Most critically, dealing with human life, well-being, and health requires a high level of quality, reliability, and effective product functioning not only to achieve satisfactory product performance, but also to avert product deficiencies and field failures that could cause safety issues and put users at risk.
As a result, engineers and technical managers in the medical device sector are constantly seeking out tools that will provide them with additional technical insights, a thorough exploration of the design space, alternative and redundant checks on reliability, and communication techniques that can turn volumes of data and complex findings into a clear, concise, and meaningful explanation for team members from different disciplines.
Engineering analysis and virtual test software are enjoying wider uptake in medical design because they offer solutions in all of these areas. The ability to present predictive visualizations and animations of engineering entities like stresses, deformation, temperature gradients, and fluid flow patterns in 3D product models communicates design issues in a comprehensible way and makes data easier to grasp. The ability to easily change material properties, product geometry, and applied loads in simulations enables an exploration of material tolerances, manufacturing variability, design options, and performance boundaries.
Plus, simulations bring another perspective and an additional check on hand calculations, benchtop prototypes, and test data.
One indication of the growing implementation of simulation software in the medical field is the U. The following small sample of Finite Element Analysis FEA and Computational Fluid Dynamics CFD related topics addressed in this forum gives an idea of the breadth of applications receiving attention: computer-aided design of drug-eluting coatings, joint kinematics to predict prosthetic wear, modeling of fatigue behavior of Nitinol stents, and CFD analysis of coronary arteries.
There are four data categories that device manufacturers submit and the FDA reviews in the pre-market setting to demonstrate required safety and performance: benchtop, computational, animal, and human. An FEA linear statics study enabled a design with less stress for similar loading in the product in the foreground.
Right b : An FEA contour plot of a bone screw with color gradations for different ranges of stress. Higher stress level areas are red, lower are blue. The aim of this article is to provide a basic taxonomy of FEA and CFD software that will allow OEMs to match real-world mechanical design problems in medical devices with appropriate engineering analysis software.
This exercise can also serve as a hierarchical framework for specifying software, as well as a survey of software solutions currently available for common engineering problems. Identifying appropriate software is a matter of working through a hierarchy of criteria.
For medical design, a sound system would be to consider criteria in the following order: analysis type, material property modeling capabilities, tools for achieving adequate fidelity, and finally, features needed for productivity and ease of use.
The software world groups solutions based on the engineering topic, the mathematical underpinnings used in setting up the problem, and the underlying numerical methods needed to arrive at a solution. Once the underlying physics of the problem is clear, the type of analysis can be defined. The types of mechanical analyses needed for medical device design are fairly extensive because these products serve the full range of medical disciplines and functions.
Consider the diverse physical phenomena encountered in just a few medical disciplines — orthopedics, ophthalmology, dentistry, and cardiology. In addition to diversity in the medical disciplines, products fall into multiple functional categories: monitoring and diagnostics, replacement or augmentation of body functions, prevention of injury and disease, and tools and equipment for surgical and other procedures.
A small random sampling of medical products illustrates this breadth: orthopedic bone screws, intraocular lenses, vascular stents, cochlear hearing implants, robotic surgical equipment, drug delivery devices, magnetic resonance imaging. Nonetheless, mechanical design issues faced by medical product development teams can be sorted into a couple of main disciplines: Structural Mechanics, Heat Transfer, Fluid Mechanics, and Acoustics. We can further subdivide these main disciplines into more specialized analysis types.
This article will limit its focus to Structural Mechanics and consider the following analyses under that heading: Statics, Buckling, Dynamics, Kinematics, Fatigue, and Impact.
Several real-world examples will be used to illustrate the use of FEA software for several of these analysis types and show how applying criteria for material modeling, fidelity, and productivity can achieve product development success on a technical, project management, and business basis. Among the analysis types cited previously, statics is the most widely used in FEA software. This is because it answers questions fundamental to every piece of hardware. Is the structure capable of handling the expected loading?
Where are the weak or critical points in the structure? What can be done to improve stress levels, reduce weight, save material, or make the part simpler? An example of a statics analysis is provided by the following design study on orthopedic bone screws. An FEA linear statics analysis was conducted on a titanium implantable bone screw design to examine stress levels that would occur in the part during the insertion process. The case study determined that a redesign could produce a part with less stress for similar loading.
In Fig. Linear and nonlinear behavior can be present in each of the analysis types. If significant nonlinear behavior exists in the phenomenon being modeled, the analysis needs to account for it and the software must have the capabilities to accommodate it. Otherwise, the simulation will not be accurate. In statics analysis, linear behavior assumes deflection is directly proportional to the applied load, the highest stress is within the linear range of the material stress-strain curve characterized as a straight line from the origin, and maximum displacement is considerably smaller than the characteristic dimension of the part.
Many applications of metals and plastics are intended to use just the elastic portion of the stress-strain curve and therefore fall into the linear category. However, if these conditions are not present, then a nonlinear analysis is required. It is important to note that nonlinear effects can arise from a number of conditions. The material has nonlinear properties or the structure is operating beyond the yield point in the nonlinear plastic range of the material.
Geometry changes resulting from deformations of the structure affect stiffness or applied forces. Or, there are changes in the boundary conditions resulting from contact.
Medical device design often makes use of the nonlinear properties of different materials, vascular stents being one example see the section of this article on Material Modeling Capabilities. Similarly, contact of different types is a common design condition. Nonlinear capabilities in analysis software are often used to expand the range of simulations that can be performed, adding a powerful, sophisticated dimension to design studies. The design of intraocular lenses IOL and their implantation provides an example of a nonlinear buckling analysis and geometric nonlinearity.
In addition, the lens is highly flexible and is pushed or supported by surrounding media which requires accommodating geometric nonlinearity and modeling of 3D contact. Once the type of analysis to be performed is identified, consideration must be given to the materials that will be involved in the simulation studies. The medical field can offer challenges in this regard because the breadth of materials encountered can extend beyond even the comprehensive FEA libraries of metals and thermoplastics used in most industry segments.
The FEA software must be able to mathematically handle the idiosyncratic properties among candidate materials. Consider the range of materials medical design engineers might use: metals like biocompatible titanium and shape memory alloys like Nitinol with hyperelastic properties; thermoplastics and polymers like polyether ether ketone PEEK for mimicking the structural behavior of bone, and medical-grade ultra-high-molecular-weight polyethylene UHMWPE for hip, knee, and spine implants; silicon-based organic polymer polydimethylsiloxane PDMS with viscoelastic behavior used in contact lenses; composites ranging from common glass fiber reinforced systems to special formula carbons, Kevlar and matrix systems with all manner of ply layups, orientations, and local reinforcements.
Composites, because of their orthotropic nature, require a degree of sophistication not required with isotropic metals. To deliver a superior and safe experience to patients, medical device manufacturers need to continuously innovate the devices with the help of software. However, with the benefits of software come the risk of defects and bugs. Medical device testing thus demands rich experience of the domain, local and federal legislations, knowledge of devices, infrastructure and capability to support the testing.
Adopting DevOps in the healthcare industry is necessary to align the technological developments with the rapid medical advancements at speed.
Cigniti has integrated well with our needs by providing on and offshore capabilities while helping us drive test automation as a key strategy.
They partner with us to ensure we are satisfied and on the rare occasion when we are not, they work quickly to address the concern.
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