Finite element analysis is the computational approach to solving complex problems with boundary conditions by dividing it into many small sub-functions and solving each in turn. This is commonly used to analyse physical performance and integrity of manufactured parts before commitment to production to provide surety the part will perform as required Used for part design optimization such as minimizing weight while maximising performance. Software such as ANSYS or FEMAP import parametric 3D file from CAD for the analysis
A virtual mesh is applied to the model and the intersection points are called nodes. Material characteristics and parameters are applied to the nodes to simulate the material. Bed slat shoe for the Evolution sleep system This was a productionisation and Santoprene - Hytrel, half weight. Same feel
FDA encouraging simulation as parts of submission packages. To support animal, bench and human testing FEA is a requirement to achieve FDA approval for many devices that are implanted in the body – e.g. stents Recognised that better results can be derived from computational process
Finite element modelling and analysis is increasingly being used in medical device developments. This is an example by Bausch and Lomb the contact lens and eye health specialist who used FEA in a biomedical context to develop highly flexible intraocular lenses (IOL) for cataract surgery. During cataract surgery a small incision is made in the cornea and the lens is inserted. Bausch and Lomb set the target to reduce this slit from 1.8mm to 1mm to reduce patient recovery time. What we are looking at here is a cross section of a lens insertion tool. The green shape is the highly flexible hydrophobic acrylic and silicone intraocular lens and the blue part is the inserter tip . As a result the flexible lens’ have to fold in the inserter tool and pass through the slit so FEA was used to analyse the strain on the lens and visualise the deformation as it passes through the applicator channel into the eye The FEA model was compared and calibrated against physical test data to ensure the peak strain measurements correlated to previously experienced real-world failures points. This simulation approach has resulted in higher assurance of what will work when production is committed and failure modes mitigated in use.
The traditional engineering development process places the analysis after the development to validate the design pre-compliance
Integrating analysis and simulation into the design cycles moving it forward in the process means designs can quickly evolve and improve. This is effectively making the shift from using simulation as a validation tool to a research tool which can be used to derive insights early in the process that can be translated into innovation.
This is an example where we used FEA to explore and research in a biomedical context. Since early 2011 we have been working with a start-up company in Tauranga to develop and take to market a range of hip protectors aimed at preventing hip fracture in the elderly. Hip fracture is a growing and pressing global issue with projections of hip fracture incidence to exceed 6 million annually by 2050
Describe the product
Designed and built a rig to the IHPRG standard but achieved different results when tested on another rig with a different configuration soft tissue model Background to project - Completed a research project at the start of this year with an intern from the bioengineering faculty of Auckland University to explore the use of FEA in the development of biomechanical test apparatus for hip protectors. Use the tool to model and analyse biological components which means replicating these materials in the software package - this is complex because these materials aren't linear isotropic materials like engineering polymers or metals, these are biology materials which have complex non-linear behaviours
Literature research to identify the mechanical characteristics of the bio components. Important point for the process that requires a range of research skills for the best results. Required digging deep into biological research to identify the parameters. Biological materials are complex and highly non-linear which is difficult to model. They are filled with water which is affected hydration levels and the collagen fibres create an anistropic property where the mechanical characteristics differ in different directions which means they require more complex computation. This demonstrates the need to currently run physical testing to best gather this information - stress/strain sample testing or indentation testing of biological tissues.
A long way to go with this model to calibrate it to a realworld response but plenty of insight was derived from the preliminary model A view into the leg making what was previously invisible, visible Which soft tissue areas are best to shunt the fall energy Stresses in the proximal femur Stresses in the femoral neck
Then we moved to translate the material knowledge into a more representative physical model Matching to artificial materials - silicone is the closest match because of the non-linear, viscoelastic properties 2 grades identified - one to represent skin and muscle, a softer grade for fat
Further physical impact testing to clarify the position
Once the model has been developed and calibrated we can then iterate our parametric CAD models, adjusting materials and geometries, import into the model and validate before committed to material expense Thermal analysis can be run to evaluate comfort related factors Pressure analysis for understanding pressure sores Possible that soft tissue can't be accurately represented in artificial materials due to material limitations so the most accurate simulation is computationally.
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The Digital Body
Computer Simulation in Medical Device Developments
Health Congress 2013
Accelerate Innovation – Building Blocks
1.Jonathan Jones – Computer Simulation
2.Professor Simon Fraser – Additive Manufacture
3.Timothy Allan – Lean Start-Up Models
What is FEA?
Finite Element Analysis
Dividing complex models into many small sub-functions;
Interpretation into useful information;
Parametric input from CAD;
Software includes: FEMAP & ANSYS;
Used for design optimization and validation.
Encouraged by the FDA
Encouraging simulation in submission packages;
Support other test areas: animal, bench & human;
A requirement for many invasive products;
Recognise better results can be derived from FEA.