replicate how they are stressed in the body to determine the fatigue life of the device. A “worst case” loading condition is usually employed and several dozen tests are typically required. These tests are useful in identifying gross design flaws; however the quantity of test samples is usually too small to identify the subtle design issues that affect the reliability of the product once it is put into the market. This is true not only in the medical device community, but in all industries as you simply cannot conduct enough physical testing at enough conditions to cover all possibilities.
To this point, there is tremendous variability in device application. Patient anatomy and lifestyles are different resulting in different loading conditions. Device installation techniques may vary. Subtle variations in device geometry and material homogeneity cause each individual device to respond differently even if the loading is identical. All of these variations combine to cause each device to have a performance level and expected life that may be revealed through premature failure.
With this understanding, it becomes clear there are several places where computational tools can be inserted into the current medical device design and analysis practice and provide valuable benefit. One obvious place is to simulate the testing of devices. Today cost and time constraints limit physical testing to a few samples and a few conditions. Virtual testing (simulation) can extend the actual testing to evaluate thousand of samples over many conditions quickly and economically. This allows manufactures to continue to use the same design analysis practice but with a more comprehensive set of “test data”.
The presentation, “Integrated Computational Material Engineering for Virtual Life Management® of Medical Devices,” was given by VEXTEC and Boston Scientific at the 2013 Design for Medical Devices Conference held at the University of Minnesota in Minneapolis. The presentation describes how VLM was used to conduct virtual fatigue testing and evaluate the durability of CRM pacing leads and airway stents under varying conditions. Scanning electron microscopes (SEM) were used to determine the variations in material microstructure and a limited number of laboratory tests were used to identify the material damage mechanisms. Finite element structural analysis was used to evaluate the device geometry and loading. These inputs were integrated with probabilistic computational material models within VLM to simulate literally thousands of lead and stent products. VLM can be continually used to evaluate a myriad of possible material – design – loading conditions in an effort to understand product limitations and facilitate the design of higher reliability medical devices.