Nonlinear Simulation for Complex Biomedical Applications

1. Nonlinear Simulation for Complex Biomedical Applications Dr. Ir. Bert Knops MSC.Software Europe

2. Why performing simulations? Introduction to nonlinear FEA Application to biomedical components Conclusions Contents

3. Conventional product development • Design, build, test, redesign • Based on a trial and error process • Expensive • Time (and money) consuming process • Large time-to-market • ….. build design test redesign

4. Predictive engineering simulation-driven design evaluation process within design loop • Virtual manufacturing and virtual simulation of final component • Cost reduction • Minimal rework loops • Reduced time-to-market • ….. build test design decision Virtual (Computer) Simulation Clinical trials and approval to market redesign

5. Accelerate product development Reduce product development cost More effective and efficient use of limited resources Reduce time and cost for testing Reduce cost for animal and human clinical trials Improve product performance Improve patient effectiveness SIMULATION ADDS VALUE TO YOUR PROCESS AND AT THE END BRINGS MONEY BY MEANS OF COST REDUCTION AND REVENUE INCREASE Simulation

6. Computer simulations are completely worthless because of inaccurate boundary conditions, material properties, etc. Computer based simulations can completely replace all prototyping Two extremes

7. Between these two extremes Simulation can provide feedback on relative advantages and disadvantages of different design options (qualitative) Depending on the knowledge concerning boundary conditions, material properties, etc. simulation will give also accurate results from a quantitative point of view (automotive, aerospace) Simulation will never replace prototyping and testing completely but it will reduce the number of prototypes and tests Common ground

8. Introduction to nonlinear FEA

9. Major types of nonlinearities • Geometric Nonlinearity • Large displacements • Large rotations • Material Nonlinearity • large strain elasticity • Plasticity • Creep • Viscoelasticity • ..... • Boundary Nonlinearity • Contact • Follower force

10. Major problems in nonlinear FEA • How to define contact between structures • How to create an initial mesh that can undergo large deformations • How to define the time steps for transient analysis • Defining nonlinear material laws • Meshing and Element Technology • Large CPU times

11. How to tackle them? • Fully automated contact analysis • Automated adaptive meshing and rezoning during the analysis, which allows the introduction of a new undistorted mesh at any time in the analysis process • Adaptive loading to assure convergence and stability • Full range of material laws for metallic and nonmetallic materials • Automated meshing (hex as well as tets) • Full parallel processing

12. Manufacturing of spring

13. Simulation of Gear Systems

14. Simulation of Welding

15. Simulation of Super Plastic Forming

16. Biomedical Applications

17. Characteristics of Biomedical Applications • Nonlinear materials (plastics, elastomers, biological tissue) • Large deformations • Permanent deformations • Contact between numerous deformable “bodies”

18. Design Verification & Product Validation • Simulation enables design engineers to perform Design Verification and Product Validationwithout the need for building many Prototypes: • Verification that a product will meet the design specifications • Product validation (product will meet or exceed end-user requirements and expectations)

19. Hip Joint Prosthesis • Goal: investigate hip joint prosthesis for strength, geometric parameters, interactions between bone and implant and its displacements.

20. Hip Joint Prosthesis

21. Knee Implant • High fatigue loads on tibial inserts due to daily ambulation • may result in polyethylene debris into joint space • Optimize geometric and material processing variables • minimization of pitting and delamination stresses

22. Knee Implant Typical simulation

23. Knee Implant Contact Pressure for 2 Designs • indication for surface abrasion

24. Knee Implant Maximum Principal Stress for 2 Designs • indication for cracking

25. Knee Implant Von Mises Stress for 2 Designs • indication for delamination

26. prosthesis abutment implant Oral Implant • Establish insight in role of mechanical load on bone response around oral implants • calculation of strain/stress distribution

27. equiv. rek (me) 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 818 me Oral Implant Bone loading around a screw-shaped implant

28. Oral Implant Bone loading around a screw-shaped implant Axial loading Lateral loading

29. mCT segmentation 1360 1269 1179 1088 997 907 816 725 635 544 453 363 272 181 91 0 shape calculation MSC.Marc Oral Implant Modeling of trabecular bone

30. Oral Implant mCT-based FE calculation (via CAD)

31. Oral Implant Micro-Strain Results 6500 6067 5633 5200 4767 4333 3900 3467 3033 2600 2167 1733 1300 867 433 0 4200 3920 3640 3360 3080 2800 2520 2240 1960 1680 1400 1120 840 560 280 0

32. Implantation of Intra-Ocular Lens

33. Implantation of Intra-Ocular Lens Capsular bag Bag: thin-shell element Zonule: 3D truss element Intra-Ocular Lens IOL: 3D brick element

34. Stiffness: Visco-elastic layer: at t=0: large stiffness at t=: stiffness = zero Capsular bag: real stiffness Visco-elastic layer Capsular bag Visco-elastic layer Implantation of Intra-Ocular Lens Capsular bag modeled by composite with three layers

35. Implantation of Intra-Ocular Lens Contact forces between capsular bag and IOL

36. Implantation of Intra-Ocular Lens Axial displacements of the capsular bag

37. Implantation of Intra-Ocular Lens Von Mises stress distribution Note: The stress range of the plots are not the same

38. Implantation of Intra-Ocular Lens

39. Implantation of Intra-Ocular Lens Conclusions • It is possible to analyze the capsular bag deformations • FEM results give better understanding of mechanical behavior • Only relative comparison of IOL geometry possible

40. Cardiovascular Stent • FDA approval requires FE based: • Inflation Simulation • Fatigue Analysis • Crush Strength • Added benefit: • Reduced Time to Market

41. Cardio Vasc Stent Analysis MSC.Marc nonlinear finite element analysis objectives • Evaluation of the maximum stress as a result of stent installation, inflation and cyclic loads • Inside diameter of 3.5 mm (.138in ) and 4.5 mm (.177in) • Determine the Safety factor for infinite life of stent • Fatigue analysis after full inflation of diameter • External cyclic pressure ranging from 1-4 psi • Inducing fatigue stress in the material • Reduce the number of designs that will undergo actual fatigue testing . FDA Fatigue test requirement is 400 Million cycles – requires one month.

42. Flat Pattern configuration of stent Formed Stent Configuration

43. Cardio Vasc Stent Analysis • Material Model of the stent • 316 stainless steel alloy with work hardening characteristics • Isotropic linear elastic solid up to the yield point . • Beyond yield point, time independent inelastic behavior considered using von Mises yield function

44. Cardio Vasc Stent Analysis • Alternative material model: shape memory alloys (Nitinol) • Phenomenology is characterized by hysteresis

45. Cardio Vasc Stent Analysis • Stent Compression During Assembly • From outside diameter 2.56mm (0.101 in) to 1.01mm (0.040 in) • Compressed with 9 rigid bodies – see figure below • Radially inward to effect stent compression

46. Cardio Vasc Stent Analysis • STENT INFLATION • After compression, prescribed, radial boundary conditions were used with an internal tube to inflate stent • Radially outward to a maximum inside diameter of 4.5 mm (.177 in) • Free of artificial constraints, the stent was free to rotate around tube

47. Cardiovascular Stent Inflation

48. Cardiovascular Stent Inflation

49. Cardio Vasc Stent Analysis • Fatigue Analysis Objective: • Determine the fatigue stresses of the inflated stent design when subjected to external fluctuating stresses • External fluctuating pressure cycles on stent • Systolic and diastolic blood pressures • Many mechanical components tested safe under static load conditions can fail as a result of fatigue stresses, below the material’s ultimate strength

50. Cardio Vasc Stent Analysis • To establish a relationship between alternating stress and mean stress with minimal material characteristics available: (yield stress, ultimate stress , endurance limit) the modified Goodman method was used • Commonly used for ductile metallic alloys • Graphical approach for relating stress amplitude and mean stresses with the material strength limits