This document summarizes research on designing porous lattice structures for bone implants using additive manufacturing. It describes: 1. Using CAD software to design unit cell models with varying porosity, pore size, and scaling to optimize mechanical properties and bone ingrowth. Finite element analysis is used to analyze stress distribution and strength. 2. Parameters for design like porosity, surface area to volume ratio, pore size and connectivity that affect mechanical strength and bone ingrowth are studied. Models with up to 93% porosity are designed. 3. Future work plans to develop bone growth models, graded scaffold designs, additive manufacturing of structures, and mechanical and biological testing including implantation to validate designs.

1. Authors:
Surya Pratap Singh ,Tarun Bhardwaj , Mukul Shukla
MED, MNNIT, Allahabad
Lattice Modeling and Finite Element Simulation for
Additive Manufacturing of Porous Scaffolds
IEEE International Conference on
Advances in Mechanical, Industrial, Automation and Management Systems
(AMIAMS 2017)
Department of Mechanical Engineering
Motilal Nehru National Institute of Technology, Allahabad(India)

2. Content
• Introduction
• Parameters for Designing
• Designing Method
• Designed Models
• FEA Method
• FEA Results
• Future Work

3. Introduction
• Research Area: Design of lattice structure for use in segmental
bone defect as an orthopaedic implant
• Limitations in use of Natural bone scaffold has increased the use
of Synthetic bone scaffold.
• Fabrication of Synthetic bone scaffold by Additive Manufacturing
is a new area of research.
• SLM, EBM techniques are used for fabrication of lattice based
structure.
• Metals available for fabrication are Stainless Steel,
Ti6Al4V,Tanatalum,Co-CrAlloy, Ni-Ti alloy.

4. Designing for
Segmental Bone Defect
4
Segmental bone defect Bone defect filled with metallic
lattice structure
Full view of assembly of bone plate and
lattice structure
Ref: Jan Wieding et.al Finite element analysis on the biomechanical stability of open porous titanium scaffolds for large segmental
bone defects under physiological load conditions “Medical Engineering & Physics 35 (2013) 422–432”

5. Conceptualization
Segmental
Bone Defect
Scaffold
Design & FEA
Additive
Manufacturing
Bone Implant
in Human
5

6. Lattice Structure Generation
• Designing
• FEM Analysis- Mechanical ,Biological
• .Stl file format preparation
• Additive Manufacturing -SLM
• SEM, Micro CT scan
• Testing- Mechanical, Biological-In Vivo, In Vitro
6

7. Different Types of scaffold Modeling
7
Ref:S. Gómez et.al. Design and properties of 3D scaffolds for bone tissue engineering Acta Biomaterialia 42 (2016) 341–350
Three main methods to design lattice structure are widely used by researchers
3. By Micro CT scan data
2. Implicit Surface based design
1. CAD based geometric modeling

8. Lattice
Structure
Design FEA
Shape
optimization
CFD
Research Methodology

9. Designing of Lattice
9

10. Design Parameters
1. Porosity (P) ,Pore Size
2. Surface Area to Volume ratio (S/Vs)
3. Mechanical Strength
 Lattice Structure’s need connected pore space.
 Pore connectivity is a very important factor for bone in growth.

11. Design of Unit Cell
Hollow Cube
(Scaffold)
Bone Model

12. Steps for getting the design
Step-1 Step-2 Step-3
Step-4 Step-5

13. Design
Parameters
Porosity
Diameter of hole
(10,8,6,4,2,0)
Surface
Area
Scaling of Unit Cell
(1,8,64,512,4096)
Strength
Stress Distribution,
Effective Young’s
Modulus
Design of Lattice Structure

14. Mathematical Analysis of Design
Length of
cube
(‘l’)mm
Diameter of
pore(‘d’) mm
Area of Pore
‘A’ (mm2)
l/d ratio Volume Porosity
10 2 3.14 5 917 8.03%
10 4 12.56 2.5 713 28.7%
10 6 28.56 1.67 457 54.3%
10 8 50.24 1.25 216 78.4%
10 9.8 75.4 1.02 68.13 93.2%
10 10 78.5 1 Design Not Possible
•Maximum possible porosity in this design is =93.2%

15. Porosity Variation
D=2 D=4 D=6
D=8 D=9 D=9.8
L=10
L=10

16. Porosity Variation
D=4,L=10 D=6,L=10 D=8,L=10
L/D=2.5 L/D=1.67 L/D=1.25
Porosity=29% Porosity=54% Porosity=78%
Surface Area to
Volume Ratio=
766/714=1.072
Surface Area to
Volume Ratio=
690/457=1.51
Surface Area to
Volume Ratio=
509/216=2.36
L=10L=10
L=10 L=10 L=10
D=4 D=6 D=8

17. Porosity Calculation
• Total Volume of cube:
• Volume of scaffold=216
• Porosity=
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3826579/
1000101010)(  dddV total
%2.78100
1000
216
1 Porosity
%1001 
total
solid
V
V

18. Scaling of Unit Cell
Unit Cell=1
(1x1x1)
L=10,D=8
Area of
pore=50.24
Unit Cell=8
(2x2x2)
L=5,D=4
Area of
pore=12.56
Unit Cell=64
(4x4x4)
L=2.5,D=2
Area of
pore=3.14
Unit Cell=512
(8x8x8)
L=1.25,D=1
Area of
pore=.785
Length of cube for each specimen remains same=10x10x10mm
L/D ratio is same for all above specimens= 10/8=5/4=2.5/2=1.25
L/D ratio governs porosity, which is 78% for L/D=1.25

19. Surface Area/Volume Ratio
Unit Cell l/d ratio=1.25 No. of unit cell in same
volume
(10x10x10)=1000 (mm 3)
Pore Area(mm2),
Pore Size
Surface Area (mm2)
/Volume (mm 3)
1. (10/8)=1.25 1 50.24,
8000micron
509/216=2.36
2. (5/4)=1.25 8 12.56,
4000micron
720/216=3.33
3. (2.5/2)=1.25 64 3.14,
2000micron
1142/216=5.28
4. (1.25/1)=1.25 512 .785,
1000micron
1985/216=9.18
5. (.625/.5)=1.25 4096 .196,
500micron
(Min by SLM)
3710/216=17.1

20. Properties from SolidWorks

21. FEA of Lattice
21

22. Steps in FEA
Import the .iges file form CAD Software
Defining material property
Creating Steps
Creating Assembly
Defining Interaction
Defining Loading and Boundary Condition
Meshing
Job Submission
Post- Processing

23. FEA

24. Animation of compressive behavior of
Unit Cell
Initial Shape Deformed Shape Stress Distribution Deformation in steps

25. Comparison of Results

26. Calculation of Compressive Modulus
S.No No. of
unit cell
Porosity Stress=
Force/Area
Effective
Compressive
Modulus
(Stainless Steel)
Effective
Compressive
Modulus
(Ti 6Al 4V)
1. 1 78.4% 27X10^6 27GPa 15.4GPa
2. 8 78.4% 31.4X10^6 31.4GPa 18.1GPa
3. 64 78.4% 34X10^6 34GPa 19.4GPa
4. 512 78.4% 35x10^6 35GPa 20GPa

27. Future Work
Scaffold –Bone growth Model Graded scaffold Model
 Development of Scaffold –Bone growth Model
 Graded scaffold Modeling
 Additive Manufacturing of lattice structures
 Mechanical and biological testing
 Real life implantation

28. References
1. X. Wang, S. Xu, S. Zhou, W. Xu, M. Leary, P. Choong, M. Qian, M. Brandt and Y. M. Xie,
"Topological design and additive manufacturing of porous metal for bone scaffolds and
orthopedics implants: A review," Biomaterials, vol. 83, pp. 127-141, 2016.
2. J. Parthasarathy, B. Starly and S. Raman, "A design for the additive manufacture of functionally
graded porous structures with tailored mechanical properties for biomedical applications,"
Journal of Manufacturing Processes, vol. 13, pp. 160-170, 2011.
3. Q. Chen and G.A. Thouas, "Metallic implant biomaterials," Materials Science and Engineering
R, vol. 87, pp. 1-57, 2015.
4. J. Wieding, R. Souffrant, W. Mittelmeier and R. Bader, "Finite element analysis on the
biomechanical stability of open porous titanium scaffolds for large segmental bone defects under
physiological load conditions," Medical Engineering & Physics, vol. 35, pp. 422-432, 2013.
5. G. Ryan, A. Pandit and D. P. Apatsidis, "Fabrication methods of porous metals for use in
orthopaedic applications," Biomaterials, vol. 27, pp. 2651-2670, 2006.
6. M. Leary, M. Mazur, J. Elambasseril, M. McMillan, T. Chirent, Y. Sun, M. Qian, M. Easton and
M. Brandt, “ Selective laser melting (SLM) of AlSi12Mg lattice structures," Materials and
Design, vol. 98, pp. 344–357, 2016.
7. L. E. Murr, E. Martinez, K. N. Amato, S. M. Gaytan, J. Hernandez, D. A. Ramirez, P. W. Shindo,
F. Medina and R. B. Wicker, "Fabrication of Metal and Alloy Components by Additive
Manufacturing: Examples of 3D Materials Science," Journal of Materials Research and
Technology” vol. 1, pp. 42-54, 2012. 28

29. Thank You ...
29

30. Surface Name
• NS- Neovius Surface
• SP- Schwarz primitive
• SD- Schwarz Diamond
• SG- Schwarz Gyroid
• SW- Schwarz W
30